Cancer-associated Infectious Agents: Understanding the Role of Viral Oncogenesis

1. Cancer Etiology1. Introduction 2. Chemical Factors in Carcinogenesis 3. Physical Factors in Carcinogenesis4. Viral Oncogenesis5. Genetic Predisposition Jimin Shao shaojimin@zju.edu.cn

2. Cancer-associated Infectious Agents • Persistent infection with one of several pathogens is an important cause of about 20 percent of cancers worldwide. • This knowledge has enabled the development of new cancer prevention strategies that use medicines and vaccines to eliminate or prevent infection with these agents.

3. Viral Oncogenesis • RNA Oncovirus (Retrovirus) • DNA Oncovirus 3

4. RNA Oncovirus • Retroviruses: • ssRNA viruses • Reverse transcriptase • Oncogenes • Rous sarcoma in chickens (RSV): in 1911 • Human T-cell lymphotropic virus (HTLV-I,II) • Human immunodeficiency virus (HIV)

5. Structure of RNA Oncovirus 5

6. Genome of RNA Oncovirus and Gene Products 6

7. Life cycle • Receptor binding and membrane fusion • Internalization and uncoating • Reverse transcription of the RNA genome to form double-stranded linear DNA • Nuclear entry of the DNA • Integration of the linear DNA into host chromosomal DNA to form the provirus • Transcription of the provirus to form viral RNAs Splicing and nuclear export of the RNAs Translation of the RNAs to form precursor proteins Assembly of the virion and packaging of the viral RNA genome Budding and release of the virions Proteolytic processing of the precursors and maturation of the virions 7

8. Replication of RNA Oncovirus 8

9. Mechanisms of Oncogenesis Induced by RNA Oncovirus • Transducing Retrovirus v-onc • cis-Activating Retrovirus c-onc • trans-Activating Retrovirus tax trans-acting x p40tax rex repressive expression x p27rex,p21rex 9

10. Oncogene transduction • Acutely transforming in vivo and in vitro • Transform cells by the delivery (transduction) of anoncogene from the host cell (v-onc) to a target cell • Cause the formation of polyclonal tumors • Most of this group of viruses are replication defective (the requirement of a helper virus) • Examples: RSV (v-src); Abelson murine leukemia virus (v-Abl) 10

11. Insertional activation • Long latent periods, Less efficient • Do not induce transformation of cells in vitro • Usually are replication competent • No oncogenes • Tumors are usually monoclonal • Provirus (LTR) is found within the vincity of a proto-oncogene (c-myc) • Examples: lymphoid leukosis virus; 11

12. Grow stimulation and two-step oncogenesis • The defective spleen focus-forming virus (SFFV) and its helper, the Friend murine leukemia virus (Fr-MuLV) • Induce a polyclonal erythrocytosis in mice • Require the continued viral replication • A mutant env protein gp55 of SFFV binds and stimulated the erythropoietin receptor, thus inducing erythroid hyperplasia • Fr-MuLV or SFFV integration inactivates p53 12

13. Transactivation • HTLV-1 and 2 • Like cis-activation group: replication competent, carries no oncogene, induces monoclonal leukemia, and latent • Like transducing group: can immortalize cells in vitro, has no specific integration site • Unique 3’ genomic structure: the X region; Encodes at least three proteins: Tax (p40), Rex (p27, p21) • Tax is the focus • Transactivate the viral LTR, results in a 100- to 200-fold increase in the rate of proviral transcription • Transactivate cellular enhancers and promoters, including genes for IL-2, granulocyte-macrophage colony-stimulating factor (GM-CSF), c-fos, and others. Genome of HTLV 13

14. Immunodeficiency • AIDS patients have an extraordinary increased rate of developing high-grade lymphomas and Kaposi’s sarcoma (KS) • Probably secondary • However, Tat protein of HIV (the transactivating protein) may induce KS-like lesions in mice. 14

15. Endogenous retroviruses • Exo or endo: somatic vs germline • 0.5-1% mammalian genome is composed of retroviral proviruses • Some properties: • Most are defective • Great variations between species or within • Variable level of expression • Generally not pathogenic • The potential to induce disease is notable 15

16. DNA Oncovirus Papilloma virus: HPV Polyoma virus Herpes virus: EBV Hepatitis B virus Hepatitis C virus 16

17. Mechanism of Oncogenesis Induced by DNA Oncovirus Transforming proteins 1. HPV E6 interact with P53 E7 interact with RB 2. Adenovirus E1a interact with RB E1b 3. Polyoma virus SV40 Large T interact with RB Py virus Large and Middle T Transcription activators 1. EB virus EBNA-2 and LMP 2. HBV p28 X protein 17

18. Gene Map and Function of HPV ORF Function E1 Virus proliferation E2 Regulation of transcription E5、E6、E7 Cell transformation L1、L2 Encoding capsid protein E4 Encoding late cytosolic protein E3、E8 Unkown • E5: activates growth factor receptor • E6: ubiquitin-mediated degradation of p53 • E7: binds and inactivates unphosphorylated pRb 18

20. Genome of EB Virus EBNA (EB virus Nuclear Antigen) EBNA-1 Immortalization of cell EBNA-2 trans-acting transcription activator EBNA-3 Function unknown LP:Leader Protein RNA Processing LMP: Latent MembraneProtein Activation of NF-κB TP:Terminal Protein Function unknown 20

21. Genome and Products of HBV Transforming gene: X gene X protein activates gene transcription via XRE 21

22. Genetic Predisposition • Hereditary Cancer • Tumor Genetic Susceptibility • Immunity • Metabolism • Hormones • Psychological factors • others 22

23. Tumor Genetic Susceptibility • Some individuals are at increased risk of certain cancers because they inherited a cancer-predisposing genetic mutation. • Tumor susceptibility genes(DNA repair genes, Tumor suppressor genes, Cytochrome P450 family, etc). • Not all potentially inheritable causes of cancer have been identified, but if an individual suspects that a relative has a cancer caused by one of the 17 known cancer-predisposing genetic mutations, he or she should consult a physician and consider genetic testing for verification.

25. Beyond inherited cancers, some medical conditions with higher risk for certain types of cancer • Inflammation and Cancer：for example, ulcerative colitis and Crohn disease increase an individual’s risk for colorectal cancer six fold. • Obesity and Cancer: Obesity increases risk for a growing number of cancers, most prominently the adenocarcinoma subtype of esophageal cancer, and colorectal, endometrial, kidney, pancreatic, and postmenopausal breast cancers. It also negatively impacts tumor recurrence, metastasis, and patient survival for several types of cancers. • Type 2 Diabetes Mellitus and Cancer: • Those with type 2 diabetes are most at risk for developing liver, pancreatic, and endometrial cancers, but also have an increased risk for developing biliary tract, bladder, breast, colorectal, esophageal, and kidney cancers, as well as certain forms of lymphoma. • it is not well established how type 2 diabetes increases cancer risk. • Similar to obesity, type 2 diabetes increases levels of insulin and causes persistent inflammation. • Energy balance is a complex dynamic that is not only influenced by calorie consumption and physical activity, but also by other factors such as genetics, diet composition, body weight or body composition, and sleep. How changes in energy balance promote cancer is an area of intense research investigation.

26. Hormones and cancer Major carcinogenic consequence of hormone exposure: cell proliferation How to get exposure: contraceptives, hormone replacement therapy, or during prevention of miscarriage The emergence of a malignant phenotype depends on a series of somatic mutation; Germline mutations may also occur Epidemiological studies

27. Hormone-related cancer Breast cancer and estrogen Endometrial cancer: Estrogen replacement therapy Ovarian cancer: follicle stimulating hormone Vaginal adenocarcinoma: in utero diethylstilbestrol (DES) exposure Prostate cancer and androgen • Cervical cancer • Thyroid cancer: the pituitary hormone thyroid stimulating hormone (TSH) • Osteosarcoma: incidence associates with the pattern of childhood skeleton growth; and hormonal activity is a primary stimulus for skeleton growth