HER-2 overexpression differentially alters transforming growth factor-beta responses in luminal versus mesenchymal human breast cancer cells.
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.
Wilson
Cindy A
CA
Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA. cawilson@ucla.edu
Cajulis
Elaina E
EE
Green
Jennifer L
JL
Olsen
Taylor M
TM
Chung
Young Ah
YA
Damore
Michael A
MA
Dering
Judy
J
Calzone
Frank J
FJ
Slamon
Dennis J
DJ
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
D018719:Erb-b2 Receptor Tyrosine Kinases; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C508960:TGFB1 protein, human