title: Evidence for a role of protein kinase C in luteinizing hormone synthesis and secretion. Impaired responses to gonadotropin-releasing hormone in protein kinase C-depleted pituitary cells.
abstract: The role of protein kinase C in luteinizing hormone (LH) release was analyzed in studies on the actions of phorbol esters and gonadotropin-releasing hormone (GnRH) in normal and protein kinase C (Ca2+/phospholipid-dependent enzyme)-depleted pituitary cell cultures. LH secretory responses of normal pituitary cells to GnRH were reduced but not abolished in Ca2+-deficient medium, consistent with the existence of extracellular Ca2+-dependent and -independent components of GnRH action. Both of these components could be elicited by treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA). The LH secretory responses to TPA and GnRH were additive only at low doses and converged to a common maximum at high concentrations of the agonists in the presence or absence of extracellular Ca2+. The release of stored LH by GnRH and TPA was accompanied by secretion of newly synthesized LH from 2 to 5 h during stimulation by either of the agonists. LH synthesis was increased in a progressive and dose-dependent manner by GnRH and TPA, and the ratio between newly synthesized and released hormone was near 1:2. TPA caused rapid and complete translocation of cytosolic protein kinase C to the particulate fraction of pituitary cells, followed by a progressive decrease in total enzyme content to approximately 10% after 6 h. Partial recovery of the cytosolic enzyme (to 20%) occurred after washing and reincubation for 15 h. Such kinase C-depleted cells showed prominent, dose-dependent reductions in the actions of GnRH and TPA on LH release and synthesis in both normal and Ca2+-deficient media. These observations support the hypothesis that protein kinase C participates in LH biosynthesis and secretion in pituitary gonadotrophs and is involved in the actions of GnRH upon these processes.
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007700:Kinetics; D007986:Luteinizing Hormone / Q000096:biosynthesis* / Q000378:metabolism; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate