title: Enhancement by 1 alpha,25-dihydroxyvitamin D3 of chemically induced transformation of BALB 3T3 cells without induction of ornithine decarboxylase or activation of protein kinase C1.
abstract: We reported previously that 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3], a hormonally active form of vitamin D3, markedly enhanced methylcholanthrene-induced transformation of BALB 3T3 A31-1-1 cells. When the cells were treated with methylcholanthrene (1 microgram/ml) for 72 h and then with 1 alpha,25(OH)2D3 (5 ng/ml) for 2 wk, the transformation frequency was 1.95 +/- 0.73 (SD) foci/dish in 8 independent experiments, which was about 20 times that in cultures treated with methylcholanthrene only. Even at a physiological concentration in plasma, i.e., 0.05 ng/ml, 1 alpha,25(OH)2D3 enhanced the transformation frequency significantly (P less than 0.001). 1 alpha,25(OH)2D3 was not cytotoxic but slightly inhibited growth of the cells. Cells treated with 1 alpha,25(OH)2D3 were thin and became arranged in a meshwork with wide intercellular spaces. These morphological changes were reversible. 1 alpha,25(OH)2D3 induced DNA synthesis in quiescent BALB 3T3 cells dose and time dependently, but this effect was less than that of 12-O-tetradecanoylphorbol-13-acetate. Unlike 12-O-tetradecanoylphorbol-13-acetate, 1 alpha,25(OH)2D3 did not interfere with the binding of epidermal growth factor or phorbol dibutyrate. 1 alpha,25(OH)2D3 did not induce ornithine decarboxylase. Moreover, it did not activate protein kinase C in quiescent BALB 3T3 cells or this enzyme isolated from mouse brain. BALB 3T3 cells and their transformants contain a specific cytosol receptor for 1 alpha,25(OH)2D3, but the binding sites of the transformants were fewer and had lower affinity than those of untransformed BALB 3T3 cells. These effects of 1 alpha,25(OH)2D3 were specific, because other derivatives of vitamin D3 induced the same effects only at 200 times or more higher concentrations.
mesh_terms: D000818:Animals; D029742:Caenorhabditis elegans Proteins; D002117:Calcitriol / Q000494:pharmacology*; D002352:Carrier Proteins; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D004247:DNA / Q000096:biosynthesis; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors; D008748:Methylcholanthrene / Q000494:pharmacology; D051379:Mice; D009955:Ornithine Decarboxylase / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism; D011955:Receptors, Drug; D011971:Receptors, Immunologic / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D011956:Receptors, Cell Surface; D011955:Receptors, Drug; D011971:Receptors, Immunologic; C083141:phorbol ester binding protein; C027776:phorbol ester receptor; D008748:Methylcholanthrene; D004815:Epidermal Growth Factor; D004247:DNA; D066246:ErbB Receptors; D011493:Protein Kinase C; D009955:Ornithine Decarboxylase; D002117:Calcitriol; D013755:Tetradecanoylphorbol Acetate