Differential Expression of Protein Kinase A, AKAP 79, and PP2B in Pregnant Human Myometrial Membranes Prior to and During Labor

Abstract

We have previously shown that the association of protein kinase A (PKA) with purified myometrial plasma membrane declined at the end of pregnancy in the rat. This study was designed to determine if a similar decline in PKA occurred in pregnant human myometrium. Myometrial plasma membranes were isolated from lower uterine segment tissues from not-in-labor (NIL) and in-labor (IL) patients undergoing cesarean delivery. Membrane proteins were subjected to Western blot analysis to detect PKA-catalytic (PKA-cat) and PKA-regulatory (PKA-reg) subunits, the PKA binding protein A-kinase anchoring protein 79 (AKAP79), protein phosphatase 2B (PP2B), and Galphaq, a guanosine triphosphate (GTP)-binding protein. Protein levels were expressed relative to caveolin-1, which was invariant between the two groups. The amount of PKA-cat, PKA-reg, AKAP79, and PP2B in plasma membranes from myometrium of women in early labor decreased significantly compared with that in tissues from women not in labor. In contrast, Galphaq did not change. All proteins were localized to myometrial smooth muscle cells by immunohistochemistry. Expression of PKA, PP2B, and AKAP79 is consistent with the presence of a functional AKAP-mediated signaling complex in pregnant human myometrial membranes. A small but significant decrease in PKA, AKAP79, and PP2B in myometrial tissues from women in labor may contribute to a decrease in negative feedback on and enhancement of contractant signals at term.