ANISOMYCIN-ACTIVATED PROTEIN KINASE-P45 AND KINASE-P55 BUT NOT MITOGEN-ACTIVATED PROTEIN KINASE-ERK-1 AND KINASE-ERK-2 ARE IMPLICATED IN THE INDUCTION OF C-FOS AND C-JUN

Independent of its ability to block translation, anisomycin intrinsica lly initiates intracellular signals and immediate-early gene induction [L. C. Mahadevan and D. R. Edwards, Nature (London) 349:747-749, 1991 ]. Here, we characterize further its action as a potent, selective sig nalling agonist. In-gel kinase assays show that epidermal growth facto r (EGF) transiently activates five kinases: the mitogen-activated prot ein (MAP) kinases ERK-1 and -2, and three others, p45, p55, and p80. A nisomycin, at inhibitory and subinhibitory concentrations, does not ac tivate ERK-1 and -2 but elicits strong sustained activation of p45 and p55, which are unique in being serine kinases whose detection is enha nced with poly-Glu/Tyr or poly-Glu/Phe copolymerized in these gels. Tr anslational arrest using emetine or puromycin does not activate p45 an d p55 but does prolong EGF-stimulated ERK-1 and -2 activation. Rapamyc in, which blocks anisomycin-stimulated p70/85(S6k) activation without affecting nuclear responses, has no effect on p45 or p55 kinase. p45 a nd p55 are activable by okadaic acid or UV irradiation, and both kinas es phosphorylate the c-Jun NH2-terminal peptide 1-79, putatively placi ng them within c-Jun NH2-terminal kinase/stress-activated protein kina se (JNK/SAPK) subfamily of MAP kinases. Thus, the EGF- and anisomycin- activated kinases p35 and p55 are strongly implicated in signalling to c-fos and c-jun, whereas the MAP kinases ERK-1 and -2 are not essenti al for this process.