No abstract

Increasing evidence suggests that the aryl hydrocarbon receptor (AhR) pathway has an important role in the regulation of inflammatory responses. Most recently, we have shown that the activation of the AhR pathway by a potent AhR agonist inhibits the development of dextran sodium sulfate (DSS)-induced colitis, a model of human ulcerative colitis, by the induction of prostaglandin E2 (PGE2) in the large intestine. Because several strains of probiotic lactic acid bacteria have been reported to inhibit DSS-induced colitis by unidentified mechanisms, we hypothesized that particular strains of lactic acid bacterium might have the potential to activate the AhR pathway, thereby inhibiting DSS-induced colitis. This study investigated whether there are specific lactic acid bacterial strains that can activate the AhR pathway, and if so, whether this AhR-activating potential is associated with suppression of DSS-induced colitis. By using AhR signaling reporter cells, we found that Lactobacillus bulgaricus OLL1181 had the potential to activate the AhR pathway. OLL1181 also induced the mRNA expression of cytochrome P450 family 1A1 (CYP1A1), a target gene of the AhR pathway, in human colon cells, which was inhibited by the addition of an AhR antagonist, α-naphthoflavon (αNF). In addition, mice treated orally with OLL1181 showed an increase in CYP1A1 mRNA expression in the large intestine and amelioration of DSS-induced colitis. Thus, OLL1181 can induce activation of the intestinal AhR pathway and inhibit DSS-induced colitis in mice. This strain of lactic acid bacterium has therefore the potential to activate the AhR pathway, which may be able to suppress colitis.

The aryl hydrocarbon receptor (AhR) recognizes numerous small xenobiotic and natural molecules, such as dioxin and natural chemicals, and is involved in the metabolism of these compounds. AhR also has a regulatory role in inflammatory responses. This study investigated whether the activation of the AhR pathway affects dextran sodium sulfate (DSS)-induced colitis, an ulcerative colitis-like model, in mice. DSS-induced colitis was ameliorated by pretreatment with a potent AhR activator, 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD), in mice. In addition, the mice pretreated with TCDD showed increased prostaglandin E2 (PGE2) production in the colon, and inhibition of PGE2 production by indomethacin abrogated the inhibitory effects of TCDD on DSS-induced colitis. Collectively, the activation of the AhR pathway by TCDD may ameliorate DSS-induced colitis, at least in part, through PGE2 production.

Subtilase cytotoxin (SubAB) is the prototype of a newly identified family of AB5 cytotoxins produced by Shiga toxigenic Escherichia coli. SubAB specifically cleaves the essential endoplasmic reticulum (ER) chaperone BiP (GRP78), resulting in the activation of ER stress-induced unfolded protein response (UPR). We have recently shown that the UPR following ER stress can suppress cellular responses to inflammatory stimuli during the later phase, in association with inhibition of NF-κB activation. These findings prompted us to hypothesize that SubAB, as a selective UPR inducer, might have beneficial effects on inflammation-associated pathology via a UPR-dependent inhibition of NF-κB activation. The pretreatment of a mouse macrophage cell line, RAW264.7, with a subcytotoxic dose of SubAB-triggered UPR and inhibited LPS-induced MCP-1 and TNF-α production associated with inhibition of NF-κB activation. SubAA272B, a SubAB active site mutant that cannot induce UPR, did not show such effects. In addition, pretreatment with a sublethal dose of SubAB, but not SubAA272B, protected the mice from LPS-induced endotoxic lethality associated with reduced serum MCP-1 and TNF-α levels and also prevented the development of experimental arthritis induced by LPS in mice. Collectively, although SubAB has been identified originally as a toxin associated with the pathogenesis of hemolytic uremic syndrome, the unique ability of SubAB to selectively induce the UPR may have the potential to prevent LPS-associated inflammatory pathology under subcytotoxic conditions.

In many cancers, somatic mutations confer tumorigenesis and drug-resistance. The recently established clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system is a potentially elegant approach to functionally evaluate mutations in cancers. To reproduce mutations by homologous recombination (HR), the HR pathway must be functional, but DNA damage repair is frequently impaired in cancers. Imatinib is a tyrosine kinase inhibitor for BCR-ABL1 in Philadelphia chromosome-positive (Ph+) leukemia, and development of resistance due to kinase domain mutation is an important issue. We attempted to introduce the T315I gatekeeper mutation into three Ph+ myeloid leukemia cell lines with a seemingly functional HR pathway due to resistance to the inhibitor for poly (ADP) ribose polymerase1. Imatinib-resistant sublines were efficiently developed by the CRISPR/Cas9 system after short-term selection with imatinib; resulting sublines acquired the T315I mutation after HR. Thus, the usefulness of CRISPR/Cas9 system for functional analysis of somatic mutations in cancers was demonstrated.