Malloy Peter J, Feldman David
Division of Endocrinology, Gerontology, and Metabolism, Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
Endocrinology. 2009 Feb;150(2):679-86. doi: 10.1210/en.2008-1217. Epub 2008 Oct 1.
Calcitriol actions are mediated by the vitamin D receptor (VDR), a nuclear transcription factor of the steroid-retinoid-thyroid nuclear receptor gene superfamily. Calcitriol inhibits the growth of many cells including cancer cells by inducing cell cycle arrest. In some cancer cell lines, calcitriol also induces apoptosis. In the LNCaP prostate cancer cell line, induction of apoptosis and caspase-3/7 activities by staurosporine (STS) abolished [(3)H]1,25-dihydroxy vitamin D(3) binding and VDR protein, suggesting that the VDR may be targeted for inactivation by caspases during apoptosis. A potential caspase-3 site (D(195)MMD(198)S) was identified in the human VDR ligand-binding domain. Mutations D195A, D198A, and S199A were generated in the putative capase-3 cleavage site. In transfected COS-7 cells, STS treatment resulted in the cleavage of the wild-type (WT) VDR and S199A mutant VDR but not the D195A or D198A mutants. In in vitro assays, the WT VDR and S199A mutant VDR were cleaved by caspase-3, although the D195A and D198A mutants were resistant to caspase-3. In vitro, the WT VDR was also cleaved by caspase-6 and caspase-7 and in extracts of STS-treated LNCaP cells. In STS-treated LNCaP cells and human skin fibroblasts, the proteasome inhibitor MG-132 protected the VDR caspase cleavage fragment from further degradation by the 26S proteasome. The rat VDR that does not contain the caspase-3 cleavage site was not cleaved in STS-treated COS-7 cells. In conclusion, our results demonstrate that the human VDR is a target of caspase-3 and suggest that activation of caspase-3 may limit VDR activity.
骨化三醇的作用是由维生素D受体（VDR）介导的，VDR是类固醇 - 视黄酸 - 甲状腺核受体基因超家族的一种核转录因子。骨化三醇通过诱导细胞周期停滞来抑制包括癌细胞在内的许多细胞的生长。在一些癌细胞系中，骨化三醇还可诱导细胞凋亡。在LNCaP前列腺癌细胞系中，星形孢菌素（STS）诱导的细胞凋亡和半胱天冬酶 - 3/7活性消除了[（3）H]1,25 - 二羟基维生素D（3）结合和VDR蛋白，这表明在细胞凋亡过程中VDR可能是半胱天冬酶失活的靶点。在人VDR配体结合域中鉴定出一个潜在的半胱天冬酶 - 3切割位点（D（195）MMD（198）S）。在假定的半胱天冬酶 - 3切割位点产生了突变D195A、D198A和S199A。在转染的COS - 7细胞中，STS处理导致野生型（WT）VDR和S199A突变体VDR的切割，但不导致D195A或D198A突变体的切割。在体外试验中，WT VDR和S199A突变体VDR被半胱天冬酶 - 3切割，尽管D195A和D198A突变体对半胱天冬酶 - 3具有抗性。在体外，WT VDR也被半胱天冬酶 - 6和半胱天冬酶 - 7以及在STS处理的LNCaP细胞提取物中切割。在STS处理的LNCaP细胞和人皮肤成纤维细胞中，蛋白酶体抑制剂MG - 132保护VDR半胱天冬酶切割片段不被26S蛋白酶体进一步降解。不含半胱天冬酶 - 3切割位点的大鼠VDR在STS处理的COS - 7细胞中未被切割。总之，我们的结果表明人VDR是半胱天冬酶 - 3的靶点，并提示半胱天冬酶 - 3的激活可能会限制VDR活性。
