CCND1 and cancer: CtBP knockdown resulted in the significant retardation of cell proliferation indicated by BrdU incorporation assay in both cells (Figures 1a and b), and led to decreased Cyclin D1 and upregulated p21waf1/cip1 (Supplementary Figure 1), which indicate the decreased cell proliferation.20, 21 These data suggest that CtBP is essential to promote cancer cell growth.