Mechanisms of oncogenesis by DNA viruses Azam Ghaziasadi virology student Introduction Cancer is a genetic disease result from functional mutation in protooncogenes and inactivation of tumorsupressor gene that accumulates mutation. Viruses are contributing factor in 20% of all human cancer. hallmarks of cancers: self-sufficient in growth stimuli insensitive to anti-growth signals capable of causing tissue invasion (will be cause metastasis) proliferative potential is unrestricted cause angiogenesis resistant to apoptosis Common properties of oncogenic virus Virus encode proteins that can engage and modulate the cell cycle or block programmed cell death(apoptosis)has the potential to transform cell. All or part of the genome is usually retained in the transformed cell Cellular transformatin is accompanied by the continuous expression of specific viral sequence. overview Transformation by Activation of Cellular Signal transduction pathways Transformation via cell Cycle Control Pathway Other Mechanism of Transformation and Oncogenesis Control of cell proliferation 1-Sensing the environment 2-Phase of the cell cycle 3-The cell cycle Engine Virus Human associated cancer Adenovirus * SV40 * BKV/JCV Brain tumors CMV Colorectal cancer EBV Burkitts lymphoma HHV-6 Lymphoproliferative disorders HHV-8 Kaposi sarcoma, Primary effusion lymphoma Multicentric Castlemans disease HSV-1 Oropharyngeal cancer (?) HBV Hepatocellular carcinoma HPV (16/18) Cervical carcinoma Transformation by Activation of Cellular Signal Transduction pathway Viral mimic of cellular signaling molecule. Viral protein cellular protein that need for transformation and function AdenovirusE1A Rb family members (Rb,p107,and p130) nuclear phosphoprotein regulate cell cycle,binding E2f family members,disrupt Rb-E2f complexes P300/Cbp nuclear coactivator for stimulation of transcription,E1A inhibit activity pCaf Histon acetyltransferase,E1A binding via CR1 inhibit the latter activity p27 Nuclear inhibitor of G1/S phase cyclin-Cdks.E1A binding inhibit cell cycle arrest Ubc9 Ubiquitin- conjugating enzyme. Human papillomavirus E6 type 16 or 18 P53: nuclear transcriptional regulatory induce G1 or apoptosis arrest Paxillin : cytoplasmic protein that participate in signal transduction Interferon regulatory factor 3(Irf3): transcriptional regulator activated in response to interferon.E6 binding inhibit induction of Irf3 mRNA Other Viral Homology of Cellular Gene The genome large DNA virus contain coding sequence that are clearly related to cellular genes encoding signal transduction molecule. v-gpcr HHV-8 gene induces morphological transformation and secretion of vascular endothelial growth factor and induces angiogenesis vaccinia virus growth factor is a functional analoge of cellular epidermal growth factor Alter Cellular Signaling Pathways Virus Membrane protein Epstein-Barr virus LMP-1 Participate in signaling by TNF member to activate Nf-kb and AP-1 Herpesvirus Saimiri Saimiri transformation proteins(STPs) bind to the same cellular protein as LMP-1 activate Nf-kb Human herpesirus 8 K1 interact with cellular signal transduction protein Signaling by Epstein-Barr virus (LMP1) Polyomavirus mT Protein Deubiquitination versus Ubiquitination Wnt signaling pathway has been the object of intense attention in diverse biological areas. A central effector of the Wnt pathway is -catenin, a multifunctional protein. -catenin in the cytoplasm is tightly regulated by rapid degradation through the ubiquitin-proteasome system. it forms a complex with the T-cell factor (TCF)/Lef transcription factor and transactivates the expression of Wnt targets such as c-myc, cyclin D1, and others LANA Kaposis sarcoma,The LT- polyomavirus JC virus,LMP2 of EBV Ubiquitin-proteasome-mediated degradation of -catenin is the key mechanism for the regulation of -catenin levels in cells. Transformation via cell cycle control pathway Inhibition of Rb function by viral protein Adenovirus E1A Polyomavirus LT Papillomavirus E7 Human herpesvirus 8 v-cyclin Epstein-Barr virus EBNA 3C/EBNA5 Hepadnavirus ? Inhibition of Rb function by viral protein Adenoviral E1A protein- simian virus 40 LT E7 HPV induce DNA synthesis and cell proliferation. Disrupt Rb-E2f complexes. As a result They induce transcription of E2f dependent gene and entery of cell into S phase. CR1 sequence of the adenoviral E1A protein dismantle the Rb-E2f complex Conformational alteration of Rb seem likely to be important. Members of the E2f family such as E2f-1 and E2f-4 are unstable protein that are degraded by the proteasome following ubiquitination. Model for active dismantling of the Rb-E2f complex by simian virus 40 LT Organization of the large adenoviral E1A protein Regulation of Rb-Related protein The Rb,p107,and p130 protein bind preferentially to different members of the E2f Family during different phases of the cell cycle. Rb bind to E2f-1,2,or 3 during the G1 phase. P107 associated with E2f-4 during the G1,S,and G2 phase. p130 binding to E2f-4 and E2f-5 appears to be critical for maintaining cell in the quiescent state. Inhibition of p53 function Adenovirus E1B/E4ORF6 Polyomavirus LT Papillomavirus E6 Hepadenavirus HBx CMV IE2-86 EBV BZLF1/EBNA-5 HHV-6 DR7 HHV-8 LANA/v IRF/K8/ORF50 HSV-1 ICP0 Poxvirus B1R kinase Regulation of the stability and activity of the P53 protein * Mdm-2 is a p53-specific ubiquitin ligase that catalyzes polyubiquitination of p53 that allow recognition by the proteasome.availability and activity of Mdm-2 Regulated by Arf protein. * Mdm-2 protein maintain inactive p53 at low concentration. * Signaling pathway initiated in response to damage the genome that lead to stabilization of p53. * P53 stabilized in multiple ways: phosphorylation of P53 at specific serine by Atm and checkpoint kinase 2(chk2)- binding to the c-Abl tyrosine kinase, sequestration of the Mdm-2 by Arf, and deubiquitination of p53 by the Hausp(herpesvirus-associated ubiquitin- specific protease). * association with the transcriptional coactivators p300/Cbp. Inactivation of the p53 protein by adenoviral,papillomaviral,and polyomaviral protein Adenoviral E1A protein induce increased concentration of p53 The E6 protein of human papillomavirus type 16 and 18 bind to p53 via the cellular E6-associated protein(E6-Ap).the latter protein is a ubiquitin protein ligase that ubiquitinate P53 and targeting P53 for degradation by the proteasome. Binding of simian virus 40 LT to P53,sequesters the cellular protein in inactive complexes. The adenoviral E1B 55-kDa and E4 ORF6 proteins bind to P53 at the N-terminal activation domain and a C-terminal region near the tetramerization domain,respectively. Binding of the E4 ORF6 protein increase the rate of degradation of P53. such increased degradation of P53 also requires the E1B 55-kDa protein. Other Mechanism of Transformation and Oncogenesis genomic instability abnormalities in the size (hypertrophy) or number (amplification) of centrosomes have been repeatedly noticed in transformed cells facilitating the onset of aneuploidy. Mps1, a protein kinase acting as a positive inducer of centrosome duplication. G1 Cyclin/Cdk 2 activity is the major link between centrosome duplication and the cell cycle machinery HPV E6 and E7, as well as Adenovirus E1A, induce mitotic abnormalities,aneuploidy and genomic instability.the SV40 LT Ag also disrupts the effectiveness of mitotic checkpoint controls. -tubulin and centrin, is impaired by thePP2A the mitotic spindle cannot assemble. recently identified the Ran GTPase as a novel target of viral oncoproteins. E1A, E7 and SV40 LT Ag all interact with Ran. A major function of Ran is the control of nucleocytoplasmic transport of RNA and proteins in interphase cells. RanGTP promotes mitotic spindle assembly Telomerase hTERT gene * immortalization in cancer cells is generally associated with activation of telomerase and subsequent telomere maintenance. * A major mechanism to regulate telomerase activity is transcriptional control of the telomerase catalytic subunit gene hTERT. * Several transcription factors, including oncogene products (e.g. c-Myc) and tumor suppressor gene products (e.g. WT1 and p53), are able to control hTERT transcription when over-expressed. * trans activation of the hTERT: HPV E6 protein contributes to keratinocyte immortalization- KSHV LANA target and affect the Sp1 protein bound to the hTERT promoter. * Cis activation of the hTERT: HBV is integrated non-random in the hTERT promoter region in HCC.The HBV enhancer located upstream of the hTERT transcription start site and cis-activation by the vira genome. EBERs (Epstein-Barr virus encoded RNAs) EBV virus is associated with malignancies, Burkitts lymphoma(BL), nasopharyngeal Carcinoma (NPC) and AIDS-associated lymphoma. EBV-encoded RNAs(EBERs) are the most abundant viral transcripts in latently EBV-infected cells. The feature recognised in BL is chromosome translocation between the c-myc gene and immunoglobulin gene. EBERs compete with dsRNA for binding to PKR, EBER could inhibit PKR autophosphorylation and phosphorylation of two substrates of PKR, eIF-2 and I B, thus resulting in the maintenance of protein synthesis. These results suggested that EBERs antagonise the IFN-induced antiviral activity by blockage of the PKR pathway, and contribute to the protection of EBV from the effect of IFN during the establishment of latent infections Suggested that EBERs confer resistance to IFNinduced apoptosis by blockage of PKR activation in EBV infected cells EBERs induce human IL-10 expression in BL cells as an autocrine growth factor for BL. IL-10 is known to suppress T-helper 1 (Th1) CTL EBV escapes both IFN-mediated non-pecific immunity and Th1-mediated specific immunity through the action of EBERs. HBV oncogenicity Multiple interactions of HBx with cellular partners. HBx inactivating p53 functions. Activation of Src is mediated activation of the Ras-Raf-MAPK cascade, leads to induction of the transcription factors AP-l. HBx induces nuclear translocation of the NF-b and NF-AT transcription factors by various mechanisms. In the nucleus, HBs binds transcription factors of the bZIP family, and co-activate transcription.Interaction of HBx with UVDDB Complex playa major role in diverse biological functions of HBx. inappropriate expression of the large S protein has the potential to be directly cytotoxic to the hepatocyte and may initiate a cascade of events that ultimately progress to malignant transformation. Deletion of the carboxy-terminal region of the S gene generates a novel transcriptional transactivation activity.