ER-phagy receptors: structural mechanisms in selective ER degradation and disease implications.

The endoplasmic reticulum (ER) is a central organelle for protein synthesis and folding, lipid metabolism and calcium signaling, etc. To maintain ER homeostasis, cells employ a specific autophagy process termed ER-phagy (reticulophagy), which depredates ER components via three forms: macro-ER-phagy (involving bulk ER sequestration), micro-ER-phagy (lysosome-direct), and ER-to-lysosome-associated degradation (ERLAD). The identification of specific ER-phagy receptors including FAM134A, FAM134B, FAM134C, TEX264, SEC62, RTN3L, CCPG1, ATL3, CALCOCO1 and others has significantly advanced our understanding of ER quality control mechanisms. In this review we summarize the current knowledge on ER-phagy receptors, and emerging evidence linking ER-phagy dysfunction to various disease pathologies including neurological disorders, cancer, metabolic diseases, cardiovascular diseases, infections and immune disorders. Recent evidence shows that ER-phagy receptors can form novel ER-derived structures, such as ER-tubular bodies (ER-TBs) consisted of ATL3 and RTN3L, which mediate Golgi-bypassing unconventional protein secretion under stress conditions, revealing non-degradative functions of these receptors beyond quality control. Targeting ER-phagy receptors may provide insights into potential therapeutic strategies for diseases associated with this fundamental cellular process.