Cyclin-D1-binding protein 1 is a protein that in humans is encoded by the CCNDBP1 gene.

This gene was identified by the interaction of its gene product with Grap2, a leukocyte-specific adaptor protein important for immune cell signaling. The protein encoded by this gene was shown to interact with cyclin D. Transfection of this gene in cells was reported to reduce the phosphorylation of Rb gene product by cyclin D-dependent protein kinase, and inhibit E2F1-mediated transcription activity. This protein was also found to interact with helix-loop-helix protein E12 and is thought to be a negative regulator of liver-specific gene expression. Several alternatively spliced variants have been found for this gene. [provided by RefSeq, Apr 2009].
Function: May negatively regulate cell cycle progression. May act at least in part via inhibition of the cyclin-D1/CDK4 complex, thereby preventing phosphorylation of RB1 and blocking E2F-dependent transcription.