Regulated compartmentalization of enzymes in Golgi by GRASP55 controls cellular glycosphingolipid profile and function

Abstract

22Glycans are important regulators of cell and organismal physiology. This requires that the 23 glycan biosynthesis be controlled to achieve specific cellular glycan profiles. Glycans are 24 assembled in the Golgi apparatus on secretory cargoes that traverse it. The mechanisms by 25which Golgi apparatus ensures cell and cargo-specific glycosylation remain obscure. We 26 investigated how Golgi apparatus regulates glycosylation by studying biosynthesis of 27 glycosphingolipids, glycosylated lipids with critical roles in signalling and differentiation. 28Glycosylation enzymes have compartmentalized localization in the Golgi stack, but the 29 molecular machineries involved are unknown. We identified Golgi matrix protein GRASP55 as a 30 prototype controller of Golgi enzyme localization that specifically binds and compartmentalizes 31 key glycosphingolipid biosynthetic enzymes by promoting their anterograde transport in the 32Golgi. Impairing GRASP55-enzyme interaction decompartmentalizes these enzymes, changes 33 the cargo flux across competing glycosylation pathways that results in alteration of cellular 34 glycosphingolipid profile. This GRASP55 regulated pathway of enzyme compartmentalization 35 allows cells to make cell density dependent adaptations to glycosphingolipid biosynthesis to suit 36 cell growth needs. Thus, Golgi apparatus controls cellular glycan (glycosphingolipid) profile by 37 governing competition between biosynthetic reactions through regulated changes in enzyme 38 compartmentalization. 39 40

Adaptation of the Golgi Apparatus in Cancer Cell Invasion and Metastasis

“…Disruption of the Golgi by knocking out GRASP55 and GRASP65 reduces Gb3 expression but increases GM1 level (Bekier et al, 2017). A more recent study demonstrated that GRASP55 specifically binds and compartmentalizes key glycosphingolipid biosynthetic enzymes; the correct compartmentalization of these enzymes at the Golgi promises accurate biosynthetic reactions and regulates cellular glycosphingolipid profile (Pothukuchi et al, 2020). Gb3 expression is correlated with gastric, colon, and breast cancer progression and Gb3 is associated with mechanisms in the EMT pathway (Cumin et al, 2021).…”

GOLPH3 tunes up glycosphingolipid biosynthesis for cell growth

“…By changing GOLPH3 levels, cells can therefore adjust the fraction of enzymes that is retained in the Golgi versus send to lysosomal degradation. Interestingly, the authors recently showed that the Golgi matrix protein GRASP55 prevents the entry of glycosyltransferases into retrograde transport vesicles, thereby acting as a retainer of these enzymes in the trans‐Golgi (preprint: Pothukuchi et al, 2020). Thus, the balance between GOLPH3‐mediated retrograde transport and GRASP55‐mediated trans‐Golgi retention determines intra‐Golgi levels and localization of client enzymes.…”