Biomedical Sciences Graduate Program(s)
Biomedical Sciences Graduate Programs
We have two major research interests, including regulation of pituitary hormones
by hypothalamic peptides and sex steroids, and estrogen action and cross-talk
with intracellular signaling pathways in breast cancer.
Hypothalamic and steroid regulation of pituitary hormones, estrogen
action in neuroendocrine tissues:
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.
Walsh HE, Shupnik MA Proteasome regulation of dynamic transcription factor occupancy on the GnRH-stimulated luteinizing hormone beta-subunit promoter. Mol Endocrinol 2009; 23:237-250.
Wen J, Lu Y, Li R, Shupnik MA. Decreased BRCA1 confers tamoxifen resistance in breast cancer cells by altering Estrogen Receptor-coregulator interactions Oncogene 2009; 28:575-586.
Fox EM, Bernaciak TM, Wen J, Weaver AM, Shupnik MA, Corinne M. Silva. STAT5b, c-Src, and EGFR signaling play integral roles in estrogen-stimulated proliferation of ER-positive breast cancer cells. Mol Endocrinol 2008; 22:1781-1796.
Haisenleder DJ, Burger LL, Walsh HE, Stevens J, Aylor KW, Shupnik MA, JC Marshall. Pulsatile GnRH stimulation of gonadotropin subunit transcription in rat pituitaries: Evidence for the involvement of Jun N-Terminal kinase (JNK), but not p38. Endocrinology 2008; 149:139-145.
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