Protein kinase C activation reduces microglial cyclic AMP response to prostaglandin E2 by interfering with EP2 receptors.
We studied the modulation by protein kinase C (PKC) of the cyclic AMP (cAMP) accumulation induced by prostaglandin (PG) E2 in rat neonatal microglial cultures. Short pretreatment of microglia with phorbol 12-myristate 13-acetate (PMA) or 4beta-phorbol 12,13-didecanoate, which activate PKC, but not with the inactive 4alpha-phorbol 12,13-didecanoate, substantially reduced cAMP accumulation induced by 1 microM PGE2. The action of PMA was dose and time dependent, and the maximal inhibition (approximately 85%) was obtained after 10-min preincubation with 100 nM PMA. The inhibitory effect of PMA was mimicked by diacylglycerol and was prevented by the PKC inhibitor calphostin C. As PMA did not affect isoproterenol- or forskolin-stimulated cAMP accumulation, we investigated whether activation of PKC decreased cAMP production by acting directly at PGE2 EP receptors. Neither sulprostone (10(-9)-10(-5) M), a potent agonist at EP3 receptors (coupled to adenylyl cyclase inhibition), nor 17-phenyl-PGE2 (10(-6)-10(-5) M), an agonist of EP1 receptors, modified cAMP accumulation induced by forskolin. On the contrary, 11-deoxy-16,16-dimethyl PGE2, which does not discriminate between EP2 and EP4 receptors, both coupled to the activation of adenylyl cyclase, and butaprost, a selective EP2 agonist, induced a dose-dependent elevation of cAMP that was largely reduced by PMA pretreatment, as in the case of PGE2. These results indicated EP2 receptors as a possible target of PKC and suggest that PKC-activating agents present in the pathological brain may prevent the cAMP-mediated microglia-deactivating function of PGE2.
Patrizio
M
M
Neurobiology Section, Laboratory of Pathophysiology, Istituto Superiore di Sanità, Rome, Italy.
Colucci
M
M
Levi
G
G
D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D015232:Dinoprostone / Q000494:pharmacology*; D004789:Enzyme Activation / Q000502:physiology; D017628:Microglia / Q000187:drug effects* / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018078:Receptors, Prostaglandin E / Q000819:agonists / Q000037:antagonists & inhibitors*; D058307:Receptors, Prostaglandin E, EP2 Subtype; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
C545646:Ptger2 protein, rat; D018078:Receptors, Prostaglandin E; D058307:Receptors, Prostaglandin E, EP2 Subtype; D000242:Cyclic AMP; D011493:Protein Kinase C; D015232:Dinoprostone; D013755:Tetradecanoylphorbol Acetate