Margaret A. Shupnik
Primary AppointmentGerald D. Aurbach Professor of Endocrinology, Medicine: Endocrinology and Metabolism
- BS, Chemistry & Biochemistry, Pennsylvania State University, University Park, PA
- PhD, Biochemistry, University of Wisconsin
- Postdoc, Endocrinology/Toxicology, Harvard School of Public Health
Hypothalamic Peptide and Steroid Regulation of Pituitary Gene Transcription; Estrogen Action in Neuroendocrine and Reproductive Tissues; Estrogen Action in Breast Cancer
Pituitary hormones play a critical role in many processes, including growth, metabolism, reproduction and development. Our laboratory is interested in how hypothalamic peptides and steroids such as estrogen (E) and testosterone (T) directly and indirectly modulate pituitary hormone gene transcription. As one model, we study the gonadotropins, LH (luteinizing hormone) and FSH (follicle stimulating hormone), which control gamete development and the production of E and T from the gonads. LH and FSH each consist of a common alpha and specific beta subunit. We showed subunit-specific regulation of each gene by E and T, and frequency-dependent, subunit-specific modulation of transcription by hypothalamic GnRH. We have found that the genes have both common and unique regulatory elements, and are regulated by cooperative interactions between these regions. We are continuing to define the transcription factors binding to these regions and the coactivator proteins that modulate their activity. By performing chromatin immunoprecipitation (ChIP) assays, we find that there are defined patterns of transcription factor occupancy of the LHbeta gene after GnRH treatment, with intervals corresponding to the physiological GnRH pulse frequency. Our working hypothesis is that pulsatile regulation of gonadotropin gene transcription by GnRH is regulated by transcription factor synthesis and modification, differential activation by intracellular signaling pathways, and proteasome activity. We are testing this by mRNA and protein microarray analysis of transcription factor and signaling genes, measurement of activated signaling molecules, examination of transcription factor modification, and protein degradation studies. Comparison of the subunit genes for GnRH and steroid modulation by transfection, transcription and ChIP analysis will allow us to determine common and distinct regulatory mechanisms. We have also identified and cloned a unique truncated form of the estrogen receptor (ER)-alpha in female rat pituitaries. This receptor, TERP, is transcribed from its own intronic promoter and its expression is regulated by E and physiological state. TERP can modulate ER activity on model promoters positively by titrating repressor proteins, and negatively by forming heterodimers that cannot bind DNA. To understand the physiological role of this receptor, we are examining the interaction of the ER and TERP with regulatory proteins that may modify their activity, regulation of endogenous genes and physiological promoters by TERP, and the physiological consequences of a TERP promoter knock-out in mice.Estrogen action in breast cancer:
Estrogen is a critical component in the development of breast cancer, and its nuclear receptor is often a target for antiestrogen therapy. We have found that estrogen, acting through its receptor, can rapidly activate some cytoplasmic enzymes, and we are examining interactions between the estrogen receptor and components of growth factor intracellular signaling pathways, including the STAT transcription factors. The STATS are activated in response to both EGF receptor activation and estrogen, and we propose that they may serve as a common pathway to both steroid and growth factor-dependent forms of breast cancer. We have found that estrogen receptor alpha (ERa) is a powerful modulator of STAT activity, and we have some evidence that this can occur in both the cytoplasm and nucleus. We are examining the biochemical and biological interactions of these pathways, and the role such interactions may have on breast cancer cell proliferation and apoptosis.