NOTCH dimerization contributes to maintenance of intestinal homeostasis

A tri-protein complex containing NICD, RBPj and MAMl1 binds DNA as monomer or, cooperatively, as dimers to regulate transcription. Mice expressing Notch dimerization-deficient (DD) alleles Notch1DD and Notch2DD (NDD) are sensitized to environmental insults but otherwise develop and age normally. Transcriptomic analysis of colonic spheroids uncovered no evidence of dimer-dependent target gene miss-regulation, confirmed impaired stem cell maintenance in-vitro, and discovered an elevated signature of epithelial innate immune response to symbionts, the likely underlying cause for heightened sensitivity in NDD mice. TurboID followed by quantitative nano-spray MS/MS mass-spectrometry analyses in a human colon carcinoma cell line expressing either Notch2DD or Notch2 revealed an unbalanced interactome, with reduced interaction of Notch2DD with the transcription machinery but relatively preserved interaction with the HDAC2 interactome suggesting it is dimer independent. To ask if elevated HDAC2 activity contributes to Notch loss of function phenotypes, we used the HDAC2 inhibitor Valproic acid (VPA) and discovered it could block the intestinal consequences of gamma secretase inhibitor (DBZ or DAPT) treatment in mice and spheroids, suggesting synergy between HDAC activity and pro-differentiation program in intestinal stem cells which may be exploitable therapeutically.