Penelope Duerksen-Hughes, PhD
Professor & Associate Dean
Division of Biochemistry
School of Medicine
Loma Linda University
Loma Linda, CA 92350
HPV and Cervical Cancer
Cervical cancer is the second most common cancer for women worldwide, with a mortality rate of approximately 50 percent. This disease is almost always caused by high-risk strains of the human papillomavirus, a sexually transmitted agent, and disproportionately affects minority populations. HPV codes for E6 and E7, two oncogenes that work together to transform cells and cause cancer. The Duerksen-Hughes laboratory has discovered that one of the ways in which E6 contributes to HPV oncogenicity is by preventing host cells from responding to signals, such as those that might be generated during an immune response or chemotherapy, that would normally signal the virus-infected cell to die.
E6 functions, at least in part, by protecting the cells that express it from host-generated apoptotic responses such as those triggered by TNF, Fas, and TRAIL. Each of these apoptotic pathways involves several signaling molecules. We discovered that E6 binds to several of these molecules, thereby inhibiting transmission of the apoptotic signal. For example, when E6 binds to the TNF receptor TNF R1, the receptor cannot bind to the next molecule in the pathway, TRADD. Another possible consequence is the degradation of signaling intermediates, noted following the binding of E6 to FADD or to procaspase 8. We are working to further define these interactions with a long-term goal of developing small molecule inhibitors of such binding, which would have the potential to function as therapeutic reagents. We have already identified several candidates and are pursuing their testing and optimization.
E6 occurs in two versions due to alternative splicing. The two isoforms have some characteristics in common, while they differ in other respects. For example, while both versions bind to procaspase 8, only the full-length version accelerates its degradation. One intriguing observation is that E6* inhibits tumor formation, perhaps by blocking the action of the full-length isoform. This observation suggested that perhaps the ability of E6* to reduce tumor formation could lead to ideas for novel and effective therapeutic agents. A second intriguing observation is that the truncated version (E6*), but not the full-length isoform, causes increased oxidative stress in cells, possibly contributing to viral integration.
Normally, the HPV virus exists in cells as an episome and does not integrate. In rare cases, however, integration can occur in such a way as to enable increased expression of the E6 and E7 oncogenes, thereby setting the stage for cancer formation. One focus of our studies is to understand how and why integration sometimes happens, and to find ways to prevent it. Integration requires breaks in both the viral episome and the human genome, suggesting that events that cause breaks in DNA are likely to lead to increased integration. Oxidative stress is a likely candidate for causing these breaks, and can be caused by both environmental and viral factors (including E6*). If we can demonstrate that integration frequency can be increased by agents that increase oxidative stress, and decreased by agents that reduce that stress, we will have laid the groundwork for decreasing cancer formation.
Finally, we have used microarray analysis to discover that E6 affects the cellular responses to apoptotic signals induced by DNA damage by changing the expression patterns of genes involved in the early response, and these studies have identified a number of potential new targets for the development of chemotherapeutic reagents. Together, our results indicate that HPV 16 has acquired a number of mechanisms designed to thwart host-triggered apoptosis and to ensure the survival of the virus and its host cell. A clear understanding of these host-virus interactions will facilitate efforts to develop novel and effective therapeutic approaches.
1. Filippova, M., W. Evans, R. Aragon, V. Filippov, V. Williams, L. Hong, M. E. Reeves, and P. J. Duerksen-Hughes. The Small splice variant of HPV16 E6, E6*, reduces tumor formation in cervical carcinoma xenografts. Virology. 450-451:153-164, 2014. PMID: 24503078
2. Yu, Y., J. Fuscoe, C. Hao, C. Guo, M. Jia, T. Qing, D. Bannon, L. Lancashire, W. Bao, T. Du, H. Luo, Z. Su, W. Jones, C. Moland, W. Branham, F. Qian, B. Ning, Y. Li, H. Hong, L. Guo, N. Mei, T. Shi, K. Wang, Y. Nikolsy, R. Wolfinger, S. Walker, P. Duerksen-Hughes, C. Mason, W. Tong, J. Thierry-Mieg, D. Thierry-Mieg, L. Shi and C. Wang. A rat RNA-Seq transcriptomic Bodymap across eleven organs and four developmental stages. Nature Communications. 5:3230, 2014. PMID: 24510058.
3. Williams, V. M., M. Filippova, V. Filippov, K. J. Payne and P. J. Duerksen-Hughes. HPV 16 E6* induces oxidative stress and DNA damage. J. Virology 88:6751-6761, 2014. PMID: 2469478. Selected for a JVI Spotlight Feature.
4. Filippova, M., V. Filippov, W. M. Williams, K. Zhang, A. Kokoza, S. Bashkirova and P. J. Duerksen-Hughes. Cellular levels of oxidative stress affect the response of cervical cancer cells to chemotherapeutic agents. Biomed. Res. Int. 2014:57659, 2014. PMID: 25478571
5. Yuan, C.-H., M. Filippova, S. S. Tungteakkhun, P. J. Duerksen-Hughes and J. L. Krstenansky. Small molecule inhibitors of the HPV16-E6 interaction with caspase 8. Bioorganic and Medicinal Chemistry Letters, 22:2125-2129. 2012. PMID: 22300659
6. Filippov, V., M.A. Song, K. Zhang, H. V. Vinters, S. Tung, W. M. Kirsch, J. Yang, and P. J. Duerksen-Hughes. Increased Ceramide in brains with Alzheimer’s and other neurodegenerative diseases. Journal of Alzheimer’s Disease, 29:537-547, 2012. PMID: 22258513
7. Haynes, T.-A. S., V. Filippov, M. Filippova, J. Yang, K. Zhang, and P. J. Duerksen-Hughes. DNA damage induces down-regulation of UDP-Glucose Ceramide Glucosyltransferase, increases ceramide levels and triggers apoptosis in p53-deficient cancer cells. BBA – Molecular and Cell Biology of Lipids, 1821:943-953, 2012. PMID: 22349266
8. Whitaker, E. L., V. Filippov, M. Filippova, C. F. Guerrero-Juarez, and P. J. Duerksen-Hughes. Splice variants of mda-7/IL-24 differentially affect survival and induce apoptosis in U2OS cells. Cytokine, 56:272-281, 2011. PMID: 21843952
9. Tungteakkhun, S. S., M. Filippova, N. Fodor and P. J. Duerksen-Hughes. The Full Length Isoform of HPV 16 E6 and its Splice Variant E6* Bind to Different Sites on Procaspase 8 DED. J. Virol. 84:1453-1463, 2010. PMID: 19906919
10. Filippova, M., V. A. Filippov, M. Kagoda, T. Garnett, N. Fodor and P. J. Duerksen-Hughes. Complexes of Human Papillomavirus 16 E6 Proteins Form Pseudo-DISC Structures During TNF-Medicated Apoptosis. J. Virol. 83:210-227, 2009. PMID: 18842714
11. Tungteakkhun, S., M. Filippova, J. W. Neidigh, N. Fodor and P. J. Duerksen-Hughes. The Interaction Between HPV 16 E6 and FADD is Mediated by a Novel E6 Binding Domain. J. Virol. 82:9600-9614, 2008. PMID: 18632871
12. Filippov, V., E. L. Schmidt, M. Filippova and P. J. Duerksen-Hughes. Splicing and splice factor SRp55 participate in the response to DNA damage by changing isoform ratios of target genes. Gene. 420:34-41, 2008. PMID: 18571879
13. Filippov, V., M. Filippova and P. J. Duerksen-Hughes. The Early Response to DNA Damage Can Lead to Activation of Alternative Splicing Activity Resulting in CD44 Splice Pattern Changes. Cancer Research. 67:7621-7630, 2007. PMID: 17699766
14. Garnett, T. O., M. Filippova and P. J. Duerksen-Hughes. Bid is Cleaved Upstream of Caspase-8 Activation During TRAIL-Mediated Apoptosis in Human Osteosarcoma Cells. Apoptosis. 12:1299-1315, 2007. PMID: 17431792
15. Filippova, M., M. M. Johnson, M. Bautista, V. Filippov, N. Fodor, S. S. Tungteakkhun, K. Williams and P. J. Duerksen-Hughes. The Large and Small Isoforms of HPV 16 E6 Bind to and Differentially Affect Procaspase 8 Stability and Activity. J. Virology. 81:4116-4129, 2007. PMID: 17267478
16. Garnett T. O., M. Filippova and P. J. Duerksen-Hughes. Accelerated degradation of FADD and procaspase 8 in cells expressing human papillomavirus 16 E6 impairs TRAIL-mediated apoptosis. Cell Death and Differentiation 13:1915-1926, 2006. PMID: 16528366
17. Filippova, M., T. A. Brown-Bryan, C. A. Casiano and P. J. Duerksen-Hughes. The human papillomavirus 16 E6 can render cells either sensitive or resistant to TNF: Effect of dose. Cell Death and Differentiation 12:1622-1635, 2005. PMID: 15933739
18. Filippova, M., Parkhurst, L. and P. J. Duerksen-Hughes. HPV 16 E6 Binds to FADD and Modulates Fas-Triggered Apoptosis. J. Biol. Chem. 279:25729-25744, 2004. PMID: 15073179
19. Filippova, M., H. Song, J. L. Connolly, T. S. Dermody, and P. J. Duerksen-Hughes. The human papillomavirus 16 E6 protein binds to TNF R1 and protects cells from TNF-triggered apoptosis. J. Biol. Chem. 277:21730-21739, 2002. PMID: 11934887
20. Yang, J. and P. J. Duerksen-Hughes. Activation of a p53 -independent, sphingolipid-mediated cytolytic pathway in p53-negative mouse fibroblast cells treated with N-methyl-N-nitro-N-nitrosoguanidine. J. Biol. Chem. 276:27129-27135, 2001. . PMID: 11369765