Schönbühler Bianca, Schmitt Verena, Huesmann Heike, Kern Andreas, Gamerdinger Martin, Behl Christian
Institute of Pathobiochemistry, University Medical Center of the Johannes Gutenberg University, D-55099 Mainz, Germany.
Int J Mol Sci. 2016 Dec 30;18(1):69. doi: 10.3390/ijms18010069.
The maintenance of cellular proteostasis is dependent on molecular chaperones and protein degradation pathways. Chaperones facilitate protein folding, maturation, and degradation, and the particular fate of a misfolded protein is determined by the interaction of chaperones with co-chaperones. The co-factor CHIP (C-terminus of HSP70-inteacting protein, STUB1) ubiquitinates chaperone substrates and directs proteins to the cellular degradation systems. The activity of CHIP is regulated by two co-chaperones, BAG2 and HSPBP1, which are potent inhibitors of the E3 ubiquitin ligase activity. Here, we examined the functional correlation of HSP72, CHIP, and BAG2, employing human primary fibroblasts. We showed that HSP72 is a substrate of CHIP and that BAG2 efficiently prevented the ubiquitination of HSP72 in young cells as well as aged cells. Aging is associated with a decline in proteostasis and we observed increased protein levels of CHIP as well as BAG2 in senescent cells. Interestingly, the ubiquitination of HSP72 was strongly reduced during aging, which revealed that BAG2 functionally counteracted the increased levels of CHIP. Interestingly, HSPBP1 protein levels were down-regulated during aging. The data presented here demonstrates that the co-chaperone BAG2 influences HSP72 protein levels and is an important modulator of the ubiquitination activity of CHIP in young as well as aged cells.
细胞蛋白质稳态的维持依赖于分子伴侣和蛋白质降解途径。伴侣蛋白促进蛋白质折叠、成熟和降解，错误折叠蛋白质的特定命运由伴侣蛋白与共伴侣蛋白的相互作用决定。辅助因子CHIP（热休克蛋白70相互作用蛋白C末端，STUB1）使伴侣蛋白底物泛素化，并将蛋白质导向细胞降解系统。CHIP的活性受两种共伴侣蛋白BAG2和HSPBP1的调节，它们是E3泛素连接酶活性的有效抑制剂。在这里，我们用人原代成纤维细胞研究了HSP72、CHIP和BAG2的功能相关性。我们发现HSP72是CHIP的底物，并且BAG2在年轻细胞和衰老细胞中均能有效阻止HSP72的泛素化。衰老与蛋白质稳态的下降有关，我们观察到衰老细胞中CHIP和BAG2的蛋白质水平升高。有趣的是，衰老过程中HSP72的泛素化显著减少，这表明BAG2在功能上抵消了CHIP水平的升高。有趣的是，衰老过程中HSPBP1的蛋白质水平下调。此处给出的数据表明，共伴侣蛋白BAG2影响HSP72的蛋白质水平，并且是年轻细胞和衰老细胞中CHIP泛素化活性的重要调节剂。
