Pro-inflammatory Cytokines Stimulate Mitogen-activated Protein Kinase Subfamilies, Increase Phosphorylation of c-Jun and ATF2 and Upregulate c-Jun Protein in Neonatal Rat Ventricular Myocytes

A. Clerk, J. G. Harrison, C. S. Long and P. H. Sugden. Pro-inflammatory Cytokines Stimulate Mitogen-activated Protein Kinase Subfamilies, Increase Phosphorylation of c-Jun and ATF2 and Upregulate c-Jun Protein in Neonatal Rat Ventricular Myocytes. Journal of Molecular and Cellular Cardiology (1999) 31, 2087–2099. Pro-inflammatory cytokines may be important in the pathophysiological responses of the heart. We investigated the activation of the three mitogen-activated protein kinase (MAPK) subfamilies [c-Jun N-terminal kinases (JNKs), p38-MAPKs and extracellularly-responsive kinases (ERKs)] by interleukin-1 β (IL-1 β ) or tumour necrosis factor α (TNF α ) in primary cultures of myocytes isolated from neonatal rat ventricles. Both cytokines stimulated a rapid (maximal within 10 min) increase in JNK activity. Although activation of JNKs by IL-1 β was transient returning to control values within 1 h, the response to TNF α was sustained. IL-1 β and TNF α also stimulated p38-MAPK phosphorylation, but the response to IL-1 β was consistently greater than TNF α. Both cytokines activated ERKs, but to a lesser degree than that induced by phorbol esters. The transcription factors, c-Jun and ATF2, are phosphorylated by the MAPKs and are implicated in the upregulation of c-Jun. IL-1 β and TNF α stimulated the phosphorylation of c-Jun and ATF2. However, IL-1 β induced a greater increase in c-Jun protein. Inhibitors of protein kinase C (PKC) (Ro318220, GF109203X) and the ERK cascade (PD98059) attenuated the increase in c-Jun induced by IL-1 β, but LY294002 (an inhibitor of phosphatidylinositol 3′ kinase) and SB203580 (an inhibitor of p38-MAPK, which also inhibits certain JNK isoforms) had no effect. These data illustrate that some of the pathological effects of IL-1 β and TNF α may be mediated through the MAPK cascades, and that the ERK cascade, rather than JNKs or p38-MAPKs, are implicated in the upregulation of c-Jun by IL-1 β.