title: Modulation of vascular smooth muscle cell growth by magnesium-role of mitogen-activated protein kinases.
abstract: We tested the hypothesis that Mg(2+) influences growth of vascular smooth muscle cells (VSMCs) by modulating cell cycle activation through mitogen-activated protein (MAP) kinase-dependent pathways. Rat VSMCs were grown in culture medium containing normal Mg(2+) (1.02 mmol/L, control) and increasing concentrations of Mg(2+) (2-4 mmol/L) for 1-8 days. Effects of varying extracellular Mg(2+) concentration ([Mg(2+)](e)) on intracellular free Mg(2+) concentration ([Mg(2+)](i)) were assessed using mag-fura. Growth actions of Mg(2+) were evaluated by measuring cell cycle activation, DNA synthesis, and protein synthesis. Expression of cell cycle promoters, cyclin D1, cyclin E, Cdk2, and Cdk4 was assessed by immunoblotting. Phosphorylation of cell cycle inhibitors p21(cip1) and p27(kip1) and MAP kinases, ERK1/2, p38MAP kinase, and JNK was evaluated using phospho-specific antibodies. [Mg(2+)](i) increased in a dose-dependent manner in response to increasing [Mg(2+)](e). These effects were evident within 2 days and maximal responses were obtained after 6 days. High [Mg(2+)](e) induced cell cycle activation with a lower proportion of cells in G(1) phase (75 +/- 1.0%) and a higher fraction of cells in S phase (12 +/- 0.7%) versus control (G(1), 88.5 +/- 1.4%; S, 6.8 +/- 1.2%; P < 0.05). This was associated with increased protein content of cyclin D1 and Cdk4 and decreased activation of p21(cip1) and p27(kip1). In cells exposed to 2 mmol/L Mg(2+), DNA and protein synthesis was increased approximately threefold. Phosphorylation of MEK1/2 and ERK1/2 was enhanced two to threefold in cells grown in 2 mmol/L Mg(2+). These effects were rapid, occurring within 2 days. Phosphorylation of MEK3/6, p38 MAP kinase, and JNK was unaltered by increasing [Mg2](e). PD98059 (10(-5) mol/L), specific MEK1/2 inhibitor, but not SB202190 (10(-5) mol/L) (specific p38 MAP kinase inhibitor), attenuated Mg(2+)-induced growth actions. These data demonstrate the novel findings that cell cycle activation and growth regulation by Mg(2+) occurs via ERK1/2-dependent, p38 MAP kinase-independent pathways.
authors.affiliation: Canadian Institute for Health Research, Clinical Research Institute of Montreal, University of Montreal, Quebec, Canada. touyzr@ircm.qc.ca
authors.forename: Rhian M
authors.initials: RM
authors.lastname: Touyz
authors.forename: Guoying
authors.initials: G
authors.lastname: Yao
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000187:drug effects / Q000378:metabolism; D016213:Cyclins / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology; D048031:JNK Mitogen-Activated Protein Kinases; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D011921:Rats, Inbred WKY; D025521:Tumor Suppressor Proteins / Q000187:drug effects / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: C493958:Cdkn1a protein, rat; C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D008274:Magnesium