KLF4 and hepatocellular carcinoma: The final results from CCK-8 assays and colony formation assays indicated that knockdown of CD9 or CD81 notably attenuated the inhibitory effects induced by KLF4 overexpression (Fig. 4e and f), hinting that CD9 and CD81 may functionally act as downstream effectors of KLF4 during HCC cell proliferation.