Transforming Growth Factor Beta Promotes Inflammation and Tumorigenesis in Smad4‐Deficient Intestinal Epithelium in a YAP‐Dependent Manner

Transforming growth factor beta (TGF‐β), a multifunctional cytokine, plays critical roles in immune responses. However, the precise role of TGF‐β in colitis and colitis‐associated cancer remains poorly defined. Here, it is demonstrated that TGF‐β promotes the colonic inflammation and related tumorigenesis in the absence of Smad family member 4 (Smad4). Smad4 loss in intestinal epithelium aggravates colitis and colitis‐associated neoplasia induced by dextran sulfate sodium (DSS) and azoxymethane/dextran sulfate sodium (AOM/DSS), leading to over‐activated immune responses and increased TGF‐β1 levels. In Smad4‐deficient organoids, TGF‐β1 stimulates spheroid formation and impairs intestinal stem cell proliferation and lineage specification. YAP, whose expression is directly upregulated by TGF‐β1 after Smad4 deletion, mediates the effect of TGF‐β1 by interacting with Smad2/3. Attenuation of YAP/TAZ prevents TGF‐β1‐induced spheroid formation in Smad4 ( − / – ) organoids and alleviates colitis and colitis‐associated cancer in Smad4‐deficient mice. Collectively, these results highlight an integral role of the TGF‐β/Smad4 axis in restraining intestinal inflammation and tumorigenesis and suggest TGF‐β or YAP signaling as therapeutic targets for these gastrointestinal diseases intervention.