The Role of ELMO1 in the Pathogenesis of Infections with Gram-Negative Bacteria
The clearance of enteric bacteria by phagocytes plays an essential role in the host response of infection. Previously, we have reported that BAI1 (Brain Angiogenesis Inhibitor 1) binds bacterial Lipopolysaccharide (LPS) and facilitates engulfment of Gram-negative bacteria by activating ELMO1 (Engulfment and cell motility protein 1). Using Salmonella as a model organism, we hypothesized that ELMO1 regulates bacterial clearance, activates autophagy and modulates the endosomal lysosomal pathway. The data from Salmonella infection in J774 murine macrophages with depleted ELMO1 expression, by genetic modification, suggest that ELMO1 is important for LC3BII accumulation. There was a compounded decrease in LC3BII accumulation when ELMO1 and ATG-5 were simultaneously inhibited. These observations suggest that ELMO1 is upstream of ATG-5 and important for its function. The effect of ULK-1 depleted macrophages on LC3BII accumulation was insignificant when compared to control macrophages. Therefore, it appears that Salmonella is cleared mostly by LC3-associated phagocytosis in an ELMO1-dependent manner. ELMO1-depleted macrophages showed delayed bacterial clearance post infection. ELMO1 was found to interact with the late endosomal protein Rab9, which is involved in lysosome biogenesis and cellular trafficking. The accumulation of the lysosomal enzyme cathepsin B varried in a time-dependent manner and decreased in ELMO1-depleted macrophages compared to control macrophages 12 h post infection. The expression of genes associated with the Salmonella Pathogenicity Island-2 (SPI-2), important for bacterial survival inside macrophages, decreased in ELMO1-depleted macrophages compared to control macrophages at 6 hours post infection. The understanding of the host response to enteric infections is important because they persistently reoccur.