title: Transforming growth factor beta receptor type III is a tumor promoter in mesenchymal-stem like triple negative breast cancer.
abstract: BACKGROUND
  There is a major need to better understand the molecular basis of triple negative breast cancer (TNBC) in order to develop effective therapeutic strategies. Using gene expression data from 587 TNBC patients we previously identified six subtypes of the disease, among which a mesenchymal-stem like (MSL) subtype. The MSL subtype has significantly higher expression of the transforming growth factor beta (TGF-β) pathway-associated genes relative to other subtypes, including the TGF-β receptor type III (TβRIII). We hypothesize that TβRIII is tumor promoter in mesenchymal-stem like TNBC cells.
  
  
  METHODS
  Representative MSL cell lines SUM159, MDA-MB-231 and MDA-MB-157 were used to study the roles of TβRIII in the MSL subtype. We stably expressed short hairpin RNAs specific to TβRIII (TβRIII-KD). These cells were then used for xenograft tumor studies in vivo; and migration, invasion, proliferation and three dimensional culture studies in vitro. Furthermore, we utilized human gene expression datasets to examine TβRIII expression patterns across all TNBC subtypes.
  
  
  RESULTS
  TβRIII was the most differentially expressed TGF-β signaling gene in the MSL subtype. Silencing TβRIII expression in MSL cell lines significantly decreased cell motility and invasion. In addition, when TβRIII-KD cells were grown in a three dimensional (3D) culture system or nude mice, there was a loss of invasive protrusions and a significant decrease in xenograft tumor growth, respectively. In pursuit of the mechanistic underpinnings for the observed TβRIII-dependent phenotypes, we discovered that integrin-α2 was expressed at higher level in MSL cells after TβRIII-KD. Stable knockdown of integrin-α2 in TβRIII-KD MSL cells rescued the ability of the MSL cells to migrate and invade at the same level as MSL control cells.
  
  
  CONCLUSIONS
  We have found that TβRIII is required for migration and invasion in vitro and xenograft growth in vivo. We also show that TβRIII-KD elevates expression of integrin-α2, which is required for the reduced migration and invasion, as determined by siRNA knockdown studies of both TβRIII and integrin-α2. Overall, our results indicate a potential mechanism in which TβRIII modulates integrin-α2 expression to effect MSL cell migration, invasion, and tumorigenicity.
authors.forename: Bojana
authors.initials: B
authors.lastname: Jovanović
authors.forename: J Scott
authors.initials: JS
authors.lastname: Beeler
authors.forename: Michael W
authors.initials: MW
authors.lastname: Pickup
authors.forename: Anna
authors.initials: A
authors.lastname: Chytil
authors.forename: Agnieszka E
authors.initials: AE
authors.lastname: Gorska
authors.forename: William J
authors.initials: WJ
authors.lastname: Ashby
authors.forename: Brian D
authors.initials: BD
authors.lastname: Lehmann
authors.forename: Andries
authors.initials: A
authors.lastname: Zijlstra
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Pietenpol
authors.forename: Harold L
authors.initials: HL
authors.lastname: Moses
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics; D049109:Cell Proliferation; D002470:Cell Survival / Q000235:genetics; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D016000:Cluster Analysis; D004195:Disease Models, Animal; D005260:Female; D015870:Gene Expression; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D064593:Heterografts; D006801:Humans; D039421:Integrin alpha2 / Q000235:genetics; D059630:Mesenchymal Stem Cells / Q000473:pathology; D051379:Mice; D011509:Proteoglycans / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics*; D018874:Spheroids, Cellular; D064726:Triple Negative Breast Neoplasms / Q000235:genetics* / Q000473:pathology*; D047368:Tumor Burden; D014407:Tumor Cells, Cultured
chemical_list: D039421:Integrin alpha2; D011509:Proteoglycans; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D018125:Receptors, Transforming Growth Factor beta; C071736:betaglycan