Cell condition-dependent regulation of ERK5 by cAMP.

ERK5 activity is increased by agents known to activate receptor tyrosine kinases, G-protein coupled receptors, and stress response pathways. We now find a role for cAMP in the regulation of ERK5. ERK5 is activated by forskolin, isoproterenol, and epinephrine in NIH3T3 cells and C2C12 myoblasts. ERK1/2 are also activated by cAMP in NIH3T3 cells, but not in C2C12 myoblasts, demonstrating differential regulation of ERK5 and ERK1/2 by cAMP. We examined the effect of cell context on activation of ERK5 and discovered ERK5 activity is inhibited, rather than activated, by cAMP in confluent, serum-deprived NIH3T3 cells and C2C12 myoblasts. Our results suggest that regulation of MAP kinase pathways by cAMP is not only dictated by cell type, but also by cell context.