title: Lyn, a Src family kinase, regulates activation of epidermal growth factor receptors in lung adenocarcinoma cells.
abstract: BACKGROUND
  Activation of receptors for growth factors on lung epithelial cells is essential for transformation into tumor cells, supporting their viability and proliferation. In most lung cancer patients, EGFR is constitutively activated without evidence of mutation. Defining mechanisms for constitutive activation of EGFR could elucidate additional targets for therapy of lung cancers.
  
  
  METHODS
  The approach was to identify lung cancer cell lines with constitutively activated EGFR and use systematic selection of inhibitors to evaluate their effects on specific EGFR phosphorylations and downstream signaling pathways. Interactions between receptors, kinases, and scaffolding proteins were investigated by co-immunoprecipitation plus Western blotting.
  
  
  RESULTS
  The results revealed a dependence on Src family of tyrosine kinases for downstream signaling and cell growth. Lyn, a Src family kinase functional in normal and malignant B-lymphocytes, was a defining signal transducer required for EGFR signaling in Calu3 cell line. Src family kinase activation in turn, was dependent on PKCßII. Lyn and PKC exist in membrane complexes of RACK1 and in association with EGFR which pairs with other receptor partners. Silencing of Lyn expression with interfering siRNA decreased EGFR activation and cell viability.
  
  
  CONCLUSIONS
  The importance of Src family kinases and PKCßII in the initiation of the EGFR signaling pathway in lung tumor cells was demonstrated. We conclude that phosphorylation of EGFR is mediated through PKCßII regulation of Lyn activation, and occurs in association with RACK1 and Cbp/PAG proteins. We suggest that protein complexes in cell membranes, including lipid rafts, may serve as novel targets for combination therapies with EGFR and Src Family Kinase inhibitors in lung cancer.
authors.affiliation: Department of Medical Laboratory Sciences, Rush University Medical Center, Chicago, IL 60612, USA.
authors.forename: Parnetta
authors.initials: P
authors.lastname: Sutton
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Borgia
authors.forename: Philip
authors.initials: P
authors.lastname: Bonomi
authors.forename: Janet M D
authors.initials: JM
authors.lastname: Plate
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism*; D000077192:Adenocarcinoma of Lung; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002470:Cell Survival / Q000235:genetics; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D064546:Protein Kinase C beta; D019859:Proto-Oncogene Proteins c-met / Q000378:metabolism; D015398:Signal Transduction; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D066246:ErbB Receptors; D019859:Proto-Oncogene Proteins c-met; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D011493:Protein Kinase C; D064546:Protein Kinase C beta