Joseph D. Fondell, Ph.D.
Laboratory of Molecular Endocrinology
Members of the nuclear receptor superfamily function as hormone dependent transcriptional regulators when bound to response elements of target genes. Transcriptional adaptor/imtermediatory factors appear to be involved in mediating the hormone-dependent functions of the receptor. The research in our lab examines the molecular mechanism of transcriptional regulation by the thyroid hormone receptor (TR) and strives to identify specific nuclear factors which interact with the receptor and modulate TR function. Toward this end, we have immunopurified epitope-tagged TR from stable cell lines grown with thyroid hormone and identified at least nine TR associated proteins (TRAPs) ranging in size from 80 to 230 kDa. Using in vitro transcription assays, we find that TRAPs markedly enhance liganded-TR’s ability to activate transcription, strongly suggesting a functional role for TRAPs as gene-specific coactivators. Currently, we are focusing on the cDNA cloning and molecular characterization of the individual TRAP subunits. By utilizing cellular, molecular and biochemical assays, the long term goal is to elucidate the mechanism of action of the TRAPs in terms of their functional interaction with nuclear receptors, other transcriptional cofactors and the basal transcription machinery. Relative to the general study of nuclear receptors, we are also examining the role of estrogen and antiestrogen mediated gene expression in both normal and breast cancer cells. These studies focus on two major questions: First, what nuclear factors or coactivators associate with the estrogen receptor (ER) and potentiate ER function? Secondly, what molecular mechanisms account for the differential effects of estrogen versus antiestrogens on ER function in different tissues. To address these issues, we are utilizing several experimental approaches including: 1) establishing stable cell lines which transiently or stably express epitope-tagged ER; 2) protein interaction assays (i.e. GST-pull down, immunoprecipitations, yeast two-hybrid); 3) in vivo footprinting; and 4) in vitro transcription assays.
Recent Publications:Fondell JD, Roy AL, Roeder RG 1993 Unliganded thyroid hormone receptor inhibits formation of a functional preinitiation complex: Implications for active repression. Genes & Dev 7:1400-1410.
Fondell JD, Brunel F, Hisatake K, Roeder RG 1996 Unliganded thyroid hormone receptor a can target the TATA-binding protein for transcriptional repression. Molecular Cellular Biology 16:281-287.
Fondell JD, Ge H, Roeder RG 1996 Ligand induction of a transcriptionally active thyroid hormone receptor protein complex. Proceedings National Academy Science USA 93:8329-8333.
Lemon BD, Fondell JD, Freedman LP 1997 Retinoid X receptor: Vitamin D3 receptor heterodimers promote stable preinitiation complex formation and direct 1,25-dihydroxyvitamin D3-dependent cell-free transcription. Molecular Cellular Biology 17:1923-1937.
