Roles of Src and Epidermal Growth Factor Receptor Transactivation in Transient and Sustained ERK1/2 Responses to Gonadotropin-releasing Hormone Receptor Activation

Abstract

The duration as well as the magnitude of mitogenactivated protein kinase activation has been proposed to regulate gene expression and other specific intracellular responses in individual cell types. Activation of ERK1/2 by the hypothalamic neuropeptide gonadotropin-releasing hormone (GnRH) is relatively sustained in ␣T3-1 pituitary gonadotropes and HEK293 cells but is transient in immortalized GT1-7 neurons. Each of these cell types expresses the epidermal growth factor receptor (EGFR) and responds to EGF stimulation with significant but transient ERK1/2 phosphorylation. However, GnRH-induced ERK1/2 phosphorylation caused by EGFR transactivation was confined to GT1-7 cells and was attenuated by EGFR kinase inhibition. Neither EGF nor GnRH receptor activation caused translocation of phospho-ERK1/2 into the nucleus in GT1-7 cells. In contrast, agonist stimulation of GnRH receptors expressed in HEK293 cells caused sustained phosphorylation and nuclear translocation of ERK1/2 by a protein kinase C-dependent but EGFR-independent pathway. GnRH-induced activation of ERK1/2 was attenuated by the selective Src kinase inhibitor PP2 and the negative regulatory C-terminal Src kinase in GT1-7 cells but not in HEK293 cells. In GT1-7 cells, GnRH stimulated phosphorylation and nuclear translocation of the ERK1/2-dependent protein, p90 RSK-1 (RSK-1). These results indicate that the duration of ERK1/2 activation depends on the signaling pathways utilized by GnRH in specific target cells. Whereas activation of the G q /protein kinase C pathway in HEK293 cells causes sustained phosphorylation and translocation of ERK1/2 to the nucleus, transactivation of the EGFR by GnRH in GT1-7 cells elicits transient ERK1/2 signals without nuclear accumulation. These findings suggest that transactivation of the tightly regulated EGFR can account for the transient ERK1/2 responses that are elicited by stimulation of certain G protein-coupled receptors.

Adenosine A1 receptor-mediated transactivation of the EGF receptor produces a neuroprotective effect on cortical neurons in vitro

“…Our data are similar to those published in a previous report [28] , in which GnRH was shown to induce transient www.nature.com/aps Xie KQ et al Acta Pharmacologica Sinica npg ERK1/2 activation through EGFR transactivation in GT1-7 cells, but the sustained activation of ERK1/2 in HEK293 cells was shown to occur without transactivation of EGFR. In the case of growth factor-induced ERK1/2 activation, it is known that the magnitude and longevity of the activation depend on the nature of the signaling cascades that are elicited by the stimulation of different growth factors [29] .…”

Neuropeptide-induced Transactivation of a Neuronal Epidermal Growth Factor Receptor Is Mediated by Metalloprotease-dependent Formation of Heparin-binding Epidermal Growth Factor

“…We have recently defined an essential role of EGF-R transactivation in GnRH-induced MAPK signaling in GT1-7 neuronal cells (11), and our preliminary results suggested metalloprotease involvement in this cascade (18). It is well established that metalloprotease activation can cause the release of several ligands and growth factors that can interact with RTKs.…”

“…For example, both GnRH and EGF fail to cause nuclear translocation of activated ERK1/2 in GT1-7 cells but act through RSK-1 to induce transcriptional responses in the nucleus (18). To determine whether HB-EGF mimics the effects of EGF stimulation, we examined its actions on the phosphorylation and cellular localization of RSK-1 in GT1-7 cells.…”

“…As in GT1-7 cells, EGF-Rs are endogenously expressed in renal HEK293 cells, and their stimulation causes marked activation of the ERK1/2 cascade (18,29,30). However, although GnRH-induced ERK1/2 phosphorylation in GT1-7 cells is primarily mediated through transactivation of the EGF-R, this mechanism is not operative in HEK293 cells expressing the GnRH receptor (18).…”

Phosphorylation of TNF-α converting enzyme by gastrin-releasing peptide induces amphiregulin release and EGF receptor activation

“…EGFR activation by GPCRs has been proposed to be mediated by Src family kinases, phosphatidylinositol 3-kinase (PI3-K) and͞or PKC signaling (11). Src family kinases have been reported to regulate GPCR ligand-induced EGFR phosphorylation in the colon cancer cell line Caco-2, gastric epithelial cells RGM1, Cos-7 cells, GT1-7 neuronal cells, lung cancer cell 201T, and head and neck cancer cells (12)(13)(14)(15)(16). PI3-K also has been implicated in GPCR and EGFR crosstalk (17)(18)(19).…”