Growth hormone-releasing factor does not activate protein kinase C in somatotrophs.
The purpose of this study was to investigate the involvement of protein kinase C in growth hormone-releasing factor (GRF) action by directly measuring the effect of GRF on protein kinase C activity in purified male rat somatotrophs. Somatotrophs were incubated with GRF (10(-7) M) for 0.33, 1, 3, 10, 30 and 90 min. Protein kinase C present in soluble and particulate fractions was partially purified using DEAE-cellulose chromatography, and protein kinase C activity was assayed. In control experiments, to insure protein kinase C activity could be activated, two known protein kinase C activators, phorbol 12-myristate 13-acetate (PMA) and dioctanoyl-rac-glycerol (diC8) were added for 3 min. Protein kinase C activity is present in somatotrophs. Under basal conditions the majority of the enzyme activity is located in the cytosol (approximately 90%). The protein kinase C activators caused a significant translocation of protein kinase C activity from soluble to particulate fractions at 3 min. GRF did not cause a translocation of protein kinase C activity even though GH release was significantly increased by 3 min. GRF did not significantly alter the specific activity of protein kinase C in the soluble or particulate fractions, except for a small (approximately 10%) increase in soluble activity at 90 min. We conclude that protein kinase C is present in the somatotrophs of the anterior pituitary. Protein kinase C, however, does not mediate the action of GRF and its role in signal transduction in somatotrophs awaits elucidation.
Department of Physiology, University of Western Ontario, London, Canada.
M B
MB
French
B C
BC
Moor
B T
BT
Lussier
J
J
Kraicer
D000595:Amino Acid Sequence; D000818:Animals; D002848:Chromatography, DEAE-Cellulose; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008969:Molecular Sequence Data; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000201:enzymology*; D011493:Protein Kinase C / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004075:Diglycerides; C044295:1,2-dioctanoylglycerol; D013007:Growth Hormone-Releasing Hormone; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate