Adaptor protein-2 sigma subunit mutations causing familial hypocalciuric hypercalcaemia type 3 (FHH3) demonstrate genotype-phenotype correlations, codon bias and dominant-negative effects.
Adaptor protein-2 sigma subunit mutations causing familial hypocalciuric hypercalcaemia type 3 (FHH3) demonstrate genotype-phenotype correlations, codon bias and dominant-negative effects.
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DOI：
10.1093/hmg/ddv226
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发表时间：
2015-09-15
影响因子：
3.5
通讯作者：
Thakker RV
中科院分区：
文献类型：
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作者：
Hannan FM;Howles SA;Rogers A;Cranston T;Gorvin CM;Babinsky VN;Reed AA;Thakker CE;Bockenhauer D;Brown RS;Connell JM;Cook J;Darzy K;Ehtisham S;Graham U;Hulse T;Hunter SJ;Izatt L;Kumar D;McKenna MJ;McKnight JA;Morrison PJ;Mughal MZ;O'Halloran D;Pearce SH;Porteous ME;Rahman M;Richardson T;Robinson R;Scheers I;Siddique H;Van't Hoff WG;Wang T;Whyte MP;Nesbit MA;Thakker RV
适配蛋白-2 σ亚基（AP2σ2）是网格蛋白介导的质膜成分（如钙敏感受体（CaSR））内吞作用的关键。AP2σ2 Arg15残基突变导致家族性低钙性高钙血症3型（FHH3），这是一种细胞外钙（Ca2+o）稳态紊乱。为了阐明AP2σ2在Ca2+o调控中的作用，我们研究了65个不含其他FHH相关突变的FHH先证，对AP2σ2突变的功能后果进行了表征，并研究了导致FHH3的遗传机制。在17个先证中发现AP2σ2突变，其中Arg15Cys突变5个，Arg15His突变4个，Arg15Leu突变8个。Arg15Leu突变与显著高钙血症存在基因型-表型相关性。FHH3先证者拥有额外的表型，如认知功能障碍。所有三种引起fhh3的AP2σ2突变均以显性负向方式破坏CaSR信号转导。在AP2σ2 Arg15残基上观察到突变偏置，因为在FHH先证中没有检测到其他可预测的错义替换（Arg15Gly、Arg15Pro和Arg15Ser），这些错义替换也会导致CaSR功能丧失，并且发现这些突变减少了表达CaSR的细胞数量。与CaSR突变的FHH1先显子相比，FHH3先显子血清钙（sCa）和镁（sMg）浓度显著升高，尿钙与肌酐清除率（CCCR）降低，计算出的sCa × sMg/100 × CCCR指数≥5.0，FHH3的诊断敏感性和特异性分别为83%和86%。因此，我们的研究表明AP2σ2突变导致更严重的FHH表型，具有基因型-表型相关性，并且在Arg15残基上具有突变偏倚的显性-负作用机制。
The adaptor protein-2 sigma subunit (AP2σ2) is pivotal for clathrin-mediated endocytosis of plasma membrane constituents such as the calcium-sensing receptor (CaSR). Mutations of the AP2σ2 Arg15 residue result in familial hypocalciuric hypercalcaemia type 3 (FHH3), a disorder of extracellular calcium (Ca2+o) homeostasis. To elucidate the role of AP2σ2 in Ca2+o regulation, we investigated 65 FHH probands, without other FHH-associated mutations, for AP2σ2 mutations, characterized their functional consequences and investigated the genetic mechanisms leading to FHH3. AP2σ2 mutations were identified in 17 probands, comprising 5 Arg15Cys, 4 Arg15His and 8 Arg15Leu mutations. A genotype–phenotype correlation was observed with the Arg15Leu mutation leading to marked hypercalcaemia. FHH3 probands harboured additional phenotypes such as cognitive dysfunction. All three FHH3-causing AP2σ2 mutations impaired CaSR signal transduction in a dominant-negative manner. Mutational bias was observed at the AP2σ2 Arg15 residue as other predicted missense substitutions (Arg15Gly, Arg15Pro and Arg15Ser), which also caused CaSR loss-of-function, were not detected in FHH probands, and these mutations were found to reduce the numbers of CaSR-expressing cells. FHH3 probands had significantly greater serum calcium (sCa) and magnesium (sMg) concentrations with reduced urinary calcium to creatinine clearance ratios (CCCR) in comparison with FHH1 probands with CaSR mutations, and a calculated index of sCa × sMg/100 × CCCR, which was ≥ 5.0, had a diagnostic sensitivity and specificity of 83 and 86%, respectively, for FHH3. Thus, our studies demonstrate AP2σ2 mutations to result in a more severe FHH phenotype with genotype–phenotype correlations, and a dominant-negative mechanism of action with mutational bias at the Arg15 residue.