Changes in cAMP-dependent protein kinase (PKA) and progesterone secretion in luteinizing human granulosa cells

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) IIalpha/catalytic (C)alpha expression by Western blotting. Although basal progesterone secretion increased progressively throughout culture, cAMP levels remained unchanged. Under basal conditions, PKA RIIalpha/Calpha 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 RIIalpha and Calpha 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.