Molecular determinants of bHLH-PAS transcription factor function

Occupational And Environmental Health

The expression of genes in response to specific stimuli is carried out by a large group of proteins known as transcription factors.  In order to direct transcription in an appropriate spatial and temporal fashion, these proteins must direct the coordinated assembly and disassembly of large protein machines on chromatin.  The objective of my research program is to understand how ancillary proteins are recruited to, and dismissed from gene expression machinery during activated transcription by a family of transcription factors termed basic-Helix-Loop-Helix-PAS (bHLH-PAS) proteins. In addition, it is our goal to understand how these changes in transcriptional machinery alter protein function in response to different signals. In order to do so, we have chosen to study 2 tightly regulated and robust model systems; aryl hydrocarbon receptor (AHR)-regulated CYP1A1 activity; and, hypoxia-inducible factor-1a (HIF-1a)-regulated VEGF and EPO expression.  We have established that estrogens, through the estrogen receptor-a (ERa), can repress AHR function via direct protein-protein interactions.  Furthermore, ERa does so by facilitating an exchange for the histone deacetylase, HDAC4 for the co-repressor protein, RIP140 at the regulatory elements of AHR target genes. We propose to elucidate the molecular determinants of estrogen receptor repression of AHR-regulated transcription.  In addition, we have designed a series of experiments to better understand how estrogen-responsive recruitment of the repressor RIP140 modulates AHR activity and to determine the role HDAC4 plays in maintaining RIP140 in a state conducive to AHR-mediated gene transcription.  The second part of this proposal outlines our experimental plan to elucidate the role of the retinoblastoma protein (Rb) on HIF-1a regulated transcription. We have demonstrated that the co-activator TRIP230 is essential for transcriptional activation by HIF-1a.  In addition, we have evidence that mediated HIF-1a-dependent transcriptional activity is negatively regulated by Rb. Together, these studies will increase our understanding of normal AHR physiology, vasculogenesis, and transcription factor function in general.  In addition, this added information will aid in the rational design of novel therapies that exploit transcription factor function and are directly targeted at their activities.