title: A novel interaction of nucleophosmin with BCL2-associated X protein regulating death evasion and drug sensitivity in human hepatoma cells.
abstract: Death evasion is crucial for both carcinogenesis and resistance to anticancer therapies. Recently, we identified nucleophosmin (NPM) as a key factor counteracting death stimuli in human hepatocellular carcinoma (HCC) cells. Here we report the identification of a novel NPM-BCL2-associated X protein (BAX) pathway orchestrating death evasion in human HCC cells. Silencing of NPM expression significantly sensitized HCC cells-particularly those bearing inactivated p53 gene (Huh7, Hep3B, and Mahlavu)-to ultraviolet irradiation, mitomycin C, doxorubicin, cisplatin, sorafenib, and lapatinib. This sensitizing effect was not changed further, as p53 expression had been simultaneously silenced. Following cell stress, NPM and BAX were induced and exported out of the nucleoli and nucleus, respectively. BAX was translocated to cytoplasm in cells with relatively high NPM level, or accumulated in the mitochondria in cells with relatively low NPM level and undergoing apoptosis. Subcellular fractionation revealed that silencing of NPM expression greatly enhanced mitochondrial translocation and oligomerization of BAX in Huh7 and Mahlavu cells. In situ proximity ligation assays and reciprocal co-immunoprecipitation revealed a direct interaction between NPM and BAX in the cytoplasm. Silencing of BAX expression abolished the sensitization effect exerted by silencing of NPM in HCC cells. Clinically, up-regulation of NPM was significantly associated with advanced tumor stage and poor prognosis.
  
  
  CONCLUSIONS
  By directly blockading BAX mitochondrial translocation and activation, NPM helps human HCC cells evade death induction independently of p53-mediated cell death. Silencing of NPM significantly sensitized HCC cells to anticancer therapies. NPM is a potential cotarget in combination with other therapies for HCC, particularly those that harbor inactivated p53 gene. Our findings are of clinical significance because NPM up-regulation and p53 mutations are usually found in advanced human cancers, including HCC.
authors.affiliation: Liver Research Unit, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
authors.forename: Shao-Jung
authors.initials: SJ
authors.lastname: Lo
authors.forename: Li-Ching
authors.initials: LC
authors.lastname: Fan
authors.forename: Yow-Fu
authors.initials: YF
authors.lastname: Tsai
authors.forename: Kuo-Yang
authors.initials: KY
authors.lastname: Lin
authors.forename: Hsiao-Ling
authors.initials: HL
authors.lastname: Huang
authors.forename: Tong-Hong
authors.initials: TH
authors.lastname: Wang
authors.forename: Hsuan
authors.initials: H
authors.lastname: Liu
authors.forename: Tse-Chin
authors.initials: TC
authors.lastname: Chen
authors.forename: Shiu-Fen
authors.initials: SF
authors.lastname: Huang
authors.forename: Chee-Jen
authors.initials: CJ
authors.lastname: Chang
authors.forename: Yu-Jr
authors.initials: YJ
authors.lastname: Lin
authors.forename: Benjamin Yat-Ming
authors.initials: BY
authors.lastname: Yung
authors.forename: Sen-Yung
authors.initials: SY
authors.lastname: Hsieh
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use*; D017209:Apoptosis / Q000502:physiology*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008875:Middle Aged; D008930:Mitochondria, Liver / Q000502:physiology; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism*; D000090243:Nucleophosmin; D016896:Treatment Outcome; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000502:physiology; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; C000716967:NPM1 protein, human; D009687:Nuclear Proteins; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D000090243:Nucleophosmin