Luteinization of follicular granulosa cells leads to an increase in progesterone secretion that is regulated by luteinizing hormone (LH). LH acts mainly by elevating intracellular cyclic 3′,5′-adenosine monophosphate (cAMP) and activating cAMP-dependent protein kinase (PKA). In this study, we have examined the role of PKA in relation to progesterone output by luteinizing human granulosa cells. Human granulosa cells were obtained by percoll gradient centrifugation of follicular aspirates of patients undergoing oocyte retrieval for assisted conception. Cells were cultured in serum-supplemented medium for up to 3 days in the presence and/or absence of human (h)LH and other cAMP-elevating agents. Spent medium was assayed for cAMP and progesterone content by specific RIA. Cell lysates were collected and assessed for PKA regulatory (R)IIα/catalytic (C)α expression by Western blotting. Although basal progesterone secretion increased progressively throughout culture, cAMP levels remained unchanged. Under basal conditions, PKA RIIα/Cα expression appeared to increase throughout the 3-day culture period. In the presence of hLH and other cAMP-elevating agents, progesterone secretion increased in a dose-dependent manner coincident with an increase in cAMP. However, despite the increase in both progesterone secretion and cAMP accumulation, there was a dose-dependent decrease in both PKA RIIα and Cα expression. Thus, data presented in this study show that increases in progesterone secretion in luteinizing human granulosa cells can be dissociated from increases in PKA expression. This notion implies that progesterone secretion may be regulated by PKA-dependent as well as PKA-independent mechanisms.
E C Chin, T E Harris and D R E Abayasekara
C Chandras, T E Harris, A López Bernal, D R E Abayasekara and A E Michael
In luteinizing granulosa cells, prostaglandin E2 (PGE2) can exert luteotrophic actions, apparently via the cAMP signalling pathway. In addition to stimulating progesterone synthesis, PGE2 can also stimulate oxidation of the physiological glucocorticoid, cortisol, to its inactive metabolite, cortisone, by the type 1 11β-hydroxysteroid dehydrogenase (11βHSD1) enzyme in human granulosa–lutein cells. Having previously shown these human ovarian cells to express functional G-protein coupled, E-series prostaglandin (PTGER)1, PTGER2 and PTGER4 receptors, the aim of this study was to delineate the roles of PTGER1 and PTGER2 receptors in mediating the effects of PGE2 on steroidogenesis and cortisol metabolism in human granulosa–lutein cells. PGE2-stimulated concentration-dependent increases in both progesterone production and cAMP accumulation (by 1.9 ± 0.1- and 18.7 ± 6.8-fold respectively at 3000 nM PGE2). While a selective PTGER1 antagonist, SC19220, could partially inhibit the steroidogenic response to PGE2 (by 55.9 ± 4.1% at 1000 nM PGE2), co-treatment with AH6809, a mixed PTGER1/PTGER2 receptor antagonist, completely abolished the stimulation of progesterone synthesis at all tested concentrations of PGE2 and suppressed the stimulation of cAMP accumulation. Both PGE2 and butaprost (a preferential PTGER2 receptor agonist) stimulated concentration-dependent increases in cortisol oxidation by 11βHSD1 (by 42.5 ± 3.1 and 40.0 ± 3.0% respectively, at PGE2 and butaprost concentrations of 1000 nM). Co-treatment with SC19220 enhanced the ability of both PGE2 and butaprost to stimulate 11βHSD1 activity (by 30.2 ± 0.2 and 30.5 ± 0.6% respectively), whereas co-treatment with AH6809 completely abolished the 11βHSD1 responses to PGE2 and butaprost. These findings implicate the PTGER2 receptor–cAMP signalling pathway in the stimulation of progesterone production and 11βHSD1 activity by PGE2 in human granulosa–lutein cells.