CCNDBP1 (cyclin D1 binding protein 1) is a helix-loop-helix nuclear protein that functions as a negative regulator of cell proliferation and a potential tumor suppressor 1. In cell cycle regulation, CCNDBP1 inhibits the cyclin D1/CDK4 complex, preventing RB1 phosphorylation and blocking E2F-dependent transcription 2. The protein acts as a general transcriptional repressor, interacting with histone deacetylase proteins HDAC1 and HDAC3 to suppress cyclin D1 promoter activity and other gene expression 2. CCNDBP1 expression is frequently downregulated in multiple human cancers including colorectal, breast, lung, and prostate tumors, with restoration of expression inhibiting tumor cell colony formation 1. Beyond cancer, CCNDBP1 functions as a positive regulator of skeletal myogenesis by enhancing MyoD binding to target genes, with Ccndbp1-knockout mice showing reduced muscle mass and impaired regeneration 3. In inflammatory disease, CCNDBP1 contributes to DNA damage responses and apoptosis in colitis through Atm-Chk2 pathway activation 4. Genetic variants in CCNDBP1 regulatory regions (rs66651343 and rs12909095) alter CCNDBP1 expression and confer lung cancer susceptibility 5, while CCNDBP1 also interacts with alcohol consumption to influence blood pressure 6.