USP22 and hepatocellular carcinoma: USP22 expression was analyzed in seven established human HCC cell lines (Bel-7402, HepG2, HuH-7, SK-Hep-1, Hep3B, QGY-7701 and SMMC-7721) and a normal hepatic cell line LO2 using RT-PCR and Western blot assay.