Stimulation of multiple MAPK pathways by mechanical overload in the perfused amphibian heart

The mitogen-activated protein kinase (MAPK) signal transduction pathway act ivated by mechanical stress was investigated in the isolated perfused amphi bian (Rana ridibunda) heart. High perfusion pressure induced the rapid (30 s) and prolonged (30 min) phosphorylation of a p43-extracellular regulated kinase, a response almost completely inhibited by 25 muM PD98059. c-Jun NH2 -terminal kinase (JNK) was also phosphorylated with maximal values attained at 15 min and remained elevated over 30 min. In-gel kinase assays verified that phosphorylated JNKs are active, phosphorylating the transcription fac tor c-Jun. Furthermore, pressure overload rapidly stimulated the p38-MAPK p hosphorylation (30 s), a transient process (5 min) abolished by 1 muM SB-20 3580. In-gel kinase assays revealed that with phosphorylation, active p38-M APKs phosphorylate their substrate MAP kinase-activated protein kinase 2. B iochemical analysis along with immunohistochemical studies showed that with activation, the three MAPK subfamily members examined are localized not on ly in the cytoplasm but in the nucleus as well. Present results therefore d emonstrate for the first time in an amphibian species the involvement of mu ltiple MAPK pathways in the mechanical overload-induced adaptive responses of the heart as well as their possible physiological roles.