Protein kinase A anchoring to the myometrial plasma membrane is required for cyclic adenosine 3',5'-monophosphate regulation of phosphatidylinositide turnover.

The importance of the localization of protein kinase A (PKA) to the plasma membrane for cAMP-mediated inhibition of phosphatidylinositide turnover was tested in an immortalized pregnant human myometrial (PHM1-41) cell line, and the putative A kinase anchoring protein (AKAP) involved was identified. Preincubation in PHM1-41 cells with chlorophenylthio-cAMP (CPT-cAMP), forskolin, or relaxin inhibited the ability of oxytocin to stimulate phosphatidylinositide turnover. The addition of a peptide that specifically disrupts interactions of PKA RII subunits with AKAPs (S-Ht31) reversed the effects of these agents, whereas a control peptide was ineffective. The pharmacology of S-Ht31 on this particular membrane event was further characterized. A 10-min incubation with S-Ht31 at a concentration of 1 microM completely reversed the inhibitory effect of relaxin on phosphatidylinositide turnover. S-Ht31 inhibited cAMP-stimulated PKA activity in PHM1-41 cell plasma membranes and decreased the concentration of PKA. Overlay analysis detected a single AKAP of approximately 86 kDa associated with the plasma membrane of PHM1-41 cells, suggesting that the association of PKA with this AKAP is important for the cAMP inhibitory mechanism. The mol wt of this AKAP was similar to that of an AKAP associated with the plasma membrane in the human brain, AKAP79. Antibodies against AKAP79 recognized a band at 86 kDa in purified plasma membranes from the PHM1-41 cells, indicating similar determinants in these proteins. These data suggest that PKA is anchored to the myometrial plasma membrane through association with an AKAP similar to AKAP79, and that this anchoring is required for the cAMP-mediated inhibition of phosphatidylinositide turnover in PHM1-41 cells.