Phospholipase C beta 3 Mediates LH-Induced Granulosa Cell Differentiation

Previous studies showed that under certain conditions LH can stimulate not only adenylate cyclase (AC) but also phospholipase C beta(PLC beta) signaling in target cells; however, the physiological involvement of PLC beta in LH-induced ovarian follicular cell differentiation has not been determined. To address this, ex vivo expression analyses and specific PLC beta targeting were performed in primary bovine granulosa cells. Expression analyses in cells from small (2.0-5.9 mm), medium (6.0-9.9 mm), and ovulatory-size (10.0-13.9 mm) follicles revealed an increase in mRNA and protein levels of heterotrimeric G protein subunits-alpha s, -alpha q, -alpha 11, and -alpha i2 in ovulatory-size follicles, simultaneous with a substantial increase in LH receptor expression. Among the four known PLC beta isoforms, PLC beta 3 (PLCB3) was specifically up-regulated in cells from ovulatory-size follicles, in association with a predominantly cytoplasmic location of PLCB3 in these cells and a significant inositol phosphate response to LH stimulation. Furthermore, RNA interference-mediated PLCB3 down-regulation reduced the ability of LH to induce hallmark differentiation responses of granulosa cells, namely transcriptional up-regulation of prostaglandin-endoperoxide synthase 2 and down-regulation of both aromatase expression and estradiol production. Responses to the AC agonist, forskolin, however, were not affected. In addition, PLCB3 down-regulation did not alter cAMP responses to LH in granulosa cells, ruling out a primary involvement of AC in mediating the effects of PLCB3. In summary, we provide evidence of a physiological involvement of PLC beta signaling in ovulatory-size follicles and specifically identify PLCB3 as a mediator of LH-induced differentiation responses of granulosa cells. (Endocrinology 152: 2857-2869, 2011)