MODULATION OF CELL-PROLIFERATION AND CELL-CYCLE, AND INHIBITION OF CYTOKINESIS BY 1,25-DIHYDROXYVITAMIN-D3 IN C3H/10T1/2 FIBROBLASTS

The growth-modulating effects of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] were studied on three mouse embryo fibroblast cell lines. Concentrations ranging from 0.1 to 100 nM inhibited dose-dependently proliferation in the non-tumorigenic C3H/10T1/2 Cl 8 (10T1/2) and the chemically transformed C3H/10T1/2 Cl 16 (Cl 16) cells. The hormone had a biphasic effect on the transformed cell line C3H/10T1/2 TPA 482 (TPA 482) in which growth was stimulated by low concentrations. Exposure to 10 nM 1,25-(OH)2D3 for 5 days resulted in a 90% growth inhibition of 10T1/2 cells, and the hormone was 10 and 100 times less potent in Cl 16 and TPA 482 cells, respectively. The inhibition of cell replication was fully reversible on removal of the hormone. Treatment of 10T1/2 and Cl 16 cells with 10 nM 1,25-(OH)2D3 reduced the saturation density to 30 and 37% that of controls, respectively, suggesting an enhancement of cell-cell contact mediated growth inhibition. 1,25-(OH)2D3 inhibited cytokinesis in 10T1/2 cells, inducing the formation of binucleated cells. Flow cytometric studies showed that 1,25-(OH)2D3-treated cells accumulated in the G0/G1 phase while the number of cells in S phase decreased. This in vitro model system seems to be useful for studies of the molecular mechanisms of the growth modulating effect of 1,25-(OH)2D3.