Expression and intracellular localization of protein phosphatases 2A and 2B, protein kinase a, A-Kinase anchoring protein (AKAP79), and binding of the regulatory (RII) subunit of protein kinase a to AKAP79 in human myometrium.

Abstract

To determine the expression and intracellular localization of protein phosphatases 2A (PP2A) and 2B (PP2B), protein kinase A (PKA), and A-kinase anchoring protein (AKAP79), and expression of PKA (RII subunit) binding to AKAP79 in human postmenopausal and pregnant myometrium and to correlate their expressions to blood levels of estradiol, progesterone, and oxytocin. Myometrial samples were taken from postmenopausal hysterectomy specimens (group 1, n = 5), from pregnant nonlaboring women (group 2, n = 7) and pregnant laboring women (group 3, n = 5) at cesarean. Western immunoblotting, immunohistochemical, and RII overlay assays were performed. Blood samples were assayed for estradiol, progesterone, and oxytocin levels. There were no significant differences in expression of PP2A, PKA, AKAP79, or PKA(RII) binding to AKAP79 between the three groups. Expression of PP2B was significantly greater in the nonlabor group (group 2) compared with groups 1 and 3. Protein phosphatase 2B, PKA, and AKAP79 expressions were localized in myometrial cytoplasm, but PP2A was localized in blood vessel endothelium. There was no significant correlation between the protein expression and the hormone level in the three groups. Human postmenopausal and pregnant (nonlabor and labor) myometrium expressed PP2A, PP2B, PKA, AKAP79, and PKA (RII)-AKAP79 binding. Levels of PP2A, PKA, and AKAP79 expression did not appear to be determinants of human myometrial contractility at parturition. Expression of PP2B may play a role in uterine quiescence. No association was found between protein expression and hormone level.