Role of epidermal growth factor receptor transactivation in endothelin-1-induced enhanced expression of Gi protein and proliferation in A10 vascular smooth muscle cells

We have recently shown that vasoactive peptides such as angiotensin II (Ang II) and endothelin-1 (ET-1) increase the expression of Gi proteins and the proliferation of A10 vascular smooth muscle cells (VSMC) through mitogen-activated protein (MAP) kinase--phosphoinositide (PI) 3-kinase pathways. This study was intended to examine the implication of epidermal growth factor receptor (EGFR) activation in ET-1-induced enhanced expression of Gi proteins and proliferation of A10 VSMC, and to further investigate the underlying mechanisms responsible for these increases. Cell proliferation was determined by [³thymidine incorporation and the expression of Gi proteins; extracellular signal-regulated kinases 1 and 2 (ERK1/2) and EGFR phosphorylation was determined by Western blotting. Treatment of A10 VSMC with ET-1 enhanced the expression of Gi proteins, which was attenuated by BQ123 and BQ788, antagonists of [ET.sub.A] and [ET.sub.B] receptor respectively. In addition, ET-1 enhanced the phosphorylation of EGFR in A10 VSMC, which was restored to the control levels by EGFR inhibitor and [ET.sub.A] and [ET.sub.B] receptor antagonists. Furthermore, ET-1 also augmented the proliferation and ERK1/2 phosphorylation of A10 VSMC, which were restored to the control levels by inhibition of EGFR. These data suggest that ET-1 transactivates EGFR, which, through MAP kinase signaling, may contribute to the enhanced expression of Gi proteins and thus increased proliferation of A10 VSMC. Key words: ET-1, EGFR, ERK1/2, Gi proteins, VSMC proliferation. Nous avons recemment montre que les peptides vasoactifs comme l'angiotensine II (Ang II) et l'endotheline-1 (ET-1) augmentent l'expression des proteines Gi et la proliferation des cellules musculaires lisses vasculaires (CMLV) par l'intermediaire des voies MAP kinase--PI 3-kinase. La presente etude a ete realisee afin d'examiner l'implication de l'activation du recepteur de l'EGF (EGFR) dans l'augmentation de l'expression des proteines Gi et de la proliferation des CMLV A10 induites par l'ET-1, et d'examiner plus en profondeur les mecanismes sous-jacents responsables de ces augmentations. La proliferation cellulaire a ete determinee par incorporation de [³H]thymidine, et l'expression des proteines Gi ainsi que la phosphorylation de ERK1/2 et du EGFR ont ete determinees par buvardage Western. Le traitement de cellules A10 avec l'ET-1 augmentait l'expression des proteines Gi, laquelle etait attenuee par le BQ123 et le BQ788, des antagonistes des recepteurs [ET.sub.A] et [E.sub.TB] respectivement. En outre, l'ET-1 augmentait la phosphorylation du EGFR chez les cellules A10, laquelle etait ramenee aux niveaux controles par un inhibiteur du EGFR et par les antagonistes des recepteurs [ET.sub.A] et [ET.sub.B]. De plus, l'ET-1 augmentait aussi la proliferation et la phosphorylation de ERK1/2 chez les cellules A10, lesquelles etaient ramenees aux niveaux controles par un inhibiteur du EGFR. Ces donnees suggerent que l'ET-1 trans-active le EGFR qui, par l'intermediaire de la signalisation par les MAP kinases, peut contribuer a l'augmentation de l'expression des proteines Gi et consequemment, stimuler la proliferation des cellules A10. [Traduit par la Redaction] Mots-cles: ET-1, EGFR, ERK1/2, proteines Gi, proliferation des CMLV.
Introduction Guanine-nucleotide-binding regulatory proteins (G proteins), a family of GTP-binding proteins play an important role in the regulation of a variety of physiological functions, including blood pressure, through the activation [...]