ERK2 is required for FGF1-induced JNK1 phosphorylation in Xenopus oocyte expressing FGF receptor 1.

A possible connection between the ERK2 and JNK1 MAP kinases transduction cascades was investigated in Xenopus oocytes expressing FGFR1 stimulated by FGF1. Injection of various inhibitors for the Shc/Grb2/Ras/Mos/MEK/ERK2 cascade blocked FGF1-induced germinal vesicle breakdown (GVBD), as well as ERK2 and JNK1 phosphorylation. JNK1 was found to be activated downstream of ERK2, since injection of an active ERK2 triggered JNK1 phosphorylation and inhibition of ERK2 either by a MEK inhibitor or the MKP3 phosphatase blocked JNK1 phosphorylation. These results demonstrated that in FGFR1 signalling JNK1 phosphorylation depends on ERK2.