Unilever R&D, Colworth Science Park, Sharnbrook, Bedfordshire, MK44 1LQ, UK.
Adv Exp Med Biol. 2013;961:95-107. doi: 10.1007/978-1-4614-4756-6_9.
Natural human skin colour is determined both by environmental exposure to ultraviolet light and through inherited genetic variation in a very limited number of genes. Variation of a non-synonymous single-nucleotide polymorphism (nsSNP; rs1426654) in the gene (SLC24A5) encoding the NCKX5 protein is associated with differences in constitutive skin colour in South Asians. The nsSNP encodes the substitution of alanine for threonine at residue 111 (A111T) near a transmembrane region required for exchanger activity, a region which is highly conserved across different species and between NCKX family members. We have shown that NCKX5 is located at the trans-Golgi network of melanocytes and functions as a potassium-dependent sodium-calcium exchanger. When heterologously expressed, the 111T variant of NCKX5 shows significantly lower exchanger activity than the A111 variant. We have postulated that lower exchanger activity causes the reduced melanogenesis and lighter skin in Thr111-positive individuals. We used gene expression microarrays with qPCR replication and validation to assess the impact of siRNA-mediated knockdown of SLC24A5 on the transcriptome of cultured normal human melanocytes (NHM). Very few genes associated with melanogenesis were altered at the transcript level except for MC1R, suggesting that SLC24A5 interacts with at least one well-characterized melanogenic signalling pathway. More surprisingly, the expression of a number of cholesterol homeostatic genes was altered after SLC24A5 knockdown, and the total cholesterol content of NHM was increased. Cholesterol has previously been identified as a potential melanogenic regulator, and our data imply that NCKX5 exchanger function influences natural variation in skin pigmentation via a novel, unknown mechanism affecting cellular sterol levels.
人类的自然肤色既受环境中紫外线暴露的影响，也受少数几个基因中遗传变异的影响。基因（SLC24A5）编码的 NCKX5 蛋白中的非同义单核苷酸多态性（nsSNP；rs1426654）的变异与南亚人固有肤色的差异有关。该 nsSNP 编码的是在交换器活性所需的跨膜区附近的第 111 位残基（T111）上的丙氨酸替换为苏氨酸（A111T），该区域在不同物种和 NCKX 家族成员之间高度保守。我们已经表明，NCKX5 位于黑素细胞的反高尔基网络中，作为一种钾依赖性钠-钙交换器发挥作用。当异源表达时，NCKX5 的 111T 变体的交换器活性明显低于 A111 变体。我们推测，较低的交换器活性导致 Thr111 阳性个体的黑色素生成减少和肤色变浅。我们使用基因表达微阵列和 qPCR 复制和验证来评估 SLC24A5 的 siRNA 介导的敲低对培养的正常人黑素细胞（NHM）转录组的影响。除了 MC1R 之外，很少有与黑色素生成相关的基因在转录水平上发生改变，这表明 SLC24A5 至少与一个已经很好地描述的黑色素生成信号通路相互作用。更令人惊讶的是，SLC24A5 敲低后，许多胆固醇稳态基因的表达发生改变，NHM 的总胆固醇含量增加。胆固醇先前被鉴定为潜在的黑色素生成调节剂，我们的数据表明，NCKX5 交换器功能通过影响细胞固醇水平的未知机制影响天然皮肤色素沉着的变异。
