title: Silencing thioredoxin induces liver cancer cell senescence under hypoxia.
abstract: OBJECTIVE
  Although thioredoxin 1 (TXN) has pleiotropic cellular functions as a redox-sensitive protein, very little is known about its role in tumor survival and growth under hypoxia. MHCC97H hepatocellular carcinoma cells have a high metastatic potential and high thioredoxin expression levels compared with their parent cell line, MHCC97. Thus, we used this cell line to explore the functional connections between TXN and hypoxia.
  
  
  METHODS
  MHCC97H cells were cultured under normoxia and hypoxia for specific periods after nucleofection with TXN siRNA or control siRNA. We assessed the β-phenylethyl isothiocyanate (PEITC) sensitivity of the cells, cell proliferation, cell cycle and senescence, and DNA damage response by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, colony formation assays, flow cytometry, β-galactosidase staining, western blotting, and immunohistochemistry.
  
  
  RESULTS
  β-phenylethyl isothiocyanate treatment shifted reduced TXN to oxidized TXN in MHCC97H cells. Although silencing of TXN via siRNA had no effect on the PEITC sensitivity of the cells, it suppressed cell proliferation and colony formation under both normoxia and hypoxia. Under hypoxia, silencing TXN did not induce apoptosis but induced DNA damage response and cellular senescence.
  
  
  CONCLUSIONS
  High TXN levels in MHCC97H cells protect them from DNA damage and cellular senescence under hypoxia. Targeting TXN might enhance the chemotherapeutic effects of some DNA-damaging agents against hepatocellular carcinoma.
authors.affiliation: Department of Hepatobiliary Surgery, Tianjin Cancer Hospital, Tianjin Medical University, Tianjin, China             Department of Surgical Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Ti
authors.initials: T
authors.lastname: Zhang
authors.forename: Heping
authors.initials: H
authors.lastname: Liu
authors.forename: Cihui
authors.initials: C
authors.lastname: Zhu
authors.forename: Katrina
authors.initials: K
authors.lastname: Briggs
authors.forename: Ya'an
authors.initials: Y
authors.lastname: Kang
authors.forename: Jason A
authors.initials: JA
authors.lastname: Fleming
authors.forename: Steven A
authors.initials: SA
authors.lastname: Curley