title: Quantitative proteomic signature of liver cancer cells: tissue transglutaminase 2 could be a novel protein candidate of human hepatocellular carcinoma.
abstract: Hepatocellular carcinoma (HCC) is one of the most common diseases worldwide, with extremely poor prognosis due to failure in diagnosing it early. Alpha-fetoprotein (AFP) is the only available biomarker for HCC diagnosis; however, its use in the early detection of HCC is limited, especially because about one-third of patients afflicted with HCC have normal levels of serum AFP. Thus, identifying additional biomarkers that may be used in combination with AFP to improve early detection of HCC is greatly needed. A quantitative proteomic analysis approach using stable isotope labeling with amino acids in cell culture (SILAC) combined with LTQ-FT-MS/MS identification was used to explore differentially expressed protein profiles between normal (HL-7702) and cancer (HepG2 and SK-HEP-1) cells. A total of 116 proteins were recognized as potential markers that could distinguish between HCC and normal liver cells. Certain proteins, such as AFP, intercellular adhesion molecule-1 (ICAM-1), IQ motif containing GTPase activating protein 2 (IQGAP2), claudin-1 (CLDN1) and tissue transglutaminase 2 (TGM2), were validated both in multiple cell lines and in 61 specimens of clinical HCC cases. TGM2 was overexpressed in some of the AFP-deficient HCC cells (SK-HEP-1 and Bel-7402) and in about half of the tumor tissues with low levels of serum AFP (17/32, AFP-negative HCC). Trace amounts of TGM2 were found to be expressed in the samples with high serum AFP (26/29, AFP-positive HCC). Moreover, TGM2 expression in liver tissues showed an inverse correlation with the level of serum AFP in HCC patients. Notably, TGM2 existed in the supernatant of the AFP-deficient SK-HEP-1, SMMC-7721 and HLE cells, and it was found to be induced in AFP-producing cells (HepG2) by specific siRNA silence assay. Serum TGM2 levels of 109 HCC patients and 42 healthy controls were further measured by an established ELISA assay; the levels were significantly higher in HCC patients, and they correlated with the histological grade and tumor size. These data suggest that TGM2 may serve as a novel histological/serologic candidate involved in HCC, especially for the individuals with normal serum AFP. These novel findings may provide important clues to identify new biomarkers of HCC and indirectly improve early detection of the disease.
authors.affiliation: State Key Laboratory of Molecular Oncology, Department of Abdominal Surgery, Cancer Institute & Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, 100021 P. R. China.
authors.forename: Yulin
authors.initials: Y
authors.lastname: Sun
authors.forename: Wei
authors.initials: W
authors.lastname: Mi
authors.forename: Jianqiang
authors.initials: J
authors.lastname: Cai
authors.forename: Wantao
authors.initials: W
authors.lastname: Ying
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
authors.forename: Haizhen
authors.initials: H
authors.lastname: Lu
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Qiao
authors.forename: Wei
authors.initials: W
authors.lastname: Jia
authors.forename: Xinyu
authors.initials: X
authors.lastname: Bi
authors.forename: Ning
authors.initials: N
authors.lastname: Lu
authors.forename: Shangmei
authors.initials: S
authors.lastname: Liu
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Qian
authors.forename: Xiaohang
authors.initials: X
authors.lastname: Zhao
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D020869:Gene Expression Profiling; D006801:Humans; D007150:Immunohistochemistry; D008113:Liver Neoplasms / Q000378:metabolism*; D008969:Molecular Sequence Data; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D040901:Proteomics; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D034741:RNA, Small Interfering; C000717608:TGM2 protein, human; D000091345:Protein Glutamine gamma Glutamyltransferase 2