GOLPH3 and GOLPH3L are broad-spectrum COPI adaptors for sorting into intra-Golgi transport vesicles

Abstract

The fidelity of Golgi glycosylation is, in part, ensured by compartmentalization of enzymes within the stack. The COPI adaptor GOLPH3 has been shown to interact with the cytoplasmic tails of a subset of Golgi enzymes and direct their retention. However, other mechanisms of retention, and other roles for GOLPH3, have been proposed, and a comprehensive characterization of the clientele of GOLPH3 and its paralogue GOLPH3L is lacking. GOLPH3’s role is of particular interest as it is frequently amplified in several solid tumor types. Here, we apply two orthogonal proteomic methods to identify GOLPH3+3L clients and find that they act in diverse glycosylation pathways or have other roles in the Golgi. Binding studies, bioinformatics, and a Golgi retention assay show that GOLPH3+3L bind the cytoplasmic tails of their clients through membrane-proximal positively charged residues. Furthermore, deletion of GOLPH3+3L causes multiple defects in glycosylation. Thus, GOLPH3+3L are major COPI adaptors that impinge on most, if not all, of the glycosylation pathways of the Golgi.

Critical Determinants in ER-Golgi Trafficking of Enzymes Involved in Glycosylation

“…At the same time, the content of C2GnT and SiaTI in COPI vesicles was significantly decreased [ 110 ]. In recent studies, GOLPH3 was proved to interact with not only the LxxR motif but the positively charged amino acids upstream of the LxxR motif, [ 111 ], which further confirmed the function of GOLPH3/ Vps74p in retaining the cargo protein in the Golgi cisternae and preventing cargo from leaving to the TGN [ 111 , 112 ]. The protein was transported to lysosomes when it escaped the GOLPH3-mediated cisternal inter-conversion mechanism.…”

Supply chain logistics – the role of the Golgi complex in extracellular matrix production and maintenance

“…Cargo is selected for inclusion into COPI vesicles by binding coatomer directly, or through binding to adaptor proteins that bridge the cargo to the coat. Adaptors include the KDEL receptor, which facilitates recycling of escaped resident proteins to the ER ( Newstead and Barr, 2020 ), and GOLPH3, which mediates recycling of numerous Golgi enzymes proteins within the Golgi stack ( Welch et al, 2021 ). Scission of COPI vesicles is poorly understood but appears to be promoted by ARF1 with possible involvement of additional factors such as CtBP/BARS ( Arakel and Schwappach, 2018 ).…”

“…Another way in which changes in Golgi glycosylation can result in tumorigenesis is through GOLPH3, a COPI adaptor for numerous Golgi enzymes ( Eckert et al, 2014 ; Rizzo et al, 2021 ; Tu et al, 2008 ; Welch et al, 2021 ). GOLPH3 is an oncoprotein and is overexpressed in a number of cancers.…”

Getting Sugar Coating Right! The Role of the Golgi Trafficking Machinery in Glycosylation

“…Golgi enzymes can cycle between the Golgi cisternae [ 32 , 33 ] as well as between the Golgi and ER [ 34 ], and the majority of recycling occurs in COPI-coated vesicles. Yeast α-1,6-mannosyltransferase (Mnn9p) is one such example [ 35 , 36 ].…”

“…GOLPH3 and GOLPH3L are human homologs of Vps74. They have an affinity for PI4P enriched in the trans-Golgi and recognize membrane-proximal polybasic residues on the cytoplasmic tails of a subset of Golgi enzymes, including ST6Gal1 and N-acetylgalactosaminyltransferase-2 (GALNT2) [ 33 , 43 ]. About half the number of enzymes involved in glycosphingolipid synthesis have an LXX[R/K] consensus motif recognized by GOLPH3 on their cytosolic tails [ 44 ].…”