Molecular analysis of vitamin D receptor defect and regulation of expression of vitamin D action

维生素D受体（Vitamin D receptor， VDR）是一种结合人骨钙素基因中维生素D应答元件（Vitamin D response element， VDRE）并调控其表达的核转录因子。人类VDR缺陷在VDR基因相同点突变的患者中表现出临床异质性。此外，在6至24年的随访期间，停止治疗后佝偻病没有复发。为了阐明这些临床发现，我们研究了1,25-二羟基维生素D_3（1,25(OH)_2D_3）、维甲酸（RA）和/或三碘甲状腺原氨酸（T3）处理过的皮肤成纤维细胞的VDRE复合物和核提取物的形成，作为转录活性的分子参数。0.1nM、1nM、10nM 1,25(OH)_2D_3、100nM RA或100nM T3处理均能促进对照细胞复合体的形成，但未发现加性效应。在患者细胞中，125 (OH)_2D_3、RA或T3均能促进复合物的形成，但两者均无加性刺激作用。这些结果表明，1,25(OH)_2D_3。RA和T3通过调节骨钙素的表达参与骨重塑。因此，在VDR缺陷患者的临床观察中，骨钙素表达调控的重叠控制可能至少部分解释了这一点。

Vitamin D receptor(VDR) is a nuclear transcription factor which binds to vitamin D response element(VDRE) of human osteocalcin gene and regulates expression. Human VDR defect shouws clinical heterogeneity among patients with the same point mutation their VDR gene. In addition, rickets did not recur after the cessation of therapy during 6 to 24 years of follow up. To elucidate these clinical findings, the complex formations of VDRE and nuclear extracts of cultured skin fibroblasts treated with 1,25-dihydroxyvitamin D_3(1,25(OH)_2D_3), retinoic acid(RA) and/or triiodothyronine(T3) were investigated as a molecular parameters of transcriptional activity. The complex formation in control cells was increased by the treatment of either 0.1nM, 1nM, 10nM 1,25(OH)_2D_3, 100nM RA or 100nM T3, however additive effect of these combinations was not found. In patient's cells, either 1,25(OH)_2D_3, RA or T3 increased the complex formation, while neither combination also additively stimulated. These results indicated that 1,25(OH)_2D_3. RA and T3 had some role in the regulation of bone remodeling through modulating osteocalcin expression. Therefore, clinical observation in patients with VDR defect might be at least patrly explained by overlapping control in the regulation of osteocalcin expession.