Involvement of protein kinase-C in the effect of angiotensin-II on adenosine 3',5'-monophosphate production in lactotroph cells.
When applied to rat anterior pituitary cells, angiotensin-II (AII) exerted two opposite effects on adenylate cyclase (AC) activity: a pertussis toxin (PTX)-sensitive inhibition of the enzyme with a maximal effect of -42 +/- 2% in crude cell membrane preparations, and, in contrast, a non-PTX-sensitive stimulation of cAMP production (maximal effect = 38 +/- 3%) in intact cells. The apparent affinity of both effects was equal to 1.8 nM. The stimulation of cAMP formation parallels the stimulation of PRL release. Under the same conditions, dopamine (DA) inhibited both membrane AC activity and cAMP formation in intact cells by a PTX-sensitive mechanism. After separation of pituitary cell types by sedimentation at unit gravity, the effects of AII and DA on intracellular cAMP and membrane AC activity coincided in the same fractions (those enriched in PRL cells). The stimulatory effect of AII on cAMP formation was about 5 times weaker than that of peptides positively coupled to AC as vasoactive intestinal peptide in total as well as in PRL-enriched cells. Since the AII receptor is also coupled to phospholipase-C (PLC) in a non-PTX-sensitive manner, we investigated whether protein kinase-C (PKC) could indirectly account for the positive effect of AII on cAMP formation. 12-O-Tetradecanolylphorbol 13-acetate (TPA), a stimulator of PKC was indeed able to increase intracellular cAMP; this effect was not additive with that of AII. conversely, application of the PKC inhibitors H7 [1-(5-isoquinolylsulfonyl)2-methyl-piperazine] and staurosporine or desensitization of PKC by long exposure of the cells to TPA abolished the cAMP response to TPA as well as that to AII. In addition, thyreoliberin, another activator of the PLC pathway, was able to stimulate cAMP formation in a PKC-dependent manner. DA inhibition of intracellular cAMP was not affected by any PKC inhibition. We conclude that in lactotroph cells, 1) the AII inhibitory coupling to AC observed in membrane preparations does not exist in intact cells, at least under basal conditions; and 2) the AII intracellular cAMP stimulation observed is not accounted for by a direct coupling with AC; it is due to a cross-talk of the PLC pathway mediated by PKC, an effect that might be shared by other PLC-stimulating mediators and may participate in the regulation of PRL release.
Audinot
V
V
U.159 INSERM, Centre Paul Broca, Paris, France.
Rasolonjanahary
R
R
Bertrand
P
P
Priam
M
M
Kordon
C
C
Enjalbert
A
A
D000262:Adenylyl Cyclases / Q000378:metabolism; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D004298:Dopamine / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D011493:Protein Kinase C / Q000494:pharmacology*; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D007295:Inositol Phosphates; D000804:Angiotensin II; D014660:Vasoactive Intestinal Peptide; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D000242:Cyclic AMP; D011493:Protein Kinase C; D000262:Adenylyl Cyclases; D004298:Dopamine