cAMP response element-binding protein (CREB)-binding protein (CBP) is a multifunctional transcriptional co-activator that plays important roles in cell proliferation and differentiation. CBP is expressed in murine embryonic orofacial tissue and is developmentally regulated. To identify nuclear factors associating with CBP in developing orofacial tissue, a yeast two-hybrid screen of a cDNA library derived from embryonic orofacial tissue from gestational days 11-13 mouse embryos was conducted. The carboxy terminal region of CBP (including the C/H3 region) was utilized as a bait. C53, a 57 kDa protein known to bind to the p25 activator of cyclin-dependent kinase 5, was identified as a novel binding partner of CBP. The association of C53 with CBP was confirmed in vitro by glutathione S-transferase pull-down assays, and in vivo by co-immunoprecipitation. Reporter assays demonstrated that C53 had little effect on CBP mediated transcriptional activation. These results identify C53 as a novel binding partner for CBP. Recent research on presenilin-loss induced neurodegeneration demonstrated decreased expression of CBP and increased levels of the Cdk5 activator p25, both C53 binding proteins, suggesting that C53 might play a role in regulating neuronal proliferation, migration and/or differentiation in embryonic development.

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