Human Cancer Viruses Chapter 43

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Questions and Answers

What percentage of all human tumors is estimated to have a viral cause?

35–40%

15–20% (correct)

5–10%

25–30%

Which group of viruses is NOT classified as a DNA tumor virus?

Adenoviruses

Epstein-Barr virus

Papillomaviruses

Hepatitis C virus (correct)

How do DNA tumor viruses primarily affect host cells?

By promoting immune responses

By destroying cellular membranes

By inhibiting viral replication

By encoding viral oncoproteins (correct)

What is the primary function of the reverse transcriptase in retroviruses?

To construct a DNA copy of the RNA genome Signup and view all the answers

Which of the following cancers is strongly associated with human cancer viruses?

Cervical cancer Signup and view all the answers

Which of the following is a characteristic of RNA tumor viruses?

They require reverse transcriptase for infection Signup and view all the answers

Which type of virus can directly cause nephrotoxicity as part of multistep carcinogenesis?

Hepatitis B virus Signup and view all the answers

What is the role of candidate human cancer viruses in research?

They assist in finding new cancer-associated viruses Signup and view all the answers

What characteristic property of RNA tumor viruses is noted regarding their effect on normal cells?

They do not lethally affect cells in which they replicate. Signup and view all the answers

What is a key factor that influences the susceptibility of cells to viral replication?

The presence of surface receptors for the virus. Signup and view all the answers

How do RNA tumor viruses generally behave in immunosuppressed individuals?

They are less likely to be detected by the immune system. Signup and view all the answers

Which of the following best describes the genetic composition of retroviruses?

Single-stranded RNA, linear and usually diploid. Signup and view all the answers

What type of tumors are associated with the tissue specificity of some viruses?

Single tumor types as well as multiple tumor types. Signup and view all the answers

What percentage of RNA composition is typically found in retroviruses?

2% Signup and view all the answers

Which of the following is NOT a component of the virion structure of retroviruses?

Cylindrical exterior Signup and view all the answers

In what condition are cancer cells more likely to escape host immune control?

When the host is immunosuppressed. Signup and view all the answers

What role do oncogenes play in tumor viruses?

They may trigger cellular transformation. Signup and view all the answers

What factor is critical for the viral gene expression and tissue specificity of tumor viruses?

The intracellular factors present in the host cell. Signup and view all the answers

What is the role of tumor suppressor genes in cancer development?

They require the inactivation of both alleles for tumor formation. Signup and view all the answers

Which tumor suppressor gene is primarily involved in the inhibition of cells entering S phase?

Rb Signup and view all the answers

Which statement about tumor viruses is correct?

They can be associated with multiple types of tumors. Signup and view all the answers

How does the p53 gene contribute to cancer prevention?

By regulating synthesis of cell cycle inhibiting proteins. Signup and view all the answers

What is a common consequence of the loss of Rb gene function?

Development of retinoblastoma and other tumors. Signup and view all the answers

Which virus is associated with Adult T-cell leukemia?

Human T-lymphotropic virus Signup and view all the answers

What is necessary for the development of tumors with a viral etiology?

Viruses are cofactors in the malignancy process Signup and view all the answers

Which of the following is an example of a tyrosine-specific protein kinase?

src Signup and view all the answers

What role do growth factors like sis play in cell behavior?

They act as mitogens for connective tissue cells Signup and view all the answers

Which receptor is associated with mutated growth factor activity?

Erb-B receptor Signup and view all the answers

What is a consequence of incorrect expression of cellular components related to cancer?

Uncontrolled growth of cells Signup and view all the answers

Which type of cancer is associated with the Hepatitis C virus?

Hepatocellular carcinoma Signup and view all the answers

What is typically required to convert a benign proto-oncogene into a cancer gene?

Genetic damage Signup and view all the answers

Which statement about tumor viruses is true?

They are necessary but not sufficient for tumor development Signup and view all the answers

What is the function of GTP-binding proteins like Ha-ras in cellular signaling?

Promoting cell growth and division Signup and view all the answers

What is required for cell growth in tumors characterized by Merkel cell virus?

Integration of viral genomes Signup and view all the answers

What type of disease might SV40 cause in rhesus monkeys?

Progressive multifocal leukoencephalopathy-like disease Signup and view all the answers

Which family do human-infecting papillomaviruses belong to?

Papillomaviridae Signup and view all the answers

What distinguishes papillomaviruses from polyomaviruses?

Differences in genome organization Signup and view all the answers

Which of these is a characteristic of tumors associated with Merkel cell virus?

Clonal integration of virus DNA in tumor cells Signup and view all the answers

What role does oncogene expression play in tumors known to be associated with viral infections?

It is crucial for cell growth Signup and view all the answers

In terms of viral oncogenesis, what is the significance of mutations in the T antigen gene?

They prevent viral DNA replication Signup and view all the answers

How does SV40 affect experimental subjects like hamsters and transgenic mice?

It contributes to significant tumor induction Signup and view all the answers

What genera within the Papillomaviridae family contains members that infect humans?

Alpha-, Beta-, Gamma-, Mupa-, and Nupapillomavirus Signup and view all the answers

How are the papillomaviruses and polyomaviruses related in terms of structure?

They share similar morphology Signup and view all the answers

Study Notes

Human Cancer Viruses Overview

Viruses contribute to the development of various human tumors, notably cervical and liver cancer.
Approximately 15–20% of all human tumors worldwide are associated with viral causes.

Major Human Tumor Viruses

Common oncogenic viruses include:
- Human Papillomaviruses (HPVs)
- Epstein-Barr Virus (EBV)
- Human herpesvirus 8
- Hepatitis B Virus
- Hepatitis C Virus
- Human retroviruses

Tumor Virus Categories

DNA tumor viruses:
- Belong to families like papillomavirus, polyomavirus, adenovirus, herpesvirus, hepadnavirus, and poxvirus.
- Encode viral oncoproteins that influence cellular growth control pathways.
RNA tumor viruses:
- Primarily belong to the retrovirus family.
- Use reverse transcriptase to integrate viral RNA into the host genome as DNA (provirus).

Mechanisms of Tumorigenesis

Tumor viruses act as cofactors, providing some necessary steps for malignant cell transformation.
Viral infections can lead to genetic damage but are not solely responsible for tumor development.
Immunosuppression increases cancer risk in individuals, facilitating tumor development from infected cells.

Virus-Induced Genetic Changes

Oncogenes convert from proto-oncogenes through mutations or aberrant expression, often involving growth factors and protein kinases.
Tumor suppressor genes, such as Rb and p53, prevent tumor formation by regulating cell cycle progress.
Loss of function in these genes is linked to several cancers.

Retinoblastoma and p53

Rb gene dysfunction contributes to retinoblastoma, a pediatric ocular tumor.
p53 acts as a critical transcription factor for inhibiting cell cycle kinases and preventing tumor growth.

Tumor Specificity and Integration

Certain tumors show tissue specificity related to viral surface receptor presence and intracellular factors.
Example: Merkel cell virus DNA is integrated into tumor cells, affecting oncogene expression.

Papillomaviruses Classification

Papillomaviridae consists of multiple genera, with five known to infect humans.
It was previously categorized under the Papovaviridae family; however, differences in genome structure led to their reclassification.

Implications for Patients

Individuals with immunosuppressive conditions, such as organ transplant recipients or those with HIV, face an increased risk of virus-related malignancies, including EBV-associated lymphomas and HPV-related diseases.

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Description

This quiz explores the role of viruses in the etiology of human tumors, focusing on significant cancers such as cervical cancer. It covers the genotypes and biophysical characteristics of various human cancer viruses. Test your knowledge on this critical aspect of virology and oncology.