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"KAPOSI`S SARCOMA-ASSOCIATED HERPESVIRUS LYTIC TRANSACTIVATORS IN PATHOGENESIS"

by
Sophia Spadavecchia
Department of Microbiology and Molecular Genetics
B.S. 2003, Montclair State University


Thesis Advisor: David M. Lukac, Ph.D.

Assistant Professor

Department of Microbiology and Molecular Genetics

Thursday, December 10, 2009
12:00 p.m., ICPH-Auditorium


Abstract

The KSHV Rta protein transcriptionally transactivates delayed early promoters during reactivation of the virus from latency. While Rta is necessary and sufficient for reactivation, not every infected cell that expresses Rta leads to lytic cycle completion. We propose that Rta transactivation can lead to alternative gene expression pathways, either leading to an abortive lytic cycle or complete lytic replication. During an abortive lytic cycle. Rta upregulates expression of DE oncogenes and leads to cell proliferation. Alternatively, Rta can also upregulate expression of the commitment factor, Mta, that will permit full lytic replication resulting in cell lysis. Additionally, in the context of a dual-infection with KSHV and EBV, crosstalk between both viruses is necessary to maintain a balance of latency and reactivation. We demonstrate that KSHV Rta stimulates transactivation of EBV latent oncogenes as it does DE KSHV lytic genes.
KSHV is the etiologic agent of primary effusion lymphoma (PEL). All PEL cell lines are infected with KSHV, and 70% are co-infected with EBV. Dually infected PELs are more aggressive than singly infected PELs. KSHV reactivation from latency requires promoter-specific transactivation by the KSHV Rta protein through interactions with RBP-Jk (CSL), the cellular DNA binding component of the Notch signal transduction pathway. EBV transformation of primary B cells requires EBV nuclear antigen (EBNA)-2 to interact with RBP-Jk to direct the latent gene expression program, particularly through activation of the EBV latency C (Cp) and the Latent Membrane Protein (LMP)-1 promoters. We have found that EBV LMP-1 is expressed in less than 5% of KSHV+/EBV+ PEL cells, but is induced in an Rta-dependent fashion when KSHV reactivates. In uninfected cells, KSHV Rta transactivates the EBV latency promoters in an RBP-Jk-dependent fashion and forms a ternary complex with RBP-Jk on the promoters. In B cells that are conditionally transformed by EBV, our data suggest that KSHV Rta complements the EBNA2 growth deficiency in an autocrine/paracrine manner. Although complementation by Rta depends on RBP-Jk and LMP-1, cellular proteomic analyses reveal that EBNA2 and Rta rescue the growth defect in distinct manners. We demonstrate that Rta transactivation is required for optimal growth of KSHV+/EBV+ PEL lines. Our data suggest that Rta can contribute to EBV-driven cellular growth promotion by transactivating RBP-Jk-dependent EBV latency oncogenes as it does KSHV DE genes.


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