Notch1 regulates the effects of matrix metalloproteinase-9 on colitis-associated cancer in mice

Background & Aims: Inflammatory bowel disease increases the risks of colon cancer and colitis-associated cancer (CAC). Epithelial cellderived matrix metalloproteinase (MMP)-9 mediates inflammation during acute colitis and the cleavage and activation of the transcription factor Notch1, which prevents differentiation of progenitor cells into goblet cells. However, MMP-9 also protects against the development of CAC and acts as a tumor suppressor. We investigated the mechanisms by which MMP-9 protects against CAC in mice. Methods: C57/B6 wild-type mice were given a single dose of azoxymethane and 2 cycles of dextran sulfate sodium (DSS). Mice were also given the γ-secretase inhibitor difluorophenacetyl-l-alanyl-S-phenylglycine t-butyl ester (DAPT) or dimethyl sulfoxide (control) during each DSS cycle; they were killed on day 56. We analyzed embryonic fibroblasts isolated from wild-type and MMP-9^-/- mice and HCT116 cells that were stably transfected with MMP-9. Results: Wild-type mice were more susceptible to CAC following inhibition of Notch1 by DAPT, shown by increased numbers of tumors and level of dysplasia compared with controls. Inhibition of Notch1 signaling significantly reduced protein levels of active Notch1, p53, p21^WAF1/Cip1, Bax-1, active caspase-3, as well as apoptosis, compared with controls. Similar results were observed in transgenic HCT116 cells and embryonic fibroblasts from MMP-9 ^-/- mice on γ-radiationinduced damage of DNA. Conclusions: MMP-9 mediates Notch1 signaling via p53 to regulate apoptosis, cell cycle arrest, and inflammation. By these mechanisms, it might prevent CAC.