title: Hypoxia and retinoic acid-inducible NDRG1 expression is responsible for doxorubicin and retinoic acid resistance in hepatocellular carcinoma cells.
abstract: Hypoxia may activate survival signals in cancer cells. Moreover, hypoxic cells are less sensitive than normoxic cells to doxorubicin cytotoxicity, a potent activator of the p53 tumor suppressor gene. N-myc downstream-regulated gene-1 (NDRG1) is a hypoxia- and retinoic acid-inducible protein, and has been previously implicated in carcinogenesis. As this protein is also a downstream target of p53 and hepatocellular carcinoma (HCC) cells frequently evidence resistance to retinoic acid (RA) cytotoxicity, we attempted to determine whether the suppression of NDRG1 expression may sensitize HCC cells to doxorubicin and/or RA cytotoxicity. HCC cells expressed NDRG1 protein, and the expression of this protein was hypoxia- and RA-inducible. Doxorubicin treatment induced HCC cell cytotoxicity via the activation of mitochondrial apoptotic signals, including caspase-9 activation. Hypoxic HCC cells are less sensitive to doxorubicin-induced apoptosis. The suppression of NDRG1 expression either by siRNA or flavopiridol sensitized hypoxic HCC cells to doxorubicin cytotoxicity, and this was attributed to more profound augmentation of JNK and caspase-9 activation. The suppression of NDRG1 expression also sensitized RA-resistant HCC cells to RA-induced apoptosis, and this sensitization was more apparent in hypoxic HCC cells than in normoxic cells. Glutaredoxin2 expression was down-regulated in NDRG1-suppressed HCC cells. These results show that hypoxia- and RA-inducible NDRG1 expression is responsible for doxorubicin and RA resistance in HCC cells. Thus, the selective interruption of NDRG1 signaling may prove to be therapeutically useful in HCCs, particularly in the advanced infiltrative type of tumors exposed to hypoxic environments.
authors.affiliation: Department of Internal Medicine and Liver Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Eun Uk
authors.initials: EU
authors.lastname: Jung
authors.forename: Jung-Hwan
authors.initials: JH
authors.lastname: Yoon
authors.forename: Youn-Jae
authors.initials: YJ
authors.lastname: Lee
authors.forename: Jeong-Hoon
authors.initials: JH
authors.lastname: Lee
authors.forename: Bo Hyun
authors.initials: BH
authors.lastname: Kim
authors.forename: Su Jong
authors.initials: SJ
authors.lastname: Yu
authors.forename: Sun Jung
authors.initials: SJ
authors.lastname: Myung
authors.forename: Yoon Jun
authors.initials: YJ
authors.lastname: Kim
authors.forename: Hyo-Suk
authors.initials: HS
authors.lastname: Lee
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D018797:Cell Cycle Proteins / Q000378:metabolism*; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D046228:Microarray Analysis; D014212:Tretinoin / Q000494:pharmacology*; D000099259:N-myc Downstream-Regulated Gene 1 Protein
chemical_list: D018797:Cell Cycle Proteins; D004317:Doxorubicin; D047908:Intracellular Signaling Peptides and Proteins; D014212:Tretinoin; D000099259:N-myc Downstream-Regulated Gene 1 Protein