cAMP Response Element-binding Protein Interacts with the Homeodomain Protein Cdx2 and Enhances Transcriptional Activity

Cdx2 encodes for a homeodomain protein that is expressed in intestinal epithelial cells. The Cdx2 protein triggers intestinal differentiation in cell lines and is necessary for maintenance of the intestinal phenotype in mice. CBP (cAMP response element-bindingprotein) is a transcriptional co-activator that interacts with many transcription factors and components of the basal transcriptional machinery. In this study, we demonstrate that CBP is markedly induced upon differentiation of the Caco-2 intestinal cell line and augments Cdx2-dependent transcriptional activity. Cdx2 interacts with the amino-terminal domain of CBP, and the two proteins coexist in vivo within the same nuclear protein complex. Moreover, expression of the CBP domain that interacts with Cdx2 acts as a dominant-negative inhibitor of transcriptional activation by Cdx2. These findings demonstrate a direct interaction between an intestinal homeodomain protein and CBP and suggest that CBP participates in the network of transcriptional proteins that direct intestinal differentiation.