Unconventional roles of nonlipidated LC3 in ERAD tuning and coronavirus infection.

Bernasconi, Riccardo; Noack, Julia; Molinari, Maurizio

Secretory and membrane proteins attain their native structure in the endoplasmic reticulum (ER). Folding-defective polypeptides are selected for degradation by processes collectively defined as ER-associated degradation (ERAD). Enhanced ERAD activity may interfere with protein biogenesis by inappropriately targeting not-yet-native protein folding intermediates for disposal. The regulation of ERAD is therefore crucial to maintain cellular proteostasis. At steady-state, select ERAD regulators are constitutively removed from the ER in a series of processes collectively defined as ERAD tuning. This sets the ERAD activity at levels that do not interfere with completion of ongoing folding programs. Our latest work highlights a crucial, autophagy-independent role of nonlipidated LC3 (LC3-I) as part of a membrane-bound receptor that insures the vesicle-mediated clearance of at least two ERAD regulators from the ER, EDEM1 and OS9. This pathway is hijacked by coronaviruses (CoV), and silencing of LC3 substantially inhibits viral replication.