GOLPH3 and GOLPH3L maintain Golgi localization of LYSET and a functional mannose 6-phosphate transport pathway
Brooke L. Brauer, Zilei Chen, Felix Beirow, Jiaran Li, Daniel Meisinger, Emanuela Capriotti, Michaela Schweizer, Lea Wagner, Jascha Wienberg, Laura Hobohm, Lukas Blume, Wenjie Qiao, Yoshiki Narimatsu, Jan E. Carette, Henrik Clausen, Dominic Winter, Thomas Braulke, Sabrina Jabs, Matthias Voß
Abstract
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.