RNase-L Deficiency Exacerbates Experimental Colitis and Colitis-associated Cancer

Abstract

Background The endoribonuclease RNase-L is a type-I interferon (IFN)-regulatedcomponent of the innate immune response that functions in antiviral, antibacterial and antiproliferative activities. RNase-L produces RNA agonists of RIG-I-like receptors (RLRs), sensors of cytosolic pathogen-associated RNAs that induce cytokines including IFNβ. IFNβ and RLR signaling mediate protective responses against experimental colitis and colitis-associated cancer (CAC) and contribute to gastrointestinal (GI) homeostasis. Therefore, we investigated a role for RNase-L in murine colitis and CAC and its association with RLR signaling in response to bacterial RNA. Methods Colitis was induced in wild type (WT) and RNase-L-deficient mice (RNase-L−/−) by administration of dextran sulphate sodium (DSS). CAC was induced by DSS and azoxymethane (AOM). Histological analysis and immunohistochemistry were performed on colon tissue to analyze immune cell infiltration and tissue damage following induction of colitis. Expression of cytokines was measured by qRT-PCR and ELISA. Results DSS-treated RNase-L−/− mice exhibited a significantly higher clinical score, delayed leukocyte infiltration, reduced expression of IFNβ, TNFα, IL-1β and IL-18at early times post-DSS exposure and increased mortalityas compared to WT mice. DSS/AOM-treated RNase-L−/−mice displayed an increased tumor burden. Bacterial RNA triggeredIFNβproductionin an RNase-L-dependent manner and provided a potential mechanism by whichRNase-L contributes to the GI immune response to microbiota and protects against experimental colitis and CAC. Conclusions RNase-L promotes the innate immune response to intestinal damage and ameliorates murine colitis and CAC. The RNase-L-dependent production of IFNβ stimulated by bacterial RNA may be a mechanism to protectagainst GI inflammatory disease.

Enteropathogenic Escherichia coli Inhibits Type I Interferon- and RNase L-Mediated Host Defense To Disrupt Intestinal Epithelial Cell Barrier Function

“…Therefore, RNase L may contribute to IFN-mediated GI functions by multiple mechanisms. In support of this view, we previously identified a role for RNase L in antibacterial immunity (52) and recently reported a protective role for RNase L in the immune response to commensal bacteria following GI injury in a mouse colitis model (45). This protective effect corresponded to an RNase L-dependent increase in IFN induction, suggesting that RNase L is an important mediator of IFN functions in the GI tract.…”

“…RNase L, an endoribonuclease that functions to regulate IFN induction and as a downstream mediator of IFN action (47,51,69,79,80), is implicated in IEC activities (45). Therefore, RNase L represented a candidate target of EPEC effectors that may account for the observed T3SS-dependent effects on cytokine induction and barrier function.…”

“…RNase L is the terminal component of this pathway that functions in IFN induction in response to microbial infections (47,69) and is a key downstream mediator of IFN-induced activities (48)(49)(50)70). Furthermore, RNase L functions in the innate immune response to bacteria in the GI tract (45) and thus may be a mechanism by which IFN-␤ mediates host defense from EPEC infection. To examine a role for RNase L in response to EPEC infection, Caco-2 cells were stably transfected with control (nonspecific sequence; shNS) or RNase L-targeted (shRNase L) shRNA.…”

“…Type I IFNs are induced as a primary response to diverse microbial infections (31,44,59). In the GI tract, IFNs play integral roles in monitoring commensal bacteria and in regulating the immune response to luminal microbes when intestinal barrier function is compromised (30,31,45). EPEC is an important enteric pathogen that disrupts IEC barrier function as a key component of its pathogenesis.…”

“…Consistent with its important roles in GI functions, dysregulation of upstream regulators and downstream effectors of IFN is associated with human GI disorders (e.g., nucleotide-binding oligomerization domain-containing protein 2 [NOD2]) (40,41) and mouse models of GI diseases (42,43). IFN mediates its biologic activities through the induction of IFN-stimulated genes (ISGs) (44); accordingly, ISGs that function in GI immune and homeostatic activities have been identified (36,37,45,46). Among the gene products, the endoribonuclease RNase L mediates the biologic activities of the IFN-regulated 2-5A pathway and functions as an upstream regulator of IFN induction (47) and a downstream effector of IFN action (48)(49)(50)(51).…”