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40. tv

  1. 1. Viruses cause cancer Download lecture at: flemingtonlab.com
  2. 2. Viruses cause cancer Why has the study of viruses and cancer been important?
  3. 3. Viruses cause cancer Why has the study of viruses and cancer been important? - We learn about the basic mechanisms of specific types of tumors .
  4. 4. Viruses cause cancer Why has the study of viruses and cancer been important? - We learn about the basic mechanisms of specific types of tumors . - We identify fundamental pathways important for oncogenesis - viruses are lower complexity - We can identify potential unique therapeutic targets for viral associated tumors
  5. 5. Viruses cause cancer <ul><li>30-40% of cancers are known to have viral etiology </li></ul><ul><li>But as more research is done, </li></ul><ul><li>this percentage is likely to be found to be higher </li></ul>
  6. 6. Major human Oncogenic Viruses DNA Viruses Small DNA tumor viruses - Adenovirus - SV40 - Human Papilloma virus (HPV) Herpesviruses (large) - Epstein Barr virus (EBV) - Kaposi’s Sarcoma Herpesvirus (KSHV) Other - Hepatitis virus B RNA viruses Human T-cell Leukemia Virus 1 (HTLV1) Hepatitis virus C
  7. 7. Changes in cell that are at the roots of cancer
  8. 8. Changes in cell that are at the roots of cancer <ul><li>Genetic and epigenetic alterations: </li></ul>
  9. 9. Changes in cell that are at the roots of cancer <ul><li>Genetic and epigenetic alterations: </li></ul><ul><ul><ul><li>Mutations </li></ul></ul></ul><ul><ul><ul><li>Deletions </li></ul></ul></ul><ul><ul><ul><li>Recombinations </li></ul></ul></ul><ul><ul><ul><li>Transpositions </li></ul></ul></ul><ul><ul><ul><li>Epigenetic alterations (DNA methylation, imprinting) </li></ul></ul></ul><ul><ul><ul><li>Acquisition of viral genetic material </li></ul></ul></ul>
  10. 10. Changes in cell that are at the roots of cancer <ul><li>Genetic and epigenetic alterations: </li></ul><ul><ul><ul><li>Mutations </li></ul></ul></ul><ul><ul><ul><li>Deletions </li></ul></ul></ul><ul><ul><ul><li>Recombinations </li></ul></ul></ul><ul><ul><ul><li>Transpositions </li></ul></ul></ul><ul><ul><ul><li>Epigenetic alterations (DNA methylation, imprinting) </li></ul></ul></ul><ul><ul><ul><li>Acquisition of viral genetic material </li></ul></ul></ul><ul><ul><li>Various combinations of these lead to the development of cancers - some viruses contribute single hits while others contribute multiple hits. </li></ul></ul>
  11. 11. <ul><li>Inherited </li></ul><ul><li>Somatic </li></ul><ul><ul><li>Random </li></ul></ul><ul><ul><li>Transposition </li></ul></ul><ul><ul><li>Exposure to deleterious environmental agents </li></ul></ul><ul><ul><ul><li>Radiation </li></ul></ul></ul><ul><ul><ul><li>carcinogenic chemicals </li></ul></ul></ul><ul><ul><ul><li>Viruses </li></ul></ul></ul><ul><ul><ul><li>Other persistent infections </li></ul></ul></ul>Source of genetic alterations
  12. 12. <ul><li>Integrations that cause activation or inactivation of oncogenes or tumor suppressors (e.g. RNA viruses) </li></ul><ul><li>Expression of genes that alter key signal transduction pathways - this is our focus </li></ul><ul><li>Chronic activation of inflammatory responses </li></ul>How do Viruses contribute to cancer?
  13. 13. Why do viruses cause cancer?
  14. 14. <ul><li>Viruses and cancer cells have similar needs </li></ul><ul><ul><li>Proliferation control </li></ul></ul><ul><ul><li>Cell death control </li></ul></ul><ul><ul><li>Modulation of immune response </li></ul></ul><ul><ul><li>Induction of vascularization </li></ul></ul><ul><ul><li>Metastasis (tumor)/cell migration (viruses) </li></ul></ul>Why do viruses cause cancer?
  15. 15. If you’re infected, does this mean that you will get cancer?
  16. 16. <ul><li>No </li></ul><ul><ul><li>Viruses did not specifically evolve with the need to cause cancer - they simply have similar (but distinct) needs </li></ul></ul>If you’re infected, does this mean that you will get cancer?
  17. 17. <ul><li>No </li></ul><ul><ul><li>Viruses did not specifically evolve with the need to cause cancer - they simply have similar (but distinct) needs </li></ul></ul><ul><ul><ul><li>Development of tumors almost always requires: </li></ul></ul></ul><ul><ul><ul><ul><li>Additional genetic alterations and/or </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Compromised host (e.g. immuno-suppression) </li></ul></ul></ul></ul>If you’re infected, does this mean that you will get cancer?
  18. 18. Major human Oncogenic Viruses DNA Viruses Small DNA tumor viruses - Adenovirus - SV40 - Human Papilloma virus (HPV) Herpesviruses (large) - Epstein Barr virus (EBV) - Kaposi’s Sarcoma Herpesvirus (KSHV) Other - Hepatitis virus B RNA viruses Human T-cell Leukemia Virus 1 (HTLV1) Hepatitis virus C
  19. 19. <ul><li>Adenovirus </li></ul><ul><ul><li>Human virus but only causes cancer in non-human cells </li></ul></ul><ul><li>SV40 </li></ul><ul><ul><li>Mesothelioma </li></ul></ul><ul><li>HPV </li></ul><ul><ul><li>Cervical Cancer </li></ul></ul><ul><ul><li>Squamous cell anal carcinoma </li></ul></ul><ul><ul><li>Penile cancer </li></ul></ul><ul><ul><li>Oral cancers </li></ul></ul>Small DNA tumor viruses
  20. 20. <ul><li>HPV </li></ul><ul><li>SV40 </li></ul><ul><li>Adenovirus </li></ul><ul><li>Normally replicate episomally but almost always found integrated in associated tumors - why? </li></ul>Small DNA tumor viruses
  21. 21. <ul><li>HPV </li></ul><ul><li>SV40 </li></ul><ul><li>Adenovirus </li></ul><ul><li>Normally replicate episomally but almost always found integrated in associated tumors - why? </li></ul><ul><ul><li>Replication must be abortive </li></ul></ul><ul><ul><li>HPV, viral encoded negative regulatory factor must be deleted </li></ul></ul>Small DNA tumor viruses
  22. 22. DNA Tumor Viruses In Human Cancer 10% of human cancers may be HPV-linked 16% of all female cancers linked to HPV Papilloma Viruses urogenital cancer wart malignant squamous cell carcinoma Papilloma viruses are found in 91% of women with cervical cancer
  23. 23. DNA Tumor Viruses In Human Cancer <ul><li>Papilloma Viruses </li></ul><ul><li>>100 types identified - most common are types 6 and 11 </li></ul><ul><li>Most cervical, vulvar and penile cancers are ASSOCIATED with types 16 and 18 (70% of penile cancers) </li></ul>Effective Vaccine (quadrivalent recombinant HPV 6, 11, 16 and 18 proteins made in yeast - Gardasil)
  24. 24. Papilloma Viruses <ul><li>The important transforming genes in papilloma viruses are the non-structural regulatory genes, E6 and E7 </li></ul><ul><li>HPV is normally episomal but is always integrated in tumors </li></ul>
  25. 26. Adenoviruses Highly oncogenic in animals Only part of virus integrated Always the same part Early (regulatory) genes E1A and E1B = Oncogenes
  26. 27. SV40 <ul><li>The important transforming gene is T Ag </li></ul><ul><li>- provides similar functions as E1A + E1B (Adenovirus) and E6 and E7 (HPV) </li></ul>
  27. 28. Abortive replication is key to oncogenesis by these small viruses <ul><li>Expression of early (regulatory) genes in absence of structural genes and virus production </li></ul><ul><ul><li>Can occur by infection of non-permissive host </li></ul></ul><ul><ul><li>Can occur by integrations that delete regions of viral genome required for replication but leave early genes intact. </li></ul></ul>
  28. 29. Small DNA Tumor Viruses <ul><li>What are the needs of small DNA tumor viruses that make them oncogenic and </li></ul><ul><li>What are the key mechanisms through which they attain their needs? </li></ul>
  29. 30. Need cells that are in S-phase to replicate viral genome Host enzymes Small DNA Tumor Viruses DNA viral genome Host RNA polymerase Viral mRNA Viral protein Utilizes Host Cell DNA Replication Machinery
  30. 33. Inappropriate activation of cell cycle
  31. 34. Inappropriate activation of cell cycle Apoptosis
  32. 35. Inappropriate activation of cell cycle <ul><li>Apoptosis </li></ul><ul><li>e.g. </li></ul><ul><li>Overexpression of E2F1 or c-Myc induces cell cycle and apoptosis </li></ul><ul><ul><ul><li>Defense mechanism against rogue proliferating cells? </li></ul></ul></ul>
  33. 36. Inappropriate activation of cell cycle Apoptosis e.g. - Overexpression of E2F1 or c-Myc induces cell cycle and apoptosis - Same is true for over-expression of Adenovirus E1A or HPV E7
  34. 37. Encode early genes that inhibit apoptosis Adenovirus E1B HPV E6 SV40 T Ag
  35. 38. SV40 and HPV
  36. 39. Adenovirus E1B is Bcl2 family member - blocks function of pro-apoptotic Bcl2 family members through dimerization
  37. 40. Summary Small DNA tumor viruses usually replicate in episomal form but are found integrated in viral associated tumors Early genes promote cell cycle progression and prevent apoptosis Adenovirus - E1A (cell cycle) and E1B (apoptosis) HPV - E7 (cell cycle) and E6 (apoptosis) SV40 - T Ag (cell cycle and apoptosis)
  38. 41. Herpes viruses <ul><li>Oncogenic members: </li></ul><ul><li>Epstein Barr virus (EBV) </li></ul><ul><li>Kaposi’s Sarcoma Herpes virus (KSHV) </li></ul><ul><li>Oncogenic mechanisms are distinct from small </li></ul><ul><li>DNA tumor viruses </li></ul><ul><li>- Don’t need to integrate </li></ul><ul><li>- Cell cycle is not driven by lytic replication regulatory genes </li></ul>
  39. 42. Herpes viruses Hallmark of herpesviruses:
  40. 43. Herpes viruses Hallmark of herpesviruses: Existence of latent stage (in addition to lytic/replicative stage)
  41. 44. Herpes viruses Lytic replication phase for herpesviruses:
  42. 45. Herpes viruses Lytic replication phase for herpesviruses: - Herpesviruses are large and encode 80-100 lytic associated genes - Encode their own DNA polymerase and replication accessory enzymes - Therefore, they don’t require an S-phase environment for replication - Encode early genes that induce cell cycle arrest
  43. 46. Herpes viruses Latency: - Small subset of viral genes are expressed that are not expressed during lytic replication. - Latency is partly a way for virus to hide from immune system - In cases of EBV and KSHV, latency genes can also induce cell differentiation/activation programs that facilitate expansion of infected cell population and induce trafficking to specific lymphoid compartments that are suited to the life cycle of the virus
  44. 47. Herpes viruses Human Herpesviruses and latency function: Epstein Barr virus (EBV) - multiple functions Kaposi’s Sarcoma Herpes virus (KSHV) - multiple functions Cytomegalovirus (CMV) - Stealth mechanism Herpes Simplex (HSV) - Stealth mechanism
  45. 48. Epstein Barr virus <ul><li>Pathologies in immuno- competent individuals </li></ul><ul><li>Infectious mononucleosis </li></ul><ul><li>Burkitt’s Lymphoma </li></ul><ul><li>Hodgkin’s lymphoma </li></ul><ul><ul><li>Nasopharyngeal carcinoma </li></ul></ul><ul><li>Pathologies in immuno- compromised individuals </li></ul><ul><li>Post-transplant lymphoproliferative diseases (PTLD) </li></ul><ul><li>Hodgkin’s lymphoma </li></ul><ul><li>A variety of non-Hodgkin’s lymphoblastoid malignancies </li></ul>
  46. 49. Epstein Barr virus <ul><li>Latency genes </li></ul><ul><li>Non-antigenic </li></ul><ul><li>EBNA1 (Epstein Barr Nuclear Antigen 1) - episomal replication and segregation function </li></ul><ul><li>Antigenic </li></ul><ul><li>EBNA2 </li></ul><ul><li>EBNA3A, 3B, 3C </li></ul><ul><li>EBNA-LP </li></ul><ul><li>LMP1 (Latent Membrane Protein 1) </li></ul><ul><li>LMP2A </li></ul>Those in Red are key regulatory genes involved in B cell activation
  47. 51. Epstein Barr virus 4 different types of latency True Latency - no viral gene expression EBNA1 only - EBNA1 (non-antigenic) Default - EBNA1, LMP1, and LMP2 (moderately antigenic) Growth - EBNA1, LMP1, LMP2, EBNA2, EBNA-LP, EBNA3A, 3B, 3C (highly antigenic) <ul><li>Growth program </li></ul><ul><li>Initial infection (prior to immune response) </li></ul><ul><li>Immuno-compromised individuals </li></ul><ul><li>- in vitro infection of naïve peripheral blood lymhocytes </li></ul>
  48. 54. Epstein Barr virus <ul><li>Greater than 90% of US population are carriers of EBV </li></ul><ul><li>Only small percentage of carriers develop tumors - who? </li></ul><ul><li>Immuno-compromised - allows full set of oncongenic genes to be expressed </li></ul><ul><li>Immuno-competent who have multiple additional genetic hits </li></ul>EBV does not integrate - exists as an extrachromosomal episome
  49. 55. Kaposi’s Sarcoma Herpes Virus - HHV-8 <ul><li>Hematologic malignancies </li></ul><ul><li>Primary effusion lymphoma </li></ul><ul><li>Multicentric Castleman's disease (MCD) – a rare lymphoproliferative disorder (AIDS) </li></ul><ul><li>MCD-related immunoblastic/plasmablastic lymphoma </li></ul><ul><li>Various atypical lymphoproliferative disorders </li></ul>Kaposi’s sarcoma
  50. 56. Hepatitis B and C Long latency period to development of HCC (Hepatocellular Carcinoma) 20-30 years Mechanism is probably due to chronic inflammatory response
  51. 57. Silver lining to viral associate cancers Offer unique targets not common to normal uninfected cells <ul><li>Examples: </li></ul><ul><li>HPV </li></ul><ul><li>Gardasil </li></ul><ul><li>EBV </li></ul><ul><li>In vitro production of EBV specific CTLs for PTLD </li></ul><ul><li>Treatment with agents that induce lytic cycle </li></ul><ul><li>(butyrate plus Gancyclovir) </li></ul><ul><li>KSHV </li></ul><ul><li>- Anti-retroviral therapy </li></ul>

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