title: HER-2 overexpression differentially alters transforming growth factor-beta responses in luminal versus mesenchymal human breast cancer cells.
abstract: BACKGROUND
  Amplification of the HER-2 receptor tyrosine kinase has been implicated in the pathogenesis and aggressive behavior of approximately 25% of invasive human breast cancers. Clinical and experimental evidence suggest that aberrant HER-2 signaling contributes to tumor initiation and disease progression. Transforming growth factor beta (TGF-beta) is the dominant factor opposing growth stimulatory factors and early oncogene activation in many tissues, including the mammary gland. Thus, to better understand the mechanisms by which HER-2 overexpression promotes the early stages of breast cancer, we directly assayed the cellular and molecular effects of TGF-beta1 on breast cancer cells in the presence or absence of overexpressed HER-2.
  
  
  METHODS
  Cell proliferation assays were used to determine the effect of TGF-beta on the growth of breast cancer cells with normal or high level expression of HER-2. Affymetrix microarrays combined with Northern and western blot analysis were used to monitor the transcriptional responses to exogenous TGF-beta1 in luminal and mesenchymal-like breast cancer cells. The activity of the core TGF-beta signaling pathway was assessed using TGF-beta1 binding assays, phospho-specific Smad antibodies, immunofluorescent staining of Smad and Smad DNA binding assays.
  
  
  RESULTS
  We demonstrate that cells engineered to over-express HER-2 are resistant to the anti-proliferative effect of TGF-beta1. HER-2 overexpression profoundly diminishes the transcriptional responses induced by TGF-beta in the luminal MCF-7 breast cancer cell line and prevents target gene induction by a novel mechanism that does not involve the abrogation of Smad nuclear accumulation, DNA binding or changes in c-myc repression. Conversely, HER-2 overexpression in the context of the mesenchymal MDA-MB-231 breast cell line potentiated the TGF-beta induced pro-invasive and pro-metastatic gene signature.
  
  
  CONCLUSIONS
  HER-2 overexpression promotes the growth and malignancy of mammary epithelial cells, in part, by conferring resistance to the growth inhibitory effects of TGF-beta. In contrast, HER-2 and TGF-beta signaling pathways can cooperate to promote especially aggressive disease behavior in the context of a highly invasive breast tumor model.
authors.affiliation: Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA. cawilson@ucla.edu
authors.forename: Cindy A
authors.initials: CA
authors.lastname: Wilson
authors.forename: Elaina E
authors.initials: EE
authors.lastname: Cajulis
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Green
authors.forename: Taylor M
authors.initials: TM
authors.lastname: Olsen
authors.forename: Young Ah
authors.initials: YA
authors.lastname: Chung
authors.forename: Michael A
authors.initials: MA
authors.lastname: Damore
authors.forename: Judy
authors.initials: J
authors.lastname: Dering
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Calzone
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: Slamon
mesh_terms: D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D049109:Cell Proliferation; D018450:Disease Progression; D004847:Epithelial Cells; D005260:Female; D020869:Gene Expression Profiling; D005818:Genetic Engineering; D006801:Humans; D042361:Mammary Glands, Human / Q000166:cytology; D008648:Mesoderm; D009361:Neoplasm Invasiveness; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis*; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000502:physiology*; D053773:Transforming Growth Factor beta1
chemical_list: D018719:Erb-b2 Receptor Tyrosine Kinases; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C508960:TGFB1 protein, human