BREFELDIN-A PROVOKES INDIRECT ACTIVATION OF CDC2 KINASE (MPF) IN XENOPUS OOCYTES, RESULTING IN MEIOTIC CELL-DIVISION

Brefeldin A, a fungal metabolite which disrupts protein traffic, provo kes indirect activation of cdc2 protein kinase in Xenopus oocytes. Cdc 2 protein kinase activation was judged by MPF (M-phase factor) transfe r activity, histone H1 kinase activity, and phosphorylation in vivo of the guanine-nucleotide exchange complex EF-1 beta gamma delta. Oocyte s resumed complete meiosis upon brefeldin A treatment. Cdc2 protein ki nase, MAP kinase, cyclin B, MPF, and protein synthesis changes were al l comparable in brefeldin A-treated oocytes and in progesterone-induce d oocytes. ED(50) for brefeldin A was 0.6 mu M. Brefeldin A activation of cdc(2) protein kinase occurs with a long time course. Simultaneous treatment of the oocytes at a subthreshold concentration of 1 nM prog esterone and 30 mu M brefeldin A considerably shortened the kinetics o f maturation. Brefeldin A induction of maturation was sensitive to dru gs that act on cAMP metabolism. ID50 for IBMX was 0.1 mM, compared to 1 mM for progesterone-treated oocytes. Brefeldin A inhibited protein t raffic in oocytes as determined from protein export experiments. ID50 was between 0.1 and 1 mu M. Our results give new insights into the pos sible mechanism of induction of meiotic maturation and further demonst rate that brefeldin A acts on cell cycle regulatory elements. (C) 1995 Academic Press, Inc.