CDK4 and neoplasm: KLF6 regulates tumor cell proliferation and apoptosis through the following mechanisms: directly binding to and activating the p21CIP1/WAF1 gene promoter in a p53-independent manner [18], interfering between cyclin D1 and CDK4 [35] interaction, upregulating ATF3, caspase-3, and TGF-β expression [34], and inhibiting c-jun and E-cadherin gene expression [36, 37].