title: Tribbles homolog 3 denotes a poor prognosis in breast cancer and is involved in hypoxia response.
abstract: BACKGROUND
  Hypoxia in solid tumors is associated with treatment resistance, resulting in poor prognosis. Tribbles homolog 3 (TRIB3) is induced during hypoxia and is involved in multiple cellular pathways involved in cell survival. Here, we investigated the role of TRIB3 in breast cancer.
  
  
  METHODS
  TRIB3 mRNA expression was measured in breast tumor tissue from 247 patients and correlated with clinicopathological parameters and clinical outcome. Furthermore, we studied TRIB3 expression regulation in cell lines, xenografts tissues and human breast cancer material using Reverse transcriptase, quantitative polymerase chain reaction (RT-qPCR) and immunohistochemical staining. Finally, the effect of small interfering RNA (siRNA) mediated TRIB3 knockdown on hypoxia tolerance was assessed.
  
  
  RESULTS
  Breast cancer patients with low, intermediate or high TRIB3 expression exhibited a mean disease free survival (DFS) of 80 (95% confidence interval [CI] = 74 to 86), 74 (CI = 67 to 81), and 63 (CI = 55 to 71) months respectively (P = .002, Mantel-Cox log-rank). The prognostic value of TRIB3 was limited to those patients that had received radiotherapy as part of their primary treatment (n = 179, P = .005) and remained statistically significant after correction for other clinicopathological parameters (DFS, Hazard Ratio = 1.90, CI = 1.17 to 3.08, P = .009). In breast cell lines TRIB3 expression was induced by hypoxia, nutrient starvation, and endoplasmic reticulum stress in an hypoxia inducible factor 1 (HIF-1) independent manner. TRIB3 induction after hypoxia did not increase with decreasing oxygen levels. In breast tumor xenografts and human breast cancer tissues TRIB3 co-localized with the hypoxic cell marker pimonidazole. The induction of TRIB3 by hypoxia was shown to be regulated via the PERK/ATF4/CHOP pathway of the unfolded protein response and knockdown of TRIB3 resulted in a dose-dependent increase in hypoxia sensitivity.
  
  
  CONCLUSIONS
  TRIB3 is independently associated with poor prognosis of breast cancer patients, possibly through its association with tumor cell hypoxia.
authors.affiliation: Department of Laboratory Medicine, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands. m.wennemers@labgk.umcn.nl
authors.forename: Marloes
authors.initials: M
authors.lastname: Wennemers
authors.forename: Johan
authors.initials: J
authors.lastname: Bussink
authors.forename: Blanca
authors.initials: B
authors.lastname: Scheijen
authors.forename: Iris D
authors.initials: ID
authors.lastname: Nagtegaal
authors.forename: Hanneke W M
authors.initials: HW
authors.lastname: van Laarhoven
authors.forename: James A
authors.initials: JA
authors.lastname: Raleigh
authors.forename: Mahesh A
authors.initials: MA
authors.lastname: Varia
authors.forename: Joop J T M
authors.initials: JJ
authors.lastname: Heuvel
authors.forename: Kasper M
authors.initials: KM
authors.lastname: Rouschop
authors.forename: Fred C G J
authors.initials: FC
authors.lastname: Sweep
authors.forename: Paul N
authors.initials: PN
authors.lastname: Span
mesh_terms: D051701:Activating Transcription Factor 4 / Q000235:genetics / Q000378:metabolism; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology / Q000628:therapy*; D018797:Cell Cycle Proteins / Q000235:genetics*; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D018572:Disease-Free Survival; D059865:Endoplasmic Reticulum Stress; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D011379:Prognosis; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics; D034741:RNA, Small Interfering; D012097:Repressor Proteins / Q000235:genetics*; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism
chemical_list: D051701:Activating Transcription Factor 4; D018797:Cell Cycle Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D017346:Protein Serine-Threonine Kinases; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase; C497109:ATF4 protein, human; C497249:DDIT3 protein, human; C497442:HIF1A protein, human; C474831:TRIB3 protein, human