Inhibitors of protein kinase-C modulate desensitization of the parathyroid hormone receptor-adenylate cyclase system in opossum kidney cells.
The mechanisms involved in mediating desensitization and down-regulation of renal PTH receptors have not been defined. Recent studies indicate that PTH binding promotes not only stimulation of adenylate cyclase and activation of protein kinase-A (PK-A), but also, stimulation of phospholipase-C, leading to activation of PK-C. PK-C has been shown to alter both receptor and adenylate cyclase function in other systems. Therefore, the present studies were conducted to test whether PK-C might play a role in the regulation of the PTH receptor-cyclase system after exposure to PTH. Exposure of confluent cultures of opossum kidney (OK) cells to rat PTH-(1-34) (100 nM) for 6 h resulted in a 48 +/- 8% (n = 5) decrease in stimulation of cAMP accumulation in response to further exposure to PTH. PTH receptor binding, assessed with 125I-[Nle8,Nle21,Tyr34]rat PTH-(1-34)NH2 as radioligand, was decreased to a similar extent. Phorbol ester (4 beta-12,13-didecanoate; 1 microM) treatment of the cells in the absence of PTH caused a 58 +/- 3% decrease in PTH-stimulated cAMP production, but equilibrium PTH receptor binding was not different from the control value. Both 50 microM H-7 and 0.5 microM Staurosporine (inhibitors of PK-C) completely blocked the effects of phorbol ester. Pretreatment with PTH, however, in the presence of H-7 or Staurosporine resulted in a completely normal cAMP response to restimulation with PTH. Thus, two inhibitors of PK-C completely prevented desensitization to PTH. The decrease in equilibrium PTH binding, seen after incubation with PTH alone, was also blunted by the inhibitors of PK-C. These data indicate that activation of PK-C by stimulation with PTH may play a role in the regulation of the PTH receptor-cyclase system in OK cells.
Pernalete
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Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
Garcia
J C
JC
Betts
C R
CR
Martin
K J
KJ
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D009893:Opossums; D010879:Piperazines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018016:Receptors, Parathyroid Hormone; D019311:Staurosporine
D000470:Alkaloids; D007546:Isoquinolines; D010879:Piperazines; D011956:Receptors, Cell Surface; D018016:Receptors, Parathyroid Hormone; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000242:Cyclic AMP; D011493:Protein Kinase C; D000262:Adenylyl Cyclases; D019311:Staurosporine