Intracellular lipopolysaccharide binds FAM134B to regulate ER remodeling upon bacterial infection

Selective autophagy of the endoplasmic reticulum (ER), termed ER-phagy, plays a key role in organelle remodeling and cellular homeostasis. However, whether and how ER-phagy is regulated during Gram-negative bacteria infection to influence host responses remains unclear. Here, we show that Salmonella enterica serovar Typhimurium releases lipopolysaccharide (LPS) that colocalizes with FAM134B, a reticulon-like ER-resident receptor for ER-phagy. Cytosolic delivery of LPS, either during infection or via transfection, markedly increases FAM134B- and LC3B-decorated ER fragments. Mechanistically, pulldown assays demonstrate that LPS directly binds FAM134B through interactions between lipid A and positively charged residues within its amphipathic helices and C-terminal region. This interaction promotes FAM134B oligomerization and drives ER membrane fragmentation, a process further amplified by the O-antigen moiety of LPS. The resulting ER fragments accumulate around LC3-positive Salmonella -containing vacuoles, facilitating bacterial clearance. Importantly, both intracellular and extracellular Salmonella exploit outer membrane vesicles (OMVs) to deliver LPS into the host cytosol, triggering FAM134B activation and ER remodeling. Collectively, our findings reveal a previously unrecognized host response by which LPS of Gram-negative bacteria are sensed by the host ER-phagy machinery to promote xenophagy and enhance antibacterial defense.