title: HGF-independent potentiation of EGFR action by c-Met.
abstract: The c-Met receptor is a potential therapeutic target for non-small cell lung cancer (NSCLC). Signaling interactions between c-Met and the mutant epidermal growth factor receptor (EGFR) have been studied extensively, but signaling intermediates and biological consequences of lateral signaling to c-Met in EGFR wild-type tumors are minimally understood. Our observations indicate that delayed c-Met activation in NSCLC cell lines is initiated by wild-type EGFR, the receptor most often found in NSCLC tumors. EGFR ligands induce accumulation of activated c-Met, which begins at 8 h and continues for 48 h. This effect is accompanied by an increase in c-Met expression and phosphorylation of critical c-Met tyrosine residues without activation of mitogen-activated protein kinase (MAPK) or Akt. Gene transcription is required for delayed c-Met activation; however, phosphorylation of c-Met by EGFR occurs without production of hepatocyte growth factor (HGF) or another secreted factor, supporting a ligand-independent mechanism. Lateral signaling is blocked by two selective c-Met tyrosine kinase inhibitors (TKIs), PF2341066 and SU11274, or with gefitinib, an EGFR TKI, suggesting kinase activity of both receptors is required for this effect. Prolonged c-Src phosphorylation is observed, and c-Src pathway is essential for EGFR to c-Met communication. Pretreatment with pan-Src family kinase inhibitors, PP2 and dasatinib, abolishes delayed c-Met phosphorylation. A c-Src dominant-negative construct reduces EGF-induced c-Met phosphorylation compared with control, further confirming a c-Src requirement. Inhibition of c-Met with PF2341066 and siRNA decreases EGF-induced phenotypes of invasion by ~86% and motility by ~81%, suggesting that a novel form of c-Met activation is utilized by EGFR to maximize these biological effects. Combined targeting of c-Met and EGFR leads to increased xenograft antitumor activity, demonstrating that inhibition of downstream and lateral signaling from the EGFR-c-Src-c-Met axis might be effective in treatment of NSCLC.
authors.affiliation: Department of Pharmacology & Chemical Biology, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Dulak
authors.forename: C T
authors.initials: CT
authors.lastname: Gubish
authors.forename: L P
authors.initials: LP
authors.lastname: Stabile
authors.forename: C
authors.initials: C
authors.lastname: Henry
authors.forename: J M
authors.initials: JM
authors.lastname: Siegfried
mesh_terms: D000081247:CSK Tyrosine-Protein Kinase; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000473:pathology*; D045744:Cell Line, Tumor; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000502:physiology*; D017228:Hepatocyte Growth Factor / Q000502:physiology*; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000473:pathology*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology*; D015398:Signal Transduction; D019061:src-Family Kinases
chemical_list: C066855:HGF protein, human; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D004815:Epidermal Growth Factor; D017228:Hepatocyte Growth Factor; C512478:EGFR protein, human; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human