Brefeldin A provokes indirect activation of cdc2 kinase (MPF) in Xenopus oocytes, resulting in meiotic cell division

Abstract

Brefeldin A, a fungal metabolite which disrupts protein traffic, provokes indirect activation of cdc2 protein kinase in Xenopus oocytes. Cdc2 protein kinase activation was judged by MPF (M-phase factor) transfer activity, histone H1 kinase activity, and phosphorylation in vivo of the guanine-nucleotide exchange complex EF-1βγδ. Oocytes resumed complete meiosis upon brefeldin A treatment. Cdc2 protein kinase, MAP kinase, cyclin B, MPF, and protein synthesis changes were all comparable in brefeldin A-treated oocytes and in progesterone-induced oocytes. ED50 for brefeldin A was 0.6 μM. Brefeldin A activation of cdc2 protein kinase occurs with a long time course. Simultaneous treatment of the oocytes at a subthreshold concentration of 1 nM progesterone and 30 μM brefeldin A considerably shortened the kinetics of maturation. Brefeldin A induction of maturation was sensitive to drugs that act on cAMP metabolism. ID50 for IBMX was 0.1 mM, compared to 1 mM for progesterone-treated oocytes. Brefeldin A inhibited protein traffic in oocytes as determined from protein export experiments. ID50 was between 0.1 and 1μM. Our results give new insights into the possible mechanism of induction of meiotic maturation and further demonstrate that brefeldin A acts on cell cycle regulatory elements. © 1995 by Academic Press, Inc.