DNA Tumor Viruses – Ogris PDF

DNA Tumorviren – Ogris “The Emperor of All Maladies” by Siddhartha Mukherjee is a comprehensive “biography” of cancer, chronicling its history from ancient times to modern advancements in understanding and treating the disease. It blends scientific exploration with personal stories, highlighting th...

DNA Tumorviren – Ogris “The Emperor of All Maladies” by Siddhartha Mukherjee is a comprehensive “biography” of cancer, chronicling its history from ancient times to modern advancements in understanding and treating the disease. It blends scientific exploration with personal stories, highlighting the profound challenges and triumphs in the ongoing battle against cancer. Discovery of tyrosine phosphorylation: The discovery of tyrosine phosphorylation was a pivotal moment in molecular biology, first identified in 1979 during studies on polyomavirus middle T antigen and v-Src-associated kinase activities. Researchers observed that a specific protein modification involved the addition of phosphate groups to tyrosine residues, which was previously unknown. This breakthrough, detailed in studies by Tony Hunter and colleagues, revealed tyrosine phosphorylation as a novel regulatory mechanism critical to cell signaling, particularly in cancer progression. - Polyoma T antigen immunoprecipitates contain a protein kinase-like activity. - Major acceptor of phosphate is the polyoma medium T antigen. - Phosphorylated residue behaves identically to phosphotyrosine. The polyomavirus middle T antigen (MT) is a viral protein crucial for the transformation of host cells, enabling the virus to cause tumors. MT is anchored to the host cell’s plasma membrane, where it acts as a scaffold to recruit and activate cellular signaling proteins, including tyrosine kinases like c-Src and PI3K. These interactions trigger signaling cascades that promote cell proliferation and survival, contributing to the virus oncogenic potential. It was central to the discovery of tyrosine phosphorylation, highlighting its significance in cancer research. In mammalian cells, phosphorylation is a common post-translational modification, with approximately one-third of cellular proteins being phosphorylated at any given time. Phosphorylation predominantly occurs on serine (~90%) and threonine (~10%) residues, while tyrosine phosphorylation is rarer (~0.05%). However, this frequency increases significantly (up to 1-3%) in cells transformed by oncogenic viruses, highlighting its role in regulating protein function and signaling pathways essential for cell proliferation, survival, and transformation. Discovery of the tumor suppressor p53: The tumor suppressor p53 as a significant milestone in cancer research. In 1979, researchers identified p53 in SV40-transformed cells, noting its association with the large tumor antigen of the SV40 virus. This breakthrough revealed p53’s role in cellular processes and its function as a tumor suppressor. Dubbed the “Guardian of the Genome,” p53 plays a critical role in maintaining genetic stability by responding to DNA damage. It activates repair mechanisms, induces cell cycle arrest in the G1 phase via the Cdk-inhibitor protein p21, or initiates apoptosis if the damage is irreparable. Mutations in the p53 gene are implicated in over 50% of human cancers, underlining its vital role in preventing cancer development by protecting the integrity of the genome. The Retinoblastoma Protein (pRB) and Adenovirus E1A: The retinoblastoma protein (pRB), a crucial tumor suppressor, was found to coimmunoprecipitate with the adenovirus E1A oncoprotein. This interaction revealed a direct link between viral oncogenes and cellular tumor suppressors. The binding of E1A to pRB disrupts its normal function, promoting uncontrolled cell proliferation by preventing pRB from regulating the E2F family of transcription factors. The Role of pRB as a Tumor Suppressor: pRB is another essential tumor suppressor that regulates the cell cycle. It acts by binding to and inhibiting E2F transcription factors, thereby controlling the transition from the G1 to the S phase of the cell cycle. Loss or inactivation of pRB leads to deregulated cell cycle progression, a hallmark of cancer. This protein is particularly significant in early-life cancers such as retinoblastoma and plays a broader role in the suppression of tumorigenesis. Discovery of Phosphoinositide 3-Kinase (PI3K): The discovery of phosphoinositide 3- kinase (PI3K) was a groundbreaking development in understanding cellular signaling. Researchers identified PI3K activity in association with the polyomavirus middle T antigen, noting its role as a lipid kinase that phosphorylates the 3-position of the inositol ring. This discovery elucidated a new pathway critical for cell growth and survival. PI3K Signaling Pathway in Cell Growth and Survival: The PI3K signaling pathway is vital for regulating cell growth, survival, and metabolism. Activation of PI3K leads to the production of phosphatidylinositol-3,4,5-triphosphate (PIP3), which recruits and activates downstream effectors such as Akt. This pathway promotes cell proliferation and inhibits apoptosis, making it a key player in normal cellular processes and a common target for dysregulation in cancer. Tumor suppressors like PTEN act as negative regulators of this pathway, and their loss contributes to oncogenic transformation. AstraZeneca Vaxzevria: he AstraZeneca Vaxzevria COVID-19 vaccine is based on a chimpanzee adenovirus vector (ChAdOx1), which has been engineered to lack the E1 and E3 genes, ensuring it cannot replicate in human cells. To facilitate its growth in HEK293 cells, parts of the E4 region of the chimpanzee adenovirus have been replaced with equivalent regions from a human adenovirus (HuAd5). This design enhances the safety and effectiveness of the vaccine while leveraging the viral vector to deliver the SARS-CoV-2 spike protein, inducing an immune response. Cancer remains one of the most significant global health challenges due to its high morbidity and mortality rates. - Austria (2013 vs. 2022): In 2013, cancer accounted for 20-25% of mortality in Austria, with common cancers in men being prostate, colon, and lung cancer, and in women, breast, colon, and lung cancer. In 2022, there were approximately 20 million new cancer cases worldwide and 9.7 million deaths. Lung cancer was the most common type globally, with 2.5 million cases (12.4%), followed by breast cancer (2.3 million cases, 11.6%) and colorectal cancer (1.9 million cases, 9.6%). - Morbidity vs. Mortality: While cancer morbidity (new cases) is high, early detection and treatment can significantly reduce mortality. In the United States, for instance, 1,762,450 new cases were diagnosed in 2018, but 606,880 deaths were reported, reflecting the gap between diagnosis and fatal outcomes. How to Prevent Cancer: Avoiding Risk Factors: Many cancers are preventable by addressing modifiable risk factors that damage DNA and initiate carcinogenesis. Key strategies include: - Avoiding Carcinogens: Refrain from exposure to tobacco smoke and harmful chemicals. - Reducing Radiation Exposure: Limit ultraviolet (UV) light exposure, a major cause of skin cancer. - Preventing Infections: Address infections by viruses like Hepatitis B and HPV, which account for 15-20% of cancers worldwide, through vaccination and safer practices. - Lifestyle Modifications: Maintain a healthy diet, regular exercise, and minimize alcohol consumption. Public health measures, such as vaccination campaigns and promoting safe practices, are vital for reducing cancer incidence globally. These preventive strategies not only lower the individual risk but also lessen the overall burden of cancer on healthcare systems. Viruses, Bacteria, and Parasites in Cancer Development: Approximately 15-20% of human cancers are linked to infections caused by viruses, bacteria, and parasites. This association is more pronounced in less developed countries, where infections contribute to 22.9% of cancer cases compared to 7.4% in developed regions. Notable cancer-causing agents include Helicobacter pylori, hepatitis B and C viruses, and human papillomaviruses (HPV), which are responsible for cancers such as gastric, liver, and cervical cancers. Among women, cervical cancer accounts for about 50% of infection-related cancers, while in men, liver and gastric cancers dominate, comprising over 80% of such cases. Public health interventions, including vaccination, safer injection practices, and antimicrobial treatments, have proven effective in reducing these risks, emphasizing the importance of preventive measures to combat infection-related cancers. Viruses Involved in Human Cancer Development: Several viruses are directly implicated in cancer development. These include: - DNA viruses such as: - Hepatitis B virus (HBV): Linked to hepatocellular carcinoma. - Human papillomavirus (HPV): Strongly associated with cervical cancer and other anogenital and oropharyngeal cancers. - Epstein-Barr virus (EBV): Connected to nasopharyngeal carcinoma and certain lymphomas. Spontaneous lytic replication and epitheliotropism define an epstein-barr virus strain found in carcinomas. - Merkel cell polyomavirus (MCV): Causes most Merkel cell carcinoma and was discovered in 2008. - RNA viruses such as: - Hepatitis C virus (HCV): A major cause of liver cancer. HCV contains a positive- strand RNA genome. - Human T-lymphotropic virus (HTLV): Associated with adult T-cell leukemia/lymphoma. These viruses contribute to oncogenesis through mechanisms such as chronic inflammation, immune system evasion, and the direct activation of oncogenic pathways. Global Burden of Infection-Attributable Cancers (2008): In 2008, approximately 2 million of the 12.7 million new cancer cases worldwide were attributed to infections. This burden was disproportionately higher in less developed regions, where infection- attributable cancers were more prevalent. H. pylori, HBV, HCV, and HPV were the most significant contributors, collectively responsible for 1.9 million cancer cases globally. HBV has HbsAg (Hebatitis B surface antigen). The data underscores the importance of addressing infectious causes of cancer, particularly in resource-limited settings, where public health measures such as vaccination, early detection, and treatment could significantly reduce the cancer burden. Attributable Fraction of Cancer Related to Viral Infections (2012): In 2012, an estimated 16.1% of all new cancer cases globally (around 2 million cases) were attributable to viral infections. This fraction was significantly higher in less developed countries (22.9%) compared to developed regions (7.4%). The primary viruses contributing to this burden were Hepatitis B (HBV), Hepatitis C (HCV), and Human Papillomavirus (HPV), which together caused the majority of these cancers. HBV and HCV are predominantly associated with liver cancer, while HPV is linked to cervical and other anogenital cancers. Hepatitis B infection: Transmission and Epidemiology: Hepatitis B is a highly infectious virus that attacks the liver, causing acute and chronic diseases. It is 50–100 times more infectious than HIV and spreads through contact with infected blood or body fluids. Modes of transmission include perinatal transmission, unsafe injections, and sexual contact. Approximately 254 million people were living with chronic HBV infection in 2022, with 1.2 million new infections annually. Symptoms: Acute hepatitis B is often asymptomatic but can cause jaundice, dark urine, fatigue, and abdominal pain. Chronic infections can lead to cirrhosis or hepatocellular carcinoma (HCC). Disease Burden: Around 50% of people with chronic HBV infections develop progressive liver disease, with 1–2% developing HCC annually. Chronic HBV infections cause 60% of liver cancer cases in Africa and Asia and 20% in Europe and the US. Prevention and Treatment: The hepatitis B vaccine, introduced in 1982, provides 98- 100% protection. It is recommended for infants within 24 hours of birth, dramatically reducing chronic infection rates. Chronic HBV infections are treated with antiviral agents like tenofovir and entecavir, though a complete cure remains elusive. HBV is a small DNA virus with a partially double-stranded genome of 3.2 kb. It encodes four genes: - S Gene: Produces the hepatitis B surface antigen (HBsAg). - C Gene: Encodes the core antigen (HBcAg) forming the viral nucleocapsid. - P Gene: Encodes a reverse transcriptase essential for viral replication. - X Gene: Produces the regulatory HBx protein, which promotes viral replication and contributes to oncogenesis by protecting infected cells from immune destruction. Prevalence of Chronic Hepatitis B in Populations Born Before and After Vaccine Introduction: Before the introduction of the HBV vaccine, chronic infection rates in children were 8–15% in endemic areas. Vaccination has reduced this prevalence to less than 1% among immunized children under five years old. This significant reduction demonstrates the vaccine’s efficacy in preventing long-term liver diseases and liver cancer. HPV Infection: HPV is the most common sexually transmitted infection, with over 100 types identified. Of these, 12 are high-risk types (e.g., HPV16, HPV18) that cause cervical, anal, vulvar, vaginal, penile, and oropharyngeal cancers. HPV-related cancers include nearly all cervical cancer cases, 70% of oropharyngeal cancers, and over 90% of anal cancers. Vaccines like Gardasil® and Gardasil 9® provide protection against the most oncogenic HPV types, significantly reducing cancer incidence. HPVs are double-stranded DNA viruses with a circular genome. High-risk types like HPV16 and HPV18 encode oncoproteins E6 and E7, which inactivate tumor suppressors p53 and pRB, respectively. This leads to unregulated cell proliferation and genomic instability. HPV infects epithelial cells, and its life cycle is closely tied to host cell differentiation, allowing it to evade immune responses and establish persistent infections. Common Cancers in Women: Globally, the most common cancers in women are breast cancer, cervical cancer, and colorectal cancer. Cervical cancer is the third most common female cancer in women aged 15 to 44 and remains a significant health challenge, particularly in low-income countries. Example of a Malignant Tumor: Cervical Cancer: Staging and Histopathology: - Staging: Cervical cancer progresses from precancerous lesions (CIN1, CIN2, CIN3) to invasive carcinoma. Early-stage tumors are confined to the cervix, while advanced stages spread to surrounding tissues and distant organs. - Histopathology: The transformation zone of the cervix, where columnar epithelium meets squamous epithelium, is particularly susceptible to HPV- induced changes. Precancerous lesions show cellular dysplasia, while invasive cancer is characterized by poorly differentiated cells with high mitotic activity. The Pap Smear Technique: This screening method involves collecting cervical cells to detect precancerous or cancerous changes. It has been instrumental in reducing cervical cancer incidence and mortality through early detection and treatment. Combined with HPV vaccination and routine screening, cervical cancer is now considered a preventable disease. HPV Vaccination and Gardasil 9: HPV vaccination is a critical tool in preventing cervical cancer and other HPV-associated cancers. Vaccines such as Gardasil® and Gardasil 9® protect against high-risk HPV types, including HPV 16 and 18, which cause the majority of cervical cancers. Gardasil 9®, approved in 2014, provides broader protection by covering nine HPV types (6, 11, 16, 18, 31, 33, 45, 52, and 58), significantly reducing infection and precancerous lesions caused by these types. The vaccine is most effective when administered before exposure to HPV, typically recommended for girls and boys starting at age 9. The 2017 Lasker-DeBakey Award: The 2017 Lasker-DeBakey Clinical Medical Research Award was given to Douglas R. Lowy and John T. Schiller for their groundbreaking technological advances in developing HPV vaccines. These vaccines have proven to be highly effective in preventing cervical cancer and other HPV-induced malignancies, marking a milestone in cancer prevention. Efficacy of HPV Vaccination: The HPV vaccine has demonstrated remarkable efficacy in reducing HPV infections and related diseases. Studies show that within ten years of its introduction, infections from the targeted HPV types decreased by 86% among females aged 14–19 and by 71% among those aged 20–24. Vaccination has also significantly reduced the prevalence of anogenital warts and high-grade cervical lesions (CIN2+), with modeling data estimating reductions of up to 87% in cervical cancer cases for cohorts vaccinated early. Proportion of Australians Diagnosed with Genital Warts: Following the introduction of the HPV vaccination program in Australia, the incidence of genital warts dramatically declined. Among Australian-born women, diagnoses fell significantly, particularly in those aged 15–19 years. A similar trend was observed in heterosexual men, attributable to herd immunity from female vaccination. Vaccination Against Invasive HPV-Associated Cancers: HPV vaccination provides protection against invasive cancers caused by HPV, including cervical, anal, and oropharyngeal cancers. By preventing persistent HPV infections that lead to malignancies, the vaccine has become a cornerstone of public health efforts to combat these cancers worldwide. Vaccine Safety Monitoring Data: Over 135 million doses of HPV vaccines have been distributed in the United States, and safety monitoring data confirm their strong safety profile. Most side effects are mild, including pain or redness at the injection site, dizziness, or headache. Severe allergic reactions are extremely rare, occurring at a rate of 3 cases per million doses. Large-scale studies have found no association between HPV vaccination and autoimmune diseases, reinforcing the vaccine’s safety. A Cervical Cancer-Free Future: The World Health Organization (WHO) has set a global target to eliminate cervical cancer through vaccination, screening, and treatment. By 2030, the goal is to have 90% of girls vaccinated with the HPV vaccine by age 15, 70% of women screened by age 35 and 45, and 90% of cervical disease cases treated. Achieving these targets could avert 74 million new cases of cervical cancer and 62 million deaths, especially in low- and middle-income countries where the burden is greatest. Impact of Vaccines: Vaccines have a profound impact on public health, preventing millions of deaths and severe illnesses. For example, vaccination against measles prevents subacute sclerosing panencephalitis (SSPE), a rare but fatal neurological complication that can occur years after a measles infection. Before widespread vaccination, measles caused significant mortality, with 1–3 children per 1,000 dying from complications. Vaccination campaigns have nearly eradicated such devastating outcomes. The Lancet MMR Autism Fraud: In 1998, Andrew Wakefield falsely linked the MMR vaccine (measles, mumps, and rubella) to autism, a claim that was later exposed as fraudulent. Wakefield’s study was retracted, and he was found guilty of professional misconduct. This fraud caused a significant drop in vaccination rates, leading to outbreaks of measles and mumps, unnecessary deaths, and long-term disabilities. Extensive scientific reviews have since confirmed no link between the MMR vaccine and autism. Unethical Criticism by Opponents of Vaccination and the Parachute Analogy: Opponents of vaccination often use unethical or scientifically unsound arguments to discredit vaccines. An ironic analogy likened vaccination critics to someone refusing to use a parachute without randomized controlled trials proving its efficacy. This satirical comparison highlights the absurdity of demanding unnecessary proof for well- established life-saving measures, illustrating how vaccines, like parachutes, are essential for survival under certain conditions. This critique underscores the importance of evidence-based health policies in countering vaccine misinformation. Immune Responses to Human Papillomavirus (HPV): HPV has developed sophisticated mechanisms to evade the host immune system, enabling persistent infections that can lead to malignancies. These mechanisms affect both innate and adaptive immune responses. Innate Immune Evasion: - Lack of Inflammatory Signals: HPV replicates in the differentiated keratinocytes of the skin or mucosa, cells that die naturally without inducing inflammation. This minimizes the release of pro-inflammatory cytokines. - Limited Immune Recognition: Viral particles are produced in superficial epithelial layers, away from antigen-presenting cells (APCs) such as Langerhans cells, reducing the likelihood of immune activation. - Downregulation of Type I Interferon Response: HPV inhibits the production and signaling of type I interferons, critical components of the antiviral innate immune response. - Absence of Viremia: The virus remains localized in the epithelium without entering the bloodstream, preventing systemic immune activation. Adaptive Immune Response: Despite HPV’s evasion strategies, most individuals eventually develop a robust adaptive immune response, primarily mediated by: - Cell-Mediated Immunity: - The adaptive response is dominated by Th1-type CD4+ T cells, which produce interferon-gamma (IFN-γ) to promote cytotoxic responses. - CD8+ cytotoxic T lymphocytes (CTLs) target infected basal keratinocytes expressing early viral proteins, such as E6 and E7, essential for the viral lifecycle. - Humoral Immunity: - Neutralizing antibodies, predominantly against the L1 capsid protein, are produced following exposure. These antibodies block viral entry into host cells during subsequent infections. However, these antibodies are type-specific and may not protect against different HPV types. - Natural infection with HPV often induces low antibody titers due to the virus’s limited systemic spread, making reinfection possible. Role of Viral Proteins in Immune Evasion: - E6 and E7 Oncoproteins: These proteins interfere with immune detection by degrading tumor suppressors (e.g., p53 and pRB), preventing apoptosis, and promoting immune evasion. - Capsid Proteins: Entry of HPV capsids into APCs fails to activate Langerhans cells effectively, limiting the priming of adaptive responses. - E5 Protein: This protein delays endosomal acidification, impairing antigen processing and presentation. Vaccination and Immune Response: HPV vaccines like Gardasil® and Cervarix® induce a strong immune response by presenting virus-like particles (VLPs) composed of the L1 protein. These vaccines elicit higher antibody titers than natural infection, providing long-lasting immunity and cross-protection against related HPV types. Importantly, vaccination primes the immune system to respond effectively upon exposure, bypassing HPV’s natural evasion mechanisms. By targeting both innate and adaptive immune responses, ongoing research aims to develop second-generation vaccines and therapies that overcome HPV’s immune evasion strategies, ensuring better prevention and treatment of HPV-associated diseases. Benign versus Malignant Tumors and Benign Tumors in General: Benign tumors are non-cancerous growths localized to their site of origin. They are non-invasive, do not metastasize, and are often encapsulated by a fibrous capsule. While benign tumor cells resemble normal cells and are generally non-harmful, their size or location can cause medical issues, such as pressure on adjacent tissues or overproduction of hormones. Examples of Benign Tumors: - Warts: Benign skin growths caused by viruses, such as HPV. - Plantar Warts: Painful growths on the soles of the feet, often treated with salicylic acid or surgical removal. Malignant Tumors = Cancer: Malignant tumors, or cancers, are characterized by uncontrolled growth, invasiveness, and the ability to metastasize to distant sites. These tumors consist of poorly differentiated cells with high nuclear-to-cytoplasmic ratios, prominent nucleoli, and frequent mitoses. Unlike benign tumors, malignant cells invade surrounding tissues, spread via the bloodstream or lymphatic system, and form secondary growths in other organs. The Incidence of Most Types of Human Cancers Increases with Age: Cancer incidence rises with age due to the accumulation of genetic mutations over time. Age- related declines in immune surveillance also contribute to the increased susceptibility to cancer in older individuals. Colon Cancer - An Example of the Multi-Hit Model of Cancer Induction: Colon cancer exemplifies the multi-hit model of carcinogenesis, where multiple genetic mutations accumulate over time to drive tumor development. These mutations often involve the activation of proto-oncogenes (e.g., KRAS) and inactivation of tumor suppressor genes (e.g., APC and TP53), leading to the stepwise progression from benign polyps to invasive carcinoma. Polyposis Colon Hereditary Colorectal Cancer Syndrome: Familial adenomatous polyposis (FAP) is a hereditary syndrome characterized by the development of numerous colorectal polyps due to mutations in the APC gene. If untreated, these polyps almost invariably progress to colorectal cancer, demonstrating the critical role of genetic predisposition in cancer development. Wnt Proteins Bind to Frizzled Receptors and Inhibit the Degradation of Beta- Catenin: The Wnt signaling pathway is a critical regulator of cell proliferation, differentiation, and survival. Central to this pathway is the interaction between Wnt proteins and their receptors, which leads to the stabilization and accumulation of beta- catenin, a key signaling molecule. Mechanism of Wnt Signaling: - Wnt Binding: Wnt proteins are secreted glycoproteins that bind to Frizzled receptors (a family of G-protein-coupled receptors) on the cell surface. This binding also requires low-density lipoprotein receptor-related proteins (LRP5/6) as co-receptors, which are essential for propagating the signal.  - Activation of the Signalosome: Wnt binding induces the clustering of Frizzled and LRP5/6 receptors, leading to the recruitment of intracellular proteins like Dishevelled (Dvl). Dishevelled inhibits the destruction complex composed of Axin, APC (adenomatous polyposis coli), and glycogen synthase kinase 3-beta (GSK-3β). - Inhibition of Beta-Catenin Degradation: In the absence of Wnt, the destruction complex phosphorylates beta-catenin, marking it for ubiquitination and protosomal degradation. Upon Wnt activation, the destruction complex is disrupted, preventing beta-catenin phosphorylation and degradation. - Beta-Catenin Stabilization and Nuclear Translocation: Stabilized beta-catenin accumulates in the cytoplasm and translocates into the nucleus. In the nucleus, beta-catenin interacts with TCF/LEF transcription factors, activating the transcription of Wnt target genes that promote cell proliferation and survival. Biological Significance of Wnt/Beta-Catenin Signaling: - Developmental Processes: The Wnt pathway plays a crucial role in embryonic development, regulating cell fate determination, axis formation, and organogenesis. - Tissue Homeostasis: In adults, Wnt signaling maintains tissue renewal in systems such as the intestinal epithelium, where beta-catenin drives the proliferation of stem and progenitor cells. - Cancer and Pathology: Dysregulation of the Wnt pathway, particularly mutations in APC or beta-catenin, is a hallmark of many cancers, including colorectal cancer. Aberrant activation leads to unchecked cell proliferation and tumorigenesis, highlighting the pathway as a target for cancer therapies. Therapeutic Implications: Targeting the Wnt pathway offers promising avenues for cancer treatment. Potential strategies include: - Inhibiting Wnt ligand secretion (e.g., blocking porcupine, a key enzyme in Wnt protein maturation). - Targeting beta-catenin activity directly with small molecules to disrupt its interaction with TCF/LEF transcription factors. - Modulating Frizzled and LRP5/6 receptor interactions to regulate pathway activation. The Wnt/beta-catenin signaling pathway underscores the fine balance between normal physiological processes and pathological conditions like cancer, making it a crucial focus of biomedical research. Neoplasm (Tumor) Size: Tumor size often correlates with disease severity and progression. Larger tumors may be more likely to invade surrounding tissues or metastasize, posing a greater threat to the host. The Six Hallmark Capabilities of Cancer: The six classic hallmarks of cancer, as identified by Hanahan and Weinberg, include: 1. Sustaining proliferative signaling. 2. Evading growth suppressors. 3. Resisting cell death. 4. Enabling replicative immortality. 5. Inducing angiogenesis. 6. Activating invasion and metastasis. Emerging Hallmarks and Enabling Characteristics: Hanahan and Weinberg later expanded the model to include emerging hallmarks, such as deregulating cellular energetics and avoiding immune destruction, and enabling characteristics, including genome instability and tumor-promoting inflammation. Hallmarks of Cancer: The evolving understanding of cancer biology now incorporates the tumor microenvironment, including stromal and immune cells, as key contributors to cancer progression. These dimensions highlight the complex interplay between cancer cells and their surroundings. Neoplasm/Tumor: A neoplasm or tumor arises when the balance between cell proliferation and death shifts toward excessive growth. This imbalance can result from the activation of proto-oncogenes, inactivation of tumor suppressor genes, or evasion of apoptosis, leading to the accumulation of abnormal cells. Tumors may be benign, confined to their site of origin, or malignant, with the ability to invade and metastasize. Neoplasm Formation: A neoplasm or tumor arises when the balance between cell proliferation and cell death shifts toward an increase in cell numbers. This imbalance can occur due to: - Increased proliferation rates caused by the activation of proto-oncogenes or oncogenes. - Decreased apoptosis due to the inhibition of tumor suppressor genes or apoptosis-inducing factors. This dual effect disrupts homeostasis, leading to uncontrolled cell growth and tumor formation. Increased Proliferation Rate: An increased proliferation rate in cancer cells occurs due to the activation of proliferation-inducing genes (proto-oncogenes). This activation allows cells to bypass normal growth controls, leading to unregulated cell division. Key mechanisms include:  - Oncogene Activation: Point Mutations: Example: A single-point mutation in RAS results in a permanently active protein that continuously signals for cell division via the MAPK/ERK pathway. Gene Amplification: Overexpression of genes like MYC, which regulates transcription of growth-promoting genes. - Receptor Tyrosine Kinase Activation: Growth factor receptors such as EGFR or HER2 are overexpressed or mutated, leading to persistent activation of downstream signaling pathways (e.g., PI3K/Akt/mTOR and MAPK) that promote cell cycle progression. - Disruption of Cell Cycle Checkpoints: Inactivation of the retinoblastoma protein (pRB) allows unrestricted activation of E2F transcription factors, which drive the expression of genes required for DNA replication and S-phase entry. - Loss of Feedback Regulation: Cancer cells often produce their own growth factors (autocrine signaling) or are hypersensitive to external signals, further amplifying their proliferative capacity. Decreased Death Rate: A decreased rate of apoptosis (programmed cell death) is a hallmark of cancer, allowing cells to survive despite damage or oncogenic signaling. Mechanisms include: - Inactivation of Pro-Apoptotic Proteins: p53 Mutation: Loss of p53 function disables the cell’s ability to initiate apoptosis in response to DNA damage or oncogenic stress. - Overexpression of Anti-Apoptotic Proteins: Bcl-2 Family Proteins: Overexpression of Bcl-2 or Bcl-xL prevents the activation of pro-apoptotic proteins like Bax and Bak, which are necessary for mitochondrial membrane permeabilization and cytochrome c release. - Disruption of Death Receptor Signaling: Cancer cells downregulate death receptors like Fas (CD95) or decoy receptors, reducing sensitivity to external apoptosis-inducing signals (e.g., immune system attack). - Evasion of Mitochondrial Apoptosis Pathways: Cancer cells often upregulate inhibitors of apoptosis proteins (IAPs), which block the caspase cascade, halting the execution phase of apoptosis. - Altered Survival Signaling: Persistent activation of PI3K/Akt signaling promotes survival by phosphorylating and inhibiting pro-apoptotic proteins like Bad and caspase activators. Properties of Cancer Cells In Vitro and In Vivo: In Vitro Properties: - Loss of Contact Inhibition: Cancer cells continue dividing even when in contact with neighboring cells, forming foci in monolayer cultures. - Anchorage-Independent Growth: Cancer cells can proliferate in semi-solid media, such as soft agar, demonstrating their ability to survive and divide without attachment to a substrate. This property correlates with tumor-forming capacity in vivo.  - Immortalization: Cancer cells bypass senescence and achieve immortality by upregulating telomerase, which maintains telomere length during repeated cell divisions. - Increased Metabolism: Cancer cells exhibit the Warburg effect, consuming high amounts of glucose and relying on glycolysis for energy production, even in the presence of oxygen. This metabolic shift supports rapid growth and is detected using PET scans with glucose analogs. In Vivo Properties: - Tumor Formation in Immunocompromised Mice: Transformed cells injected into nude or SCID mice form tumors, indicating their capacity for growth in a live host without immune system interference. - Angiogenesis: Cancer cells stimulate blood vessel formation by secreting pro- angiogenic factors like VEGF, ensuring an adequate nutrient supply. - Invasion and Metastasis: Cancer cells degrade the extracellular matrix and invade surrounding tissues. They travel through the bloodstream or lymphatic system to colonize distant organs. - Immune Evasion: Tumor cells evade immune destruction by downregulating MHC class I molecules or expressing immune checkpoint proteins like PD-L1, which inhibit T-cell activity. These specific characteristics distinguish cancer cells from normal cells, providing insights into their behavior and potential therapeutic targets. Transformed Cells Form Foci: In cell cultures, transformed cancer cells lose contact inhibition, enabling them to form dense clusters, or foci. This behavior contrasts with normal cells, which stop dividing when they form a monolayer due to contact- dependent signals. Anchorage-Independent Growth: Cancer cells can proliferate without attachment to a solid surface, a property measured in soft agar assays. This ability reflects their capacity for metastasis, as cells that survive in suspension are more likely to colonize distant tissues. The Warburg Effect in Tumor Cells: The Warburg effect is a metabolic hallmark of cancer cells, characterized by their preference for aerobic glycolysis over oxidative phosphorylation, even in the presence of oxygen. This altered metabolism supports the rapid proliferation and survival of tumor cells. - Increased Glucose Uptake: Cancer cells upregulate glucose transporters (e.g., GLUT1) to increase glucose import. This high glucose demand is visualized clinically using PET scans with radiolabeled glucose analogs like fluorodeoxyglucose (FDG), which accumulate in tumors.  - Preferential Glycolysis: Instead of fully oxidizing glucose in the mitochondria, cancer cells convert glucose into lactate via glycolysis, even when oxygen is available. This process is less efficient in ATP production but provides intermediates for biosynthetic pathways (e.g., nucleotides, lipids) needed for rapid cell growth. - Regulation by Oncogenes and Tumor Suppressors: Myc upregulates glycolytic enzymes. PI3K/Akt/mTOR signaling enhances glucose uptake and glycolytic activity. p53 mutations disrupt mitochondrial function, further promoting glycolysis. - Microenvironmental Adaptation: Lactate accumulation acidifies the tumor microenvironment, promoting immune evasion and facilitating invasion by degrading the extracellular matrix. Test of Tumorigenicity in Nude, Immunocompromised Mice: Tumorigenicity assays involve injecting transformed cells into nude mice, which lack a functional immune system. The ability of the cells to form tumors in vivo confirms their oncogenic potential and mimics human cancer progression. DNA and RNA Tumor Viruses: - DNA Tumor Viruses: Include polyomavirus, HPV, and Epstein-Barr virus (EBV), which encode oncoproteins like E6 and E7 to inactivate p53 and pRB. - RNA Tumor Viruses: Include retroviruses such as HTLV-1, which integrate into host DNA and activate oncogenes. These viruses disrupt normal cellular processes, driving uncontrolled proliferation and transformation. Hepatitis B Virus (HBV) in Hepatocellular Carcinoma (HCC): HBV is a major cause of HCC, especially in regions with high endemicity. Chronic infection causes persistent liver inflammation, promoting cirrhosis and genetic mutations. The HBV X protein (HBx) enhances viral replication, suppresses apoptosis, and contributes to tumorigenesis by interfering with p53 and activating oncogenic pathways. The 1976 Nobel Prize in Physiology or Medicine was awarded to Baruch S. Blumberg and D. Carleton Gajdusek for their discoveries of mechanisms underlying infectious diseases. Blumberg identified the Hepatitis B virus, enabling the development of the first HBV vaccine, which later became the first vaccine to prevent a human cancer (HCC). Hepatitis B Infection and HBx: Hepatitis B virus (HBV) is a partially double-stranded DNA virus that infects liver cells, leading to acute and chronic liver disease. Chronic infection is a major risk factor for hepatocellular carcinoma (HCC) due to persistent inflammation, liver damage, and direct viral effects. HBV Genome and Lifecycle: - The HBV genome consists of four genes (S, C, P, and X): - S Gene encodes the hepatitis B surface antigen (HBsAg). - C Gene produces the core antigen (HBcAg) and the secreted antigen (HBeAg). - P Gene encodes the viral polymerase, essential for reverse transcription and replication. - X Gene encodes the HBx protein, which is critical for viral replication and pathogenesis. HBx Protein: HBx is a small regulatory protein with multiple roles in HBV infection and tumorigenesis: - Transactivation of Viral and Host Genes: HBx activates transcription of viral and cellular genes by interacting with host transcription factors, such as NF-κB, AP-1, and CREB. - Interference with Tumor Suppressors: HBx binds to and inhibits p53, impairing its DNA repair and pro-apoptotic functions. This disruption promotes genomic instability and allows cells with damaged DNA to proliferate. - Activation of Oncogenic Pathways: HBx stimulates pathways like PI3K/Akt/mTOR and Wnt/β-catenin, promoting cell survival, proliferation, and tumorigenesis. - Mitochondrial Dysfunction: HBx localizes to mitochondria, altering calcium signaling and inducing reactive oxygen species (ROS), which contribute to oxidative stress and DNA damage. Clinical Implications of HBV and HBx: - Persistent Inflammation: Chronic HBV infection triggers immune responses that lead to liver fibrosis, cirrhosis, and ultimately HCC. - Integration into Host Genome: HBV DNA integrates into the host genome, disrupting normal genes and further driving oncogenesis. - Therapeutic Targeting of HBx: Since HBx is central to HBV pathogenesis and HCC development, it is a potential target for antiviral and anticancer therapies. HBx exemplifies how a viral protein can hijack host cell processes, contributing to the transition from infection to malignancy. PAPOVA-Virus History: The history of PAPOVA viruses highlights their significant role in understanding cancer biology: - 1842: Rigoni-Stern hypothesizes a sexually transmitted agent as the cause of cervical carcinoma. - 1933: Shope isolates a papillomavirus from cottontail rabbits. - 1953: Discovery of polyomavirus by Ludwik Gross.  - 1958: The name “polyoma” is proposed due to its ability to induce various tumors in mice. - 1960: SV40 is discovered as a contaminant in polio vaccines. - 1984: Harald zur Hausen establishes the link between HPV and cervical cancer. Human Papillomavirus (HPV) and Cervical Carcinoma: HPV is the primary cause of cervical cancer, a disease affecting approximately 604,000 women worldwide annually, with 342,000 deaths reported in 2020. HPV types 16 and 18 account for about 70% of all cervical cancer cases. Persistent infection with high-risk HPV types leads to the integration of viral DNA into the host genome, disrupting cell cycle regulators and promoting malignancy. Nobel Prize in Physiology or Medicine (2008): Harald zur Hausen was awarded the Nobel Prize in Physiology or Medicine in 2008 for his groundbreaking discovery that HPV causes cervical cancer. This work overturned prior beliefs and identified HPV as the first viral cause of a common human cancer, paving the way for vaccines that prevent HPV- associated malignancies. HPV and Its Discovery: HPV is a double-stranded DNA virus with more than 100 types identified. Its discovery as the cause of cervical cancer involved decades of research by Harald zur Hausen, who demonstrated that HPV DNA is integrated into the genomes of cancer cells. This finding led to the identification of HPV types 16 and 18 as the major oncogenic strains, a breakthrough that revolutionized cancer prevention. The discovery of HPV’s role in cervical cancer: - Revealed that >5% of all cancers worldwide are caused by persistent HPV infection. - Enabled the development of vaccines (e.g., Gardasil® and Cervarix®) that provide over 95% protection against high-risk HPV types, significantly reducing cervical cancer incidence. - Highlighted the need for early screening and vaccination to prevent HPV-related cancers. Small DNA Tumor Viruses: Small DNA tumor viruses, such as polyomavirus, SV40, and HPV, are associated with cancer development. These viruses have compact genomes that encode oncogenic proteins capable of disrupting host cell cycle regulators, promoting uncontrolled proliferation and transformation. Similar Genome Organisation of PAPOVA Viruses: PAPOVA viruses share several genomic features: - Double-stranded, circular DNA genomes.  - Single origin of replication. - Genome divided into early regions (expressed before DNA replication) and late regions (expressed after replication). - Dependence on host cell machinery for replication and protein expression. Genome Organisation of Polyomavirus: The polyomavirus genome is 5,292 bp long and encodes: - Early transcripts: Three T antigens (small, middle, and large T) responsible for cell transformation and replication. - Late transcripts: Three capsid proteins necessary for viral particle assembly. - The genome is tightly regulated, with early gene expression preceding late gene expression. The Polyomavirus Early-Region: The early region of polyomavirus encodes tumor (T) antigens that modulate host cell functions: - Large T antigen binds host proteins like pRB and p53 to drive cell cycle progression. - Middle T antigen recruits kinases to activate signaling pathways such as PI3K. - Small T antigen affects protein phosphatase 2A (PP2A) activity, altering signal transduction. Genome Organisation of SV40: The SV40 genome is similar to other PAPOVA viruses, with early and late transcription units. Its early region encodes large T (LT) and small T (ST) antigens, while the late region produces structural proteins. LT plays a crucial role in DNA replication and host cell transformation. Genome Organisation of HPV: The HPV genome (~7,904 bp) is divided into early, late, and regulatory regions: - Early genes (E1-E7): - E1: Viral helicase essential for DNA replication. - E2: Regulates transcription and genome maintenance. - E4: Promotes cell cycle arrest and viral release. - E5: Enhances growth factor signaling. - E6: Inactivates p53, enabling cell survival and proliferation. - E7: Binds pRB, disrupting cell cycle control. - Late genes (L1, L2): Encode structural capsid proteins required for virion assembly. - Regulatory region (LCR): Contains origin of replication and promoters for viral transcription. Oncoproteins of SV40 and Polyomavirus: The oncoproteins of SV40 and polyomavirus (e.g., T antigens) are multifunctional. They: - Interact with host tumor suppressors (e.g., pRB, p53) to drive uncontrolled cell proliferation. - Act as molecular chaperones, modulating the activity of cellular protein complexes. - Facilitate viral DNA replication by recruiting host machinery. Multiple Functions of Large T Antigen: The large T antigen (LT) of SV40 is a nuclear phosphoprotein with diverse roles: - Binds to the viral origin of replication, acting as a helicase to initiate replication. - Interacts with host DNA polymerase and topoisomerase to facilitate replication. - Inactivates pRB and p53, promoting cell cycle progression and evasion of apoptosis. - Activates transcription of late viral genes and represses early gene expression. Functional Organization of SV40 LT: The SV40 large T antigen is organized into functional domains: - Origin-binding domain: Recognizes and binds the viral replication origin. - ATPase/helicase domain: Unwinds DNA for replication. - Host interaction domains: Bind tumor suppressors like pRB and p53 to disrupt cell cycle regulation. - Regulatory domain: Modulates viral gene transcription and coordinates the switch from early to late gene expression. This multifunctionality makes LT a critical player in both viral replication and oncogenesis: The T Antigens Function as Molecular Chaperones for Multiprotein Complexes. The T antigens of DNA tumor viruses, such as SV40 and polyomavirus, act as molecular chaperones to facilitate the assembly and regulation of multiprotein complexes involved in viral replication and host cell transformation. Specifically: - J-Domain Homology: T antigens possess a J-domain, which is homologous to the chaperone DnaJ. This domain interacts with Hsc70/DnaK, stimulating its ATPase activity to regulate protein conformation and stability. - Complex Formation: By interacting with host replication machinery, T antigens facilitate the assembly of complexes necessary for viral DNA replication, including DNA polymerase, primase, and topoisomerase. - Protein Folding and Function: T antigens ensure proper folding and functionality of viral and host proteins, enabling processes like replication, transcription, and cell cycle manipulation. Oncoproteins of DNA Tumor Viruses Inactivate Tumor Suppressors pRB and p53: DNA tumor virus oncoproteins, such as SV40 Large T antigen, HPV E6, and HPV E7, inactivate key tumor suppressors: - pRB Inactivation: Viral oncoproteins bind to the pocket domain of pRB, preventing it from inhibiting E2F transcription factors. This allows cells to bypass the G1/S checkpoint and enter S-phase prematurely. - p53 Inactivation: Oncoproteins like HPV E6 and SV40 Large T bind to and degrade or inhibit p53. This impairs DNA damage responses, apoptosis, and senescence, enabling the survival of cells with genomic instability. S-Phase Induction and p53 Inhibition by Viral Oncoproteins: Viral oncoproteins drive infected cells into S-phase to facilitate viral DNA replication. However, this inappropriate activation of the cell cycle triggers stress responses mediated by p53, leading to apoptosis. To counteract this: - Viral proteins like HPV E6 promote the degradation of p53 through interactions with E6AP (a cellular ubiquitin ligase). - This inhibition of p53 ensures that the infected cell survives, enabling persistent infection and transformation. The HPV E6 Oncoprotein Affects Several Processes Through Host Protein Interactions: The E6 oncoprotein of high-risk HPV types disrupts multiple cellular processes via specific protein interactions: - p53 Degradation: E6 binds to E6AP, an E3 ubiquitin ligase, to ubiquitinate and degrade p53. This inhibits apoptosis and facilitates cell survival despite DNA damage. - Activation of Telomerase: E6 upregulates hTERT, the catalytic subunit of telomerase, enabling replicative immortality. - Loss of Cell Polarity: E6 targets PDZ domain proteins like Dlg and ZO-1, disrupting cell-cell junctions and polarity. - DNA Damage Induction: E6 interferes with DNA repair mechanisms, increasing genomic instability. - Focal Adhesion and Anoikis Resistance: E6 activates focal adhesion kinase (FAK), promoting resistance to anoikis (detachment-induced apoptosis). The HPV E7 Oncoprotein Affects Several Processes Through Host Protein Interactions: The E7 oncoprotein also manipulates critical cellular pathways: - pRB Degradation: E7 binds to and degrades pRB, freeing E2F transcription factors to drive S-phase entry and DNA replication. - Centrosome Abnormalities: E7 induces centrosome duplication errors, leading to chromosomal instability. - DNA Damage and Genomic Instability: E7 activates the ATM pathway, contributing to DNA breaks and chromosomal alterations.  - Anoikis Resistance: E7 interacts with p600, a ubiquitin ligase, to promote anchorage-independent growth. - Immune Evasion: E7 modulates components of the interferon response (e.g., IRF1) to escape immune detection. Differences Between High-Risk and Low-Risk HPV E6 and E7 Proteins: - High-Risk E6/E7: Strongly inactivate p53 and pRB, respectively, promoting cellular transformation and tumorigenesis. - Low-Risk E6/E7: Weaker interactions with p53 and pRB, leading to benign lesions such as warts rather than malignancies. The HPV Life Cycle: The HPV life cycle is tightly linked to epithelial differentiation: - Entry and Maintenance: HPV infects basal epithelial cells, where E1 and E2 proteins maintain the viral genome as episomes. - Replication: In differentiating cells, E1 and E2 levels increase, enabling genome amplification. - Late Gene Expression: In suprabasal layers, L1 and L2 capsid proteins are expressed for virion assembly. - Release: Fully formed virions are shed with dead keratinocytes, avoiding immune detection. Integration of Viral DNA: In high-grade lesions and cancer, HPV DNA integrates into the host genome, disrupting the expression of regulatory proteins (e.g., E2). This leads to uncontrolled expression of E6 and E7, further promoting oncogenesis. Changes in Viral Gene Expression During Cancer Progression: The viral gene expression pattern shifts during cancer progression: - Low-Grade Lesions (CIN1): Viral replication is productive, with balanced expression of early and late genes. - High-Grade Lesions (CIN2/3): Late gene expression (e.g., L1 and L2) decreases, and E6/E7 levels rise. - Cancer: Viral episomes are often lost, and the integrated genome expresses E6/E7 without E1/E2, driving cell proliferation and genomic instability. Neoplasm/Tumor: A neoplasm, or tumor, arises when the balance between cell proliferation and cell death is disrupted, leading to excessive cell growth. This can result from an increased proliferation rate due to the activation of proto-oncogenes or decreased apoptosis through the inhibition of tumor suppressor genes (e.g., p53). Tumors can be benign (localized and non-invasive) or malignant (capable of invasion and metastasis). The development of tumors often follows a multi-hit model, where multiple genetic mutations accumulate over time, increasing the likelihood of cancer. Middle T Antigen and Polyomavirus Transformation: Polyomavirus transformation of host cells is primarily driven by Middle T antigen (MT). This viral protein is crucial for cellular transformation and oncogenesis. The MT antigen mimics an activated growth factor receptor, which initiates downstream signaling pathways that promote cell proliferation and survival. This mimicry is essential for the oncogenic potential of the virus. Polyomavirus Middle T Antigen Mimics Activated Growth Factor Receptor: The MT antigen of polyomavirus recruits and activates cellular proteins, mimicking the role of a constitutively active growth factor receptor. It is phosphorylated at key tyrosine residues (e.g., Y250, Y315, Y322), which facilitates the binding of signaling proteins such as Src kinase, phosphatidylinositol 3-kinase (PI3K), and phospholipase C (PLC-γ). This leads to the activation of multiple signaling cascades promoting transformation, proliferation, and survival. Assembly of the Middle T Antigen Transformation Complex: The formation of the MT transformation complex relies on the binding of Src kinase and protein phosphatase 2A (PP2A). This interaction is critical for initiating downstream oncogenic signaling pathways. Mutations in the tyrosine residues of MT impair its ability to bind Src and PP2A, reducing its transforming potential. Src kinase phosphorylates MT, further stabilizing the transformation complex. Ordered Assembly of the Middle T Antigen Transformation Complex: The assembly of the MT transformation complex follows a stepwise and ordered process: - MT is phosphorylated at Y250, which recruits Src kinase. - PP2A binds to the phosphorylated MT, facilitating additional phosphorylations at Y315 and Y322. - Recruitment of PI3K and PLC-γ activates survival and proliferation pathways, essential for cellular transformation. PP2A: A Prime Example of PSTP Multi-Subunit Architecture: Protein phosphatase 2A (PP2A) exemplifies a multi-subunit architecture characteristic of protein serine/threonine phosphatases (PSTPs). PP2A consists of three subunits: a structural A subunit, a catalytic C subunit, and a regulatory B subunit that governs substrate specificity. This combinatorial assembly allows PP2A to interact with various cellular proteins, exerting precise control over phosphorylation states and cellular signaling. Reversible Phosphorylation in Cellular Proteome: Approximately one-third of the cellular proteome is phosphorylated at any given time. The distribution of phosphorylated residues is predominantly: - Phosphoserine (~90%) - Phosphothreonine (~10%) - Phosphotyrosine (