Epidermal growth factor receptor tyrosine kinase mediates Ras activation by gonadotropin-releasing hormone.
Gonadotropin releasing hormone (GnRH) contributes to the maintenance of gonadotrope function by increasing extracellular signal-regulated kinase (ERK) activity subsequent to binding to its cognate G-protein-coupled receptor. As the GnRH receptor exclusively interacts with G(q/11) proteins and as receptor expression is regulated in a beta-arrestin-independent fashion, it represents a good model to systematically dissect underlying signaling pathways. In alphaT3-1 gonadotropes endogenously expressing the GnRH receptor, GnRH challenge resulted in a rapid increase in ERK activity which was attenuated by the epidermal growth factor receptor (EGFR)-specific tyrosine kinase inhibitor AG1478. In COS-7 cells transiently expressing the human GnRH receptor, agonist-induced ERK activation was independent of free Gbetagamma subunits but could be mimicked by short-term phorbol ester treatment. Most notably, G(q/11)-induced ERK activation was sensitive to N17-Ras and to expression of the C-terminal Src kinase but also to other dominant negative mutants of signaling components localized upstream of Ras, like Shc and the EGFR. GnRH as well as phorbol esters led to Ras activation in COS-7 and alphaT3-1 cells, which was dependent on Src and EGFR tyrosine kinases, indicating that both tyrosine kinases act downstream of protein kinase C (PKC) and upstream of Ras. However, Src did not contribute to Shc tyrosine phosphorylation. GnRH or phorbol ester challenge resulted in PKC-dependent EGFR autophosphorylation. Furthermore, a 5-min phorbol ester treatment was sufficient to trigger tyrosine phosphorylation of the platelet-derived growth factor-beta receptor in L cells. Thus, in several cell systems PKC is able to stimulate Ras via activation of receptor tyrosine kinases.
Grosse
R
R
Institut für Pharmakologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, Thielallee 67-73, D-14195 Berlin, Germany.
Roelle
S
S
Herrlich
A
A
Höhn
J
J
Gudermann
T
T
D000818:Animals; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000502:physiology*; D020549:GTP Phosphohydrolase Activators / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D006801:Humans; D007739:L Cells; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D020703:ras GTPase-Activating Proteins / Q000502:physiology*
D020549:GTP Phosphohydrolase Activators; D020703:ras GTPase-Activating Proteins; D007987:Gonadotropin-Releasing Hormone; D066246:ErbB Receptors; D020794:Receptor Protein-Tyrosine Kinases; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium