Keratinocytes uptake melanosomes from melanocytes and retain them in the perinuclear region, where they form melanin caps. Although these processes are crucial to protecting nuclear DNA against ultraviolet injury, the molecular basis of melanosome uptake and decomposition in keratinocytes is poorly understood. One of the major reasons for its being poorly understood is the lack of a specific marker protein that can be used to visualize or monitor melanosomes (or melanosome-containing compartments) that have been incorporated into keratinocytes. In this study, we performed a comprehensive localization screening for mammalian Rab family small GTPases (Rab1-45) and succeeded in identifying 11 Rabs that were enriched around melanosomes that had been incorporated into keratinocytes. We also established a new assay by using a recently developed melanosome probe (called M-INK) as a means of quantitatively assessing the degradation of proteins on incorporated melanosomes in control and each of a series of Rab-knockdown keratinocytes. The results showed that knockdown or CRISPR/Cas9-mediated knockout of Rab7B (also identified as Rab42) in keratinocytes caused strong inhibition of protein degradation on melanosomes. Our findings indicated that Rab7B/42 is recruited to melanosome-containing compartments and that it promotes protein degradation on melanosomes in keratinocytes.Key words: degradation, keratinocytes, melanocytes, melanosome, Rab small GTPase.

中文翻译：

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Rab7B/42 在功能上参与角质形成细胞黑素体的蛋白质降解。


角质形成细胞从黑素细胞摄取黑素体并将其保留在核周区域，在那里形成黑色素帽。尽管这些过程对于保护核 DNA 免受紫外线损伤至关重要，但角质形成细胞中黑素体摄取和分解的分子基础却知之甚少。对其了解甚少的主要原因之一是缺乏可用于可视化或监测已纳入角质形成细胞的黑素体（或含有黑素体的区室）的特定标记蛋白。在这项研究中，我们对哺乳动物 Rab 家族小 GTPases (Rab1-45) 进行了全面的定位筛选，并成功鉴定了 11 个富集在已融入角质形成细胞的黑素体周围的 Rab。我们还建立了一种新的测定方法，使用最近开发的黑素体探针（称为 M-INK）作为定量评估对照黑素体和一系列 Rab 敲低角质形成细胞中的每种黑素体上蛋白质降解的方法。结果表明，敲低或 CRISPR/Cas9 介导的敲除角质形成细胞中的 Rab7B（也称为 Rab42）可对黑素体的蛋白质降解产生强烈抑制。我们的研究结果表明，Rab7B/42 被招募到含有黑素体的区室中，并促进角质形成细胞中黑素体上的蛋白质降解。关键词：降解，角质形成细胞，黑素细胞，黑素体，Rab 小 GTP 酶。