Redox regulation of chemokine receptor expression

Cytokines and reactive oxygen intermediates (ROI) are frequent companions at sites of acute inflammation. We have shown previously that in human monocytes, bacterial lipopolysaccharide, IL-1, and tumor necrosis factor-α induce a rapid down-regulation of the monocyte chemotactic protein-1 receptor CCR2 (CC chemokine receptor-2). These stimuli also induce production of ROI. In this paper, we investigate the influence of antioxidants and/or ROI on chemokine-receptor expression. In human monocytes, the antioxidant pyrrolidine dithiocarbamate (PDTC) rapidly inhibited CCR2 (95–100% of inhibition) and CCR5 (77–100% of inhibition) mRNA expression by strongly decreasing transcript stability. CCR2 half-life was decreased from 1.5 h to 45 min; CCR5 half-life was decreased from 2 h to 70 min. This inhibitory activity also included CXCR4 (CXC chemokine receptor-4) but not CXCR2 receptor and, although to a lesser extent, was shared by the antioxidants N-acetyl-l-cysteine and 2-mercaptoethanol. In contrast, the ROI-generating system xanthine/xanthine oxidase increased CCR5 and CXCR4 mRNA expression and counteracted the inhibitory effect of PDTC. Accordingly, H(2)O(2) and the glutathione-depleting drug buthionine sulfoximine increased to different extents CCR2, CCR5, and CXCR4 mRNA expression. The PDTC-mediated inhibition of CCR5 and CXCR4 mRNA expression was associated with decreased chemotactic responsiveness (>90% inhibition) and with a marked inhibition of surface-receptor expression. In contrast, xanthine/xanthine oxidase opposed the bacterial lipopolysaccharide- and tumor necrosis factor-α-mediated inhibition of CCR5 and CXCR4 mRNA expression and increased both the CCR5 surface expression and the cell migration (3-fold) in response to macrophage inflammatory protein-1β. These results suggest that the redox status of cells is a crucial determinant in the regulation of the chemokine system.

细胞因子与活性氧中间产物（reactive oxygen intermediates, ROI）是急性炎症部位的常见伴随物。我们此前的研究证实，在人单核细胞中，细菌脂多糖、白细胞介素-1及肿瘤坏死因子-α可快速下调单核细胞趋化蛋白-1受体CCR2（CC趋化因子受体-2）的表达。上述刺激因子同时可诱导活性氧中间产物的产生。本文中，我们探讨了抗氧化剂及/或活性氧中间产物对趋化因子受体表达的影响。在人单核细胞中，抗氧化剂吡咯烷二硫代氨基甲酸酯（pyrrolidine dithiocarbamate, PDTC）可通过显著降低转录本稳定性，快速抑制CCR2（抑制率95%~100%）与CCR5（抑制率77%~100%）的mRNA表达。CCR2的半衰期从1.5小时缩短至45分钟，CCR5的半衰期从2小时缩短至70分钟。该抑制活性同样作用于CXCR4（CXC趋化因子受体-4），但不影响CXCR2受体；且抗氧化剂N-乙酰-L-半胱氨酸与2-巯基乙醇也可在一定程度上产生类似抑制效应，不过强度较弱。与之相反，产生活性氧中间产物的体系黄嘌呤/黄嘌呤氧化酶可上调CCR5与CXCR4的mRNA表达，并抵消PDTC的抑制作用。相应地，过氧化氢（H₂O₂）与耗竭谷胱甘肽的药物丁硫氨酸亚砜胺可在不同程度上调CCR2、CCR5及CXCR4的mRNA表达。PDTC介导的CCR5与CXCR4 mRNA表达抑制，与趋化应答能力下降（抑制率>90%）以及表面受体表达显著受抑相关。相较之下，黄嘌呤/黄嘌呤氧化酶可拮抗细菌脂多糖与肿瘤坏死因子-α介导的CCR5及CXCR4 mRNA表达抑制，并可增加CCR5的表面表达量，同时使细胞对巨噬细胞炎症蛋白-1β的迁移反应提升3倍。上述结果表明，细胞的氧化还原状态是调控趋化因子系统的关键决定因素。