Roles of ROS in cytokine-mediated signaling and immune regulation

다국어 초록 (Multilingual Abstract)

To investigate the possible roles of reactive oxygen species(ROS) in transforming growth factor-β1(TGF-β1) signal transduction, quiescent human lung fibroblast(HLF) cells were stimulated with TGF-β1. TGF-β1 stimulation resulted in a transient burst of ROS with maximal increase at 10 min after treatment. This ROS increase was inhibited by antioxidants, NAC and GSH. TGF-β1 induced protein tyrosine phosphorylation at 10 min after treatment, which was abolished by NAC, indicating that ROS mediates TGF-β1-induced tyrosine phosphorylation. Also, direct addition of H₂O₂ resulted in tyrosine phosphorylation of the same size protein. In addition, TGF-β1 treatment stimulated IL-6 gene expression and protein synthesis in HLF cells. Antioxidants including NAC, GSH, and catalase abolished TGF-β1-induced IL-6 gene expression, and direct H₂O₂ treatment induced IL-6 expression in a dose-dependent manner. Genistein, an inhibitor of tyrosine kinase, inhibited TGF-β1-induced IL-6 gene expression, while it had no effect on ROS production. Finally, NAC released the suppressive effects of TGF-β1 on HLF cell proliferation. In addition, there are growing evidences that ROS is involved in apoptosis. To understand the roles of ROS in Fas-mediated apoptosis of multiple myeloma(MM) cells, the effects of antioxidants were tested. Fas-mediated apoptosis was further increased in the presence of antioxidants. Previous our study demonstrated that okadaic acid(OKA), inhibits IL-6-mediated growth of myeloma cells via reducing IL-6 production. OKA treatment increased Fas-mediated apoptosis and reduced intracellular ROS level in myeloma cells. To clarify the direct roles of PP2A in apoptosis and ROS production, the stably transfected cell lines, sense- or antisense-PP2A transfectants, were established. Intracellular ROS level was significantly decreased in antisense-PP2A transfectant, but increased in sense-PP2A transfectant compared with vector control. Concomitantly, Fas-mediated apoptosis was remarkably induced in antisense-PP2A transfectant, indicating that the suppression of PP2A increases the susceptibility to Fas-mediated apoptosis. In addition, spontaneous IL-6 production, was reduced in antisense-PP2A transfectant, while hydrogen peroxide also increased IL-6 expression. Taken together, these results indicate that PP2A is an essential factor for survival and growth of myeloma cells via regulating ROS and IL-6 production.