PARENT SESSION
MECHANISMS OF HORMONE ACTION

Tuesday, August 3, 2004
10:30 AM–12:30 PM
Buchanan Courtyard

(349) WNT AND LH SIGNALING CONVERGE ON -CATENIN TO REGULATE GRANULOSA CELL STEROIDOGENESIS.

Parakh, Tehnaz^{1, 2, 3}, Nilson, John^{1, 2}, ¹ Washington State University, Pullman, WA² Center for Reproductive Biology, Pullman, WA³ Case Western Reserve University, Cleveland, OH

ABSTRACT- Granulosa cell (GC) steroidogenesis is regulated by unique signaling networks induced by gonadotropin stimulation, and intraovarian factors that modulate gonadotropin effects. The Wnt family of secreted glycoproteins, especially Wnt-4, have been indicted as intraovarian factors critical in gonad development. In the adult, Luteinizing Hormone (LH) regulates expression of Wnt-4 in GCs, although the functional significance remains elusive. We present preliminary evidence that LH signaling stabilizes -catenin, a transcriptional coactivator and canonical mediator of Wnt signaling. Further, we propose that Wnt-4 and LH signaling converge on -catenin to modulate the genetic network underlying ovarian steroidogenesis. Previously, we determined that transgenic mice hypersecreting LH (LHCTP) have altered gene expression of Wnt-4 and its signaling components. To determine if these alterations correlated with changes in ovarian steroidogenesis in vivo, we measured serum Progesterone and Estradiol in LHCTP and wild-type mice. Increased Progesterone (but not Estradiol) production correlated with high levels of ovarian Wnt-4, suggesting Wnt-4 may modulate LH-induced steroidogenesis. To further explore the link between LH and Wnt signaling in vitro, we transduced primary immature rat GCs with recombinant adenoviruses to direct expression of constitutively active LH receptor (D578H-LHR) and constitutively active -catenin (90<cat). Stimulation of a TCF-responsive reporter (TOPflash) was used as an index of -catenin stabilization. Results indicate that D578H-LHR selectively stabilized -catenin in a dose-dependent manner. Additionally, co-transduced D578H-LHR and 90cat synergistically activated TOPflash, further implicating -catenin as a novel downstream target of LH. Importantly, FSH stimulation (50ng/ml) had no effect on -catenin stabilization. In conclusion, our preliminary evidence suggests LH stimulation selectively stabilizes -catenin, and that Wnt-4 may play a role in LH-induced steroid production. Future experiments will determine if -catenin is necessary for LH-induced steroidogenesis, and if this reflects a Wnt-independent mechanism of -catenin stabilization.

KEY WORDS: beta-catenin, steroidogenesis, LH, Wnt-4