The p38 and JNK pathways cooperate to trans-activate vitamin D receptor via c-Jun/AP-1 and sensitize human breast cancer cells to vitamin D3-induced growth inhibition.

The signaling connection between mitogen-activated protein kinases(MAPKS) and nuclear steroid receptors is complex and remains mostly unexplored. Here we report that stress-activated protein kinases p38 and JNK trans-activate nuclear steroid vitamin D receptor (VDR) gene and increase vitamin D-3-dependent growth inhibition in human breast cancer cells. Activation of p38 and JNK by an active MAPK kinase 6 stimulates VDR promoter activity independently of the ligand vitamin D-3 and estrogen receptor expression. Moreover, stimulation of the endogenous stress pathways by adenovirus-mediated delivery of recombinant MAPK kinase 6 also activates VDR and sensitizes MCF-7 cells to vitamin D-3-dependent growth inhibition. Both the p38 and JNK MAPK pathways and the downstream transcription factor c-Jun/AP-1 are required for the VDR stimulation, as revealed by application of their dominant negatives, the specific p38 inhibitor SB203580, and site-directed mutagenesis of the AP-1 element in the VDR promoter. The essential role of the p38 and JNK stress pathways in up-regulation of VDR expression is further confirmed by using the chemical stimulator arsenite. These results establish a signaling connection between the stress MAPK pathways and steroid hormone receptor VDR expression and thereby offer new insights into regulation of cell growth by the MAPK pathways through regulation of vitamin D-3/VDR activity.