title: Receptor heterodimerization: a new mechanism for platelet-derived growth factor induced resistance to anti-epidermal growth factor receptor therapy for bladder cancer.
abstract: OBJECTIVE
  Human bladder cancer cells resistant to anti-epidermal growth factor receptor therapy often co-express platelet-derived growth factor receptor-β. We determined whether there is functional crosstalk between epidermal growth factor receptor and platelet-derived growth factor receptor-β, and how this regulates biological functions in bladder cancer cases.
  
  
  METHODS
  We determined heterodimerization and co-localization of epidermal growth factor receptor and platelet-derived growth factor receptor-β by immunoprecipitation and confocal microscopy, respectively. We tested the antiproliferative effects of specific inhibitory monoclonal antibodies to each receptor by (3)H-thymidine uptake assay. We transfected the nonplatelet-derived growth factor receptor-β expressing bladder cancer cell line UMUC5 with the platelet-derived growth factor receptor-β gene. These cells were analyzed in vitro by (3)H-thymidine uptake and by Matrigel™ invasion assay, and in vivo for tumorigenicity, metastatic potential and orthotopic growth. In a treatment study nude mice were inoculated with orthotopic tumors and treated with the inhibitory antibodies alone and in combination.
  
  
  RESULTS
  Immunoprecipitation revealed epidermal growth factor receptor/platelet-derived growth factor receptor-β heterodimers in all platelet-derived growth factor receptor-β expressing cell lines. Forced expression of platelet-derived growth factor receptor-β in epidermal growth factor receptor sensitive UMUC5 cells (50% inhibitory concentration less than 10 nM) significantly decreased responsiveness to epidermal growth factor receptor inhibition (50% inhibitory concentration greater than 100 nM) and increased invasive potential 3-fold as well as tumorigenicity. Increased invasiveness was associated with epidermal growth factor triggered platelet-derived growth factor receptor-β transactivation, increased mitogen activated protein kinase and glycogen synthase kinase-3β phosphorylation, and decreased E-cadherin. Inhibition of epidermal growth factor receptor and platelet-derived growth factor receptor-β receptors blocked cell invasion, decreased cell proliferation, reduced xenograft tumor growth and increased E-cadherin expression.
  
  
  CONCLUSIONS
  In epidermal growth factor receptor expressing bladder cancer co-expression of platelet-derived growth factor receptor-β has implications for tumor biology. Thus, it should be further evaluated as a strategy involving dual receptor targeting.
authors.affiliation: Department of Urology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Black
authors.forename: Gordon A
authors.initials: GA
authors.lastname: Brown
authors.forename: Colin P
authors.initials: CP
authors.lastname: Dinney
authors.forename: Wassim
authors.initials: W
authors.lastname: Kassouf
authors.forename: Teruo
authors.initials: T
authors.lastname: Inamoto
authors.forename: Ameeta
authors.initials: A
authors.lastname: Arora
authors.forename: David
authors.initials: D
authors.lastname: Gallagher
authors.forename: Mark F
authors.initials: MF
authors.lastname: Munsell
authors.forename: Menashe
authors.initials: M
authors.lastname: Bar-Eli
authors.forename: David J
authors.initials: DJ
authors.lastname: McConkey
authors.forename: Liana
authors.initials: L
authors.lastname: Adam
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D045744:Cell Line, Tumor / Q000187:drug effects; D000068818:Cetuximab; D019281:Dimerization; D004195:Disease Models, Animal; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D066246:ErbB Receptors / Q000187:drug effects* / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D020239:Receptor Cross-Talk; D020797:Receptor, Platelet-Derived Growth Factor beta / Q000187:drug effects / Q000378:metabolism*; D012680:Sensitivity and Specificity; D015533:Transcriptional Activation; D014162:Transfection; D014183:Transplantation, Heterologous; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D066246:ErbB Receptors; D020797:Receptor, Platelet-Derived Growth Factor beta; D000068818:Cetuximab