A selective ER‐phagy exerts procollagen quality control via a Calnexin‐FAM134B complex

• Published in: The EMBO journal 2019-01, Vol.38 (2), p.n/a
• Main Authors: Forrester, Alison, De Leonibus, Chiara, Grumati, Paolo, Fasana, Elisa, Piemontese, Marilina, Staiano, Leopoldo, Fregno, Ilaria, Raimondi, Andrea, Marazza, Alessandro, Bruno, Gemma, Iavazzo, Maria, Intartaglia, Daniela, Seczynska, Marta, van Anken, Eelco, Conte, Ivan, De Matteis, Maria Antonietta, Dikic, Ivan, Molinari, Maurizio, Settembre, Carmine
• Format: Article
• Language: English
• Subjects: Animals; Autophagy; Calnexin; Calnexin - genetics; Calnexin - metabolism; Cell Line; Clonal deletion; Collagen; CRISPR; Crosstalk; Degradation; EMBO07; EMBO20; Endoplasmic reticulum; Endoplasmic Reticulum - metabolism; FAM134B; Gene deletion; Gene Knockdown Techniques; HeLa Cells; Humans; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - metabolism; Membrane proteins; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mice; Microtubule-Associated Proteins - metabolism; Oryzias; Phagocytosis; Procollagen; Procollagen - metabolism; Proteasomes; Protein Folding; Proteins; Quality control; siRNA; Substrates
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.201899847

Autophagy is a cytosolic quality control process that recognizes substrates through receptor‐mediated mechanisms. Procollagens, the most abundant gene products in Metazoa, are synthesized in the endoplasmic reticulum (ER), and a fraction that fails to attain the native structure is cleared by autophagy. However, how autophagy selectively recognizes misfolded procollagens in the ER lumen is still unknown. We performed siRNA interference, CRISPR‐Cas9 or knockout‐mediated gene deletion of candidate autophagy and ER proteins in collagen producing cells. We found that the ER‐resident lectin chaperone Calnexin (CANX) and the ER‐phagy receptor FAM134B are required for autophagy‐mediated quality control of endogenous procollagens. Mechanistically, CANX acts as co‐receptor that recognizes ER luminal misfolded procollagens and interacts with the ER‐phagy receptor FAM134B. In turn, FAM134B binds the autophagosome membrane‐associated protein LC3 and delivers a portion of ER containing both CANX and procollagen to the lysosome for degradation. Thus, a crosstalk between the ER quality control machinery and the autophagy pathway selectively disposes of proteasome‐resistant misfolded clients from the ER. Synopsis Unfolded procollagen in the endoplasmic reticulum (ER) is an ER‐associated degradation‐resistant substrate that has to be cleared by autophagy. The ER chaperone Calnexin and the ER‐phagy receptor FAM134B recognize misfolded procollagen and mediate its LC3‐dependent delivery to the lysosome for autophagic degradation. A candidate deletion screen shows that calnexin and FAM134B are required for ER quality control of endogenous procollagens Calnexin acts as co‐receptor recognizing misfolded procollagen within the ER lumen FAM134B binds misfolded procollagen through Calnexin and links it to LC3 on autophagosomal membranes Graphical Abstract Calnexin and the ER‐phagy receptor FAM134B recognize misfolded procollagen in the ER and mediate its LC3‐dependent delivery to the lysosome for autophagic degradation.