title: p28(GANK) prevents degradation of Oct4 and promotes expansion of tumor-initiating cells in hepatocarcinogenesis.
abstract: OBJECTIVE
  Hepatocellular carcinoma (HCC) is believed to arise from tumor-initiating cells (T-ICs), although little is known about their stem cell-like properties.
  
  
  METHODS
  We quantified levels of p28(GANK) (Gankyrin), OV6, and Oct4 in 130 human HCC samples using immunohistochemistry. Magnetic-activated cell sorting was used to isolate OV6+ HCC cells. T-IC properties were evaluated by quantitative reverse-transcription polymerase chain reaction, flow cytometry, and spheroid formation. We used a coimmunoprecipitation assay to study interactions among p28(GANK), Oct4, and WWP2. Tumorigenicity and pulmonary metastasis were examined in nonobese diabetic and severe combined immunodeficient mice.
  
  
  RESULTS
  In HCC samples, high levels of p28(GANK) correlated with expansion of OV6+ tumor cells; the combination of high levels of p28(GANK) and OV6 was associated with progression of HCC. p28(GANK) was predominantly expressed in liver T-ICs, isolated by magnetic sorting, and undifferentiated primary HCC spheroids. Increased levels of p28(GANK) in T-ICs increased their percentages in HCC samples, expression of stem cell genes, self-renewal potential, chemoresistance in vitro, and tumorigenicity and ability to develop into pulmonary metastases in mice. Conversely, knockdown of p28(GANK) reduced their T-IC properties. p28(GANK) likely activates liver T-ICs by impeding ubiquitination and degradation of the transcription factor Oct4 by WWP2. In support of this concept, levels of p28(GANK) correlated with those of Oct4 in HCC samples.
  
  
  CONCLUSIONS
  p28(GANK) activates and maintains liver T-ICs in HCCs by preventing degradation of Oct4. Inhibitors of p28(GANK) might therefore be developed to inactivate T-ICs and slow tumor progression.
authors.affiliation: International Cooperation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute/Hospital, Shanghai, China.
authors.forename: You-Wen
authors.initials: YW
authors.lastname: Qian
authors.forename: Yao
authors.initials: Y
authors.lastname: Chen
authors.forename: Wen
authors.initials: W
authors.lastname: Yang
authors.forename: Jing
authors.initials: J
authors.lastname: Fu
authors.forename: Jie
authors.initials: J
authors.lastname: Cao
authors.forename: Yi-Bin
authors.initials: YB
authors.lastname: Ren
authors.forename: Jun-Jie
authors.initials: JJ
authors.lastname: Zhu
authors.forename: Bo
authors.initials: B
authors.lastname: Su
authors.forename: Tao
authors.initials: T
authors.lastname: Luo
authors.forename: Xiao-Fang
authors.initials: XF
authors.lastname: Zhao
authors.forename: Rong-Yang
authors.initials: RY
authors.lastname: Dai
authors.forename: Juan-Juan
authors.initials: JJ
authors.lastname: Li
authors.forename: Wen
authors.initials: W
authors.lastname: Sun
authors.forename: Meng-Chao
authors.initials: MC
authors.lastname: Wu
authors.forename: Gen-Sheng
authors.initials: GS
authors.lastname: Feng
authors.forename: Hong-Yang
authors.initials: HY
authors.lastname: Wang
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D045744:Cell Line, Tumor; D018450:Disease Progression; D019008:Drug Resistance, Neoplasm; D055785:Gene Knockdown Techniques; D020868:Gene Silencing; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism / Q000503:physiopathology* / Q000556:secondary; D008175:Lung Neoplasms / Q000556:secondary; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D014411:Neoplastic Stem Cells / Q000378:metabolism / Q000502:physiology*; D050814:Octamer Transcription Factor-3 / Q000378:metabolism*; D011379:Prognosis; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D000943:Antigens, Differentiation; D050814:Octamer Transcription Factor-3; C403591:PSMD10 protein, human; C494174:Pou5f1 protein, mouse; D011518:Proto-Oncogene Proteins; C115011:oval cell marker OV-6; C487995:Wwp2 protein, mouse; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex