Oncogenesis and Viral Proteins
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Questions and Answers

Which of the following oncogenic viruses is associated with Adult T cell leukemia?

  • Human Papillomavirus 16 and 18
  • Hepatitis C virus
  • Epstein-Barr Virus
  • Human T-lymphotropic virus-I (correct)

    • What is the primary mechanism of oncogenesis in retroviruses?

  • Inhibition of tumor suppressor genes
  • Chronic infection and inflammation
  • Insertional mutagenesis (correct)
  • Activation of cellular oncogenes

    • Which of the following is a characteristic of DNA tumor viruses?

  • They have a lipid envelope
  • They are single-stranded RNA viruses
  • They have a reverse transcriptase enzyme
  • They express viral oncogenes (correct)

    • What is the name of the herpesvirus associated with Kaposi's sarcoma?

    <p>Human Herpesvirus 8</p> Signup and view all the answers

    What is the name of the gene that is used for the synthesis of structural proteins in retroviruses?

    <p>Gag</p> Signup and view all the answers

    Which of the following is an example of an indirect carcinogen?

    <p>Hepatitis B virus</p> Signup and view all the answers

    What is the term for the process by which retroviruses integrate their genetic material into the host cell DNA?

    <p>Proviral integration</p> Signup and view all the answers

    Which of the following is a feature of the retroviral genome?

    <p>LTR-gag-pol-env-LTR</p> Signup and view all the answers

    What is the role of the tax protein in HTLV-1 oncogenesis?

    <p>To interact with cellular transcription factors and signaling molecules</p> Signup and view all the answers

    What is the consequence of DNA tumor virus replication in permissive cells?

    <p>Cell lysis and cell death</p> Signup and view all the answers

    Which of the following is NOT a mechanism of oncogenesis by DNA tumor viruses?

    <p>Stimulating immune response</p> Signup and view all the answers

    What is the effect of E6 and E7 proteins of HPV on cellular gene expression?

    <p>Inhibition of p53 and RB</p> Signup and view all the answers

    What is the role of HBx protein in HBV oncogenesis?

    <p>Inactivation of p53</p> Signup and view all the answers

    What is the characteristic feature of DNA tumor viruses?

    <p>They are double-stranded DNA viruses</p> Signup and view all the answers

    What is the consequence of viral DNA integration into host chromosomes in non-permissive cells?

    <p>Cell transformation and oncogenesis</p> Signup and view all the answers

    What is the common mechanism of retroviral oncogenesis?

    <p>All of the above</p> Signup and view all the answers

    What is a characteristic of slow-transforming retroviruses?

    <p>They integrate randomly in the DNA</p> Signup and view all the answers

    What is the percentage of HTLV-I carriers that develop disease?

    <p>2-5%</p> Signup and view all the answers

    What is the outcome of oncogene activation by retroviral insertion?

    <p>Cell transformation is a rare event</p> Signup and view all the answers

    What is the name of the disease caused by HTLV-I?

    <p>Adult T cell leukemia</p> Signup and view all the answers

    What is the mechanism of oncogenesis by slow-transforming retroviruses?

    <p>Integration of promoter sequences and viral enhancers near cellular growth-stimulating genes</p> Signup and view all the answers

    What is the estimated number of people infected with HTLV-I worldwide?

    <p>10-20 million</p> Signup and view all the answers

    What is the primary mechanism by which acutely transforming retroviruses cause rapid tumor development?

    <p>Overproduction of oncogenic proteins</p> Signup and view all the answers

    What occurs when a cellular proto-oncogene is captured by a retrovirus during viral replication?

    <p>The proto-oncogene is inserted into the viral genome</p> Signup and view all the answers

    What is the characteristic feature of tumors formed as a result of retroviral transduction of oncogenes?

    <p>They are polyclonal and form rapidly</p> Signup and view all the answers

    What is the term for the oncogene resulting from the capture of a cellular proto-oncogene by a retrovirus?

    <p>Viral oncogene (v-onc)</p> Signup and view all the answers

    Which of the following is an outcome of retroviral transduction of oncogenes?

    <p>Uncontrolled cellular proliferation</p> Signup and view all the answers

    What is the process by which a retrovirus captures a cellular proto-oncogene and incorporates it into its genome?

    <p>Transduction</p> Signup and view all the answers

    What is the primary mechanism by which essential viral proteins contribute to oncogenesis?

    <p>By activating cellular transcription factors</p> Signup and view all the answers

    How do DNA tumor viruses interfere with cell-cycle regulating proteins?

    <p>By encoding proteins that interfere with p53, retinoblastoma, and others</p> Signup and view all the answers

    What is the characteristic feature of RNA tumor viruses in relation to oncogenes and tumor suppressor genes?

    <p>They activate oncogenes and inactivate tumor suppressor genes</p> Signup and view all the answers

    What is the role of the viral genome in oncogenesis by DNA tumor viruses?

    <p>It encodes proteins that interfere with cell-cycle regulating proteins</p> Signup and view all the answers

    What is the consequence of viral DNA integration into host chromosomes in non-permissive cells?

    <p>Viral DNA integration into different sites of cell chromosomes</p> Signup and view all the answers

    What is the mechanism of oncogenesis by essential retrovirus proteins?

    <p>By activating cellular transcription factors</p> Signup and view all the answers

    What is the characteristic feature of DNA tumor viruses in relation to their replication strategy?

    <p>They have two life forms, depending on the type of infected cell</p> Signup and view all the answers

    What is the primary mechanism by which acute transforming retroviruses induce oncogenesis in host cells?

    <p>Insertional mutagenesis</p> Signup and view all the answers

    What is the common mechanism of oncogenesis by DNA tumor viruses?

    <p>All of the above</p> Signup and view all the answers

    Which of the following is an example of oncogene activation by insertion of a retrovirus?

    <p>Avian leukosis virus-mediated bursal lymphoma</p> Signup and view all the answers

    What is the process by which retroviruses can transduce cellular oncogenes into host cells?

    <p>Viral transduction</p> Signup and view all the answers

    Which of the following retroviral proteins is essential for oncogenesis?

    <p>Tax protein</p> Signup and view all the answers

    What is the term for the viral genes that have the potential to induce oncogenesis in host cells?

    <p>Viral oncogenes</p> Signup and view all the answers

    Which of the following is an example of a viral oncogene that can induce oncogenesis through the activation of cellular signaling pathways?

    <p>v-src gene</p> Signup and view all the answers

    What is the consequence of the activation of viral oncogenes in host cells?

    <p>Cellular transformation</p> Signup and view all the answers

    Which of the following is a characteristic of viral oncogenes that can induce oncogenesis through the activation of cellular signaling pathways?

    <p>They can activate cellular signaling pathways</p> Signup and view all the answers

    What is the primary mechanism by which essential retrovirus proteins contribute to oncogenesis?

    <p>Activation of cellular signal transduction pathways</p> Signup and view all the answers

    What occurs when a retrovirus captures a cellular proto-oncogene during viral replication?

    <p>The retrovirus incorporates the proto-oncogene into its genome</p> Signup and view all the answers

    What is the outcome of oncogene activation by insertion of a retrovirus?

    <p>The activated oncogene induces rapid tumor development</p> Signup and view all the answers

    What is the primary mechanism by which acute transforming retroviruses induce oncogenesis in host cells?

    <p>Insertional mutagenesis of cellular proto-oncogenes</p> Signup and view all the answers

    What is the characteristic feature of viral oncogenes that can induce oncogenesis through the activation of cellular signaling pathways?

    <p>They have the potential to induce oncogenesis in host cells</p> Signup and view all the answers

    What is the primary mechanism by which essential retrovirus proteins contribute to oncogenesis?

    <p>By stimulating cellular proliferation through modification of their functions</p> Signup and view all the answers

    What is the characteristic feature of tumors formed as a result of retroviral transduction of oncogenes?

    <p>They are polyclonal and form within days</p> Signup and view all the answers

    What occurs when a cellular proto-oncogene is captured by a retrovirus during viral replication?

    <p>The cellular proto-oncogene is incorporated into the viral genome, resulting in an oncogene</p> Signup and view all the answers

    What is the primary mechanism by which acutely transforming retroviruses cause rapid tumor development?

    <p>By encoding oncogenic proteins that stimulate cellular proliferation</p> Signup and view all the answers

    What is the term for the oncogene resulting from the capture of a cellular proto-oncogene by a retrovirus?

    <p>Viral oncogene</p> Signup and view all the answers

    What is the primary mechanism by which essential retrovirus proteins contribute to oncogenesis?

    <p>Activation of cellular signaling pathways</p> Signup and view all the answers

    What is the outcome of retroviral transduction of oncogenes?

    <p>Proto-oncogenes are converted into oncogenes</p> Signup and view all the answers

    What is the mechanism of oncogene activation by insertion of a retrovirus?

    <p>Insertion of the retrovirus into a proto-oncogene</p> Signup and view all the answers

    What is the characteristic feature of acute transforming retroviruses?

    <p>They induce oncogenesis through the insertion of viral oncogenes</p> Signup and view all the answers

    What is the characteristic feature of viral oncogenes that can induce oncogenesis through the activation of cellular signaling pathways?

    <p>They are derived from cellular proto-oncogenes</p> Signup and view all the answers

    What is the process by which a retrovirus captures a cellular proto-oncogene and incorporates it into its genome?

    <p>Oncogene activation by insertion</p> Signup and view all the answers

    What is the characteristic feature of tumors formed as a result of retroviral transduction of oncogenes?

    <p>They form within days</p> Signup and view all the answers

    What is the primary mechanism by which acutely transforming retroviruses cause rapid tumor development?

    <p>Overproduction of viral oncogenes</p> Signup and view all the answers

    What is the outcome of oncogene activation by retroviral insertion?

    <p>Single hit carcinogenesis</p> Signup and view all the answers

    What is the term for the oncogene resulting from the capture of a cellular proto-oncogene by a retrovirus?

    <p>Viral oncogene</p> Signup and view all the answers

    What is the characteristic feature of retroviral transduction of oncogenes?

    <p>Tumor growth initiated in every infected cell</p> Signup and view all the answers

    What is the primary mechanism by which acute transforming retroviruses induce oncogenesis in host cells?

    <p>Activation of cellular signaling pathways</p> Signup and view all the answers

    What is the outcome of oncogene activation by insertion of a retrovirus?

    <p>Uncontrolled cell proliferation</p> Signup and view all the answers

    What is the primary mechanism by which retroviruses transduce cellular oncogenes into host cells?

    <p>Capture of cellular proto-oncogenes</p> Signup and view all the answers

    What is the characteristic feature of viral oncogenes that can induce oncogenesis through the activation of cellular signaling pathways?

    <p>Activating cellular signaling pathways</p> Signup and view all the answers

    What is the primary mechanism by which essential retrovirus proteins contribute to oncogenesis?

    <p>Activating cellular signaling pathways</p> Signup and view all the answers

    What occurs when a retrovirus captures a cellular proto-oncogene during viral replication?

    <p>Oncogene activation</p> Signup and view all the answers

    What is the term for the viral genes that have the potential to induce oncogenesis in host cells?

    <p>Viral oncogenes</p> Signup and view all the answers

    What is the common mechanism of oncogenesis by DNA tumor viruses?

    <p>Inactivating tumor suppressor genes</p> Signup and view all the answers

    What is the primary mechanism of oncogenesis by acute transforming retroviruses?

    <p>Activation of cellular proto-oncogenes through insertion</p> Signup and view all the answers

    What occurs when a retrovirus captures a cellular proto-oncogene during viral replication?

    <p>The proto-oncogene is incorporated into the viral genome and expressed as a viral oncogene</p> Signup and view all the answers

    What is the outcome of oncogene activation by insertion of a retrovirus?

    <p>The cellular proto-oncogene is expressed at higher levels, contributing to cancer cell transformation</p> Signup and view all the answers

    What is the primary mechanism of oncogenesis by essential retrovirus proteins?

    <p>Disruption of cellular signaling pathways, leading to uncontrolled cell growth</p> Signup and view all the answers

    What is the characteristic feature of viral oncogenes that can induce oncogenesis through the activation of cellular signaling pathways?

    <p>They activate cellular signaling pathways, leading to uncontrolled cell growth</p> Signup and view all the answers

    What is the consequence of the activation of viral oncogenes in host cells?

    <p>Disruption of cellular signaling pathways, leading to uncontrolled cell growth</p> Signup and view all the answers

    What is the term for the process by which a retrovirus captures a cellular proto-oncogene and incorporates it into its genome?

    <p>Retroviral transduction of oncogenes</p> Signup and view all the answers

    What is the primary mechanism by which acute transforming retroviruses induce oncogenesis in host cells?

    <p>Activation of cellular proto-oncogenes through insertion</p> Signup and view all the answers

    Study Notes

    Oncogenesis and Viral Proteins

    • HTLV-1 oncogenesis involves a nonstructural viral regulatory protein, Tax, essential for viral replication.
    • Tax interacts with cellular transcription factors and signaling molecules to enhance or repress cellular gene expression.

    DNA Tumor Viruses

    • DNA tumor viruses have diverse structures, genome organization, and replication strategies.
    • They have two life forms: in permissive cells, viral replication causes cell lysis and cell death, while in non-permissive cells, viral DNA is mostly integrated into different sites of cellular chromosomes.
    • Oncogenic mechanism in DNA tumor viruses involves the viral genome encoding proteins that interfere with cell-cycle regulating proteins such as p53, retinoblastoma, and others.

    Oncogenic Viruses in Humans

    • Examples of oncogenic viruses in humans include:
      • Epstein-Barr Virus (dsDNA) associated with Burkitt's lymphoma
      • Hepatitis B virus (dsDNA) associated with Hepatocellular carcinoma
      • Human T-lymphotropic virus-I (ss (+) RNA) associated with Adult T cell leukemia
      • Human Papillomavirus 16 and 18 (dsDNA) associated with Cervical cancer
      • Hepatitis C virus (ss (+) RNA) associated with Hepatocellular carcinoma
      • Human Herpesvirus 8 (dsDNA) associated with Kaposi's sarcoma
      • Merkel cell polyomavirus (dsDNA) associated with Merkel Cell carcinoma

    Classification of Oncogenic Viruses

    • Oncogenic viruses can be divided into two broad categories: direct carcinogens and indirect carcinogens.
    • Direct carcinogens express viral oncogenes that directly contribute to cancer cell transformation.
    • Indirect carcinogens cause cancer through chronic infection and inflammation, leading to carcinogenic mutations in host cells.
    • Some viruses, such as HBV, HCV, and HTLV-I, do not fit neatly into either category.

    RNA Tumor Viruses

    • RNA tumor viruses can be divided into two groups based on their genetic material: DNA tumor viruses and RNA tumor viruses.
    • Examples of RNA tumor viruses include retroviruses and hepatitis C virus.
    • Retroviruses have 3 basic genes (gag, pol, and env), which are used for the synthesis of structural proteins, virion-associated enzymes, and envelope glycoproteins.

    Mechanisms of Viral Transformation in Retroviruses

    • Oncogene activation by retroviral insertion occurs through the integration of promoter sequences and viral enhancers near cellular growth-stimulating genes, initiating cell transformation.
    • Retroviruses can cause oncogenesis by inserting near potential oncogenes, leading to cell transformation.
    • Cell transformation is a rare event because insertion near potential oncogenes is infrequent.
    • Monoclonal tumors result from proviral sequences integrated at the same chromosomal site.

    Acute versus Slow Transforming Retroviruses

    • The third group of RNA tumor viruses, including Human T cell Leukemia Virus type I (HTLV-I), constitutes an exception to the paradigm of retroviral oncogenesis.
    • HTLV-I is responsible for Adult T cell leukemia and HTLV-I associated myelopathy neurodegenerative disease.
    • HTLV-I is endemic in parts of Japan, South America, Africa, and the Caribbean, with an estimated 10-20 million people infected worldwide.

    Retroviral Transduction of Oncogene

    • Acute-transforming retrovirus can cause rapid tumor development by encoding oncogenic proteins, which stimulate cellular proliferation
    • Oncogenic proteins are similar to cellular proteins in cellular growth control and are called viral oncogenes (v-onc)
    • Overproduction or modification of these proteins can lead to cancer

    Origin of v-onc Genes

    • Acutely transforming viruses are generated when a cellular protooncogene is captured by insertion into the viral genome during viral replication
    • This process usually causes genetic changes in the protooncogene, resulting in an oncogene

    Outcome of Retroviral Transduction

    • Single-hit carcinogenesis: one event can initiate tumor growth
    • Polyclonal: tumor growth is initiated in every infected cell
    • Tumors form within days
    • Characteristic of animal retroviruses

    Oncogenesis Mediated by Essential Retrovirus Proteins

    • HTLV-1 oncogenesis involves a non-structural viral regulatory protein (tax) essential for viral replication
    • Tax interacts with cellular transcription factors and signaling molecules to enhance or repress cellular gene expression

    DNA Tumor Viruses

    • Diverse group of viruses with different structures, genome organization, and replication strategies
    • Oncogenic potential is linked to virus replication strategy
    • Two life forms: permissive cells (viral replication causes cell lysis and death) and non-permissive cells (viral DNA integrates into cellular chromosomes)

    Oncogenic Mechanism in DNA Tumor Viruses

    • Integrated viral genome encodes proteins that interfere with cell-cycle regulating proteins (e.g., p53, retinoblastoma)
    • Examples: HBV (HBx), HHV-4 (LMP-1), HPV (E6 and E7), HHV8 (vGPCR)

    Conclusions

    • Carcinogenesis is a multi-step process involving mutations of cellular proto-oncogenes and tumor suppressor genes
    • Oncogenic viruses can cause cancer by activating cellular signal transduction pathways, interfering with cell cycle control, and impairing DNA repair

    Classification of Oncogenic Viruses

    • Divided into direct carcinogens (expressing viral oncogenes that directly contribute to cancer cell transformation) and indirect carcinogens (causing cancer through chronic infection and inflammation)
    • Some agents (e.g., HBV, HCV, and HTLV-I) do not fit neatly into either category

    Retroviruses

    • Have 3 basic genes (gag, pol, and env) used for the synthesis of structural proteins, virion-associated enzymes, and envelope glycoproteins
    • LTR-gag-pol-env-LTR structure

    Retroviral Transduction of Oncogene

    • Acute-transforming retrovirus can cause rapid tumor development by encoding oncogenic proteins, which stimulate cellular proliferation
    • Oncogenic proteins are similar to cellular proteins in cellular growth control and are called viral oncogenes (v-onc)
    • Overproduction or modification of these proteins can lead to cancer

    Origin of v-onc Genes

    • Acutely transforming viruses are generated when a cellular protooncogene is captured by insertion into the viral genome during viral replication
    • This process usually causes genetic changes in the protooncogene, resulting in an oncogene

    Outcome of Retroviral Transduction

    • Single-hit carcinogenesis: one event can initiate tumor growth
    • Polyclonal: tumor growth is initiated in every infected cell
    • Tumors form within days
    • Characteristic of animal retroviruses

    Oncogenesis Mediated by Essential Retrovirus Proteins

    • HTLV-1 oncogenesis involves a non-structural viral regulatory protein (tax) essential for viral replication
    • Tax interacts with cellular transcription factors and signaling molecules to enhance or repress cellular gene expression

    DNA Tumor Viruses

    • Diverse group of viruses with different structures, genome organization, and replication strategies
    • Oncogenic potential is linked to virus replication strategy
    • Two life forms: permissive cells (viral replication causes cell lysis and death) and non-permissive cells (viral DNA integrates into cellular chromosomes)

    Oncogenic Mechanism in DNA Tumor Viruses

    • Integrated viral genome encodes proteins that interfere with cell-cycle regulating proteins (e.g., p53, retinoblastoma)
    • Examples: HBV (HBx), HHV-4 (LMP-1), HPV (E6 and E7), HHV8 (vGPCR)

    Conclusions

    • Carcinogenesis is a multi-step process involving mutations of cellular proto-oncogenes and tumor suppressor genes
    • Oncogenic viruses can cause cancer by activating cellular signal transduction pathways, interfering with cell cycle control, and impairing DNA repair

    Classification of Oncogenic Viruses

    • Divided into direct carcinogens (expressing viral oncogenes that directly contribute to cancer cell transformation) and indirect carcinogens (causing cancer through chronic infection and inflammation)
    • Some agents (e.g., HBV, HCV, and HTLV-I) do not fit neatly into either category

    Retroviruses

    • Have 3 basic genes (gag, pol, and env) used for the synthesis of structural proteins, virion-associated enzymes, and envelope glycoproteins
    • LTR-gag-pol-env-LTR structure

    Retroviral Transduction of Oncogene

    • Acute-transforming retrovirus can cause rapid tumor development by encoding oncogenic proteins, which stimulate cellular proliferation
    • Oncogenic proteins are similar to cellular proteins in cellular growth control and are called viral oncogenes (v-onc)
    • Overproduction or modification of these proteins can lead to cancer

    Origin of v-onc Genes

    • Acutely transforming viruses are generated when a cellular protooncogene is captured by insertion into the viral genome during viral replication
    • This process usually causes genetic changes in the protooncogene, resulting in an oncogene

    Outcome of Retroviral Transduction

    • Single-hit carcinogenesis: one event can initiate tumor growth
    • Polyclonal: tumor growth is initiated in every infected cell
    • Tumors form within days
    • Characteristic of animal retroviruses

    Oncogenesis Mediated by Essential Retrovirus Proteins

    • HTLV-1 oncogenesis involves a non-structural viral regulatory protein (tax) essential for viral replication
    • Tax interacts with cellular transcription factors and signaling molecules to enhance or repress cellular gene expression

    DNA Tumor Viruses

    • Diverse group of viruses with different structures, genome organization, and replication strategies
    • Oncogenic potential is linked to virus replication strategy
    • Two life forms: permissive cells (viral replication causes cell lysis and death) and non-permissive cells (viral DNA integrates into cellular chromosomes)

    Oncogenic Mechanism in DNA Tumor Viruses

    • Integrated viral genome encodes proteins that interfere with cell-cycle regulating proteins (e.g., p53, retinoblastoma)
    • Examples: HBV (HBx), HHV-4 (LMP-1), HPV (E6 and E7), HHV8 (vGPCR)

    Conclusions

    • Carcinogenesis is a multi-step process involving mutations of cellular proto-oncogenes and tumor suppressor genes
    • Oncogenic viruses can cause cancer by activating cellular signal transduction pathways, interfering with cell cycle control, and impairing DNA repair

    Classification of Oncogenic Viruses

    • Divided into direct carcinogens (expressing viral oncogenes that directly contribute to cancer cell transformation) and indirect carcinogens (causing cancer through chronic infection and inflammation)
    • Some agents (e.g., HBV, HCV, and HTLV-I) do not fit neatly into either category

    Retroviruses

    • Have 3 basic genes (gag, pol, and env) used for the synthesis of structural proteins, virion-associated enzymes, and envelope glycoproteins
    • LTR-gag-pol-env-LTR structure

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