title: Differential requirement of EGF receptor and its tyrosine kinase for AP-1 transactivation induced by EGF and TPA.
abstract: The transcription factor activator protein-1 (AP-1) has been implicated in a large variety of biological processes including cell differentiation, proliferation, apoptosis and oncogenic transformation. It is thought that the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced AP-1 activity is because of the activation of the PKC/MAPK/AP-1 pathway, although the detailed molecular mechanism has not been fully characterized. The tyrosine kinases of epidermal growth factor receptor (EGFR) lie at the head of a complex of signal transduction cascade that modulates cell proliferation, survival, adhesion, migration and differentiation. Currently, little is known about whether EGFR or its tyrosine kinase is necessary for TPA-induced AP-1 activation. In the present study, we investigated this issue using a well-characterized mouse fibroblast B82 cell line, which is devoid of the EGFR, and its stable transfectants with either wild-type EGFR (B82L) or tyrosine kinase-deficient EGFR (mutation at Lys-721) (B82M721). We demonstrated that the TPA or epidermal growth factor (EGF) induced AP-1 activation in the B82L cells that express wild-type EGFR, but not in the B82 cell, whereas autophosphorylation at tyrosine(1173) of EGFR in B82L cells was only induced by EGF, but not TPA. The expression of tyrosine kinase-deficient EGFR (mutation at Lys-721) (B82M721) resulted in deficiency of AP-1 induction in cellular response to EGF, while TPA treatment led to fully AP-1 activation. Furthermore, the mutation at Lys-721 of EGFR resulted in impairing of EGFR autophosphorylation at tyrosine(1173) induced by EGF. Based on these results, we conclude that TPA-induced AP-1 activation requires the basal level-EGFR protein, but not EGFR tyrosine kinase and EGFR autophosphorylation at tyrosine(1173), whereas both EGFR tyrosine kinase and EGFR autophosphorylation at Y(1173) play a critical role in EGF-induced AP-1 activation.
authors.affiliation: Nelson Institute of Environmental Medicine, New York University School of Medicine, Tuxedo, NY 10987, USA.
authors.forename: Jingxia
authors.initials: J
authors.lastname: Li
authors.forename: Cuiling
authors.initials: C
authors.lastname: Ma
authors.forename: Yi
authors.initials: Y
authors.lastname: Huang
authors.forename: Jia
authors.initials: J
authors.lastname: Luo
authors.forename: Chuanshu
authors.initials: C
authors.lastname: Huang
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology*; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts; D006801:Humans; D008239:Lysine / Q000235:genetics; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation; D017354:Point Mutation; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D018808:Transcription Factor AP-1 / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects*; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism
chemical_list: D018808:Transcription Factor AP-1; D014443:Tyrosine; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases; D008239:Lysine; D013755:Tetradecanoylphorbol Acetate