1,25-DIHYDROXYVITAMIN D-3 INHIBITS PROLIFERATION OF IMR-90 HUMAN FIBROBLASTS AND STIMULATES PYRUVATE-KINASE ACTIVITY IN CONFLUENT-PHASE CELLS

This study tested the hypothesis that 1,25-dihydroxyvitamin D-3 (1,25( OH)(2)D-3) plays a role in regulating some aspects of metabolism in IM R-90 normal human fetal lung fibroblasts. Among the enzymes studied, o nly pyruvate kinase showed a significant increase after treatment of c onfluent-phase cells with 1,25(OH)(2)D-3 at various concentrations (0. 1-100 nM range) for 24 h. A parallel increase in lactate output was ob served. Steroid specificity was established by the failure of 10 nM le vels of 25-hydroxyvitamin D-3, estradiol-17 beta and progesterone to a ffect pyruvate kinase activity. The determination of the time course o f [H-3]-2-deoxy-D-glucose transport indicated that the hormone did not influence the transmembrane transport system of D-glucose. The additi on of the inhibitors cycloheximide and actinomycin D to the culture me dium abolished, at least in part, the 1,25(OH)(2)D-3 stimulation of py ruvate kinase activity, suggesting the probable dependence of the horm one effect on cellular RNA and protein synthesis. 1,25(OH)(2)D-3 also affected fibroblast growth and DNA synthesis. Cell number significantl y decreased after 2-5 days treatment with 10 nM hormone in comparison with control fibroblasts, and also the incorporation of [H-3]thymidine into DNA decreased after treatment of the cells with 1 and 10 nM horm one for 48 h. In conclusion, these data demonstrate that 1,25(OH)(2)D- 3 stimulates pyruvate kinase activity in confluent-phase IMR-90 human fibroblasts by a mechanism probably dependent on de novo protein synth esis, and also affects cell growth and DNA synthesis in sub-confluent- phase cells.