The ELMO1, a Microbial Sensor Regulates Bacterial Clearance and Endo‐lysosomal Signaling

Abstract

Intestinal antigen presenting cells (APCs) are a major component of the mucosal immune system and maintain the gut homeostasis and the inflammation level. Microbial sensors present on APCs recognize microbes irrespective of their pathogenicity but little is known about their mechanism that leads to host cellular responses unique to bacterial pathogenesis. Previously, we found that BAI1 (Brain Angiogenesis Inhibitor 1) recognizes bacterial LPS from pathogenic and non‐pathogenic bacteria. BAI1 binds cytosolic protein ELMO1 (Engulfment and cell motility protein 1), which facilitates the engulfment of bacteria via Rac1 activation and induces the pro‐inflammatory cytokines and regulates bacterial clearance. Interestingly, ELMO1 interacts with Salmonella effector SifA involved in bacterial survival. Therefore, we hypothesized that ELMO1 is a cytosolic sensor that interacts with bacterial effectors involved in the pathogenesis of enteric infection, controls bacterial clearance and provides differential immune responses between pathogens and commensals. In silico analysis of bacterial database revealed that Salmonella effector SifA shares a WxxxE signature motif present in several effectors from other enteric pathogens, including IpgB1 in Shigella that binds ELMO1. This signature motif is not present in commensal gut microbes. Interestingly, mutation in the WxxxE motif of SifA abolished interaction with ELMO1. SifA is involved in bacterial vacuole integrity and together ELMO1‐SifA is involved in the endosomal‐lysosomal pathway by interacting with the late endosomal protein Rab9. To further elucidate the interaction of SifA and its involvement in interrupting host defenses, we did pulldown of GST‐SifA with murine macrophage cell lysate followed by the identification of host proteins via MALDI‐TOF Spectroscopy. Three major proteins that interact with SifA are Ribophorin 1(RPN1), involved in the transport of newly synthesized proteins across the membrane of the rough endoplasmic reticulum; MOGS, a glycoside hydrolase functions within the N‐glycosylation pathway; Rab14, the endosomal trafficking protein involved in lysosomal fusion. Our functional studies showed the ELMO1‐depleted macrophages had higher acidic and proteolytic lysosomal environment and increased Cathepsin B activity at earlier time points of infection but lower Cathepsin B activity and lysosomal acidification at later time points of infection. Lastly, ELMO1 depleted cells had significant delayed clearance following enteric infection. Our results suggest that ELMO1 is a novel cytosolic sensor that determines bacterial pathogenesis and provides new insight to the degradation of bacteria via mechanisms of the endosomal‐lysosomal system.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.