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

Abstract

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 1min) 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 30min (ERK1/2) and at 60 and 15min (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.