title: Selective tyrosine hyperphosphorylation of cytoskeletal and stress proteins in primary human breast cancers: implications for adjuvant use of kinase-inhibitory drugs.
abstract: OBJECTIVE
  Small-molecule growth factor receptor inhibitors block cell growth in vitro and downstream signaling in vivo, but controlled trials in patients with advanced solid tumors have yielded disappointing response rates. To clarify this discrepancy, we compared the patterns of tyrosine phosphoprotein expression in human cancer cells and primary tumors.
  
  
  METHODS
  Immunoaffinity chromatography, two-dimensional electrophoresis, and antiphosphotyrosine immunoblotting were combined with mass spectrometry to determine the phosphoproteomic signatures of 40 matched normal and malignant tissues from patients with breast or liver cancer. The identities and abundance of the detected tyrosine phosphoproteins were compared with those of ligand-responsive A431 cells.
  
  
  RESULTS
  Patterns of tyrosine-phosphorylated proteins are similar among normal tissues of the same origin but vary markedly between different tissues. Primary breast tumors exhibit a strikingly homogeneous tyrosine phosphorylation profile, whereas liver cancers display greater phosphoproteomic diversity. The main breast-tumor-specific tyrosine phosphoproteins are cytoskeletal molecules (actin, tubulin, and vimentin) and molecular chaperones (Hsp70, Hsc71, and Grp75). In contrast, control studies in ligand-stimulated A431 human cancer cells revealed an additional phosphorylated subset of promitogenic phosphoproteins (Grb2, Shc, Jnk2, phospholipase C-gamma, and phosphatidylinositol 3'-kinase).
  
  
  CONCLUSIONS
  Identification of cytoskeletal and stress proteins as the most abundant tyrosine phosphoproteins in breast tumors implicates these molecules, rather than promitogenic effectors, as the prime stoichiometric substrates for kinase-inhibitory anticancer drugs in vivo. Because phosphorylated cytoskeletal proteins and chaperones mediate cell motility and apoptotic resistance, respectively, these data raise the intriguing possibility that small-molecule tyrosine kinase inhibitors may be of greatest value either as adjuvant antimetastatic/-invasive drugs or as chemo-/radiosensitizers.
authors.affiliation: Division of Medical Sciences and Department of Surgical Oncology, National Cancer Centre, Singapore.
authors.forename: Yoon-Pin
authors.initials: YP
authors.lastname: Lim
authors.forename: Chow Yin
authors.initials: CY
authors.lastname: Wong
authors.forename: London Lucien
authors.initials: LL
authors.lastname: Ooi
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Druker
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Epstein
mesh_terms: D000818:Animals; D017209:Apoptosis; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism*; D045744:Cell Line, Tumor; D017024:Chemotherapy, Adjuvant / Q000379:methods*; D002845:Chromatography / Q000379:methods; D003599:Cytoskeleton / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional / Q000379:methods; D006360:Heat-Shock Proteins / Q000737:chemistry; D006801:Humans; D015151:Immunoblotting; D008024:Ligands; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D008807:Mice, Inbred BALB C; D009362:Neoplasm Metastasis; D009369:Neoplasms / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000737:chemistry; D015398:Signal Transduction; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D006360:Heat-Shock Proteins; D008024:Ligands; D010750:Phosphoproteins; D019000:Phosphotyrosine; D014443:Tyrosine