SIX4 Activation in Inflammatory Response Drives the Transformation of Colorectal Epithelium into Inflammation and Tumor via Feedback-Enhancing Inflammatory Signaling to Induce Tumor Stemness Signaling.

Abstract

Some colorectal cancer patients have experienced normal epithelial transformation into inflammatory and tumor states, but the molecular basis still needs to be further determined. The expression levels of SIX4 are gradually increased in dextran sodium sulfate (DSS) and azoxymethane (AOM)/DSS-induced colonic epithelial inflammation and tumors, respectively, in mice. Targeting SIX4 alleviates intestinal inflammation occurrence and reduces adenoma formation in mice. Clinical sample assays indicated that SIX4 is upregulated in inflammatory bowel disease (IBD) and colorectal cancer (CRC) tissues compared to normal colorectal tissues. In a subsequent study, we found that SIX4, transcriptionally activated by the proinflammatory IL-6/STAT3 signal, binds to c-Jun to transcribe IL-6, thus forming a positive IL-6/STAT3/SIX4/c-Jun feedback loop, which further induces intestinal inflammation occurrence. In addition, elevated SIX4 also induces the expression of DeltaNp63, rather than wild-type p63, by binding to its promoter and thus facilitates the activation of tumor stemness signals, which ultimately leads to the formation of colorectal cancer. Our study first observes that activated SIX4 in inflammation induction drives the transformation of colorectal epithelium into inflammation and tumor, which demonstrates SIX4 as a significant therapeutic target in IBD and colitis-associated colorectal cancer (CAC) and CRC pathogenesis.