Regulation of CD38 expression and function by steroid hormones in myometrium

CD38, a 45-kDa transmembrane glycoprotein, is expressed ubiquitously in many cell types, including the myometrial smooth muscle cells. CD38 is a bifunctional protein, and has both ADP-ribosyl cyclase (cyclase) and cyclic ADP-ribose (cADPR)-hydrolase (hydrolase) activities. The cyclase converts β-NAD to cADPR, a calcium mobilizing second messenger involved in fertilization, insulin secretion, and muscle contraction. CD38 expression in smooth muscle is regulated by cytokines, by the steroid hormones estrogen and progesterone, and during gestation in the rat. Estrogen increases CD38 expression, which is associated with increased cyclase, but not hydrolase, activity, indicating a differential post-translational regulation. Progesterone attenuates estrogen-induced effects on CD38 expression and activities. This will have implications for increased calcium mobilization and contractility of the myometrium during parturition.