Functional characterization of newly-discovered mutations in human SR-BI.
Functional characterization of newly-discovered mutations in human SR-BI.
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DOI：
10.1371/journal.pone.0045660
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发表时间：
2012
期刊：
影响因子：
3.7
通讯作者：
Sahoo D
中科院分区：
文献类型：
--
作者：
Chadwick AC;Sahoo D
在啮齿类动物中，SR-BI已被确定为介导HDL-胆固醇酯（CE）清除的生理学相关HDL受体。然而，其在人类脂蛋白代谢中的作用不太明确。最近，在高HDL-胆固醇（HDL-C）水平受试者中发现了人SR-BI -S112 F或T175 A中的两个独特点突变。我们假设这些保守残基的突变会损害SR-BI的胆固醇转运功能。为了检验这一假设，通过定点诱变产生S112 F-和T175 A-SR-BI。在瞬时转染后，证实了COS-7细胞中两种突变体受体的细胞表面表达，尽管T175 A-SR-BI的表达水平较低。这两种突变体受体显示缺陷HDL结合，选择性摄取HDL-CE和释放游离胆固醇（FC）从细胞到HDL。突变受体也无法重组FC的质膜池。虽然这些受损的功能与受体寡聚化无关，但T175 A-SR-BI无法介导胆固醇转运功能可能与N-连接糖基化状态改变有关。总之，在S112 F-或T175 A-SR-BI突变受体携带者中观察到的高HDL-C水平与这些SR-BI受体无法介导HDL-CE的有效选择性摄取一致，并表明在这些情况下血浆HDL浓度升高可能与心血管疾病风险降低无关。
In rodents, SR-BI has been firmly established as a physiologically relevant HDL receptor that mediates removal of HDL-cholesteryl esters (CE). However, its role in human lipoprotein metabolism is less defined. Recently, two unique point mutations in human SR-BI — S112F or T175A — were identified in subjects with high HDL-cholesterol (HDL-C) levels. We hypothesized that mutation of these conserved residues would compromise the cholesterol-transport functions of SR-BI. To test this hypothesis, S112F- and T175A-SR-BI were generated by site-directed mutagenesis. Cell surface expression was confirmed for both mutant receptors in COS-7 cells upon transient transfection, albeit at lower levels for T175A-SR-BI. Both mutant receptors displayed defective HDL binding, selective uptake of HDL-CE and release of free cholesterol (FC) from cells to HDL. Mutant receptors were also unable to re-organize plasma membrane pools of FC. While these impaired functions were independent of receptor oligomerization, inability of T175A-SR-BI to mediate cholesterol-transport functions could be related to altered N-linked glycosylation status. In conclusion, high HDL-C levels observed in carriers of S112F- or T175A-SR-BI mutant receptors are consistent with the inability of these SR-BI receptors to mediate efficient selective uptake of HDL-CE, and suggest that increased plasma HDL concentrations in these settings may not be associated with lower risk of cardiovascular disease.
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