Evidence of functional cross talk between the Notch and NF-κB pathways in nonneoplastic hyperproliferating colonic epithelium.

Abstract

The Notch and NF-κB signaling pathways regulate stem cell function and inflammation in the gut, respectively. We investigate whether a functional cross talk exists between the two pathways during transmissible murine colonic hyperplasia (TMCH) caused by Citrobacter rodentium (CR). During TMCH, NF-κB activity and subunit phosphorylation in colonic crypts of NIH Swiss mice at days 6 and 12 were associated with increases in downstream target CXC chemokine ligand (CXCL)-1/keratinocyte-derived chemokine (KC) expression. Blocking Notch signaling acutely for 5 days with the Notch blocker dibenzazepine (DBZ) failed to inhibit crypt NF-κB activity or CXCL-1/KC expression. Chronic DBZ administration for 10 days, however, blocked Notch and NF-κB signaling in the crypts and abrogated hyperplasia. Intriguingly, chronic Notch inhibition was associated with significant increases in IL-1α, granulocyte colony-stimulating factor, monocyte chemoattractant protein 1, macrophage inflammatory protein 2, and KC in the crypt-denuded lamina propria or whole distal colon, with concomitant increases in myeloperoxidase activity. In core-3(-/-) mice, which are defective in intestinal mucin, DBZ administration replicated the results of NIH Swiss mice; in Apc(Min/+) mice, which are associated with CR-induced elevation of NF-κB-p65(276) expression, DBZ reversed the increase in NF-κB-p65(276), which may have blocked rapid proliferation of the mutated crypts. DBZ further blocked reporter activities involving the NF-κB-luciferase reporter plasmid or the Toll-like receptor 4/NF-κB/SEAPorter HEK-293 reporter cell line, while ectopic expression of Notch-N(ICD) reversed the inhibitory effect. Dietary bael (Aegle marmelos) extract (4%) and curcumin (4%) restored Notch and NF-κB cross talk in NIH Swiss mice, inhibited CR/DBZ-induced apoptosis in the crypts, and promoted crypt regeneration. Thus functional cross talk between the Notch and NF-κB pathways during TMCH regulates hyperplasia and/or inflammation in response to CR infection.