PHOSPHORYLATION AND INHIBITION OF TYPE-III ADENYLYL-CYCLASE BY CALMODULIN-DEPENDENT PROTEIN-KINASE-II IN-VIVO

Inhibition of type III adenylyl cyclase (III-AC) by intracellular Ca2 in vivo provides a mechanism for attenuation of hormone-stimulated cA MP signals in olfactory epithelium, heart, and other tissues (Wayman, G. A., Impey, S., and Storm, D. R. (1995) J. Biol. Chem. 270, 21480-21 486). Although the mechanism for Ca2+ inhibition of III-AC in vivo has not been defined, inhibition is not mediated by G(i), cAMP-dependent protein kinase, or protein kinase C. However, Ca2+-inhibition of III-A C is antagonized by KN-62, a CaM-dependent kinase inhibitor. In additi on, constitutively activated CaM kinase II inhibits the enzyme. These data suggest that CaM kinase II regulates the activity of III-AC by di rect phosphorylation or by an indirect mechanism involving phosphoryla tion of a protein that inhibits III-AC. Here we report that III-AC is phosphorylated in vivo when intracellular Ca2+ is increased and that p hosphorylation is prevented by CaM-dependent kinase inhibitors. Site-d irected mutagenesis of a CaM kinase II consensus site (Ser-1076 to Ala -1076) in III-AC greatly reduced Ca2+-stimulated phosphorylation and i nhibition of III-AC in vivo. These data support the hypothesis that Ca 2+ inhibition of III-AC is due to direct phosphorylation of the enzyme by CaM kinase II in vivo.