Loma Linda University

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Faculty Directory
Penelope Duerksen-Hughes, PhD
Associate Dean, Basic Sci & Translational Rsch, Associate Dean Basic Sci & Translational Rsch
School of Medicine
Chair, Basic Sciences
School of Medicine
Vice Chair, Basic Sciences, Biochemistry Division
School of Medicine
Professor, Basic Sciences
School of Medicine
Member, Biochemistry, SM, Faculty of Graduate Studies
Publications    Scholarly Journals--Published
  • 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.

    ( 4/2014 - 6/2014 )
  • 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.


    ( 3/2014 - 6/2014 )
  • Whitaker, E. L., V. A. Filippov and P. J. Duerksen-Hughes. Interleukin 24:  Mechanisms and therapeutic potential of an anti-cancer gene.  Cytokine and Growth Factor Reviews, 23:323-331, 2012.


    ( 7/2012 - 6/2013 )

    Interleukin 24 (mda-7/IL-24) has been classified as an anti-cancer gene for its ability to selectively induce cell death in cancer cells while having little to no effect on normal cells. Although the exact mechanisms by which IL-24 functions have not been completely elucidated, several pathways have consistently been identified: endoplasmic reticulum stress, ceramide-mediated events, and the generation of reactive oxygen species. In addition to these mechanistic analyses, significant progress has also been reported regarding the clinical potential of this anti-cancer gene. For example, many groups are utilizing mda-7/IL-24 in combination with other cancer therapies. This review examines the current research and potential future of this important anti-cancer gene.

  • Gan, T. E., S. P. Xiao, Y. Jiang, H. Hu, Y. H. Wu, P. J. Duerksen-Hughes, J. T. Sheng and J. Yang.  Effects of benzo(a)pyrene on the contractile function of the thoracic aorta of Sprague-dawley rats. Biomed. Environ. Sci., 25:373-380, 2012.

    ( 7/2012 - 6/2013 )
  • C.-H. Yuan, M. Filippova and P. J. Duerksen-Hughes. Modulation of Apoptotic Pathways by HPV:  Mechanisms and Implications for Therapy. Viruses, 4:3831-3850, 2012.

    ( 7/2012 - 6/2013 )
  • Jiang, Y., X.-Y. Zhang, L. Sun, G.-L. Zhang, P. Duerksen-Hughes, X.-Q. Zhu and J. Yang.  Methyl methanesulfonate induces apoptosis in p53-deficient H1299 and Hep3B cells through a Caspase 2- and mitochondria-associated pathway.  Environmental Toxicology and Pharmacology, In Press, 2012.

    ( 7/2012 - 6/2012 )
  •  Whitaker, E. L., V. Filippov, M. Filippova, C. V. Guerrero-Jugarez, 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 ( 7/2011 - 6/2012 )
  •  K. Zhang, T.-A. S. Haynes, M. Filippova, V. Filippov and P. J. Duerksen-Hughes.  Quantification of ceramide levels in mammalian cells by high performance liquid chromatography coupled to tandem mass spectrometry with multiple-reaction-monitoring mode (HPLC-MS/MS-MRM).  Analytical Methods 3:1193-1197, 2011. ( 7/2011 - 6/2012 )
  •  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 Letters22:2125-2129, 2012.  PMID:  22300659                ( 7/2011 - 6/2012 )
  • 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

    ( 7/2011 - 6/2012 )
  • Gan, T.-E., S.-P. Xiao, Y. Jiang, H. Hu, Y.-H. Wu, P. J. Duerksen-Hughes, J.-Z. Sheng, and J. Yang.  Effects of beno(a)pyrene on contractile functions of thoracic aorta of Sprague-Dawley rats. Biomedical and Environmental Sciences, 25:549-556, 2012.  PMID: 23122312

    ( 7/2011 - 6/2012 )
  • Yan, C., Z. Chen, H. Li, G. Zhang, F. Li, P. J. Duerksen-Hughes, X. Zhu, and J. Yang.  Nuclear proteome analysis of benzo(a)pyrene-treated HeLa cells. Mutat. Res. 731:75-84, 2012.  PMID:  22138005   ( 7/2011 - 6/2012 )
  • 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 ( 7/2011 - 6/2012 )
  • Zhang, G., L. Sun, X. Lu, Z. Chen, P. J. Duerksen-Hughes, H. Hu, X. Zhu and J. Yang.  Cisplatin treatment leads to changes in nuclear protein and microRNA expression. Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 746:66-77, 2012.   ( 7/2011 - 6/2012 )
  • Williams, V. M., M. Filippova, U. Soto and P. J. Duerksen-Hughes.  HPV-DNA Integration and Carcinogenesis:  Putative Roles for Inflammation and Oxidative Stress.  Future Virology, 6(1): 45-57, 2011.  PMID:  21318095 ( 7/2010 - 6/2011 )
  •  Yan, C., J. Lu, G. Zhang, T. Gan, Q. Zheng, Z. Shao, P. J. Duerksen-Hughes, and J. Yang.  Benzo[a]pyrene Induces Complex H2AX Phosphorylation Patterns by Multipole Kinases Including ATM, ATR, and DNA-PK.  Toxicology In Vitro 25:91-91, 2011.  PMID:  20888899 ( 7/2010 - 6/2011 )
  •  Mujumdar, P., P. J. Duerksen-Hughes, A. F. Firek and D. A. Hessinger.  Long-term, Progressive Aerobic Training Increases Adiponectin in Middle-aged, Overweight, Untrained Males and Females.  Scan. J. Clin. Lab. Invest.  71:101-7, 2011. PMID:  21271804 ( 7/2010 - 6/2011 )
  • Xiong, L., A. Darwanto, S. Sharma, J. Herring, S. Hu, M. Filippova, V. Filippov, Y. Wang, C.-S. Chen, P. J. Duerksen-Hughes, L. C. Sowers, K. Zhang.  Mass spectrometric studies on epigenetic interaction networks in cell differentiation.  J. Biol. Chem.  286:13657-68, 2011.    PMID:  21335548 ( 7/2010 - 6/2011 )
  •  Tungteakkhun, S. S., M. Filippova, N. Fodor and P. J. Duerksen-Hughes.  The Full-Length Isoform of Human Papillomavirus 16 E6 and its Splice Variant E6* Bind to Different Sites on the Procaspase 8 Death Effector Domain.  J. Virology 84:1453-1463, 2010. PMID:  19906919 ( 7/2009 - 6/2010 )
  •  Yan, C., W. Wu, H. Li, G. Zhang, P. J. Duerksen-Hughes, X. Zhu and J. Yang.  Benzo[a]pyrene Treatment Leads to Changes in Nuclear Protein Expression and Alternative Splicing.  Mutat. Res. 686:47-56, 2010.  PMID:  20097212 ( 7/2009 - 6/2010 ) Link...
  •  Wu, W., C. Yan, T. Gan, Z. Chen, X. Lu, P. J. Duerksen-Hughes, X. Zhu and J. Yang.  Nuclear Proteome Analysis of Cisplatin-Treated HeLa Cells.  Mutation Research 2010.  PMID:  20540955 ( 7/2009 - 6/2010 )
  •  Tungteakkhun, S. S., M. Filippova, J. W. Neidigh, N. Fodor, and Penelope J. Duerksen-Hughes.  The Interaction between Human Papillomavirus Type 16 and FADD is Mediated by a Novel E6 Binding Domain.  J. Virol. 82:9600-9614, 2008.  PMID: 18632871 ( 7/2008 - 6/2009 )
  •  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-Mediated Apoptosis.  J. Virology 83:210-227, 2009.  PMID:  18842714 ( 7/2008 - 6/2009 )
  •  Tungteakkhun, S. S. and P. J. Duerksen-Hughes.  Cellular binding partners of the human papillomavirus E6 protein.  Arch. Virol. 153:397-408, 2008.  PMID:  18172569 ( 7/2007 - 6/2008 )
  • 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 Research67:7621-7630, 2007.  PMID:  17699766 ( 7/2007 - 6/2008 )
  •  Haynes, T.-A S., P. J. Duerksen-Hughes, M. Filippova, V. Filippov and K. Zhang.  C(18) Ceramide Analysis in Mammalian Cells Employing Reversed-Phase High Performance Liquid Chromatography Tandem Mass Spectrometry.  Analytical Biochemistry378:80-86, 2008.  PMID:  18423390 ( 7/2007 - 6/2008 )
  •  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 ( 7/2007 - 6/2008 )
  • Theodore O. Garnett, Maria Filippova and Penelope 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. (2006): 1915-1926. ( 7/2006 - 6/2007 ) Link...
    Viruses have developed sophisticated strategies to evade host defenses and facilitate the production and spread of progeny. In this study, we show that transfection of the human papillomavirus (HPV) 16 E6 oncogene into HCT116 cells provides protection from tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-mediated apoptosis. Additionally, we demonstrate that the protection provided by E6 is dose-dependent because higher levels of E6 provide greater protection. The mechanism underlying this protection involves a rapid reduction in the protein levels of both Fas-associated death domain (FADD) and procaspase 8, which results in suppression of the activation of caspase 8, 3 and 2. Interestingly, E6 does not interfere with the mitochondrial apoptotic pathway even though HCT116 cells have been classified as type II cells with regard to TRAIL signaling. These findings demonstrate that E6 has a more generalized effect on signaling by death ligands than was previously thought and support the notion that E6 can utilize p53-independent mechanisms to modulate cell survival.
  • Maria Filippova, Melyssa Johnson, Marnelli Bautista, Valery Filippov, Nadja Fodor, Sandy Tungteakkhun, Kadia Williams and Penelope Duerksen-Hughes. "The Large and Small Isoforms of HPV 16 E6 Bind to and Differentially Affect Procaspase 8 Stability and Activity." J. Virology 81. (2007): 4116-4129. ( 7/2006 - 6/2007 ) Link...
    Human papillomavirus type 16 (HPV-16) has developed numerous ways to modulate host-initiated immune mechanisms. The HPV-16 E6 oncoprotein, for example, can modulate the cellular level, and consequently the activity, of procaspase 8, thus modifying the cellular response to cytokines of the tumor necrosis factor family. E6 from HPV-16, but not E6 from the low-risk types 6b and 11, alters the cellular level of procaspase 8 in a dose-dependent manner. Both the large and small (E6*) isoforms of E6, which originate by way of alternate splicing, can modulate procaspase 8 stability. Intriguingly, although both isoforms bind to procaspase 8, the large isoform accelerates the degradation of procaspase 8 while the small isoform stabilizes it. Binding leads to a change in the ability of procaspase 8 to bind either to itself or to FADD (Fas-associated death domain), with the large version of E6 able to inhibit this binding while the small isoform does not. Consistent with this model, knockdown of the large version of E6 by small interfering RNA leads to increases in the levels of procaspase 8 and its binding to both itself and FADD. Thus, these alternatively spliced isoforms can modulate both the level and the activity of procaspase 8 in opposite directions.
  • Theodore Garnett, Maria Filippova and Penelope J. Duerksen-Hughes. "Bid is Cleaved Upstream of Caspase-8 Activation During TRAIL-Mediated Apoptosis in Human Osteosarcoma Cells." Apoptosis 12. (2007): 1299-1315. ( 7/2006 - 6/2007 ) Link...
    TRAIL induces apoptosis in many malignant cell types. In this study, we used the human papilloma virus (HPV) 16 E6 protein as a molecular tool to probe the TRAIL pathway in HCT116 colon carcinoma cells and U2OS osteosarcoma cells. Intriguingly, we found that while E6 protected HCT116 cells from TRAIL, U2OS cells expressing E6 remained sensitive to TRAIL. Furthermore, silencing FADD and procaspase-8 expression with siRNA did not prevent TRAIL-induced apoptosis in U2OS cells. However, siBid provided significant protection from TRAIL, and the cleavage kinetics of Bid and caspase-8 revealed that Bid was cleaved prior to the activation of caspase-8. Cathepsin B activity in U2OS cells was significantly activated shortly after exposure to TRAIL, and the cathepsin B inhibitor, CA074Me, inhibited both TRAIL- and anti-DR5-mediated apoptosis and delayed the cleavage of Bid. These findings suggest that TRAIL activates a pathway dependent on Bid, but largely independent of FADD and caspase-8, in U2OS cells.
  • Valery Filippov, Maria Filippova and Penelope 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 67.16 (2007): 7621-7630. ( 6/2006 - 6/2007 ) Link...
    Expression of the HPV 16 E6 oncogene interferes with several vital cellular processes, including the p53-dependent response to DNA damage. To assess the influence of E6 on the early response to DNA damage, we analyzed gene expression following mitomycin C-induced genotoxic stress in human E6-expressing U2OS cells (U2OSE64b) as well as in p53-expressing control cells (U2OSE6AS) by comparative global expression profiling. As expected, genes involved in p53-dependent pathways were activated in p53-expressing cells. In the U2OSE64b cells, however, a largely non-overlapping group of genes was identified, including two splicing factors of the SR family. Immunoblot analysis revealed increased expression of several SR proteins during the early response to DNA damage, which was accompanied by activation of alternative splicing activity. Disruption of splicing activity by treatment with siRNA directed against splicing factor SRp55 resulted in increased viability of p53-deficient cells following DNA damage. To determine whether the transient activation of splicing activity was due to E6-mediated degradation of p53 or to some other activity of E6, we compared the early response of the p53 wt and p53-/- isogenic HCT116 cell lines, and found that the increase in splicing activity was observed only in the absence of p53. Finally, both the U2OSE64b and the p53 -/- cells showed altered splicing patterns for the CD44 receptor. Together, these data show that cells lacking p53 can activate alternative splicing following DNA damage.
  • Theodore Garnett and Penelope J. Duerksen-Hughes. "Modulation of Apoptosis by HPV Oncoproteins." Archives of Virology 151. (2006): 2321-2335. ( 7/2005 - 6/2006 ) Link...
    The regulation of host-mediated apoptosis by the E6 and E7 oncoproteins has garnered attention because it is believed to be an important strategy employed by high-risk (HR)-human papillomaviruses (HPVs) to evade immune surveillance. Additionally, the revelation that E5 can protect cells from tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis suggests that it may also play a role in undermining host defense mechanisms. Cellular transformation is an unintended consequence of persistent infection by HR-HPVs, and it is therefore likely that the primary function of E5, E6 and E7 is to regulate cell survival throughout the normal viral life cycle in order to ensure viral replication and promote the spread of progeny. The purpose of this article is to review the literature on the regulation of host-mediated apoptosis by E5, E6 and E7 that describes the mechanisms employed by HR-HPVs to persist in the host and create the conditions necessary for cellular transformation.
  • Maria Filippova, Terry A. Brown-Bryan, Carlos A. Casiano, and Penelope J. Duerksen-Hughes. "The Human Papillomavirus 16 E6 Protein Can Either Protect or Further Sensitize Cells to TNF: Effect of Dose." Cell Death and Differentiation 12. (2005): 1622-1635. ( 7/2004 - 6/2005 ) Link...
    High-risk strains of human papillomavirus, including HPV 16, cause human cervical carcinomas, due in part to the activity of their E6 oncogene. E6 interacts with a number of cellular proteins involved in host-initiated apoptotic responses. Paradoxically, literature results show that E6 can both protect cells from and sensitize cells to tumor necrosis factor (TNF). To examine this apparent contradiction, E6 was transfected into U2OS cells and stable clones were treated with TNF. Intriguingly, clones with a high level of E6 expression displayed an increased sensitivity to TNF by undergoing apoptosis, while those with low expression were resistant. Furthermore, TNF treatment of cells in which the expression of E6 was regulated by the addition of doxycycline demonstrated clearly that while low levels of E6 protect cells from TNF, high levels sensitize cells. Together, these results demonstrate thata virus-host interactions can be complex and that both quantitative and qualitative aspects are important in determining outcome.
  • Jun Yang, Yingnian Yu, Shuyu Sun, and Penelope J. Duerksen-Hughes. "Ceramide and Other Sphingolipids in Cellular Responses." Cellular Biochemistry and Biophysics 40. (2004): 323-350. ( 7/2003 - 6/2004 ) Link...
    Formerly considered to serve only as structural components, sphingolipids are emerging as an important group of signaling molecules involved in many cellular revents, including cell growth, senescence, meiotic maturation, and cell death. They are also implicated in functions such as inflammation and the responses to heat shock and genotoxic stress. Defects in the metabolism of sphingolipids are related to various genetic disorders, and sphingolipids have the potential to serve as therapeutic agents for human diseases such as colon cancer and viral or bacterial infections. The best-studied member of this family, ceramide, which also serves as the structural backbone for other sphingolipids, is an important mediator in multiple cellular signaling pathways. The metabolism and functions of sphingolipids are discussed in this review, with a focus on ceramide regulation in various cellular responses.
  • Jun Yang, Zheng-Ping Xu, Yun Huang, Hope E. Hamrick, Penelope J. Duerksen-Hughes, Ying-Nian Yu. "ATM and ATR: Sensing DNA Damage." World J. Gastroenterology 10.2 (2004): 155-160. ( 7/2003 - 6/2004 ) Link...
    Cellular response to genotoxic stress is a very complex process, and it usually starts with the "sensing" or "detection" of the DNA damage, followed by a series of events that include signal transduction and activation of transcription factors. The activated transcription factors induce expression of many genes which are involved in cellular functions such as DNA repair, cell cycle arrest, and cell death. There have been extensive studies from multiple disciplines exploring the mechanisms of cellular genotoxic responses, which have resulted in the identification of many cellular components involved in this process, including the mitogen-activated protein kinases (MAPKs) cascade. Although the innitial activation of this protein kinase cascade is not fully unerstood, human protein kinases ATM (ataxia-telangiectasia, mutated) and ATR (ATM and Rad3-related) are emerging as potential sensors of DNA damage. Current progress in ATM/ATR research and related signaling pathways are discussed in this review, in an effort to facilitate a better understanding of the genotoxic stress response.
  • Maria Filippova, Lindsey Parkhurst and Penelope J. Duerksen-Hughes. "The Human Papillomavirus 16 E6 Protein Binds to Fas-associated Death Domain and Protects Cells from Fas-triggered Apoptosis." J. Biological Chemistry 279.24 (2004): 25729-25744. ( 7/2003 - 6/2004 ) Link...
    High risk strains of human papillomavirus (HPV), such as HPV 16, cause human cervical carcinoma. The E6 protein of HPV 16 mediates the rapid degradation of the tumor suppressor p53, although this is not the only function of E6 and cannot completely explain its transforming potential. Previous work in our laboratory has demonstrated that E6 can protect cells from tumor necrosis factor-induced apoptosis by binding to the C-terminal end of tumor necrosis factor R1, thus blocking apoptotic signal transduction. In this study, E6 was shown to also protect cells from apoptotis induced via the Fas pathway. Furthermore, use of an inducible E6 expression system demonstrated that this protection is dose-dependent, with higher levels of E6 leading to greater protection. Although E6 suppresses activation of both caspase 3 and caspase 8, it does not affect apoptotic signaling through the mitochondrial pathway. Mammalian two-hybrid and in vitro pull-down assays were then used to demonstrate that E6 binds directly to the death effector domain of Fas-associated death domain (FADD), with deletion and site-directed mutants enabling the localization of the E6-binding site to the N-terminal end of rhte FADD death effector domain. E6 is produced in two forms as follows: a full-length version of ~16 kDa and a smaller version of about half that size corresponding to the N-terminal half of the full-length protein. Pull-down and functional assays demonstrated that the full-length version, but not the small version of E6 was able to bind to FADD and to protect cells from Fas-induced apoptosis. In addition, binding to E6 leads to degradation of FADD, with the loss of cellular FADD proportional to the amount of E6 expressed. These results support a model in which E6-mediated degradation of FADD prevents transmission of apoptotic signals via the Fas pathway.
  • Jun Yang, Yingnian Yu and Penelope J. Duerksen-Hughes. "Protein Kinases and their Involvement in the Cellular Responses to Genotoxic Stress." Mutation Research 543. (2003): 31-58. ( 7/2002 - 6/2003 ) Link...
    Cells are constantly subjected to genotoxic stress, and much has been learned regarding their response to this type of stress during recent years. In general, the cellular genotoxic response can be thought to occur in three stages: 91) damage sensing; (2) activation of signal transduction pathways; (3) biological consequences and attenuation of the response. The biological consequences, in particular, induce cell cycle arrest and cell death. Although our understanding of the molecular mechanisms underlying cellular genotoxic stress responses remains incomplete, many cellular components have been identified over the years, including a group of protein kinases that appears to play a major role. Various DNA-damaging agents can activate these protein kinases, triggering a protein phosphorylation cascade that leads to the activation of transcription factors, and altering gene expression. In this review, the involvement of protein kinases, particularly the mitogen-activated protein kinases (MAPKs), at different stages of the genotoxic response is discussed.
  • Maria Filippova and Penelope J. Duerksen-Hughes. "Inorganic and Dimethylated Arsenic Species Induce Cellular p53." Chemical Research in Toxicology 16.3 (2003): 423-431. ( 7/2002 - 6/2003 ) Link...
    Arsenic compounds are known for their ability both to cause and to treat human cancers, although the molcular mechanisms underlying these actions are incompletely understood. The simplest explanation is that arsenic causes DNA damage that leads to mutations. However, the majority of scientific evidence indicates that arsenic is not a genotoxin or DNA-damaging agent. DNA damage typically leads to cellular responses designed to minimize the replication of damaged DNA, such as the induction of p53, and p53 induction has therefore been used as an indicator of DNA damage. Because this approach can be applied to human cells and does not rely on a specific, heritable mutation occurring at a particular site, it seemed possible that this method could detect DNA damage that was undetectable using other techniques. To examine the genotoxic potential of arsenic compounds, therefore, seven of these compounds (sodium aresenite, sodium aresenate, methyloxoarsine, iododimethylarsine, disodium methyl arsonate, dimethylarsinic acid, and arsenic trioxide) were tested for their ability to increase the cellular level of p53 as measured by ELISA. Of this group, arsenic trioxide was the strongest inducer of cellular p53, while dimethylarsinic acid, iododimethylarsine, and sodium arsenite also caused p53 induction in a dose- and time-dependent manner. Sodium arsenate, as well as the two monomethyl compounds tested, methyloxoarsine and disodium methyl arsonate, did not cause detectable increases in cellular p53. Our results indicate, therefore, that cells respond to several of these arsenic compounds as they do to chemicals that damage DNA, suggesting that exposure of cells to these compounds does in fact cause DNA damage. Such damage could then result in mutations and the observed development of cancer.
  • Jun Yang, Yingnian Yu, Hope E. Hamrick and Penelope J. Duerksen-Hughes. "ATM, ATR and DNA-PK: Initiators of the Cellular Genotoxic Stress Responses." Carcinogenesis 24.10 (2003): 1571-1580. ( 7/2002 - 6/2003 ) Link...
    Exposure to genotoxic agents is a major cause of human cancer, and cellular responses to genotoxic stress are important defense mechanisms. These responses are very complex, involving many cellular factors that form an extensive signal transduction network. This network includes a protein kinase cascade that connects the detection of DNA damage to the activation of transcription factors, which in turn regulate the expression of genes involved in DNA repair, cell cycle arrest and programmed cell death (apoptosis). The mitogen-activated protein kinases are the best-studied members of the kinase cascade with an acknowledged role in the genotoxic stress response. However, the initial activation of the protein kinase cascade is not fully understood, although several protein kinases, such as ataxia telangiectasia, muted (ATM), ATM- and Rad3-related (ATR), and DNA-dependent protein kinase (DNA-PK) in humans, are increasingly recognized for their potential roles in the sensing of DNA damage and initiating the subsequent protein kinase cascade. In this review, the properties of these three kinases are discussed and their functions in the initiation of the genotoxic stress response are explored.
  • Maria Filippova, Helen Song, Jodi L. Connolly, Terence S. Dermody and Penelope J. Duerksen-Hughes. "The Human Papillomavirus 16 E6 Protein Binds to Tumor Necrosis Factor (TNF) R1 and Protects Cells from TNF-induced Apoptosis." J. Biological Chemistry 277.24 (2002): 21730-21739. ( 7/2001 - 6/2002 ) Link...
    High risk strains of human papillomavirus (HPV), such as HPV 16, cause human cervical carcinoma. The E6 protein of HPV 16 mediates the rapid degradation of p53, although this is not the only function of E6 and cannot completely explain its transforming potential. Previous work in our laboratory has demonstrated that transfection of HPV 16 E6 into the tumor necrosis factor (TNF)-sensitive LM cell line protects expressing cells from TNF-induced apoptosis in a p53-independent manner, and the purpose of this study was to determine the molecular mechanism underlying this protection. Caspase 3 and caspase 8 activation were significantly reduced in E6-expressing cells, indicating that E6 acts early in the TNF apoptotic pathway. In fact, E6 binds directly to TNF R1, as shown both by co-immunoprecipitation and mammalian two-hybrid approaches. E6 requires the same C-terminal portion of TNF R1 for binding as does TNF R1-associated death domain, and TNF R1/TNF R1-associated death domain interactions are decreased in the presence of E6. HA-E6 also blocked cell death triggered by the transfection of the death domain of TNF R1. Together, these results provide strong support for a model in which HPV E6 binding to TNF R1 intereferes with formation of the death-inducing signaling complex and thus with transduction of pro-apoptotic signals. They also demonstrate that HPV, like several other viruses, has developed a method for evading the TNF-mediated host immune response.
  • Jun Yang and Penelope 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. Biological Chemistry 276.29 (2001): 27129-27135. ( 7/2000 - 6/2001 ) Link...
    Sphingolipids such as ceramide are important mediators of apoptosis and growth arrest triggered by ligands such as tumor necrosis factor and Fas-L binding to their receptors. When LM (expressing p53) and LME6 (lacking p53) cells were exposed to the genotoxin N-methyl-N-nitro-N-nitrosoguanidine (MNNG), both cell lines underwent cytolysis in a very similar manner, suggesting the presence of a p53-independent apoptotic response to this genotoxic stress. To determine whether sphingolipids such as ceramide might serve as mediators in this system, the responses of these cells to exogenous spingolipids as well as the changes in their endogenous sphingolipid levels after DNA damage were examined. Treatment with exogenous C2-ceramide and sphingosine led to cell death in both LM and LME6, and treatment of the LME6 cells with MNNG resulted in a transient increase in intracellular ceramide of ~50 % over a period of 3 h. Finally treatment with the de novo inhibitor of ceramide synthesis ISP-1 protected LME6 cells from MNNG-triggered cell death. This MNNG-triggered induction of ceramide was not observed in the p53-expressing LM cells, suggesting that it may be down-regulated by p53. Although ceramide-mediated cell death can proceed in the absence of p53, exogenously added C2-ceramide increased the cellular p53 level in LM cells suggesting that the two pathways do intersect.
  • Penelope J. Duerksen-Hughes, Jun Yang and Ozan Ozcan. "p53 Induction as a Genotoxic Test for Twenty-Five Chemicals Undergoing in Vivo Carcinogenicity Testing." Environmental Health Perspectives 107.10 (1999): 805-812. ( 7/1998 - 6/1999 ) Link...
    In vivo carcinogenicity testing is an expensive and time-consuming process, and as a result, only a relatively small fraction of new and existing chemicals has been tested in this manner. Therefore, the development and validation of alternative approaches is desirable. We previously developed a mammalian in vitro assay for genotoxicity based on the ability of cells to increase their level of the tumor-suppressor protein p53 in response to DNA damage. Cultured cells are treated with various amounts of the test substances, and at defined times following treatment, they are harvested and lysed. The lysates are analyzed for p53 by Western blot and/or enzyme-linked immunosorbent assay analysis. An increase in cellular p53 following treatment is interpreted as evidence for DNA damage. To determine the ability of this p53-induction assay to predict carcinogenicity in rodents and to compare such results with those obtained using alternative approaches, we subjected 25 chemicals from the predictive toxicology evaluation 2 list to analysis with this method. Five substances (citral, cobalt sulfate heptahydrate, D&C Yellow No. 11, oxymetholone, and t-butyl-hydroquinone) tested positive in this assay, and three substances (emodin, phenolphthalein, and sodium xylenesulfonate) tested as possibly positive. Comparisons between the results obtained with this assay and those obtained with the in vivo protocol, the Salmonella assay, and the Syrian hamster embryo (SHE) cell assay indicate that the p53-induction assay is an excellent predictor of the limited number of genotoxic carcinogens in this set, and that its accuracy is roughly equivalent to or better than the Salmonella and SHE assays for the complete set of chemicals.
  • Penelope J. Duerksen-Hughes, Jun Yang and Stephanie B. Schwartz. "HPV 16 E6 Blocks TNF-Mediated Apoptosis in Mouse Fibroblast LM Cells." Virology 264. (1999): 55-65. ( 7/1998 - 6/1999 ) Link...
    The interaction between hosts and the viruses that infect them is a dynamic one, and a growing literature documents the fact that many viruses have developed mechanisms designed to avoid elimination by the host immune system. One of the immune strategies used by the host and targeted by virus proteins is apoptosis triggered by the cytokine tumor necrosis factor (TNF). Mouse fibroblast LM cells are spontaneously sensitive to TNF. When the wild-type E6 protein from the human papillomavirus type 16 (HPV 16) was expressed in LM cells, the cells because resistant to TNF. This resistance was examined by several means, including cell morphology, the dose- and time-dependent response to TNF in a cell death ELISA, trypan blue exclusion, and cell proliferation. The level of p53 did not rise in TNF-treated cells prior to apoptosis, suggesting a p53-independent mechanism. Significant, though not complete, resistance to TNF was also observed following transfection of a plasmid expressing a mutant E6 protein, which is unable to mediate rapid degradation of the p53 tumor suppressor. These results indicate that the HPV 16 E6 protein can protect LM cells from TNF-triggered apoptosis and likely does so by a mechanism other than mediation of p53 degradation.
  • Jun Yang and Penelope J. Duerksen-Hughes. "A New Approach to Identifying Genotoxic Carcinogens: p53 Induction as an Indicator of Genotoxic Damage." Carcinogenesis 19.6 (1998): 1117-1125. ( 7/1997 - 6/1998 ) Link...
    The tumor suppressor gene p53 encodes a nuclear phospho-protein which is critical for cell cycle control and prevention of uncontrolled cell proliferation that can lead to cancer. Previous studies have shown that cells respond to DNA damage by increasing their levels of p53, which then acts to prevent replication of damaged DNA. This study examined the effects on p53 protein levels of several different categories of chemical carcinogens. N-Methyl-N''-nitro-nitrosoguanidine and N-ethyl-N-nitrosourea, two direct-acting genotoxic (DNA-reactive) carcinogens, caused p53 induction as early as 2 h following treatment, with peak increases within 4-12 h. Aflatoxin B1 and 2-acetyl-aminofluorene, indirect-acting genotoxic carcinogens, caused a later induction of p53, with the peak increase appearing between 16 and 24 h following treatment. These observations demonstrate a correlation between p53 inducction pattern and DNA damaging mechanism of genotoxins. Phenol, diethylstilbestrol and ethylacrylate also induced increases in cellular p53. The half-life of p53 protein was increased in cells treated with genotoxic agents. On the other hand, the epigenetic (non-DNA-reactive) carcinogens azathioprine and saccharin, as well as two substances generally considered to be non-carcinogens, dimethylsulfoxide and benzethonium chloride, had no effect on p53 protein levels of treated cells. Measurement of the cytotoxic effects of each of these chemicals led to the conclusion that p53 protein induction is not a general, non-specific consequence of the cytotoxic effect of these genotoxins. These results suggest that measurement of p53 protein induction may be an effective tool to identify environmental genotoxins.
  Scholarly Journals--Accepted
  • Ju, L., G. Zhang, C. Zhang, L. Sun, Y. Jiang, C. Yan, P. J. Duerksen-Hughes, X. Zhang, X. Zhu, F. F. Chen and J. Yang. Quantum dot-related genotoxicity perturbation can be attenuated by PEG encapsulation. Mutation Research – Genetic Toxicology and Environmental Mutagenesis. In Press, 2013.

    ( 7/2012 - 6/2013 )
  • Hsu, H. W., R. de Necochea-Campion, V. Williams, P. J. Duerksen-Hughes, A. A. Simental, Jr., R. L. Ferris, C. S. Chen and S. Mirshahidi. Linifanib (ABT-869) enhances cytotoxicity with poly (ADP-ribose) polymerase inhibitor, veliparib (ABT-888), in head and neck carcinoma cells. Oral Oncol. In Press, 2014. PMID: 24735547.

    ( 4/2014 - Present )
  Books and Chapters
  • W. Evans, M. Filippova, R. Swensen and P. Duerksen-Hughes. Modern Molecular and Clinical Approaches to Eradicate HPV-Mediated Cervical Cancer, Chapter 11,  Human Papillomavirus and Related Diseases from Bench to Bedside: A Diagnostic and Preventative Perspective. D. Vanden Broeck, editor; ISBN 978-953-51-1072-9, 2013.

    ( 7/2012 - 6/2013 )