CDK4 and hepatocellular carcinoma: In addition, overexpression of β2 spectrin markedly suppressed the expression of the proteins responsible for cell cycle checkpoint such as CDK4, cyclin D1, cyclin A2, cyclin B1, and pRb, at the same time, stabilized p53 (Fig. 3d) As show in Fig. 3e, cell proliferation assay showed that proliferative capacity of HCC cells decreased significantly upon the treatment of β2SP.