Convergence of Redox-Sensitive and Mitogen-Activated Protein Kinase Signaling Pathways in Tumor Necrosis Factor-α–Mediated Monocyte Chemoattractant Protein-1 Induction in Vascular Smooth Muscle Cells

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Abstract
—Monocyte chemoattractant protein-1 (MCP-1) is an important component of the inflammatory response of the vessel wall and has been shown to be regulated by cytokines, such as tumor necrosis factor-α (TNF-α). However, the precise signaling pathways leading to MCP-1 induction have not been fully elucidated in vascular smooth muscle cells (VSMCs). Cytokine signal transduction involves protein kinases as well as reactive oxygen species (ROS). The relation between these 2 factors is not clear. In this study, we show that TNF-α induces a parallel phosphorylation of extracellular signal–regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (p38MAPK) and increases MCP-1 mRNA expression in cultured VSMCs. Inhibition of ERK1/2 but not p38MAPK caused a partial attenuation of MCP-1 induction (43±10% inhibition). Incubation of VSMCs with multiple antioxidants (diphenylene iodonium, liposomal superoxide dismutase, catalase, n -acetylcysteine, dimethylthiourea, and pyrrolidine dithiocarbamate) had no effect on TNF-α–mediated MCP-1 upregulation. However, simultaneous blockade of the ERK1/2 and ROS pathways by using PD098059 combined with diphenylene iodonium or n -acetylcysteine potently enhanced the ability of MAPK kinase inhibitors to abrogate MCP-1 mRNA expression (100±2% inhibition). Thus, parallel ROS-dependent and ERK1/2-dependent pathways converge to regulate TNF-α–induced MCP-1 gene expression in VSMCs. These data unmask a complex but organized integration of ROS and protein kinases that mediates cytokine-induced vascular inflammatory gene expression.