title: Transactivation of epidermal growth factor receptor is involved in leptin-induced activation of janus-activated kinase 2 and extracellular signal-regulated kinase 1/2 in human gastric cancer cells.
abstract: Leptin is known to act as a growth factor through the Janus-activated kinase (JAK)/signal transducer and activator of transcription signaling pathway as well as the mitogen-activated protein kinase pathway. In this study, we showed a novel signal transduction pathway using two human gastric cancer cell lines, MKN28 and MKN74. Both gastric cancer cells expressed leptin and its receptors (Ob-R) at the protein level. We found that leptin, even at as low as 0.1 ng/mL, induced significant tyrosine phosphorylation of epidermal growth factor receptor (EGFR). Time-course experiments revealed that phosphorylation was maximal after 5 minutes of stimulation and declined thereafter. We also revealed that tyrosine phosphorylation of EGFR induced by leptin was significantly attenuated by two inhibitors, an EGFR tyrosine kinase inhibitor, AG1478, and a broad-spectrum matrix metalloproteinase inhibitor, GM6001. This indicates that the pathway of EGFR transactivation induced by leptin is dependent on proteolytically released EGFR ligands. Leptin induced JAK2 activation and extracellular signal-regulated kinase (ERK) 1/2 activation in these gastric cancer cells, both of which occurred after the peak of EGFR transactivation. Pretreatment of gastric cancer cells with AG1478 significantly reduced the degree of phosphorylation of both JAK2 and ERK1/2. These findings indicate the involvement of EGFR transactivation in the activation of JAK2 and ERK1/2. Our results reveal that EGFR transactivation is involved in the leptin signaling pathway in gastric cancer cells, which extends the physiologic action of leptin beyond its central effects in the hypothalamus to regulate body weight.
authors.affiliation: Department of Surgical Oncology, University of Tokyo Graduate School of Medicine, Tokyo, Japan. dshida-tky@umin.ac.jp
authors.forename: Dai
authors.initials: D
authors.lastname: Shida
authors.forename: Joji
authors.initials: J
authors.lastname: Kitayama
authors.forename: Ken
authors.initials: K
authors.lastname: Mori
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Watanabe
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Nagawa
mesh_terms: D045744:Cell Line, Tumor; D004151:Dipeptides / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D053614:Janus Kinase 2; D020738:Leptin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D045726:Metalloproteases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011480:Protease Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011799:Quinazolines; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000378:metabolism; D054411:Receptors, Leptin; D011994:Recombinant Proteins / Q000494:pharmacology; D013274:Stomach Neoplasms / Q000201:enzymology; D015533:Transcriptional Activation; D020032:Tyrphostins / Q000494:pharmacology
chemical_list: D004151:Dipeptides; C515448:LEPR protein, human; D020738:Leptin; C078131:N-(2(R)-2-(hydroxamidocarbonylmethyl)-4-methylpentanoyl)-L-tryptophan methylamide; D011480:Protease Inhibitors; D011518:Proto-Oncogene Proteins; D011799:Quinazolines; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; D011994:Recombinant Proteins; D020032:Tyrphostins; C101044:RTKI cpd; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D045726:Metalloproteases