1. Viral transformation and oncogenesis Fahareen –Binta –Mosharraf MNS

2. Oncogenic Viruses Cause cancer by inducing changes that affect cell proliferation Approx 20% of all human cancers causes by one of 5 viruses” –1. Epstein-Barr virus –2. Hepatitis B –3. Hepatitis C, –4. HTLV I –5. Hum. Papillomaviruses

3. Oncogenic Viruses: a Genetic Paradigm for Cancer Study of viral transformation of cells laid the foundations for our current understanding of cancer. Enabled identification of Oncogenes and Tumor Suppressor genes Foundation for the genetic paradigm of cancer

4. Oncogenic viruses and cancer FamilyAssociated Cancer(s) RNA viruses Flaviriridae Hepatitis C virusHepatocellular carcinoma RetroviridaeHaemopoetic cancers, sarcomas, carcinomas DNA viruses AdenoviridaeVarious solid tumors HepadnaviridaeHepatocellular carcinoma HerpesviridaeLymphomas, carcinomas, sarcomas PapillomaviridaePapillomas and carcinomas PolyomaviridaeVarious solid tumors PoxviridaeMyxomas and fibromas

5. Molecular mechanism Viral of Transformation

6. A. Viral transformation by Activation of Cellular Signal Transduction pathways 1. Viral mimics cellular signal transduction pathway a. Transduction of cellular genes by acutely transforming retroviruses b. Other virus homologous cellular genes 2. Viral specific signal transduction molecule 3. Alteration of expression and activity of cellular signal transduction proteins a. insertion activation by simple non transuding retroviruses b. Alteration in activity of cellular signal transduction molecules

7. B. Viral Transformation via cell Cycle Control Pathways 1. inhibition of Rb function by viral proteins 2. Production of Viral Specific Cyclins 3. Inhibition of p53 Function by binding to viral protein

8. 1. Viral mimics cellular signal transduction pathway a. Transduction of cellular genes by acutely transforming retroviruses i.Src tyrosine kinases Src protein possesses tyrosine kinase activity play an important role in signal transduction play an important role in signal trnsduction. Viral Src- v Src Cellular Src- c Src

9. Src structures Four domains 1.SH1 : tyrosine kinase domain, phosphorylates itself and regulate enzymatic activity. 2.SH2 and SH3 : mediate protein-protein interaction by binding with phospho tyrosine and proline rich domains 3.SH4: domains contain additional Myristate chain which involved in protein anchorage to cell membrane

10. Src activity is controlled by phosphorylation Src autophosphorylates and its activity is controlled by the state of phosphorylation at two Tyr residues. Y-416- phosphorylation activates enzymatic activity Y-527- phosphorylation inhibits enzymatic activity When y 527 is phosphorylated at c- terminal region of cSrc,SH2 domain binds to SH1 domain and conformation of SH 1 domain remain inactive When y 416 is phosphorylated SH3 domain binds to proline rich domain so SH2 cant bind with SH1 domain and SH 1 domain remain active

11. Src activity is controlled by Viral transformation Oncogenic variants are derived from c-Src by mutations that cause decreased phosphorylation at Tyr-527 and increased phosphorylation at Tyr-416. v-Src lacks Tyr-527 and is constitutively active.

12. Inactive Src activated by a conformational change by binding of SH3 domains with proline rich region, and by dephosphorylation of Y527 Kinase domain

14. ii. Other virus transduced oncogenes Some transduced oncogenes of retroviruses are related to cellular genes and control signal transduction pathways V-sis V- kit V-myc

15. b.Other virus homologous cellular genes Genome of some large DNA viruses contain some coding region related to cellular genes Human Herpes Virus 8 contains GPCR which mimics cellular GPCR receptors. In absence of ligands V-GPCR fully activated. Kaposis Sarcoma an extensive level of angiogenesis occurs due to excessive level of vascular endothelial growth factor.

16. 2. Viral specific signal transduction molecule EBV protein (LMP-1) act as signal transduction molecule –LMP-1 can –Immortalize human B lymphocytes –Inhibit differentiation of epithelial cell lines in culture –Induce transformation in rodent fibroblast –LMP is an integral protein of cell membrane –Functions as a constitutively active receptor –In absence of any ligand, LMP-1 oligomerizes and activates the cellular transcriptional regulator Nf- κb –LMP-1 activates the kinase cascade that normally releases this transcriptional regulator from association with cytoplasmic inhibitor

18. 3. Alteration of expression and activity of cellular signal transduction proteins a.insertion activation by simple non transuding retroviruses Insertional activation by retroviruses –Promoter insertion: produce chimeric RNA, proviral LTR linked to cellular protooncogene sequences –Transcription from LH LTR include viral coding sequences –Transcription from RH LTR Left end LTR is deleted –Enhancer insertion: Viral and cellular transcripts are not fused, enhancer increase the activity of cellular promoter

20. b. Alteration in activity of cellular signal transduction molecules i. Cell surface receptor –Signal transduction initiated by binding of growth factors to the receptor (TK) –Ligand binding induce the oligomerisation of receptor molecules and autophosphoylation of tyrosine kinase –Activated receptor internalized by endocytosis –In the endosome the ligand is released and the receptor is degraded –The E5 proteins of bovine and human papillomaviruses binds to vacuolar ATPase and interfere with the degradation of the receptor –E5 protein also increase con. Of activated receptor to the cell surface

21. ii. Src family tyrosine kinase Members of Parvoviridae and Herpesviridae have protein which permanently activate cellular ST pathways by binding to src tyrosine kinase SV40 mT protein binds to src protein, does not increase the concentration of src, but increase its catalytic activity

22. B. Viral Transformation via cell Cycle Control Pathways

23. 1. Inhibition of Rb function by viral proteins Adenoviral E1A, SV40 LT, and E7 protein of HPV disrupt Rb-E2f complex and sequester inhibitory form of Rb By capturing Rb

24. Simian Viral LT compete with E2f for binding with Rb protein.LT contains two Domains R-Domain: Binding domain J-Domain: 1. Required for cell cycle progression 2. Recruits cellular chaperon Hsc70

25. The R domains bind with LT protein at A and B domain forming Rb-LT complex J domains recruits cellular chaperon Hsc 70 and release E2f -DP1 complex from Rb

27. 2. Production of Viral Specific Cyclins Some viruses can able to produce v- cyclins which show 31% identity and 58% similarity with cyclin D2 and binds predominantly with Cdk6 This Cdk 6 associated with V-cyclin cant be inhibited by Ink4/cip/kip Cells are always in proliferating state.

28. 3. Inhibition of p53 Function by binding to viral protein Different DNA viruses block p53 function by distinct mechanisms HPV type 16 and 18 E6 proteins bind to p53 and a cellular E6 associated ubiquitin protein ligase, cause ubiquitination and protease mediate destruction of p53 SV40 LT stabilizes the p53 but sequesters in inactive complex Adenoviral E1B 55kd binds to N-terminal of p53 and convert it from activator to repressor of transcription Adenoviral E4 ORF 6 protein binds to p53 C-terminal sequences, which increases the turn over rate of p53 and decreases the p53 dependent transcription and induction of apoptosis

29. Inactivation of p53 protein by viral proteins