Claudins, and particularly claudin-2, are important regulatory components of tight junction permeability. A better understanding of the involvement of claudin-2 in intestinal barrier functions requires the characterization of its distribution and regulation in the intestine. Interestingly, the claudin-2 gene promoter harbors a number of similarities to that of sucrase-isomaltase, a marker of enterocyte differentiation. We thus investigated the expression of claudin-2 in relation to the transcription factors CDX2, HNF-1alpha, and GATA-4 in the human intestine. The characterization of claudin-2 and the expression of the above transcription factors were performed by immunofluorescence, Western blot, and RT-PCR in the developing human intestinal epithelium. The functional role of CDX2, HNF-1alpha, and GATA-4 on claudin-2 regulation was also examined by ectopic expression studies in intestinal cell models. Claudin-2 was detected in both crypt and villus cells of the small intestine but restricted to undifferentiated crypt cells in the colon. CDX2 and HNF-1alpha were expressed along the entire intestine whereas GATA-4 was undetectable in the colon. Accordingly, in the colonic Caco-2 cell model, claudin-2 was found to be present only in undifferentiated cells. Like in the colonic epithelium, GATA-4 was found to be also lacking in Caco-2 cells while CDX2 and HNF-1alpha were present at significant levels. Cotransfection experiments showed that the claudin-2 promoter was activated by CDX2, HNF-1alpha, and GATA-4 in a cooperative manner. Furthermore, forced GATA-4 expression in Caco-2 cells enhances maintenance of claudin-2 expression during differentiation. These observations suggest that optimal claudin-2 expression in the gut relies on the presence of GATA-4, suggesting a role for this factor in intestinal regionalization.

The Tip60 histone acetyltransferase belongs to a multimolecular complex that contains many chromatin remodeling enzymes including the ATPase p400, a protein involved in nucleosomal incorporation of specific histone variants and that can directly or indirectly repress some Tip60-dependent pathways. Tip60 activity is critical for the cellular response to DNA damage and is affected during cancer progression. Here, we found that the ratio between Tip60 and p400 mRNAs is affected in most colorectal carcinoma. Strikingly, reversing the p400/ Tip60 imbalance by Tip60 overexpression or the use of siRNAs resulted in increased apoptosis and decreased proliferation of colon-cancer-derived cells, suggesting that this ratio defect is important for cancer progression. Furthermore, we demonstrate that the p400/Tip60 ratio controls the oncogene-induced DNA damage response, a known anticancer barrier. Finally, we found that it is also critical for the response to 5-fluorouracil, a first-line treatment against colon cancer. Together, our data indicate that the p400/Tip60 ratio is critical for colon cancer cells proliferation and response to therapeutic drugs through the control of stress-response pathways.