Grace Gill - US grants

Studies of the transforming proteins of the small DNA tumor viruses, such as Adenovirus E1A, have provided a wealth of information about the proteins and pathways that regulate cellular proliferation. Though interactions with key cellular transcription factors, such as the Retinoblastoma tumor suppressor, E1A reprograms cellular gene expression to inhibit differentiation and promote cell cycle progression. Research in my lab has led to the identification and characterization of a novel cellular protein, TIR, that antagonizes the transcriptional activation and cellular transformation activities of the Adenovirus E1A oncoprotein. TIR specifically represses expression of certain cellular and viral promoters dependent on cell cycle control elements recognized by E2F. The studies described in this proposal are designed to test the hypothesis the, through interaction with the Retinoblastoma tumor suppressor and related proteins, TIR acts to down-regulated the activity of specific transcription factors such as E2F that are important for cell cycle progression and thereby contributes to the loss of proliferation characteristics of terminal differentiation. The specific aims of this research are to (1) investigate TIR function in proliferation and differentiation in cell culture assays, (2) identify functional domains of TIR and correlated binding to specific proteins with the promoter specific repression and cellular effects mediated by TIR, and (3) investigate the mechanism by which TIR represses transcription assays. In addition to advancing out knowledge about the specific function of TIR, these studies are likely to provide important information about the regulation of E2F- dependent transcription, the roles of pRb and related proteins during differentiation, and perhaps provide novel insight into the mechanisms of transcriptional repression. Studies of TIR may also yield unique information about the cellular pathways targeted by DNA tumor viruses in viral replication and oncogenic transformation. Since disturbances of the finely tuned transcription program often result in developmental abnormalities or predisposition to diseases such as cancer, studies of regulators such as TIR are imperative in order to increase our understanding of these processes at the cellular and molecular level.

DESCRIPTION (provided by applicant): Covalent attachment of the Small ubiquitin related modifier, SUMO, to proteins important for regulated gene expression has been correlated with inhibition of transcription. Post-translational modification by SUMO represses activity of the dual function transcription factor Sp3. Sp3 is required for post-natal survival and differentiation of bone, tooth, and hematopoietic lineages in mice. Polymorphisms in binding sites for Sp3 and the related Sp1 protein correlate with disease risk for osteoporosis, diabetes, and cancer. The studies in this proposal investigate the hypothesis that SUMO-modified Sp3 promotes formation of a repressive chromatin structure by recruiting a corepressor complex containing a SUMO-binding domain. Non-covalent interactions with SUMO-modified transcription factors is proposed to contribute to gene targeting by several chromatin modifying complexes. The specific aims of this research are to (1) investigate how SUMO modification regulates protein interactions with Sp3, (2) analyze the molecular mechanisms of repression by SUMOylated Sp3 in vivo, and (3) determine the identity and function of SUMO binding domains in chromatin modifying complexes that interact non-covalently with SUMO. These studies will identify cofactors and mechanisms underlying Sp3-dependent regulation of genes important for cell proliferation, differentiation, and survival. These studies will provide new insights into the molecular mechanisms by which SUMO modification of many transcription factors inhibits transcription, determine the structure and function of SUMO binding domains in corepressors, and provide a foundation to determine the molecular basis for context-dependent activities of Sp3 and SUMO. Studies of non-covalent SUMO binding by chromatin modifying complexes will increase understanding of the epigenetic mechanisms that regulate chromatin structure and gene expression in normal development and disease. Relevance: These studies address the fundamental mechanisms by which the SUMO protein regulates gene expression in human cells. Aberrant patterns of SUMO attachment to other proteins has been associated with pathogenic viral and bacterial infections, diabetes, cancer, and neurodegenerative diseases. Therefore, increased understanding of the fundamental mechanisms underlying SUMO function in regulation of gene expression may lay the foundation for novel therapeutic strategies that address these significant human health issues.