Mancilla E E, De Luca F, Ray K, Winer K K, Fan G F, Baron J
Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Pediatr Res. 1997 Oct;42(4):443-7. doi: 10.1203/00006450-199710000-00004.
Activating mutations of the Ca(2+)-sensing receptor (CaR) gene cause autosomal dominant hypoparathyroidism. Functional expression studies have been reported for several mutations, but have produced conflicting results. Thus, the mechanism by which these mutations activate the receptor is unclear. We describe here a new family with autosomal dominant hypoparathyroidism. The mother and three daughters experienced muscle spasms and/or seizures from early childhood. They were treated with oral calcium and vitamin D analogs, and all four patients developed hypercalciuria, nephrocalcinosis, and renal insufficiency. In this family, we identified a heterozygous missense mutation (F612S) involving the extracellular region of the CaR. The mutation cosegregated with disease. It was not present in 50 normal control individuals. We used site-directed mutagenesis to introduce this mutation into the CaR cDNA, and then expressed the mutant receptor in human embryonic kidney (HEK)-293 cells. In these cells, the accumulation of inositol phosphates was measured as a function of extracellular Ca2+ concentration. Compared with the wild-type receptor, the mutant receptor showed a left-shift in the concentration-response curve and an increase in the maximal response to high Ca2+ concentration. These effects did not appear to be mediated by changes in levels of receptor expression, as judged by ELISA, or by changes in receptor glycosylation, as judged by Western analysis. We conclude that this CaR mutation causes hypoparathyroidism by a dual increase in receptor sensitivity to extracellular Ca2+ and maximal signal transduction capacity.
钙敏感受体（CaR）基因的激活突变可导致常染色体显性遗传性甲状旁腺功能减退症。已有多项关于几种突变的功能表达研究报道，但结果相互矛盾。因此，这些突变激活受体的机制尚不清楚。我们在此描述一个患有常染色体显性遗传性甲状旁腺功能减退症的新家族。母亲和三个女儿自幼就经历肌肉痉挛和/或癫痫发作。她们接受了口服钙剂和维生素D类似物治疗，所有四名患者均出现高钙尿症、肾钙质沉着症和肾功能不全。在这个家族中，我们鉴定出一个涉及CaR细胞外区域的杂合错义突变（F612S）。该突变与疾病共分离。在50名正常对照个体中未发现此突变。我们使用定点诱变将此突变引入CaR cDNA，然后在人胚肾（HEK）-293细胞中表达突变受体。在这些细胞中，测量肌醇磷酸的积累作为细胞外Ca2+浓度的函数。与野生型受体相比，突变受体的浓度-反应曲线向左移动，对高Ca2+浓度的最大反应增加。通过ELISA判断，这些效应似乎不是由受体表达水平的变化介导的，通过蛋白质免疫印迹分析判断，也不是由受体糖基化的变化介导的。我们得出结论，这种CaR突变通过受体对细胞外Ca2+的敏感性和最大信号转导能力的双重增加导致甲状旁腺功能减退症。
