title: Granulin-epithelin precursor is an oncofetal protein defining hepatic cancer stem cells.
abstract: OBJECTIVE
  Increasing evidence has suggested that hepatocellular carcinoma (HCC) might originate from a distinct subpopulation called cancer stem cells (CSCs), which are responsible for the limited efficacy of conventional therapies. We have previously demonstrated that granulin-epithelin precursor (GEP), a pluripotent growth factor, is upregulated in HCC but not in the adjacent non-tumor, and that GEP is a potential therapeutic target for HCC. Here, we characterized its expression pattern and stem cell properties in fetal and cancerous livers.
  
  
  METHODS
  Protein expression of GEP in fetal and adult livers was examined in human and mouse models by immunohistochemical staining and flow cytometry. Liver cancer cell lines, isolated based on their GEP and/or ATP-dependent binding cassette (ABC) drug transporter ABCB5 expression, were evaluated for hepatic CSC properties in terms of colony formation, chemoresistance and tumorigenicity.
  
  
  RESULTS
  We demonstrated that GEP was a hepatic oncofetal protein that expressed in the fetal livers, but not in the normal adult livers. Importantly, GEP+ fetal liver cells co-expressed the embryonic stem (ES) cell-related signaling molecules including β-catenin, Oct4, Nanog, Sox2 and DLK1, and also hepatic CSC-markers CD133, EpCAM and ABCB5. Phenotypic characterization in HCC clinical specimens and cell lines revealed that GEP+ cancer cells co-expressed these stem cell markers similarly as the GEP+ fetal liver cells. Furthermore, GEP was shown to regulate the expression of ES cell-related signaling molecules β-catenin, Oct4, Nanog, and Sox2. Isolated GEP(high) cancer cells showed enhanced colony formation ability and chemoresistance when compared with the GEP(low) counterparts. Co-expression of GEP and ABCB5 better defined the CSC populations with enhanced tumorigenic ability in immunocompromised mice.
  
  
  CONCLUSIONS
  Our findings demonstrate that GEP is a hepatic oncofetal protein regulating ES cell-related signaling molecules. Co-expression of GEP and ABCB5 further enriches a subpopulation with enhanced CSC properties. The current data provide new insight into the therapeutic strategy.
authors.affiliation: Department of Surgery, The University of Hong Kong, Hong Kong, China.
authors.forename: Phyllis Fung Yi
authors.initials: PF
authors.lastname: Cheung
authors.forename: Christine Kei Chin
authors.initials: CK
authors.lastname: Cheng
authors.forename: Nicholas Chun Lim
authors.initials: NC
authors.lastname: Wong
authors.forename: Jenny Chung Yee
authors.initials: JC
authors.lastname: Ho
authors.forename: Chi Wai
authors.initials: CW
authors.lastname: Yip
authors.forename: Vincent Chi Hang
authors.initials: VC
authors.lastname: Lui
authors.forename: Annie Nga Yin
authors.initials: AN
authors.lastname: Cheung
authors.forename: Sheung Tat
authors.initials: ST
authors.lastname: Fan
authors.forename: Siu Tim
authors.initials: ST
authors.lastname: Cheung
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002469:Cell Separation; D002471:Cell Transformation, Neoplastic; D019008:Drug Resistance, Neoplasm; D000077155:Granulins; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology*; D051379:Mice; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000473:pathology*; D010641:Phenotype; D000077153:Progranulins; D014410:Tumor Stem Cell Assay
chemical_list: C480744:ABCB5 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; C492314:GRN protein, human; D000077155:Granulins; C120204:Grn protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D000077153:Progranulins; C031192:oncofetal antigens