Gross C, Musiol I M, Eccleshall T R, Malloy P J, Feldman D
Department of Medicine, Stanford University School of Medicine, California 94305-5103, USA.
Biochem Biophys Res Commun. 1998 Jan 26;242(3):467-73. doi: 10.1006/bbrc.1997.7986.
Recent reports have suggested that polymorphisms in the gene encoding the vitamin D receptor (VDR) determine a portion of the genetic contribution to bone mineral density (BMD). Individuals homozygous for the allele lacking the Bsm I restriction site in the intron between exons 8 and 9 (BB genotype) have been found to have lower BMD than individuals homozygous for the allele having the Bsm I site (bb genotype). Interestingly, this polymorphism has also been associated with prostate cancer risk. The observed changes in BMD and prostate cancer risk might be due to an alteration in the function or abundance of the VDR leading to differential responsiveness of target cells to the action of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. To test this hypothesis, we cultured dermal fibroblasts from donors with BB, Bb, and bb genotypes and determined the level of VDR expression and the cellular responsiveness to 1,25(OH)2D3 treatment. VDR abundance, affinity for [3H]1,25(OH)2D3, and VDR mRNA levels were not detectably different in BB cells compared to bb cells. Moreover, equal expression of both VDR gene alleles was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) on mRNA from Bb fibroblasts. Fibroblast responsiveness to 1,25(OH)2D3, assessed by induction of 24-hydroxylase mRNA, was similar between BB and bb cell types in dose-response experiments. Although there were individual variations in the parameters we measured, there were no detectable or consistent differences in mean values from our small sample of cultured dermal fibroblasts. In conclusion, we did not detect significant differences in VDR properties or cellular responsiveness to 1,25(OH)2D3 that correlated with VDR genotype. Our findings suggest that these polymorphisms do not affect VDR function, but rather may be a marker for a nearby gene that is responsible for the genotype-associated variation in osteoporosis and prostate cancer risk.
最近的报告表明，编码维生素D受体（VDR）的基因多态性决定了对骨密度（BMD）遗传贡献的一部分。已发现，在第8和第9外显子之间的内含子中缺乏Bsm I限制性位点的等位基因的纯合个体（BB基因型），其骨密度低于具有Bsm I位点的等位基因的纯合个体（bb基因型）。有趣的是，这种多态性也与前列腺癌风险相关。观察到的骨密度变化和前列腺癌风险可能是由于VDR功能或丰度的改变，导致靶细胞对1,25 - 二羟基维生素D3 [1,25(OH)2D3]作用的反应性不同。为了验证这一假设，我们培养了来自具有BB、Bb和bb基因型供体的皮肤成纤维细胞，并测定了VDR表达水平以及细胞对1,25(OH)2D3处理的反应性。与bb细胞相比，BB细胞中VDR丰度、对[3H]1,25(OH)2D3的亲和力以及VDR mRNA水平没有明显差异。此外，通过对Bb成纤维细胞mRNA进行逆转录 - 聚合酶链反应（RT - PCR），检测到VDR基因的两个等位基因表达相等。在剂量反应实验中，通过诱导24 - 羟化酶mRNA评估，BB和bb细胞类型的成纤维细胞对1,25(OH)2D3的反应性相似。尽管我们测量的参数存在个体差异，但在我们培养的少量皮肤成纤维细胞样本中，平均值没有可检测到的或一致的差异。总之，我们没有检测到与VDR基因型相关的VDR特性或细胞对1,25(OH)2D3反应性的显著差异。我们的研究结果表明，这些多态性不会影响VDR功能，而可能是附近一个基因的标记，该基因负责与基因型相关的骨质疏松症和前列腺癌风险变异。
