PROTEIN-KINASE-C DISRUPTS CANNABINOID ACTIONS BY PHOSPHORYLATION OF THE CB1 CANNABINOID RECEPTOR

We have found that phosphorylation of a G-protein-coupled receptor by protein kinase C (PKC) disrupts modulation of ion channels by the rece ptor. In AtT-20 cells transfected with rat cannabinoid receptor (CB1), the activation of an inwardly rectifying potassium current (K-ir curr ent) and depression of P/Q-type calcium channels by cannabinoids were prevented by stimulation of protein kinase C by 100 nM phorbol 12-myri state 13-acetate (PMA). In contrast, activation of K-ir current by som atostatin was unaffected, and inhibition of calcium channels was only modestly attenuated. The possibility that PKC acted by phosphorylating CB1 receptors was confirmed by demonstrating that PKC phosphorylated a single serine (S317) of a fusion protein incorporating the third int racellular loop of CB1. Mutating this serine to alanine did not affect the ability of CB1 to modulate currents, but it eliminated disruption by PMA, demonstrating that PKC can disrupt ion channel modulation by receptor phosphorylation.