A HHEX/IKKα positive feedback loop promotes intestinal inflammation

The dynamic assembly and regulation of the IκB kinase (IKK) complex in the NF-κB pathway are central to the pathogenesis and progression of inflammatory bowel disease (IBD). We recently reported that the transcription factor hematopoietically-expressed homeobox (HHEX) promotes colitis-associated colorectal cancer, but the potential role of HHEX in intestinal inflammation remains uncharacterized. Here, we found that HHEX is upregulated in inflamed colons in a colitis mouse model and in clinical IBD samples. HHEX overexpression increased inflammatory cytokine expression, and HHEX loss largely abrogated the inflammatory response in vitro and intestinal inflammation in vivo. Mechanistically, IKKα phosphorylates HHEX at S213 to stabilize HHEX in response to TNF-α by inhibiting the interaction of HHEX with the E3 ubiquitin ligase MID2 and subsequent K48-linked ubiquitination and protein degradation. Importantly, HHEX interacts with and stabilizes the IKKα/IKKβ complex via its N-terminal domain, thereby activating the NF-κB pathway and establishing a positive feedback loop that exacerbates intestinal inflammation. Our study reveals a transcription-independent function of HHEX in promoting IKK complex assembly and colitis, identifying HHEX as an IBD susceptibility gene and a potential target for IBD treatment.