Analysis of R59022 actions in Xenopus laevis oocytes

Abstract

R59022, a diacylglycerol (DAG) kinase inhibitor, stimulated meiotic maturation of Xenopus laevis oocytes when applied extracellularly. The time course of R59022-induced oocyte maturation was proportional to the concentration of R59022 in the low micromolor range, and the 30 microM-induced response was a fast or faster than progesterone-induced maturation. Dose-response analysis yielded an apparent EC50 for R59022-induced oocyte maturation of approximately 15 microM. An increase in total oocyte DAG levels was observed following treatment with 10 microM R59022. Treatment of oocytes with R59022 also resulted in a significant increase in intracellular pH similar to the increase observed with progesterone. When various phosphodiesterase (PDE) inhibitors were tested for their effects on R59022-induced oocyte maturation, papaverine (a potent nonselective inhibitor of PDE) and CI-930 (a selective PDE III inhibitor) were observed to significantly inhibit the R59022-stimulated response. The sensitivity of R59022-induced oocyte maturation to inhibition by papaverine was intermediate between the sensitivities of the IGF-1- or progesterone-induced responses. Treatment of oocytes with R59022 did not significantly affect the level of oocyte PDE activity measured in vivo, suggesting that elevated levels of DAG may parallel observed increases in PDE but do not directly lead to a stimulation of PDE. The t ime course for stimulation of ribosomal S6 kinase activity by R59022 followed the pattern for stimulation of ribosomal S6 kinase activity by R59022 followed the pattern for stimulation by progesterone rather than IGF-1. Treatment of isolated membranes with R59022 resulted in inhibition of membrane-associated adenyl cyclas e activity that was not mimicked by DAG analogs. Thus, in addition to elevating oocyte levels of DAG, R59022 also has steroid-like actions.