Chang P L, Prince C W
Department of Nutrition Sciences, University of Alabama, Birmingham 35294.
Cancer Res. 1991 Apr 15;51(8):2144-50.
Murine JB6 epidermal cells can be irreversibly transformed into tumorigenic cells by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate. One feature of this transformation is induction of the synthesis and secretion of the phosphoprotein osteopontin (also called secreted phosphoprotein 1 and previously referred to as transformation-related phosphoprotein, 2ar, bone sialoprotein 1, or Mr 44,000 bone phosphoprotein), an arginylglycylaspartic acid-containing cell adhesion glycoprotein the expression of which has been implicated in tumorigenesis and metastasis. Since 1 alpha,25-dihydroxyvitamin D3, calcitriol, also transforms JB6 cells and, in other cell types, regulates osteopontin synthesis, we hypothesized that calcitriol-mediated transformation of JB6 cells would also cause induction of osteopontin synthesis and secretion. Metabolic labeling with 32PO4 of near confluent JB6 cells (clone 41.5a) treated with calcitriol (0.1-100 ng/ml) for up to 48 h revealed only a minimal production of osteopontin, which is the major phosphoprotein secreted by 12-O-tetradecanoylphorbol-13-acetate-treated cells. Similar treatment followed by labeling with [35S]methionine showed a substantial dose-dependent increase in the synthesis and secretion of osteopontin. This induction was not associated with increased cell proliferation or with cell transformation, as assayed by anchorage-independent growth. Calcitriol-treated cells were morphologically indistinguishable from control cells, while 12-O-tetradecanoylphorbol-13-acetate-treated cells acquired a distinctive morphology. No induction of osteopontin was found with 25-hydroxyvitamin D3 or 24R,25-dihydroxyvitamin D3. These results show that calcitriol induces the synthesis and secretion of a nonphosphorylated form of osteopontin, in a cell type which normally makes little or none of this protein, and that the induction is not correlated with the tumorigenic transformation of these cells.
鼠源JB6表皮细胞可被肿瘤启动子12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯不可逆地转化为致瘤细胞。这种转化的一个特征是诱导含精氨酰甘氨酰天冬氨酸的细胞黏附糖蛋白骨桥蛋白（也称为分泌性磷蛋白1，以前称为转化相关磷蛋白2ar、骨唾液蛋白1或44000 Mr骨磷蛋白）的合成与分泌，其表达与肿瘤发生和转移有关。由于1α,25 - 二羟基维生素D3（骨化三醇）也能转化JB6细胞，并且在其他细胞类型中调节骨桥蛋白的合成，我们推测骨化三醇介导的JB6细胞转化也会导致骨桥蛋白合成与分泌的诱导。用骨化三醇（0.1 - 100 ng/ml）处理近汇合的JB6细胞（克隆41.5a）长达48小时，然后用32PO4进行代谢标记，结果显示骨桥蛋白的产生极少，而骨桥蛋白是12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯处理的细胞分泌的主要磷蛋白。类似处理后用[35S]甲硫氨酸标记显示骨桥蛋白的合成与分泌呈剂量依赖性显著增加。如通过非贴壁生长测定，这种诱导与细胞增殖增加或细胞转化无关。骨化三醇处理的细胞在形态上与对照细胞无差异，而12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯处理的细胞获得了独特的形态。用25 - 羟基维生素D3或24R,25 - 二羟基维生素D3未发现骨桥蛋白的诱导。这些结果表明，骨化三醇在通常很少产生或不产生这种蛋白质的细胞类型中诱导非磷酸化形式骨桥蛋白的合成与分泌，并且这种诱导与这些细胞的致瘤转化无关。
