The lysosome is an essential organelle to recycle cellular materials and maintain nutrient homeostasis, but the mechanism to down-regulate its membrane proteins is poorly understood. In this study, we performed a cycloheximide (CHX) chase assay to measure the half-lives of approximately 30 human lysosomal membrane proteins (LMPs) and identified RNF152 and LAPTM4A as short-lived membrane proteins. The degradation of both proteins is ubiquitin dependent. RNF152 is a transmembrane E3 ligase that ubiquitinates itself, whereas LAPTM4A uses its carboxyl-terminal PY motifs to recruit NEDD4-1 for ubiquitination. After ubiquitination, they are internalized into the lysosome lumen by the endosomal sorting complexes required for transport (ESCRT) machinery for degradation. Strikingly, when ectopically expressed in budding yeast, human RNF152 is still degraded by the vacuole (yeast lysosome) in an ESCRT-dependent manner. Thus, our study uncovered a conserved mechanism to down-regulate lysosome membrane proteins.

中文翻译：

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保守的泛素和 ESCRT 依赖性途径内化人溶酶体膜蛋白以进行降解。

溶酶体是回收细胞材料和维持营养稳态的重要细胞器，但对其膜蛋白的下调机制知之甚少。在这项研究中，我们进行了放线菌酮 (CHX) 追踪分析，以测量大约 30 种人溶酶体膜蛋白 (LMP) 的半衰期，并将 RNF152 和 LAPTM4A 鉴定为短寿命膜蛋白。两种蛋白质的降解都依赖于泛素。RNF152 是一种跨膜 E3 连接酶，可将自身泛素化，而 LAPTM4A 使用其羧基末端 PY 基序来募集 NEDD4-1 进行泛素化。泛素化后，它们被运输（ESCRT）机制所需的内体分选复合物内化到溶酶体腔中以进行降解。引人注目的是，当在萌芽酵母中异位表达时，人 RNF152 仍然以 ESCRT 依赖性方式被液泡（酵母溶酶体）降解。因此，我们的研究揭示了下调溶酶体膜蛋白的保守机制。