title: Role of L-type calcium channel blocking in epidermal growth factor receptor-independent activation of extracellular signal regulated kinase 1/2.
abstract: OBJECTIVE
  Vascular smooth muscle cell (VSMC) differentiation, growth and survival, key events in the development of cardiovascular diseases, are under the control of signaling enzymes including extracellular signal regulated kinase 1/2 (ERK 1/2), Akt and epidermal growth factor receptor (EGFR) activation. EGFR trans-activation is known to mediate thrombin- or angiotensin II (AII)-stimulated ERK 1/2 activation. However, our laboratory has demonstrated, in thrombin-stimulated VSMC, that the prevention of intracellular Ca2+ elevation ([Ca2+]i) by BAPTA-AM pretreatment unveiled EGFR-independent ERK 1/2 activation. Since calcium channel blockers (CCBs) also impair agonist-induced [Ca2+]i elevation, we investigated whether EGFR-independent ERK 1/2 activation could occur in VSMCs treated by CCBs such as amlodipine, isradipine and verapamil, and examined the possible role of Akt.
  
  
  METHODS
  Cultured VSMCs were pretreated or not with CCBs and with various inhibitors of the signaling pathways under study, prior to stimulation by thrombin or AII, and the phosphorylation/activation status of EGFR, Akt and ERK 1/2 was determined by Western blotting using phospho-specific antibodies.
  
  
  CONCLUSIONS
  Unlike BAPTA, CCBs did not impair stimulus-induced EGFR trans-activation, hence ERK1/2 phosphorylation. However, when EGFR kinase was inhibited, CCBs and BAPTA dose-dependently protected stimulus-induced ERK1/2 phosphorylation. The effect of amlodipine could not be mimicked by its R+ enantiomer, which is devoid of CCB activity, suggesting that the effects of CCBs were accounted for by their L-type Ca2+ channel-blocking property. Altogether, our results indicated that in G-protein-coupled receptor (GPCR)-stimulated VSMCs, the prevention of [Ca2+]i elevation by CCBs unmasked an EGFR kinase-independent phosphorylation of ERK 1/2. Since EGFR kinase inhibitors are supposed to be efficient in the treatment of some cancers, such a mechanism might be clinically relevant in hypertensive patients with cancer.
authors.affiliation: Centre National de la Recherche Scientifique UMR 7131, Université Pierre et Marie Curie, Hôpital Broussais, 75014, Paris, France.
authors.forename: Xing
authors.initials: X
authors.lastname: Yin
authors.forename: Evelyne
authors.initials: E
authors.lastname: Polidano
authors.forename: Claude
authors.initials: C
authors.lastname: Faverdin
authors.forename: Pierre
authors.initials: P
authors.lastname: Marche
mesh_terms: D017311:Amlodipine / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D066246:ErbB Receptors / Q000378:metabolism*; D017275:Isradipine / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017208:Rats, Wistar; D013917:Thrombin / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D002614:Chelating Agents; D011518:Proto-Oncogene Proteins; D000804:Angiotensin II; D017311:Amlodipine; D004533:Egtazic Acid; D014700:Verapamil; D066246:ErbB Receptors; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D013917:Thrombin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D017275:Isradipine