Regulation of TIP60 by the ubiquitin-proteasome pathway

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DESCRIPTION (provided by applicant): TIP60 is a cellular lysine acetyltransferase that is getting increasing attention because of its role in the regulation of gene expression, in the response of a cell to DNA damage and as a tumor suppressor. TIP60 acetylates histones and critical cellular proteins involved in DNA damage response like p53, p21 and ATM kinase. In the previous cycle of this grant we discovered that two viruses use virally encoded oncoproteins, the E6 oncoprotein from human papilloma virus (HPV) and the E1b55K+E4Orf6 oncoproteins from adenovirus, to promote the degradation of the TIP60 tumor suppressor by proteasomes. The degradation of TIP60 is important for regulating the expression of viral genes and for modulating the cell's response to DNA damage. In parallel, we discovered that a cellular deubiquitinase, USP7, stabilizes TIP60 in human cells. We now propose to investigate whether the proteasome-mediated degradation of TIP60 can be exploited for therapy. Aim 1 will test the hypothesis that the degradation of TIP60 by HPV E6 oncoprotein is mediated by direct protein-protein interactions between TIP60 and E6, and that the degradation leads to changes in cellular gene expression, cell transformation and the susceptibility to radiotherapy of HPV-infected cells and cancers. We will also test whether stabilization of TIP60 impairs the replicative life of the virusin keratinocytes in organotypic raft cultures and thus be a potential avenue of suppressing HPV infection. Aim 2 will test the hypothesis that adenovirus oncoproteins degrade TIP60 by harnessing specific cellular proteins to create a virus-specific E3 ubiquitin ligase, and that this degradation alters viral gene expression programs to facilitate viral replication. This project advances our novel discoveries on the degradation of TIP60 by viral oncoproteins. Success in this project will enhance our understanding of HPV-infected cancers and identify a new mechanism by which adenovirus oncoproteins de-regulate the cellular machinery to facilitate viral infection.