Monomerization and ER Relocalization of GRASP Is a Requisite for Unconventional Secretion of CFTR.
Induction of endoplasmic reticulum (ER)-to-Golgi blockade or ER stress induces Golgi reassembly stacking protein (GRASP)-mediated, Golgi-independent unconventional cell-surface trafficking of the folding-deficient ΔF508-cystic fibrosis transmembrane conductance regulator (CFTR). However, molecular mechanisms underlying this process remain elusive. Here, we show that phosphorylation-dependent dissociation of GRASP homotypic complexes and subsequent relocalization of GRASP to the ER play a critical role in the unconventional secretion of CFTR. Immunolocalization analyses of mammalian cells revealed that the Golgi protein GRASP55 was redistributed to the ER by stimuli that induce unconventional secretion of ΔF508-CFTR, such as induction of ER-to-Golgi blockade by the Arf1 mutant. Notably, the same stimuli also induced phosphorylation of regions near the C-terminus of GRASP55 and dissociation of GRASP homomultimer complexes. Furthermore, phosphorylation-mimicking mutations of GRASP55 induced the monomerization and ER relocalization of GRASP55, and these changes were nullified by phosphorylation-inhibiting mutations. These results provide mechanistic insights into how GRASP accesses the ER-retained ΔF508-CFTR and mediates the ER stress-induced unconventional secretion pathway.
['Kim|Jiyoon|J|', 'Noh|Shin Hye|SH|', 'Piao|He|H|', 'Kim|Dong Hee|DH|', 'Kim|Kuglae|K|', 'Cha|Jeong Seok|JS|', 'Chung|Woo Young|WY|', 'Cho|Hyun-Soo|HS|', 'Kim|Joo Young|JY|', 'Lee|Min Goo|MG|']
D002352:Carrier Proteins D019005:Cystic Fibrosis Transmembrane Conductance Regulator D004721:Endoplasmic Reticulum D059865:Endoplasmic Reticulum Stress D006056:Golgi Apparatus D057809:HEK293 Cells D006367:HeLa Cells D006801:Humans D008565:Membrane Proteins D009154:Mutation D010957:Plasmids D055503:Protein Multimerization D021381:Protein Transport D055571:Secretory Pathway D014162:Transfection
GRASP unconventional secretion CFTR ER stress ER-to-Golgi blockade