Regulation of LH receptor and PGF2α receptor signaling by the regulator of G protein signaling 2 (RGS2) in human and mouse granulosa cells

Regulators of G protein signaling (RGS) proteins bind the G protein Gα subunit in its active GTPbound state and accelerate its GTPase activity, thus halting Gα activity. Induction of RGS2 expression has been previously shown in the rat ovary in response to ovulatory stimulation; however, the significance of RGS2 in the ovary has not been established. This study reports the potential role of RGS2 in the signaling of two G protein-coupled receptors, the LH and PGF2α (FP) receptors, in the human and the mouse granulosa cell lines, KGN and NT-1. The RGS2 mRNA concentration was rapidly and transiently elevated by human chorionic gonadotropin (hCG) or PGF2α analogue cloprostenol and this was followed by a decline to basal level at 24 h. Expression of the downstream critical target gene of the LH and FP receptor signaling pathways, namely, cyclooxygenase 2 (COX2), was induced by hCG but was inhibited by cloprostenol. Overexpression of RGS2 attenuated hCG-induced COX2 transcription. However, this augmented cloprostenol-mediated suppression of COX2 transcription. Confocal microscopy and immunoblot analysis were adopted to monitor the intracellular localization of RGS2 in COS-7 cells carrying the FP receptor and expressing RGS2-GFP or FLAG-RGS2. RGS2 was initially located predominantly in the nucleus and activation of the FP receptor resulted in RGS2 translocation from nucleus to the cell membrane. Thus, RGS2 expression was upregulated by LH receptor and FP receptor activation and modulation of partner receptor signaling by RGS2 may require RGS2 translocation from the nucleus to the plasma membrane.