Stress granule formation mediates the inhibition of colonic Hsp70 translation by interferon-γ and tumor necrosis factor-α

Abstract

Mucosal inflammation, through cytokines such as interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α), has many effects on the intestinal epithelium, including selective translational inhibition of the cytoprotective protein heat shock protein 70 (Hsp70). To further elucidate the mechanisms underlying this effect, we examined the role of stress granules in mediating the actions of these proinflammatory cytokines. Using conditionally immortalized young adult mouse colonic epithelial cells, we demonstrate that IFN-γ and TNF-α, which upregulate eukaryotic initiation factor-α (eIF-2α) phosphorylation and reduce Hsp70 translation, significantly enhance stress granule formation in heat-shocked intestinal epithelial cells. The IFN-γ and TNF-α effects in upregulation of stress granule formation and downregulation of Hsp70 were eIF-2α dependent, and the effect could be negated by blocking eIF-2α phosphorylation with use of an RNA-dependent protein kinase inhibitor. Correspondingly, IFN-γ and TNF-α increased binding of cytoplasmic proteins to the 3′-untranslated region of Hsp70 mRNA, suggesting specific recruitment of Hsp70 to stress granules as the mechanism of IFN-γ and TNF-α inhibition of Hsp70 translation. We thus report a novel linkage between inflammatory cytokine production, stress granule formation, and Hsp70 translation inhibition, providing additional insights into the response of intestinal epithelial cells to inflammatory stress.