CLDN1 expression was increased in both high-grade dysplasia and ulcerative colitis-associated CRC tissue (n=6) when compared with ulcerative colitis and normal tissue (n=39)The upregulation of claudin-1 in transgenic mice induces MMP-9 and p-ERK signalling to activate Notch-signalling pathway. Here, MMP9 is linked to colorectal carcinoma.