title: Uncoupling between epidermal growth factor receptor and downstream signals defines resistance to the antiproliferative effect of Gefitinib in bladder cancer cells.
abstract: Activation of the epidermal growth factor receptor (EGFR) and downstream signaling pathways, such as phosphatidylinositol-3 kinase/Akt and Ras/mitogen-activated protein kinase (MAPK), have been implicated in causing resistance to EGFR-targeted therapy in solid tumors, including the urogenital tumors. To investigate the mechanism of resistance to EGFR inhibition in bladder cancer, we compared EGFR tyrosine kinase inhibitor (Gefitinib, Iressa, ZD1839) with respect to its inhibitory effects on three kinases situated downstream of EGFR: MAPK, Akt, and glycogen synthase kinase-3beta (GSK-3beta). We found that the resistance to the antiproliferative effects of gefitinib, in vitro as well as in vivo in nude mice models, was associated with uncoupling between EGFR and MAPK inhibition, and that GSK-3beta activation and degradation of its target cyclin D1 were indicators of a high cell sensitivity to gefitinib. Further analysis of one phenotypic sensitive (253J B-V) and resistant (UM-UC13) cell lines revealed that platelet-derived growth factor receptor-beta (PDGFRbeta) activation was responsible for short circuiting the EGFR/MAPK pathway for mitogenic stimuli. However, invasion as well as actin dynamics were efficiently reduced by EGFR inhibition in UM-UC13. Chemical disruption of signaling pathways or of PDGFR kinase activity significantly reduced the inactive pool of cellular GSK-3beta in UM-UC13 cells. In conclusion, our data show that the uncoupling of EGFR with mitogenic pathways can cause resistance to EGFR inhibition in bladder cancer. Although this uncoupling may arise through different mechanisms, we suggest that the resistance of bladder cancer cells to EGFR blockade can be predicted early in the course of treatment by measuring the activation of GSK-3beta and of nuclear cyclin D1.
authors.affiliation: Department of Urology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Wassim
authors.initials: W
authors.lastname: Kassouf
authors.forename: Colin P N
authors.initials: CP
authors.lastname: Dinney
authors.forename: Gordon
authors.initials: G
authors.lastname: Brown
authors.forename: David J
authors.initials: DJ
authors.lastname: McConkey
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Diehl
authors.forename: Menashe
authors.initials: M
authors.lastname: Bar-Eli
authors.forename: Liana
authors.initials: L
authors.lastname: Adam
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D002295:Carcinoma, Transitional Cell / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D048708:Cell Growth Processes / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D004790:Enzyme Induction; D066246:ErbB Receptors / Q000096:biosynthesis / Q000378:metabolism*; D000077156:Gefitinib; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000096:biosynthesis / Q000378:metabolism; D009361:Neoplasm Invasiveness; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011799:Quinazolines / Q000494:pharmacology*; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology
chemical_list: D000970:Antineoplastic Agents; D011799:Quinazolines; D019938:Cyclin D1; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D017479:Receptors, Platelet-Derived Growth Factor; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3; D000077156:Gefitinib