The stimulation of MAP kinase by 1,25(OH)(2)-vitamin D(3) in skeletal muscle cells is mediated by protein kinase C and calcium.

In previous work we have demonstrated that the steroid hormone 1,25(OH)(2)-vitamin D(3) [1,25(OH)(2)D(3)] stimulates in skeletal muscle cells the phosphorylation and activity of the extracellular signal-regulated mitogen-activated protein (MAP) kinase isoforms ERK1 and ERK2. In the present study we evaluated the involvement of Ca(2+) and protein kinase C (PKC) on 1,25(OH)(2)D(3)-induced activation of MAP kinase. The hormone response was found to depend on PKC stimulation since it was attenuated by the PKC inhibitors calphostin C (100 nM) and bisindolylmaleimide I (30 nM) and PKC downregulation by prolonged treatment with the phorbol ester TPA (1 microM). Removal of external Ca(2+), chelation of intracellular Ca(2+) with BAPTA (5 microM), inhibition of phosphoinositide-phospholipase C (PLC) by neomycin, the calmodulin antagonist fluphenazine (50 microM) and the specific inhibitor of calmodulin kinase II, KN-62 (10 microM), significantly decreased 1,25(OH)(2)D(3)-activation of MAP kinase. In addition, the Ca(2+)-channel blocker verapamil (5 microM) suppressed hormone-induced MAP kinase activity in these cells. Furthermore, the Ca(2+)-mobilizing agent thapsigargin and the Ca(2+)-inophore A23187 paralleled the phosphorylation of MAP kinase observed with 1,25(OH)(2)D(3). Taken together, these results indicate that PKC and Ca(2+) are two upstream activators mediating the effects of 1,25(OH)(2)D(3) on MAP kinase in skeletal muscle cells.