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Aberrant epithelial differentiation and regeneration pathways contribute to colon pathologies including inflammatory bowel disease (IBD) and colitis-associated cancer (CAC). MTG16 (also known as CBFA2T3) is a transcriptional corepressor expressed in the colonic epithelium. MTG16 interaction partners include E box-binding basic helix-loop-helix transcription factors (E proteins). MTG16-deficient mice exhibit worse colitis and increased tumor burden in inflammatory carcinogenesis. In this study, we sought to understand the role of MTG16 colonic epithelial homeostasis and the mechanisms by which MTG16 protects the epithelium in colitis and CAC. We demonstrated that MTG16 deficiency enabled enteroendocrine cell differentiation from secretory precursor cells at the expense of goblet cells. Transcriptomic analysis implicated dysregulated E protein function in MTG16-deficient colon crypts. Using a novel mouse model with a point mutation that disrupts MTG16:E protein complex formation (Mtg16P209T), we established that enteroendocrine:goblet cell balance was dependent on MTG16:E protein interactions and that the shift in lineage allocation was associated with enhanced expression of Neurog3, the central driver of enteroendocrine lineage specification. Furthermore, Mtg16 was upregulated in the previously described Ascl2+, de-differentiating cells that replenish the stem cell compartment in response to colon injury. Mtg16 expression was also increased in dextran sulfate sodium (DSS)-treated mouse colon crypts and in IBD patients compared to unaffected controls. We determined that the effects of MTG16 in regeneration are also dependent on its repression of E proteins, as the colonic epithelium failed to regenerate following DSS-induced injury in our novel mutant mouse model. Finally, we revealed that uncoupling MTG16:E protein interactions contributes to the enhanced tumorigenicity in Mtg16-/- colon in the azoxymethane(AOM)/DSS-induced model of CAC. Collectively, our results demonstrate that MTG16, via its repression of E protein targets, is a key regulator of cell fate decisions during colonic differentiation and regeneration.

CELF2 belongs to the family of RNA binding proteins implicated in mRNA splicing, editing, stability and translation. This gene is encoded in a single large gene spanning over 159 kilo bases located on chromosome 10 p13-p14 (between D10S547 and D10S223). This gene has 14 transcripts (splice variants) and the 3 major splice variants have distinct exon 1. This is an evolutionarily conserved ubiquitously expressed protein. The members of the CELF protein family contain two N-terminal RNA recognition motif (RRM) domains and one Cterminal RRM domain, and a divergent segment of 160-230 amino acids between second and third RRM domains. This divergent domain is unique to CELF2 proteins and has been shown to contain one or more activation molecules required for splicing activity. CELF2 has been shown to bind to the CUG and Au-rich element (ARE) in the target mRNA and shown to be implicated in muscular dystrophy and cancer.

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