Giri Banabihari, Dixit Vishwa D, Ghosh Manik C, Collins Gary D, Khan Islam U, Madara Karen, Weeraratna Ashani T, Taub Dennis D
Laboratory of Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
Eur J Immunol. 2007 Aug;37(8):2104-16. doi: 10.1002/eji.200636680.
Lipid rafts play an important role in signal integration and in the cellular activation of a number of cytokine and growth factor receptors. It has recently been demonstrated that flotillin proteins are recruited to lipid raft microdomains upon cellular activation and play a role in neural cell regeneration, receptor signaling and lymphocyte activation. However, little is known about the relevance of the flotillin proteins during T cell responses to chemoattractant stimulation. To this end, cytoplasmic and lipid raft fractions from human T cells were analyzed for flotillin protein redistribution prior to and after CXCL12 stimulation. Flotillin-1, but not flotillin-2, redistributes to lipid rafts upon CXCR4 ligation. Moreover, in CXCL12-treated T cells, flotillin-1 also associates with several raft proteins including LAT, CD48 and CD11a but not Lck. In addition, an increase in CXCR4 association with flotillin-1 in lipid rafts was observed after chemokine treatment. RNAi technology was also utilized to inhibit the expression of flotillin-1, resulting in an inhibition of CXCL12-mediated signaling, function and CXCR4 recruitment into lipid rafts. Together, these data suggest that the increased association of cellular flotillin-1 with lipid raft microdomains during chemokine exposure may play an important role in chemokine receptor signaling and receptor partitioning with lipid rafts.
脂筏在信号整合以及多种细胞因子和生长因子受体的细胞活化过程中发挥着重要作用。最近有研究表明，细胞活化时，弗洛蒂林蛋白会被招募到脂筏微结构域，并在神经细胞再生、受体信号传导和淋巴细胞活化中发挥作用。然而，关于弗洛蒂林蛋白在T细胞对趋化因子刺激的反应中的相关性，我们知之甚少。为此，我们分析了人T细胞的细胞质和脂筏组分在CXCL12刺激前后弗洛蒂林蛋白的重新分布情况。CXCR4被激活后，弗洛蒂林-1会重新分布到脂筏中，而弗洛蒂林-2则不会。此外，在CXCL12处理的T细胞中，弗洛蒂林-1还与包括LAT、CD48和CD11a在内的几种脂筏蛋白相关联，但不与Lck相关联。另外，趋化因子处理后，观察到脂筏中CXCR4与弗洛蒂林-1的结合增加。我们还利用RNAi技术抑制弗洛蒂林-1的表达，结果导致CXCL12介导的信号传导、功能以及CXCR4募集到脂筏中的过程受到抑制。这些数据共同表明，趋化因子暴露期间细胞弗洛蒂林-1与脂筏微结构域结合的增加可能在趋化因子受体信号传导以及受体与脂筏的分配过程中发挥重要作用。
