CELLULAR STRESSES DIFFERENTIALLY ACTIVATE C-JUN N-TERMINAL PROTEIN-KINASES AND EXTRACELLULAR SIGNAL-REGULATED PROTEIN-KINASES IN CULTURED VENTRICULAR MYOCYTES

Anisomycin or osmotic stress induced by sorbitol activated c-Jun N-ter minal protein kinases (JNKs) in ventricular myocytes cultured from neo natal rat hearts. After 15-30 min, JNK was activated by 10-20-fold. Ac tivation by anisomycin was transient, but that by sorbitol was sustain ed for at least 4 h. In-gel JNK assays confirmed activation of two ren aturable JNKs of 46 and 55 kDa (JNK-46 and JNK-55, respectively). An a ntibody against human JNK1 immunoprecipitated JNK-46 activity. Endothe lin-1, an activator of extracellular signal-regulated protein kinases (ERKs), also transiently activated JNKs by 25-fold after 30 min. Phorb ol 12-myristate 13-acetate did not activate the JNKs although it activ ated ERK1 and ERK2, which phosphorylated the c-Jun transactivation dom ain in vitro. ATP depletion and repletion achieved by incubation in cy anide + deoxyglucose and its subsequent removal from the medium activa ted the ERKs but failed to activate the JNKs. Sorbitol (but not anisom ycin) also stimulated the ERKs. Sorbitol-stimulated JNK activity could be resolved into three peaks by fast protein liquid chromatography on a Mono Q column. The two major peaks contained JNK-46 or JNK-55. Thes e results demonstrate that cellular stresses differentially activate t he JNKs and ERKs and that there may be ''cross-talk'' between these MA PK pathways.