Dynamic Glycosylation Governs the Vertebrate COPII Protein Trafficking Pathway

Abstract

The COPII coat complex, which mediates secretory cargo trafficking from the endoplasmic reticulum, is a key control point for subcellular protein targeting. Because misdirected proteins cannot function, protein sorting by COPII is critical for establishing and maintaining normal cell and tissue homeostasis. Indeed, mutations in COPII genes cause a range of human pathologies, including cranio-lenticulo-sutural dysplasia (CLSD), which is characterized by collagen trafficking defects, craniofacial abnormalities, and skeletal dysmorphology. Detailed knowledge of the COPII pathway is required to understand its role in normal cell physiology and to devise new treatments for disorders in which it is disrupted. However, little is known about how vertebrates dynamically regulate COPII activity in response to developmental, metabolic, or pathological cues. Several COPII proteins are modified by O-linked β-N-acetylglucosamine (O-GlcNAc), a dynamic form of intracellular protein glycosylation, but the biochemical and functional effects of these modifications remain unclear. Here, we use a combination of chemical, biochemical, cellular, and genetic approaches to demonstrate that site-specific O-GlcNAcylation of COPII proteins mediates their protein-protein interactions and modulates cargo secretion. In particular, we show that individual O-GlcNAcylation sites of SEC23A, an essential COPII component, are required for its function in human cells and vertebrate development, because mutation of these sites impairs SEC23A-dependent in vivo collagen trafficking and skeletogenesis in a zebrafish model of CLSD. Our results indicate that O-GlcNAc is a conserved and critical regulatory modification in the vertebrate COPII-dependent trafficking pathway.

Energetic adaptations: Metabolic control of endocytic membrane traffic

“…A number of clues suggest that O‐GlcNAcylation may more broadly control the protein machinery responsible for endocytic membrane traffic such as by control of coat proteins. Evidence for broad control of coat protein assembly and thus membrane traffic has been uncovered for coatomer protein complex (COP) II (COPII) and COPI‐mediated traffic between the ER and Golgi . Similarly, complex formation by proteins involved in tethering or fusion/fission of membranes such as SNAP‐29 and GRASP55 can be regulated by OGT, which can result in control of autophagosome interaction with endosome/lysosomes.…”

OGT Controls the Expression and the Glycosylation of E‐cadherin, and Affects Glycosphingolipid Structures in Human Colon Cell Lines

“…It is likely that these changes in cancer cell surface β1,6‐GlcNAc branching reflects perturbations in HBP flux or trafficking. Indeed OGT silencing interferes with intracellular protein transport as recently reported for coatomer COP (coat protein) I and COP II protein trafficking pathways . OGT silencing might impair vesicular trafficking, thus disrupting the glycosylation machinery and the correct localization of GTs and GHs.…”

“…The dramatic changes in GSLs composition consecutive to siOGT may originate from a modification of the trafficking or localization of biosynthetic enzymes rather than from modification of their expression levels. Vesicular trafficking is managed by many components among which the COP I and COP II complexes are pivotal, as discussed above . Recently, it has been shown that the multiprotein coatomer COP I and COP II are regulated by O ‐GlcNAcylation .…”

“…Vesicular trafficking is managed by many components among which the COP I and COP II complexes are pivotal, as discussed above . Recently, it has been shown that the multiprotein coatomer COP I and COP II are regulated by O ‐GlcNAcylation . A perturbation in O ‐GlcNAc homeostasis should affect vesicular trafficking and accordingly complex glycosylation patterns, in particular GSLs that exhibit highly dynamic conformations and adaptability.…”

Membrane Transport at an Organelle Interface in the Early Secretory Pathway: Take Your Coat Off and Stay a While

“…Thus, study of membrane traffic between the ER and ERGIC must occur using metazoan models, including Caenorhabditis elegans , Drosophila, zebrafish, rodents, and human cell lines. Moreover, particular emphasis must be placed upon the role of post‐translational modifications such as phosphorylation, ubiquitinylation, and glycosylation, all of which have been identified on COPII subunits, as well as regulators of COPII coat assembly and disassembly . Combining these efforts with structural approaches, both in vitro and in situ, will be critical to gaining a clear understanding of the mechanisms underlying the earliest step in secretory cargo trafficking.…”