N -Glycan–dependent protein folding and endoplasmic reticulum retention regulate GPI-anchor processing

• Published in: The Journal of cell biology Vol. 217; no. 2; pp. 585 - 599
• Main Authors: Liu, Yi-Shi, Guo, Xin-Yu, Hirata, Tetsuya, Rong, Yao, Motooka, Daisuke, Kitajima, Toshihiko, Murakami, Yoshiko, Gao, Xiao-Dong, Nakamura, Shota, Kinoshita, Taroh, Fujita, Morihisa
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 05.02.2018; The Rockefeller University Press
• Subjects: Anchoring; Calnexin; Cell Line; Cell surface; Deacylation; Endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Folding; Genes; Genetic screening; Glycan; Glycosylphosphatidylinositol; Glycosylphosphatidylinositols - metabolism; HEK293 Cells; Humans; Membrane Proteins - genetics; Membrane Proteins - metabolism; N-glycans; Phosphoric Monoester Hydrolases - genetics; Phosphoric Monoester Hydrolases - metabolism; Polysaccharides; Polysaccharides - metabolism; Protein Folding; Protein transport; Proteins; Quality control; Retention; Stress response
• ISSN: 0021-9525; 1540-8140; 1540-8140
• DOI: 10.1083/jcb.201706135

Glycosylphosphatidylinositol (GPI) anchoring of proteins is a conserved posttranslational modification in the endoplasmic reticulum (ER). Soon after GPI is attached, an acyl chain on the GPI inositol is removed by post-GPI attachment to proteins 1 (PGAP1), a GPI-inositol deacylase. This is crucial for switching GPI-anchored proteins (GPI-APs) from protein folding to transport states. We performed haploid genetic screens to identify factors regulating GPI-inositol deacylation, identifying seven genes. In particular, calnexin cycle impairment caused inefficient GPI-inositol deacylation. Calnexin was specifically associated with GPI-APs, dependent on N-glycan and GPI moieties, and assisted efficient GPI-inositol deacylation by PGAP1. Under chronic ER stress caused by misfolded GPI-APs, inositol-acylated GPI-APs were exposed on the cell surface. These results indicated that N-glycans participate in quality control and temporal ER retention of GPI-APs, ensuring their correct folding and GPI processing before exiting from the ER. Once the system is disrupted by ER stress, unprocessed GPI-APs become exposed on the cell surface.