Interferon-gamma signals via an ERK1/2-ARF6 pathway to promote bacterial internalization by gut epithelia.

The barrier function of the epithelium lining the intestine is essential for health by preventing the free passage of colonic bacteria into the mucosa. Epithelia treated with interferon (IFN)-? display increased bacteria transcytosis. Much is known of how IFN? affects the tight junction and paracellular permeability, yet its role in modifying transcellular traffic of commensal bacteria remains poorly understood. Using immunoblotting, ELISA and immunolocalization, IFN? was found to activate extracellular regulated kinase (ERK)1/2 in the human colon-like T84 epithelial cell line. Pharmacological inhibition of MEK/ERK1/2 signalling with U0126 significantly inhibited IFN?-induced increases in the transcytosis of non-invasive Escherichia coli (strain HB101). IFN? treatment enhanced epithelial internalization of E. coli, some of which subsequently escaped the enterocyte. Molecular analyses revealed that ERK1/2 inhibition prevented activation of the ADP-ribosylation factor (ARF)-6, a protein associated with endocytosis, and that siRNA knock-down of ARF6 expression reduced IFN?-induced E. coli internalization into T84 cells. None of these interventions affected the drop in transepithelial resistance caused by IFN?. Thus, increased transcellular passage may be a major component of IFN?-induced increases in epithelial permeability, and ERK1/2 and ARF6 are presented as important molecules in IFN?-evoked transcytosis of bacteria across gut epithelia.