Viruses can cause cancer through several mechanisms. Small DNA tumor viruses like HPV and adenovirus often integrate into the host genome and express early genes that promote cell cycle progression and prevent apoptosis. This leads to uncontrolled cell growth. Herpesviruses like EBV and KSHV can cause cancer during their latency phase by expressing genes that induce cell activation and proliferation programs. Chronic viral infections may also cause cancer over long periods through prolonged inflammation. Studying virus-associated cancers provides insights into cancer mechanisms and potential new targets for treatment.

1. Viruses cause cancer Download lecture at: flemingtonlab.com

2. Viruses cause cancer Why has the study of viruses and cancer been important?

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. 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. Viruses cause cancer 30-40% of cancers are known to have viral etiology But as more research is done, this percentage is likely to be found to be higher

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. Changes in cell that are at the roots of cancer

8. Changes in cell that are at the roots of cancer Genetic and epigenetic alterations:

9. Changes in cell that are at the roots of cancer Genetic and epigenetic alterations: Mutations Deletions Recombinations Transpositions Epigenetic alterations (DNA methylation, imprinting) Acquisition of viral genetic material

10. Changes in cell that are at the roots of cancer Genetic and epigenetic alterations: Mutations Deletions Recombinations Transpositions Epigenetic alterations (DNA methylation, imprinting) Acquisition of viral genetic material Various combinations of these lead to the development of cancers - some viruses contribute single hits while others contribute multiple hits.

11. Inherited Somatic Random Transposition Exposure to deleterious environmental agents Radiation carcinogenic chemicals Viruses Other persistent infections Source of genetic alterations

12. Integrations that cause activation or inactivation of oncogenes or tumor suppressors (e.g. RNA viruses) Expression of genes that alter key signal transduction pathways - this is our focus Chronic activation of inflammatory responses How do Viruses contribute to cancer?

13. Why do viruses cause cancer?

14. Viruses and cancer cells have similar needs Proliferation control Cell death control Modulation of immune response Induction of vascularization Metastasis (tumor)/cell migration (viruses) Why do viruses cause cancer?

15. If you’re infected, does this mean that you will get cancer?

16. No Viruses did not specifically evolve with the need to cause cancer - they simply have similar (but distinct) needs If you’re infected, does this mean that you will get cancer?

17. No Viruses did not specifically evolve with the need to cause cancer - they simply have similar (but distinct) needs Development of tumors almost always requires: Additional genetic alterations and/or Compromised host (e.g. immuno-suppression) If you’re infected, does this mean that you will get cancer?

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. Adenovirus Human virus but only causes cancer in non-human cells SV40 Mesothelioma HPV Cervical Cancer Squamous cell anal carcinoma Penile cancer Oral cancers Small DNA tumor viruses

20. HPV SV40 Adenovirus Normally replicate episomally but almost always found integrated in associated tumors - why? Small DNA tumor viruses

21. HPV SV40 Adenovirus Normally replicate episomally but almost always found integrated in associated tumors - why? Replication must be abortive HPV, viral encoded negative regulatory factor must be deleted Small DNA tumor viruses

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. DNA Tumor Viruses In Human Cancer Papilloma Viruses >100 types identified - most common are types 6 and 11 Most cervical, vulvar and penile cancers are ASSOCIATED with types 16 and 18 (70% of penile cancers) Effective Vaccine (quadrivalent recombinant HPV 6, 11, 16 and 18 proteins made in yeast - Gardasil)

24. Papilloma Viruses The important transforming genes in papilloma viruses are the non-structural regulatory genes, E6 and E7 HPV is normally episomal but is always integrated in tumors

26. Adenoviruses Highly oncogenic in animals Only part of virus integrated Always the same part Early (regulatory) genes E1A and E1B = Oncogenes

27. SV40 The important transforming gene is T Ag - provides similar functions as E1A + E1B (Adenovirus) and E6 and E7 (HPV)

28. Abortive replication is key to oncogenesis by these small viruses Expression of early (regulatory) genes in absence of structural genes and virus production Can occur by infection of non-permissive host Can occur by integrations that delete regions of viral genome required for replication but leave early genes intact.

29. Small DNA Tumor Viruses What are the needs of small DNA tumor viruses that make them oncogenic and What are the key mechanisms through which they attain their needs?

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

33. Inappropriate activation of cell cycle

34. Inappropriate activation of cell cycle Apoptosis

35. Inappropriate activation of cell cycle Apoptosis e.g. Overexpression of E2F1 or c-Myc induces cell cycle and apoptosis Defense mechanism against rogue proliferating cells?

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

37. Encode early genes that inhibit apoptosis Adenovirus E1B HPV E6 SV40 T Ag

38. SV40 and HPV

39. Adenovirus E1B is Bcl2 family member - blocks function of pro-apoptotic Bcl2 family members through dimerization

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)

41. Herpes viruses Oncogenic members: Epstein Barr virus (EBV) Kaposi’s Sarcoma Herpes virus (KSHV) Oncogenic mechanisms are distinct from small DNA tumor viruses - Don’t need to integrate - Cell cycle is not driven by lytic replication regulatory genes

42. Herpes viruses Hallmark of herpesviruses:

43. Herpes viruses Hallmark of herpesviruses: Existence of latent stage (in addition to lytic/replicative stage)

44. Herpes viruses Lytic replication phase for herpesviruses:

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

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

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

48. Epstein Barr virus Pathologies in immuno- competent individuals Infectious mononucleosis Burkitt’s Lymphoma Hodgkin’s lymphoma Nasopharyngeal carcinoma Pathologies in immuno- compromised individuals Post-transplant lymphoproliferative diseases (PTLD) Hodgkin’s lymphoma A variety of non-Hodgkin’s lymphoblastoid malignancies

49. Epstein Barr virus Latency genes Non-antigenic EBNA1 (Epstein Barr Nuclear Antigen 1) - episomal replication and segregation function Antigenic EBNA2 EBNA3A, 3B, 3C EBNA-LP LMP1 (Latent Membrane Protein 1) LMP2A Those in Red are key regulatory genes involved in B cell activation

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) Growth program Initial infection (prior to immune response) Immuno-compromised individuals - in vitro infection of naïve peripheral blood lymhocytes

54. Epstein Barr virus Greater than 90% of US population are carriers of EBV Only small percentage of carriers develop tumors - who? Immuno-compromised - allows full set of oncongenic genes to be expressed Immuno-competent who have multiple additional genetic hits EBV does not integrate - exists as an extrachromosomal episome

55. Kaposi’s Sarcoma Herpes Virus - HHV-8 Hematologic malignancies Primary effusion lymphoma Multicentric Castleman's disease (MCD) – a rare lymphoproliferative disorder (AIDS) MCD-related immunoblastic/plasmablastic lymphoma Various atypical lymphoproliferative disorders Kaposi’s sarcoma

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

57. Silver lining to viral associate cancers Offer unique targets not common to normal uninfected cells Examples: HPV Gardasil EBV In vitro production of EBV specific CTLs for PTLD Treatment with agents that induce lytic cycle (butyrate plus Gancyclovir) KSHV - Anti-retroviral therapy