Abstract
Rapid engagement of the extracellular signal-regulated kinase (ERK) cascade via the Gq/11-coupled GnRH receptor (GnRHR) is mediated by transactivation of the epidermal growth factor receptor (EGFR). Here we show that the cross-talk between GnRHR and EGFR in gonadotropic cells is accomplished via gelatinases A and B (matrix metalloproteinases (MMPs) 2 and 9), identifying gelatinases as the first distinct members of the MMP family mediating EGFR transactivation by G protein-coupled receptors. Using a specific MMP2 and MMP9 inhibitor, Ro28-2653, GnRH-dependent EGFR transactivation was abrogated. Proving the specificity of the effect, transient transfection of alphaT3-1 cells with ribozymes directed against MMP2 or MMP9 specifically blocked EGFR tyrosine phosphorylation in response to GnRH stimulation. GnRH challenge of alphaT3-1 cells furthered the release of active MMP2 and MMP9 and increased their gelatinolytic activities within 5 min. Rapid release of activated MMP2 or MMP9 was inhibited by ribozyme-targeted down-regulation of MT1-MMP or MMP2, respectively. We found that GnRH-induced Src, Ras, and ERK activation were also gelatinase-dependent. Thus, gelatinase-induced EGFR transactivation was required to engage the extracellular-signal regulated kinase cascade. Activation of c-Jun N-terminal kinase and p38 MAPK by GnRH was unaffected by EGFR or gelatinase inhibition that, however, suppressed GnRH induction of c-Jun and c-Fos. Our findings suggest a novel role for gelatinases in the endocrine regulation of pituitary gonadotropes.
Highlights
Rapid engagement of the extracellular signal-regulated kinase (ERK) cascade via the Gq/11-coupled GnRH receptor (GnRHR) is mediated by transactivation of the epidermal growth factor receptor (EGFR)
MMP9) are expressed in pituitary tumors and normal pituitary glands (24 –26), we initially focused on a potential involvement of MMP2 and MMP9 in GnRH-dependent signal transduction in gonadotropes
Prior to GnRH challenge, ␣T3-1 cells were incubated with Ro28-2653, a novel pyrimidine-2,4,6-trion-based matrix metalloproteinases (MMPs) inhibitor characterized by a high selectivity for MMP2 and MMP9 [27,28,29]
Summary
Rapid engagement of the extracellular signal-regulated kinase (ERK) cascade via the Gq/11-coupled GnRH receptor (GnRHR) is mediated by transactivation of the epidermal growth factor receptor (EGFR). We show that the cross-talk between GnRHR and EGFR in gonadotropic cells is accomplished via gelatinases A and B (matrix metalloproteinases (MMPs) 2 and 9), identifying gelatinases as the first distinct members of the MMP family mediating EGFR transactivation by G proteincoupled receptors. Gelatinase-induced EGFR transactivation was required to engage the extracellular-signal regulated kinase cascade. An attractive model providing a mechanistic explanation for EGFR activation via GPCRs is based on regulated proteolytic release of local EGF-like ligands from transmembrane precursors [5]. Because GPCR-induced EGFR transactivation is sensitive to pretreatment of cells with the broad-spectrum MMP inhibitor batimastat, a cardinal role of MMPs in the receptor cross-talk has been invoked [5].
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