Glycosylation, which plays an important role in modifying lipids and sorting of proteins, is regulated by asymmetric intra-Golgi distribution and SPPL3-mediated cleavage of Golgi enzymes. We found that cells lacking LYSET/TMEM251, a retention factor for Golgi N-acetylglucosamine-1-phosphotransferase (GNPT), display SPPL3-dependent hypersecretion of the Golgi membrane protein B4GALT5. We demonstrate that in wild-type cells B4GALT5 is tagged with mannose 6-phosphate (M6P), a sorting tag typical of soluble lysosomal hydrolases. Hence, M6P-tagging of B4GALT5 may represent a novel degradative lysosomal pathway. We also observed B4GALT5 hypersecretion and prominent destabilization of LYSET-GNPT complexes, impaired M6P-tagging, and disturbed maturation and trafficking of lysosomal enzymes in multiple human cell lines lacking the COPI adaptors GOLPH3 and GOLPH3L. Mechanistically, we identified LYSET as a novel, atypical client of GOLPH3/GOLPH3L. Thus, by ensuring the cis-Golgi localization of the LYSET-GNPT complex and maintaining its Golgi polarity, GOLPH3/GOLPH3L is essential for the integrity of the M6P-tagging machinery and homeostasis of lysosomes.

中文翻译：

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GOLPH3 和 GOLPH3L 维持 LYSET 的高尔基体定位和功能性甘露糖 6-磷酸转运途径。


糖基化在脂质修饰和蛋白质分选中起重要作用，受不对称高尔基体内分布和 SPPL3 介导的高尔基体酶裂解的调节。我们发现缺乏 LYSET/TMEM251（高尔基体 N-乙酰葡糖胺-1-磷酸转移酶 （GNPT） 的保留因子）的细胞表现出高尔基体膜蛋白B4GALT5的 SPPL3 依赖性过度分泌。我们证明，在野生型细胞中，B4GALT5被海露糖 6-磷酸 （M6P） 标记，这是一种可溶性溶酶体水解酶的典型分选标签。因此，B4GALT5 的 M6P 标记可能代表一种新的降解溶酶体途径。我们还观察到B4GALT5缺乏 COPI 衔接蛋白 GOLPH3 和 GOLPH3L 的多种人类细胞系中 LYSET-GNPT 复合物的分泌过多和显着不稳定、M6P 标记受损以及溶酶体酶的成熟和运输紊乱。从机制上讲，我们将 LYSET 确定为 GOLPH3/GOLPH3L 的新型非典型客户。因此，通过确保 LYSET-GNPT 复合物的顺式-高尔基体定位并保持其高尔基体极性，GOLPH3/GOLPH3L 对于 M6P 标记机制的完整性和溶酶体的稳态至关重要。