title: Gastrin-releasing peptide activates Akt through the epidermal growth factor receptor pathway and abrogates the effect of gefitinib.
abstract: Gastrin-releasing peptide (GRP) is a mitogen for lung epithelial cells and initiates signaling through a G-protein-coupled receptor, gastrin-releasing peptide receptor (GRPR). Because GRPR transactivates the epidermal growth factor receptor (EGFR), we investigated induction by GRP of Akt, an EGFR-activated signaling pathway, and examined effects of GRP on viability of non-small cell lung carcinoma (NSCLC) cells exposed to the EGFR tyrosine kinase inhibitor gefitinib. GRP induced Akt activation primarily through c-Src-mediated transactivation of EGFR. Transfection of dominant-negative c-Src abolished GRP-induced EGFR and Akt activation. GRP induced release of amphiregulin, and pre-incubation with human amphiregulin neutralizing antibody eliminated GRP-induced Akt phosphorylation. Pretreatment with phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 completely blocked GRP-initiated Akt phosphorylation. These results suggest that GRP stimulates Akt activation primarily via c-Src activation, followed by extracellular release of the EGFR ligand amphiregulin, leading to the activation of EGFR and PI3K. Pretreatment of NSCLC cells with GRP resulted in an increase in the IC(50) of gefitinib of up to 9-fold; this protective effect was mimicked by the pretreatment of cells with amphiregulin and reversed by Akt or PI3K inhibition. GRP appears to rescue NSCLC cells exposed to gefitinib through release of amphiregulin and activation of the Akt pathway, suggesting GRPR and/or EGFR autocrine pathways in NSCLC cells may modulate therapeutic response to EGFR inhibitors.
authors.affiliation: Department of Pharmacology, University of Pittsburgh Cancer Institute, University of Pittsburgh, Lab 2.7, 5117 Centre Ave., Pittsburgh, PA 15213, USA. Liux@upmc.edu
authors.forename: Xuwan
authors.initials: X
authors.lastname: Liu
authors.forename: Diane L
authors.initials: DL
authors.lastname: Carlisle
authors.forename: Michelle C
authors.initials: MC
authors.lastname: Swick
authors.forename: Autumn
authors.initials: A
authors.lastname: Gaither-Davis
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Grandis
authors.forename: Jill M
authors.initials: JM
authors.lastname: Siegfried
mesh_terms: D000906:Antibodies / Q000276:immunology; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D019886:Gastrin-Releasing Peptide / Q000494:pharmacology*; D005765:Gastrointestinal Agents / Q000494:pharmacology; D000077156:Gefitinib; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D011799:Quinazolines / Q000494:pharmacology*; D018004:Receptors, Bombesin / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D000906:Antibodies; D005765:Gastrointestinal Agents; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D018004:Receptors, Bombesin; D019886:Gastrin-Releasing Peptide; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt; D000077156:Gefitinib