Vesicular and non-vesicular transport feed distinct glycosylation pathways in the Golgi

Abstract

Newly synthesized proteins and lipids are transported across the Golgi complex via different mechanisms whose respective roles are not completely clear. We previously identified a non-vesicular intra-Golgi transport pathway for glucosylceramide (GlcCer)--the common precursor of the different series of glycosphingolipids-that is operated by the cytosolic GlcCer-transfer protein FAPP2 (also known as PLEKHA8) (ref. 1). However, the molecular determinants of the FAPP2-mediated transfer of GlcCer from the cis-Golgi to the trans-Golgi network, as well as the physiological relevance of maintaining two parallel transport pathways of GlcCer--vesicular and non-vesicular--through the Golgi, remain poorly defined. Here, using mouse and cell models, we clarify the molecular mechanisms underlying the intra-Golgi vectorial transfer of GlcCer by FAPP2 and show that GlcCer is channelled by vesicular and non-vesicular transport to two topologically distinct glycosylation tracks in the Golgi cisternae and the trans-Golgi network, respectively. Our results indicate that the transport modality across the Golgi complex is a key determinant for the glycosylation pattern of a cargo and establish a new paradigm for the branching of the glycosphingolipid synthetic pathway.

Role of tetanus neurotoxin insensitive vesicle-associated membrane protein in membrane domains transport and homeostasis

“…In particular, GlcCer transported by direct protein transfer is used to synthesize glycosphingolipids known as globosides in the TGN while vesicular transported GlcCer is used in the Golgi cisternae for ganglioside production such as that of GM3. 26 Along this line, an attractive hypothesis could be that complex GSL biosynthesis and GPI-anchored proteins may share similar intra-and/or outward-Golgi vesicular pathways, which would be VAMP7-dependent, and may be directly involved in Golgi homeostasis and dynamics. In conclusion, VAMP7 KO MEFs show phenotypes clearly related to the traffic of lipids and proteins known to reside in membrane domains.…”

“…Glycosphingolipid biosynthesis is completed at the Golgi apparatus 26 and GPI biosynthesis was suggested to be needed for sphingolipid biosynthesis at the ER in yeast. 38 We Figure 1.…”

“…KO cells also displayed modified content in sphingolipids, the biosynthesis of which is finalized in Golgi subdomains. 26 We thus propose here that VAMP7 contributes to the transport of domains' components to the cell surface, glycosphingolipids turnover and homeostatic equilibrium of Golgi.…”

“…Another head group, found in all eukaryotes includes a monosaccharide such as (but not only) glucose, to form GlcCer. Further glycosylations then occur on monoglycosylated ceramides, in different Golgi subdomains, 26 to give rise to a large variety of complex glycosphingolipids (GSL) which are then transported along the secretory pathway and particularly to the PM. Sphingolipid biosynthesis and turnover are regulated with cell growth and they travel via both vesicular and non-vesicular transports from ER to Golgi, and mainly via vesicles from Golgi to PM, (for reviews see 27,28 ).…”

Arfs at a Glance

“…These two localization regions of OSBP are sufficient to mediate contact between the ER and Golgi, and moreover, OSBP activity regulates this association (Mesmin et al, 2013). FAPP2-mediated delivery of glucosylceramide to the trans-Golgi has been shown to be dependent on Arf1 and also to be involved in vesicular trafficking from the Golgi to the plasma membrane (D'Angelo et al, 2007;D'Angelo et al, 2013). Hence, Arf1, by recruiting proteins that mediate the transfer of sphingolipid precursors and cholesterol, plays an important role in establishing the characteristic lipid environment of cellular membranes, an evolutionarily conserved feature of cellular organization (Bigay and Antonny, 2012).…”