title: Differences in integrin expression and signaling within human breast cancer cells.
abstract: BACKGROUND
  Integrins are used as prognostic indicators in breast cancer. Following engagement with extracellular matrix proteins, their signaling influences numerous cellular processes including migration, proliferation, and death. Integrin signaling varies between cell types through differential expression of integrin subunits, and changes within a given cell upon exposure to a cell agonist or through changes in its surroundings. These variations in signaling can profoundly affect the phenotypic, tumorogenecity and metastatic properties of cancer cells. In the present study, we investigated if there were differences in the expression of integrins, integrin structures, and integrin co-receptors within three breast cancer cells and if these differences effected integrin signaling.
  
  
  METHODS
  Expression of integrins, urokinase receptor and vascular endothelial cell growth factor receptor (VEGFR) in metastatic MDA-MB-435 and MDA-MB-231, non-metastatic MCF7 and non-breast cancer Hek-293 cells was measured by flow cytometry. Cell adhesion was assessed using collagen, fibrinogen, fibronectin and vitronectin coated plates. Changes in kinase levels following PMA stimulation, and cell adhesion-induced activation of kinases were determined by western blot analysis. Distribution of actin stress fibers and focal adhesions was assessed by immunocytochemistry.
  
  
  RESULTS
  All cells expressed αv integrins, while high β5 and αvβ5 expression was restricted to the cancer cells and high β3 and αvβ3 expression was restricted to MDA-MB-435 cells. The two metastatic cells were the least adhesive, but all cells adhered well to most proteins in the absence of PMA. All proliferating cells expressed activated pSrc, but only proliferating metastatic cells expressed high pMEK levels. PMA treatment resulted in time-dependent changes in activated kinase levels, and only MDA-MB-231 cells constitutively expressed high levels of activated pMEK. MDA-MB-435 cells formed more stress fibers and focal adhesions and only exhibited adhesion-induced activation of pMEK and pFAK. All cells expressed the urokinase receptor, but MCF7 cells had markedly higher VEGFR expression. Adhesion induced differential expression of pFAK, pMEK and pERK.
  
  
  CONCLUSIONS
  This study demonstrates that breast cancers vary in their expression of integrins, their capacity to form focal adhesion and to signal through integrins. These differences likely contribute to phenotypic variations between cancer lines and account for some of the heterogeneity of breast cancer.
authors.affiliation: Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada 7E3 5E5.
authors.forename: Aliakbar
authors.initials: A
authors.lastname: Taherian
authors.forename: Xinlei
authors.initials: X
authors.lastname: Li
authors.forename: Yongqing
authors.initials: Y
authors.lastname: Liu
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Haas
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology*; D000951:Antigens, Neoplasm / Q000096:biosynthesis / Q000235:genetics; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D002448:Cell Adhesion; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D005260:Female; D022001:Focal Adhesions; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology*; D057809:HEK293 Cells / Q000378:metabolism; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000096:biosynthesis / Q000235:genetics; D039661:Integrin beta3 / Q000096:biosynthesis / Q000235:genetics; D016023:Integrins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism; D055293:Receptors, Urokinase Plasminogen Activator / Q000096:biosynthesis / Q000235:genetics; D040262:Receptors, Vascular Endothelial Growth Factor / Q000096:biosynthesis / Q000235:genetics; D019030:Receptors, Vitronectin / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D022502:Stress Fibers / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000951:Antigens, Neoplasm; D039302:Integrin alphaVbeta3; D039661:Integrin beta3; D016023:Integrins; D009363:Neoplasm Proteins; D055293:Receptors, Urokinase Plasminogen Activator; D019030:Receptors, Vitronectin; C064660:integrin alphaVbeta5; C073878:integrin alphavbeta6; D011494:Protein Kinases; D040262:Receptors, Vascular Endothelial Growth Factor; D013755:Tetradecanoylphorbol Acetate