Jin Xiongjie, Moskophidis Demetrius, Hu Yanzhong, Phillips Andrew, Mivechi Nahid F
Center for Molecular Chaperone/Radiobiology and Cancer Virology, Augusta, Georgia 30912, USA.
J Cell Biochem. 2009 Jun 1;107(3):504-15. doi: 10.1002/jcb.22151.
Heat shock factor Hsf1 regulates the stress-inducibility of heat shock proteins (Hsps) or molecular chaperones. One of the functions attributed to Hsps is their participation in folding and degradation of proteins. We recently showed that hsf1(-/-) cells accumulate ubiquitinated proteins. However, a direct role for Hsf1 in stability of specific proteins such as p53 has not been elucidated. We present evidence that cells deficient in hsf1 accumulate wild-type p53 protein. We further show that hsf1(-/-) cells express lower levels of alphaB-crystallin and cells deficient in alphaB-crystallin also accumulate p53 protein. Reports indicate that alphaB-crystallin binds to Fbx4 ubiquitin ligase, and they target cyclin D1 for degradation through a pathway involving the SCF (Skp1-Cul1-F-box) complex. Towards determining a mechanism for p53 degradation involving alphaB-crystallin and Hsf1, we have found that ectopic expression of Fbx4 in wild-type mouse embryo fibroblasts (MEFs) expressing mutant p53 (p53R175H) leads to increase in its degradation, while MEFs deficient in hsf1 or alphaBcry are defective in degradation of this p53 protein. In addition, immunoprecipitated p53R175H from wild-type MEFs is able to pull-down both alphaB-crystallin and Fbx4. Finally, immunoprecipitated wild-type p53 from doxorubicin treated U2OS cells can pull-down endogenous alphaB-crystallin and Fbx4. These results indicate that hsf1- and alphaBcry-deficient cells accumulate p53 due to reduced levels of alphaB-crystallin in these cells. Elevated levels of p53 in hsf1- and alphaBcry-deficient cells lead to their increased sensitivity to DNA damaging agents. These data reveal a novel mechanism for protein degradation through Hsf1 and alphaB-crystallin.
热休克因子Hsf1调节热休克蛋白（Hsps）或分子伴侣的应激诱导性。Hsps的功能之一是参与蛋白质的折叠和降解。我们最近发现hsf1（-/-）细胞积累泛素化蛋白。然而，Hsf1在特定蛋白质如p53稳定性中的直接作用尚未阐明。我们提供证据表明，缺乏hsf1的细胞积累野生型p53蛋白。我们进一步表明，hsf1（-/-）细胞中αB-晶状体蛋白表达水平较低，而缺乏αB-晶状体蛋白的细胞也积累p53蛋白。报道表明，αB-晶状体蛋白与Fbx4泛素连接酶结合，它们通过涉及SCF（Skp1-Cul1-F-box）复合物的途径靶向细胞周期蛋白D1进行降解。为了确定涉及αB-晶状体蛋白和Hsf1的p53降解机制，我们发现，在表达突变型p53（p53R175H）的野生型小鼠胚胎成纤维细胞（MEFs）中异位表达Fbx4会导致其降解增加，而缺乏hsf1或αBcry的MEFs在这种p53蛋白的降解方面存在缺陷。此外，从野生型MEFs中免疫沉淀的p53R175H能够下拉αB-晶状体蛋白和Fbx4。最后，从阿霉素处理的U2OS细胞中免疫沉淀的野生型p53能够下拉内源性αB-晶状体蛋白和Fbx4。这些结果表明，缺乏hsf1和αBcry的细胞由于这些细胞中αB-晶状体蛋白水平降低而积累p53。缺乏hsf1和αBcry的细胞中p53水平升高导致它们对DNA损伤剂的敏感性增加。这些数据揭示了一种通过Hsf1和αB-晶状体蛋白进行蛋白质降解的新机制。
