Intracellular lipopolysaccharide regulates ER remodeling upon bacterial infection

The remodeling of endoplasmic reticulum (ER) is finely regulated by selective autophagy, known as ER-phagy. However, whether Gram-negative bacteria, which are known to manipulate the host membranous system, regulate ER-phagy remains elusive. We find that bacterial lipopolysaccharide (LPS) released upon infection with Salmonella Typhimurium colocalizes with FAM134B, a reticulon-like protein that operates as an ER-phagy receptor. Pulldown assays reveal that LPS binds directly to FAM134B. The interaction occurs via lipid A of LPS and positively charged amino acid residues on the amphipathic helices and C-terminal region of FAM134B. Upon binding, O-Antigen of LPS promotes FAM134B oligomerization and ER fragmentation in in vitro liposome membrane remodeling assays. Delivery of LPS into the cytoplasm via transfection significantly increases the number of FAM134B–LC3B-decorated ER fragments, which are recruited to Salmonella -containing vacuoles. Both intracellular and extracellular bacteria use outer membrane vesicles (OMVs) to deliver LPS into the cytosol for FAM134B activation and ER fragmentation. Taken together, our results show that Gram-negative bacteria subvert the host ER remodeling system to create bacteria-containing vacuoles that provide a niche for bacterial survival.

Graphical Abstract

In Brief

Cytosolic LPS binds to the ER-phagy receptor FAM134B, triggering ER fragmentation, and subsequently, the formation of FAM134B-positive vacuoles for bacterial survival.

Highlights

• Intracellular LPS induces FAM134B-mediated ER fragmentation.

• Lipid A of LPS binds to FAM134B.

• O-antigen of LPS triggers oligomerization of FAM134B and membrane fragmentation.

• FAM134B-positive Salmonella -containing vacuoles are not acidified, providing a niche for Salmonella survival.

• Outer membrane vesicles are required for cytosolic LPS delivery to activate FAM134B-mediated ER fragmentation.