Clusterin activates survival through the phosphatidylinositol 3-kinase/Akt pathway
Clusterin activates survival through the phosphatidylinositol 3-kinase/Akt pathway
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DOI：
10.1074/jbc.m800403200
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发表时间：
2008-05-09
影响因子：
4.8
通讯作者：
Closset, Jean L.
中科院分区：
文献类型：
--
作者：
Ammar, Hayet;Closset, Jean L.
胆甾醇的主要形式是一种分泌的异源二聚体二硫键连接糖蛋白（75-80 kDa）。它首先与雄激素剥夺后大鼠腹侧前列腺中的细胞死亡有关。最近的研究表明，聚集蛋白在前列腺细胞中的过表达可以保护它们免受肿瘤坏死因子α（TNF α）诱导的凋亡。然而，这种生存机制的细节仍然不确定。在这里，我们调查如何clusterin阻止细胞进行TNF α诱导的凋亡。我们利用Tet-On基因表达系统建立了一个可诱导聚集蛋白的双稳定前列腺细胞系。我们证明，50%的细胞过表达clusterin逃脱TNF α和放线菌素D诱导的细胞死亡。此外，我们证明了MLL细胞与含有分泌的丛生蛋白的条件培养基或在细胞外培养基中补充纯化的丛生蛋白的孵育显著降低了TNF α诱导的凋亡。这种细胞外作用暗示巨蛋白，推定的膜受体丛生蛋白介导的生存。事实上，clusterin过表达上调megalin的表达，并以剂量依赖性方式诱导其磷酸化。有趣的是，我们发现clusterin过表达与Akt磷酸化的上调有关。Akt的激活可诱导Bad的磷酸化，并导致细胞色素c释放的减少。这些结果使我们能够确定一种机制，通过这种机制，分泌的clusterin有利于雄激素非依赖性前列腺癌细胞的生存，涉及其受体megalin和Akt生存途径。
Clusterin is, in its major form, a secreted heterodimeric disulfide-linked glycoprotein (75-80 kDa). It was first linked to cell death in the rat ventral prostate after androgen deprivation. Recent studies have demonstrated that overexpression of clusterin in prostatic cells protects them against tumor necrosis factor alpha (TNF alpha)-induced apoptosis. However the details of this survival mechanism remain undefined. Here, we investigate how clusterin prevents cells from undergoing TNF alpha-induced apoptosis. We established a double-stable prostatic cell line for inducible clusterin by using the Tet-On gene expression system. We demonstrated that 50% of the cells overexpressing clusterin escaped from TNF alpha- and actinomycin D-induced cell death. Moreover we demonstrated that the incubation of MLL cells with conditioned medium containing the secreted clusterin or the supplementation of purified clusterin in the extracellular medium decreased the TNF alpha-induced apoptosis significantly. This extracellular action implicates megalin, the putative membrane receptor for clusterin to mediate survival. Indeed clusterin overexpression up-regulated the expression of megalin and induced its phosphorylation in a dose-dependent manner. We interestingly showed that clusterin overexpression is associated with the up-regulation of the phosphorylation of Akt. Activated Akt induced the phosphorylation of Bad and caused a decrease of cytochrome c release. These results enable us to pinpoint one mechanism by which secreted clusterin favors survival in androgen-independent prostate cancer cells, implicating its receptor megalin and Akt survival pathway.