SLC45A2 protein stability and regulation of melanosome pH determine melanocyte pigmentation.
SLC45A2 protein stability and regulation of melanosome pH determine melanocyte pigmentation.
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DOI：
10.1091/mbc.e20-03-0200
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发表时间：
2020-11-15
影响因子：
3.3
通讯作者：
Marks MS
中科院分区：
文献类型：
--
作者：
Le L;Escobar IE;Ho T;Lefkovith AJ;Latteri E;Haltaufderhyde KD;Dennis MK;Plowright L;Sviderskaya EV;Bennett DC;Oancea E;Marks MS
SLC45A2编码主要在色素细胞中表达的推定转运蛋白。SLC45A2突变导致眼皮肤白化病4型（OCA4）和多态性与色素沉着的变化，但SLC45A2及其变体的定位，功能和调节仍然未知。我们发现SLC45A2定位于一组成熟黑素体，其仅与表达氯离子通道OCA2的组群部分重叠。在HeLa细胞中异位表达的SLC45A2定位于溶酶体并升高溶酶体pH，这表明在黑素细胞中，SLC45A2表达与OCA2表达一样，导致成熟黑素体的脱酸以支持黑素合成。有趣的是，OCA2过表达补偿了色素沉着中SLC45A2表达的损失。对SLC45A2和OCA2缺陷小鼠黑素细胞的分析表明，SLC45A2在黑素体成熟过程中可能比OCA2晚发挥作用。此外，浅皮肤相关的SLC45A2等位基因F374变体仅恢复SLC45A2缺陷黑素细胞的中度色素沉着，这是由于快速的蛋白酶体依赖性降解，导致黑素体中的蛋白质表达水平低于深皮肤相关的等位基因L374变体。我们的数据表明，SLC45A2保持黑素体中和，这最初是由短暂的OCA2活性协调，以支持黑素体成熟后期的黑化，并且由于蛋白质的不稳定性，常见的等位基因变体赋予活性降低。
SLC45A2 encodes a putative transporter expressed primarily in pigment cells. SLC45A2 mutations cause oculocutaneous albinism type 4 (OCA4) and polymorphisms are associated with pigmentation variation, but the localization, function, and regulation of SLC45A2 and its variants remain unknown. We show that SLC45A2 localizes to a cohort of mature melanosomes that only partially overlaps with the cohort expressing the chloride channel OCA2. SLC45A2 expressed ectopically in HeLa cells localizes to lysosomes and raises lysosomal pH, suggesting that in melanocytes SLC45A2 expression, like OCA2 expression, results in the deacidification of maturing melanosomes to support melanin synthesis. Interestingly, OCA2 overexpression compensates for loss of SLC45A2 expression in pigmentation. Analyses of SLC45A2- and OCA2-deficient mouse melanocytes show that SLC45A2 likely functions later during melanosome maturation than OCA2. Moreover, the light skin-associated SLC45A2 allelic F374 variant restores only moderate pigmentation to SLC45A2-deficient melanocytes due to rapid proteasome-dependent degradation resulting in lower protein expression levels in melanosomes than the dark skin-associated allelic L374 variant. Our data suggest that SLC45A2 maintains melanosome neutralization that is initially orchestrated by transient OCA2 activity to support melanization at late stages of melanosome maturation, and that a common allelic variant imparts reduced activity due to protein instability.