Galectin 8 targets damaged vesicles for autophagy to defend cells against bacterial invasion

Abstract

Autophagy defends the mammalian cytosol against bacterial infection.1-3 Efficient pathogen engulfment is mediated by cargo-selecting autophagy adaptors that rely on unidentified pattern-recognition or danger receptors to label invading pathogens as autophagy cargo, typically by poly-ubiquitin coating.4-9 Here we show that galectin-8, a cytosolic lectin, is a danger receptor that restricts Salmonella proliferation. Galectin-8 monitors endo-lysosomal integrity and detects bacterial invasion by binding host glycans exposed on damaged Salmonella-containing vacuoles. By recruiting NDP52 galectin-8 activates anti-bacterial autophagy. Galectin-8-dependent recruitment of NDP52 to Salmonella-containing vesicles is transient and followed by ubiquitin-dependent NDP52 recruitment. Since galectin-8 also detects sterile damage to endosomes or lysosomes, as well as invasion by Listeria or Shigella, we suggest galectin-8 serves as a versatile receptor for vesicle-damaging pathogens. Our results illustrate how cells deploy the danger receptor galectin-8 to combat infection by monitoring endo-lysososomal integrity based on the specific lack of complex carbohydrates in the cytosol.

Recruitment of TBK 1 to cytosol‐invading Salmonella induces WIPI 2‐dependent antibacterial autophagy

“…While originally thought to control vesicular integrity and thus access of bacteria to the cytosol (Radtke et al , 2007), the unchanged recruitment of galectins to S . Typhimurium in cells lacking TBK1 placed TBK1 firmly downstream of bacterial entry (Thurston et al , 2012), while the epistatic relationship between ATG5 and TBK1 revealed in this study demonstrates that TBK1 protects cells against cytosol‐invading S . Typhimurium by controlling autophagy.…”

“…The earliest known “eat‐me” signal comprises galectin‐8, which detects damage to SCV membranes by binding cytosol‐exposed host glycans liberated by S . Typhimurium during its entry into the cytosol (Thurston et al , 2012). Galectin‐8 is a selective ligand for the cargo receptor NDP52, which is physically linked to TBK1 via Nap1 and Sintbad, two homologous adaptor proteins (Ryzhakov & Randow, 2007; Thurston et al , 2009, 2012).…”

“…Typhimurium during its entry into the cytosol (Thurston et al , 2012). Galectin‐8 is a selective ligand for the cargo receptor NDP52, which is physically linked to TBK1 via Nap1 and Sintbad, two homologous adaptor proteins (Ryzhakov & Randow, 2007; Thurston et al , 2009, 2012). The bacterial ubiquitin coat that develops subsequent to SCV damage comprises another “eat‐me” signal (Perrin et al , 2004).…”

“…Damage to the limiting membrane of the SCV during bacterial escape exposes host glycans otherwise hidden inside the vacuole as ligands for a family of cytosolic lectins, the galectins (Dupont et al , 2009; Paz et al , 2010). By binding the cargo receptor NDP52, galectin‐8 provides an “eat‐me” signal for anti‐bacterial autophagy (Thurston et al , 2012). The dense layer of poly‐ubiquitylated proteins that accumulates on cytosol‐exposed S .…”

Structural basis for recognition of autophagic receptor NDP52 by the sugar receptor galectin-8

“…During this characterization, it was found that residues 372-380 of NDP52 are responsible for the interaction with GAL8 (ref. 12). Thus, a fluorescein isothiocyanate (FITC)-labelled peptide (residues 372-385) was synthesized and its dissociation constant (K D ) to GAL8 was compared with that of full-length NDP52.…”