Impairment of the ubiquitin-proteasome system by cellular FLIP
Impairment of the ubiquitin-proteasome system by cellular FLIP
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DOI：
10.1111/j.1365-2443.2007.01087.x
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发表时间：
2007-06-01
期刊：
影响因子：
2.1
通讯作者：
Naito, Mikihiko
中科院分区：
文献类型：
--
作者：
Ishioka, Toshiyasu;Katayama, Ryohei;Naito, Mikihiko
细胞FLIP（cFLIP）是半胱天冬酶-8的同源物，不具有蛋白酶活性，其抑制由死亡受体连接引发的凋亡信号传导。我们以前报道过长型cFLIP（cFLIP-L）抑制β-连环蛋白的泛素化并增强Wnt信号传导。在这里，我们表明，cFLIP-L损害的泛素-蛋白酶体系统（UPS）的功能，并增加了各种短寿命的蛋白质，如GFP与不稳定序列，β-连环蛋白和HIF 1 α，受到快速泛素化和蛋白酶体降解共轭的积累。因此，在表达cFLIP-L的细胞中诱导β-连环蛋白和HIF 1 α介导的基因表达。外源表达的cFLIP-L在细胞核周围区域聚集，并且cFLIP-L聚集体难以溶解。与外源性表达的cFLIP-L一样，A549肺癌细胞中的内源性cFLIP在细胞中显示颗粒分布，并且超过60%的cFLIP-L难以溶解。通过RNA介导的干扰下调A549细胞中的cFLIP降低了β-连环蛋白和HIF 1 α介导的基因表达。这些结果表明cFLIP-L易于聚集并损害UPS功能，这可能参与了某些癌细胞中表达的cFLIP-L的病理功能。
Cellular FLIP (cFLIP) is a homologue of caspase-8 without protease activity that inhibits the apoptosis signaling initiated by death receptor ligation. We previously reported that a long form of cFLIP (cFLIP-L) inhibits ubiquitylation of beta-catenin and enhances Wnt signaling. Here we show that cFLIP-L impairs the function of the ubiquitin-proteasome system (UPS), and increases the accumulation of various short-lived proteins, such as GFP conjugated with destabilization sequence, beta-catenin and HIF1 alpha, that are subjected to rapid ubiquitylation and degradation by proteasomes. Accordingly, beta-catenin- and HIF1 alpha-mediated gene expressions are induced in the cFLIP-L-expressing cells. Exogenously expressed cFLIP-L accumulates in aggregates at the peri-nuclear region in the cells, and the cFLIP-L aggregates are refractory to solubilization. Like exogenously expressed cFLIP-L, the endogenous cFLIP in A549 lung cancer cells displays particulate distribution in the cells and more than 60% of cFLIP-L is refractory to solubilization. Down-regulation of cFLIP in A549 cells by RNA-mediated interference reduced beta-catenin- and HIF1 alpha-mediated gene expression. These results suggest that cFLIP-L is prone to aggregate and impairs UPS function, which could be involved in the pathological function of cFLIP-L expressed in certain cancer cells.