Western blotting results showed no change of CDK4 protein expression between prostate cancer tissues and their adjacent non-tumorous tissues or between PC3-let-7a-GFP cells and PC3-GFP cells, the expression levels of E2F2, CCND2 increased in prostate cancer tissues compared with their adjacent non-tumorous tissues, but the expression levels of E2F2, CCND2, and k-ras decreased dramatically in PC3-let-7a-GFP cells compared with that in PC3-GFP cells (Fig. 4E). This evidence concerns the gene CDK4 and prostate cancer.