Neuropeptide-induced transactivation of a neuronal epidermal growth factor receptor is mediated by metalloprotease-dependent formation of heparin-binding epidermal growth factor.
Numerous external stimuli, including G protein-coupled receptor agonists, cytokines, growth factors, and steroids activate mitogen-activated protein kinases (MAPKs) through phosphorylation of the epidermal growth factor receptor (EGF-R). In immortalized hypothalamic neurons (GT1-7 cells), agonist binding to the gonadotropin-releasing hormone receptor (GnRH-R) causes phosphorylation of MAPKs that is mediated by protein kinase C (PKC)-dependent transactivation of the EGF-R. An analysis of the mechanisms involved in this process showed that GnRH stimulation of GT1-7 cells causes release/shedding of the soluble ligand, heparin binding epidermal growth factor (HB-EGF), as a consequence of metalloprotease activation. GnRH-induced phosphorylation of the EGF-R and, subsequently, of Shc, ERK1/2, and its dependent protein, p90RSK-1 (p90 ribosomal S6 kinase 1 or RSK-1), was abolished by metalloprotease inhibition. Similarly, blockade of the effect of HB-EGF with the selective inhibitor CRM197 or a neutralizing antibody attenuated signals generated by GnRH and phorbol 12-myristate 13-acetate, but not those stimulated by EGF. In contrast, phosphorylation of the EGF-R, Shc, and ERK1/2 by EGF and HB-EGF was independent of PKC and metalloprotease activity. The signaling characteristics of HB-EGF closely resembled those of GnRH and EGF in terms of the phosphorylation of EGF-R, Shc, ERK1/2, and RSK-1 as well as the nuclear translocation of RSK-1. However, neither the selective Src kinase inhibitor PP2 nor the overexpression of negative regulatory Src kinase and dominant negative Pyk2 had any effect on HB-EGF-induced responses. In contrast to GT1-7 cells, human embryonic kidney 293 cells expressing the GnRH-R did not exhibit metalloprotease induction and EGF-R transactivation during GnRH stimulation. These data indicate that the GnRH-induced transactivation of the EGF-R and the subsequent ERK1/2 phosphorylation result from ectodomain shedding of HBEGF through PKC-dependent activation of metalloprotease(s) in neuronal GT1-7 cells.
Shah
Bukhtiar H
BH
Endocrinology and Reproduction Research Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892-4510, USA.
Farshori
M Parvaiz
MP
Catt
Kevin J
KJ
D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000187:drug effects / Q000235:genetics*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D066257:Heparin-binding EGF-like Growth Factor; D006801:Humans; D007031:Hypothalamus / Q000502:physiology; D036341:Intercellular Signaling Peptides and Proteins; D045726:Metalloproteases / Q000378:metabolism*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009474:Neurons / Q000502:physiology*; D010766:Phosphorylation; D011956:Receptors, Cell Surface / Q000378:metabolism; D011966:Receptors, LHRH / Q000502:physiology; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection
C587883:HBEGF protein, human; C587884:Hbegf protein, mouse; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D011956:Receptors, Cell Surface; D011966:Receptors, LHRH; D011994:Recombinant Proteins; D007987:Gonadotropin-Releasing Hormone; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases; D045726:Metalloproteases