CDX1 and CDX2 suppress colon cancer stemness by inhibiting beta-catenin-facilitated formation of Pol II-DSIF-PAF1C complex
Homeobox transcription factors CDX1 and CDX2 (hereafter, CDX1/2) play key roles in determining the identity of intestinal epithelial cells and regulating their stem cell functions. However, the role of CDX1/2 in regulating colon cancer stemness and the underlying mechanism have been unclear. Here, we show that the complete loss of Cdx1 or concurrent loss of Cdx1/2 increased the stemness and malignancy of intestinal tumors. Consistently, CDX1/2 reduced the expression levels of cancer stemness-related genes including LGR5. CDX1/2 bound to the downstream region of the LGR5 transcription start site (TSS), where b-catenin also binds. Despite increased H3 acetylation and an open chromatin structure, CDX1/2 reduced the levels of DRB sensitivity-inducing factor (DSIF), RNA polymerase II-associated factor 1 (PAF1), and Pol II complexes around the LGR5 TSS. Through a homeodomain, CDX1/2 cooperatively inhibited the b-catenin-promoted formation of the active Pol II complex containing DSIF and PAF1 complexes by preventing interactions between b-catenin and these complexes, in an additive manner. Our findings suggest that CDX1/2 cooperatively suppress colonic tumorigenesis and cancer stemness by antagonizing b-catenin through the DSIF and PAF1 complexes. Additionally, DSIF and PAF1 complexes act as transcriptional platforms that integrate both tumor-suppressive and oncogenic signals into the expression of genes that controls colonic tumorigenesis. Overall design: ChIP-seq of flag-tagged Cdx1 or Cdx2 in DLD1-TetOff cells.