Activation of MAPKs by 1α,25(OH)2-Vitamin D3 and 17β-estradiol in skeletal muscle cells leads to phosphorylation of Elk-1 and CREB transcription factors

The mitogen activated protein kinases (MAPKs) have been classified into at least six subfamilies, among which ERK1/2, JNK1/2 and p38 MAPK are the most extensively studied. The steroid hormones 1α,25-dihydroxy-Vitamin D3 and 17β-estradiol promote biological responses through activation of MAPK cascades in various cell types. We previously reported that 1α,25(OH)2D3 rapidly (within 1 min) activates p38 MAPK in C2C12 skeletal muscle cells. In this work, using the same muscle cell line, we demonstrate that 1α,25(OH)2D3 or 17β-estradiol phosphorylate and activate ERK1/2 and p38 MAPK after longer treatment intervals, maximal effects seen at 90 and 30 min (ERK1/2) and at 60 and 15 min (p38 MAPK) for these hormones, respectively. Hormone-dependent ERK and p38 activation was abolished by MAPK specific inhibitors U0126 and SB203580. 1α,25(OH)2D3 and 17β-estradiol also induced the phosphorylation of CREB and Elk-1 transcription factors in an ERK1/2-dependent manner. Simultaneous addition of both hormones potentiated CREB phosphorylation. 1α,25(OH)2D3- and 17β-estradiol-induced c-fos expression, which was mediated by p38 phosphorylation. The action of 17β-estradiol on c-fos levels was also dependent on ERK1/2. These results suggest that MAPK signalling pathways play an important role in regulating early gene expression through CREB and Elk-1 activation in skeletal muscle cells.