Clustering in the Golgi apparatus governs sorting and function of GPI-APs in polarized epithelial cells

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) are lipid APs attached to the extracellular leaflet of the plasma membrane (PM) via a glycolipid anchor. GPI-APs are commonly associated with cholesterol- and sphingolipid-enriched membrane microdomains. These microdomains help regulating various biological activities, by segregating different proteins and lipids in (nanoscale) membrane compartments. In fibroblasts, GPI-APs form actin- and cholesterol-dependent nanoclusters directly at the PM. In contrast, in polarized epithelial cells GPI-APs cluster in the Golgi apparatus, the major protein-sorting hub for the secretory pathway. Golgi clustering is required for the selective sorting of GPI-APs to the apical PM domain, but also regulates their organization and biological activities at the cell surface. In this review, we discuss recent advances in our understanding of the mechanism of GPI-AP sorting to the apical membrane. We focus on the roles of the protein moiety and lipids in the regulation of the clustering of GPI-APs in the Golgi apparatus.