Differential modulation of fos and jun gene expression by 1,25-dihydroxyvitamin D3.

1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) modulates the mitogenic response to alpha-thrombin either positively or negatively in vascular smooth muscle (VSM) cells depending upon the time at which cells are exposed to 1,25-(OH)2D3. We now examine the impact of 1,25-(OH)2D3 on the induction by alpha-thrombin of c-jun and c-fos mRNA. When 1,25-(OH)2D3 and alpha-thrombin were added simultaneously to rat VSM cells, c-jun expression was enhanced by five-fold compared to cells exposed to thrombin alone. However, when cells were exposed to 1,25-(OH)2D3 for 48h prior to thrombin, c-jun expression after alpha-thrombin was reduced to less than 25% of the level in cells exposed to thrombin alone. c-fos expression after alpha-thrombin was unaffected by 1,25-(OH)2D3. Thus 1,25-(OH)2D3 dramatically alters the ratio of jun/fos mRNA produced during the mitogenic response and may thus modulate the response to mitogens.