Stimulation by 1,25-dihydroxyvitamin D3 of insulin receptor expression and insulin responsiveness for glucose transport in U-937 human promonocytic cells

In the present work, we demonstrate that treatment with 1,25-dihydroxyvitamin D-3 for 24 hours increased in a dose-dependent manner the levels of the two major insulin receptor (IR) mRNAs (11 and 8.5 Kb) present in U-937 human promonocytic cells. These levels reached maximum values (1.8-fold 11 Kb; 1.4-fold 8.5 Kb) with the addition of 10(-8)M 1,25-dihydroxyvitamin D-3. In these optimal conditions the stimulatory effect of 1,25-dihydroxyvitamin D-3 was accompanied by increases in both IR capacity, and insulin responsiveness for glucose transport in these cells. Moreover, such increases appear to be mediated by an enhanced expression of the receptor for 1,25-dihydroxyvitamin D-3, measured at the level of both RNA and protein. These results provide evidence of 1,25-dihydroxyvitamin D-3 acting as genomic stimulator of the insulin response in the control of glucose transport.