Staff Biography
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MARTIN J. SAPP, PH.D.Associate Professor for Microbiology and Immunology
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ContactPhone: (318) 675-5760 Team Membership |
Education / Research / Publications
Education / Professional Experience
Postdoctoral Study, University of Rochester
Ph.D., Molecular Genetics, 1987 University of Konstanz
M.S. (Diplom), Molecular Genetics, 1984, University of Konstanz
B.S. (Vordiplom), Biology, 1981, University of Konstanz
Research Interest
Virus cell interactions, molecular pathogenesis of oncogenic human papillomaviruses
Certain types of human papillomaviruses are the major cause of virus-induced malignancies in the human, like cervical carcinoma, the second most common cancer in women worldwide. Papillomaviruses are non-enveloped DNA viruses which exclusively replicate in the skin and mucosa. Due to the dependence on terminally differentiating tissues for their propagation, the study of the papillomavirus life cycle has been hampered. The development of surrogate systems for the generation of papillomaviruses in recent years has now opened ways to investigate processes involved in virus binding, uptake, and intracellular transport as well as the assembly of progeny virus. We are specifically interested in identifying cellular factors functioning as papillomavirus receptors, in the study of virus uptake and intracellular transport, in the analysis of the uncoating process, and the passing of cellular membranes by the virus genome. We are also studying the assembly process including identification of cellular factors regulating the morphogenesis of progeny virus.
Our main interest regards the biology of human papillomaviruses (HPV), the causative infectious agent for the development of several cancers, including cervical cancer. The focus is on understanding early events of infection. Using molecular genetic, biochemical, and cell biological techniques we investigate the interaction of HPV with the extracellular matrix and cell surface molecules, as well as the internalization and intracellular transport of viral particles. We have previously identified heparan sulfate proteoglycans (HSPG) as primary attachment receptors and determined the viral determinants mediating binding to cells. We have demonstrated an essential role of the minor capsid protein L2 in endosomal release and retrograde transport along microtubules of the viral genome. We are currently studying if and which signals are induced by HPV binding to host cells, how they contribute to infection, and how the final steps of intracellular transport and establishment of transcription from the viral genome are achieved. The focus lies on the identification of cellular pathways and host cell proteins involved in these processes.
Human papillomavirus
Receptor
Signal transduction
Intracellular transport
Nuclear import
Project 1, cervical cancer: In collaboration with groups in Germany and Russia, we have identified a family of heparan sulfate-binding drugs that efficiently inhibit HPV infection. We are currently investigating their mechanism of action and utilize them to study the early events of HPV infection. So far, we found that a complex series of events including primary and secondary interaction with HSPG as well as transfer to a non-HSPG receptor and conformational changes of the viral capsid precede virus internalization. The drugs inhibit HPV infection by preventing these steps and by feeding the virus into a noninfectious entry pathway.
Project 2, cervical cancer: Following infection, viral DNA and the L2 protein are homing to subnuclear structures, called PML nuclear bodies, where viral transcription is established. We identified L2 mutants that segregate from viral DNA during intracellular transport. Mutant viruses still deliver viral genome to PML nuclear bodies but transcription is not started, suggesting that L2 homing to these sites is required for transcriptional initiation. Our experiments are designed to understand how L2 associates with the viral genome during transport processes, how L2 contributes to establishment of transcription, and to identify host cell factors involved.
Project 3, cervical cancer: We found that HPV binding to host cells induces expression of some cellular genes. In contrast to most mRNAs, induced mRNAs depend on CRM1 for nuclear export. We also observed that CRM1 activity is required for completion of the infection process. We are investigating which signal transduction pathways are involved and try to understand the contributions of induced proteins to the internalization and intracellular transport of incoming virus.
Specialized Techniques/Procedures
- Cell culture
- Transfection (siRNA, pseudovirus production)
- Pseudovirus purifications
- Immunofluorescence, confocal microscopy
- Microinjection (antibodies, DNA)
- Western blotting.
- Protein, RNA and DNA extraction.
- PCR, RT-PCR and quantitative Real-Time PCR
- cDNA representational difference analysis
- Microarray
- Site-directed mutagenesis
Selected Publications
Giroglou, T., Florin, L., Schäfer, F., Streeck, R.E., and Sapp, M. (2001): Human papillomavirus infection requires cell surface heparan sulfate. J. Virol. 75:1565-1570.
Fligge, C., Schäfer, F., Selinka, H.-C., Sapp, C., and Sapp, M. (2001): DNA-induced structural changes in the papillomavirus capsid. J. Virol. 75:7727-7731.
Florin, L., Schäfer, F., Sotlar, K., Streeck, R. E., and Sapp, M. (2002): Reorganization of nuclear domain 10 induced by papillomavirus capsid protein L2. Virology. 295:97-107.
Florin, L., Sapp, C., Streeck, R. E., and Sapp, M. (2002): Assembly and translocation of the papillomavirus capsid proteins. J. Virol. 76:10009-10014.
Selinka, H.-C., Giroglou, T., Nowak, T., and Sapp, M. (2003): Further evidence that papillomavirus capsids exist in two distinct conformations. J. Virol. 77:12961-12967.
Becker, K.A., Florin, L., Sapp, C., Selinka, H.-C., Maul, G.G., and Sapp, M. (2004): Nuclear localization but not PML is required for incorporation of papillomavirus minor capsid protein L2 into virus-like particles. J. Virol. 78:1121-1128.
Florin, L., Becker, K.A., Sapp, C., Lambert, C., Sirma, H., Müller, M., Streeck, R.E., and Sapp, M. (2004): Nuclear translocation of papillomavirus minor capsid protein L2 requires Hsc70. J. Virol. 78:5546-5553.
Kämper, N., Day, P. M., Nowak, T., Selinka, H.-C., Florin, L., Bolscher, J. G., Hilbig, L., Schiller, J. T., and Sapp, M. (2006): A membrane-destabilizing peptide in capsid protein L2 required for egress of papillomavirus genomes from endosomes. J. Virol. 80:759-768
Florin, L., Becker, K. A., Lambert, C., Nowak, T., Sapp, C., Strand, D., Streeck, R. E., and Sapp, M. (2006): Identification of a dynein interacting domain in the papillomavirus minor capsid protein L2. J. Virol. 80:6691-6696.
Knappe, M., Bodevin, S., Selinka, H.-C., Spillmann, D., Streeck, R. E., Chen, X., Lindahl, U., and Sapp, M. (2007): Surface-exposed amino acids of HPV16 L1 protein mediating interaction with cell surface heparan sulphate. J. Biol. Chem.282:27913-29222.
Selinka, H.-C., Florin, L., Patel, H.D., Freitag, K., Schmidtke, M., Makarov, V.A., Sapp, M. (2007): Inhibition of transfer to secondary receptors by heparan sulfate-binding drug or antibody induces non-infectious uptake of human papillomavirus. J. Virol. 81:10970-10980.