title: Growth hormone alters epidermal growth factor receptor binding affinity via activation of extracellular signal-regulated kinases in 3T3-F442A cells.
abstract: Epidermal growth factor receptor (EGFR) is a transmembrane protein that binds EGF in its extracellular domain and initiates signaling via intrinsic tyrosine kinase activity in its cytoplasmic domain. EGFR is important in development, cellular proliferation, and cancer. GH is a critical growthpromoting and metabolic regulatory hormone that binds the GH receptor, thereby engaging various signaling pathways, including ERKs. Prior studies suggest cross-talk between the GH receptor and EGFR signaling systems. Using the GH- and EGF-responsive 3T3-F442A preadipocyte, we previously observed that GH, in addition to causing EGFR tyrosine phosphorylation, also induced EGFR phosphorylation that was detected by PTP101, an antibody reactive with ERK consensus phosphorylation sites. This latter phosphorylation was prevented by pretreatment with MAPK kinase (MEK)1 inhibitors, suggesting ERK pathway dependence. Furthermore, GH cotreatment with EGF markedly slowed EGF-induced EGFR degradation and down-regulation, thereby potentiating EGF-induced EGFR signaling. These effects were also MEK1 dependent and suggested ERK pathway-dependent influence of GH on EGF-induced EGFR postendocytic trafficking and signaling. We now explore the impact of GH on cell surface binding of EGF in 3T3-F442A cells. We found that GH pretreatment caused transient, but substantial, lessening of (125)I-EGF binding. Competitive binding experiments revealed that the decreased binding was primarily due to decreased affinity, rather than a change in the number of EGF binding sites. The effect of GH on EGF binding was concentration dependent and temporally correlated with GH-induced ERK activation and EGFR PTP101-reactive phosphorylation. Blockade of the MEK1/ERK but not the protein kinase C pathway, prevented GH's effects on EGF binding, and our results indicate that the mechanisms of GH- and phorbol-12-myristate-13-acetateinduced inhibition of EGF binding differ substantially. Overall, our findings suggest that GH can modulate both EGF binding kinetics and the EGFR's postbinding signaling itinerary in a MEK1/ERK pathway-dependent fashion.
authors.affiliation: Department of Medicine, University of Alabama at Birmingham, 1530 3rd Avenue South, BDB 861, Birmingham, Alabama 35294-0012, USA.
authors.forename: Yao
authors.initials: Y
authors.lastname: Huang
authors.forename: Yongchang
authors.initials: Y
authors.lastname: Chang
authors.forename: Xiangdong
authors.initials: X
authors.lastname: Wang
authors.forename: Jing
authors.initials: J
authors.lastname: Jiang
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Frank
mesh_terms: D016475:3T3 Cells; D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D019382:Human Growth Hormone / Q000494:pharmacology*; D015850:Interleukin-6 / Q000494:pharmacology; D007457:Iodine Radioisotopes; D053605:Leukemia Inhibitory Factor; D008024:Ligands; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects
chemical_list: D015850:Interleukin-6; D007457:Iodine Radioisotopes; C507837:LIF protein, human; D053605:Leukemia Inhibitory Factor; C507838:Lif protein, mouse; D008024:Ligands; D019382:Human Growth Hormone; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases