Effect of protein kinase-C depletion on inositol trisphosphate-mediated and cyclic adenosine 3',5'-monophosphate-dependent protein kinase-mediated adrenocorticotropin secretion.
We studied the effect of Ca2+/phospholipid-dependent protein kinase-C (protein kinase-C) down-regulation by chronic exposure to phorbol 12-myristate 13-acetate (PMA) on ACTH secretion by dispersed male rat anterior pituitary cells in a microperifusion system. Preincubation for 24 h and preperifusion for 3 h with 0.1 and 1 microM PMA significantly inhibited (by 85% and 91%, respectively) the specific cell binding of [3H]phorbol 12,13-dibutyrate, an index of protein kinase-C concentration, and significantly reduced (by 101% and 20%, respectively) the sustained plateau (final 15-min) phase of the ACTH response to arginine vasopressin (AVP) and (by 56% and 54%, respectively) the sustained (full 20-min) response to dioctanoylglycerol (DOG), both of which are mediated by protein kinase-C activation. In contrast, the spike (initial 5-min) phase of the response to AVP, which is mediated by intracellular Ca2+ release from inositol 1,4,5-trisphosphate (InsP3)-sensitive stores, was significantly increased (by 112% and 99%, respectively), but the spike-type response to ionomycin, which releases intracellular Ca2+ by an InsP3-independent mechanism, was unaffected. AVP significantly stimulated inositol bisphosphate and InsP3, but not inositol monophosphate, accumulation, and PMA pretreatment significantly enhanced their AVP-stimulated accumulation (by 86%, 34%, and 78%, respectively), an effect that was abolished by simultaneous preperifusion with PMA and cycloheximide to inhibit new protein synthesis. Enhancement of the spike phase response to AVP and AVP-stimulated InsP3 accumulation were lost within 1 h of PMA removal, but [3H]phorbol 12,13-dibutyrate binding and the sustained responses to AVP and DOG remained suppressed after 3 h. Pretreatment with 0.1 and 1 microM PMA slightly reduced the sustained responses to CRF (by 29% and 16%, respectively) and 8-bromo-cAMP (by 8% and 12%, respectively), which are mediated by protein kinase-A activation and extracellular Ca2+ influx via L-type voltage-sensitive Ca2+ channels, but not the response to KCl, which is mediated by extracellular Ca2+ influx via all types of voltage-sensitive Ca2+ channels. The sustained response to CRF was still suppressed 1 h after PMA removal, but returned to the control level by 3 h. When new protein synthesis was inhibited by preperifusion with cycloheximide alone for 3 h after 24-h PMA pretreatment, recovery from the effects of PMA was abolished. Three-hour exposure to cycloheximide without PMA pretreatment inhibited the sustained responses to CRF, AVP, and DOG, but not the spite response to AVP.(ABSTRACT TRUNCATED AT 400 WORDS)
Department of Medicine, Veterans General Hospital-Taipei, Taiwan, Republic of China.
J G
JG
Won
W E
WE
Nicholson
K N
KN
Ching
D N
DN
Orth
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D003513:Cycloheximide / Q000494:pharmacology; D004075:Diglycerides / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D010477:Perfusion; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004075:Diglycerides; C044295:1,2-dioctanoylglycerol; D001127:Arginine Vasopressin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D015240:Phorbol 12,13-Dibutyrate; D015759:Ionomycin; D011189:Potassium Chloride; D015544:Inositol 1,4,5-Trisphosphate; D000324:Adrenocorticotropic Hormone; D003513:Cycloheximide; D000242:Cyclic AMP; D011494:Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate