A role for AKAP (a kinase anchoring protein) scaffolding in the loss of a cyclic adenosine 3 ',5 '-monophosphate inhibitory response in late pregnantrat myometrium

During pregnancy in the rat, there is a change in the ability of chlorophen ylthio (CPT)-cAMP to inhibit myometrial phosphatidylinositide turnover. Thi s is accompanied by a change in the association of proteins with a plasma m embrane A kinase anchoring protein (AKAP), Both CPT-cAMP and isoproterenol inhibited oxytocin-stimulated phosphatidylinositide turnover on days 12 thr ough 20 of gestation, whereas neither agent had an effect on day 21. Accomp anying this change was a dramatic decrease in the concentration and activit y of cAMP-dependent protein kinase [protein kinase A (PKA)] and an increase in the concentration of protein phosphatase 2B (PP2B) in plasma membranes from day 21 compared with day 19 pregnant rats. In contrast, both PKA and P P2B concentrations and activities increased in total myometrial homogenates . Both PKA and PP2B coimmunoprecipitated with an antibody against the 150-k Da AKAP found in rat myometrial plasma membranes. More PKA was associated w ith AKAP150 on day 19 than on day 21, while the reverse was true for PP2B, Disruption of PKA/AKAP association in day 19 pregnant rat myometrial cells with the specific interaction inhibitor peptide S-Ht31 resulted in the loss of the cAMP-inhibitory effect on phosphatidylinositide turnover. PP2B acti vity in myometrial homogenates dephosphorylated PLC beta(3), a PKA substrat e targeted in the inhibition of G alpha(q)-stimulated phosphatidylinositide turnover. The dramatic loss of the cAMP-inhibitory effect on day 21 of pre gnancy may alter the balance between uterine contraction and relaxation nea r parturition, The changes in the relative concentrations of PKA and PP2B a ssociated with AKAP150 are consistent with a functional role for AKAP150 sc affolding in the alteration of cellular signaling.