CAIR-1/BAG-3 abrogates heat shock protein-70 chaperone complex-mediated protein degradation - Accumulation of poly-ubiquitinated Hsp90 client proteins
CAIR-1/BAG-3 abrogates heat shock protein-70 chaperone complex-mediated protein degradation - Accumulation of poly-ubiquitinated Hsp90 client proteins
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DOI：
10.1074/jbc.m209682200
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发表时间：
2003-08-01
影响因子：
4.8
通讯作者：
Kohn, EC
中科院分区：
文献类型：
--
作者：
Doong, H;Rizzo, K;Kohn, EC
BAG家族蛋白是热休克蛋白（Hsp）70的调节辅伴侣。热休克蛋白70通过泛素介导的蛋白酶体降解促进损伤蛋白的去除。这个过程可以由格尔德霉素驱动，格尔德霉素是一种不可逆的Hsp 90阻断剂。我们推测CAIR-1/BAG-3抑制HSP介导的蛋白酶体降解。人乳腺癌细胞被工程化以过表达结合Hsp 70的全长CAIR-1（FL）或不能结合Hsp 70的BAG结构域缺失突变体（dBAG）。FL过表达阻止格尔德霉素介导的总Akt和磷酸化Akt以及其他Hsp客户蛋白的损失。dBAG不提供保护，表明需要Hsp 70结合。泛素化Akt在FL表达细胞中积累，模拟lactacystin蛋白酶体抑制的作用，表明CAIR-1以BAG结构域依赖性方式抑制蛋白泛素化远端的蛋白酶体降解。FL细胞中的蛋白质保护可推广到下游Akt靶点、GSK 3 β、P70 S6激酶、CREB和其他Hsp客户蛋白，包括Raf-1、细胞周期蛋白依赖性激酶4和表皮生长因子受体。这些研究结果表明，热休克蛋白70是一个伴侣驱动的多蛋白降解复合物和抑制性共伴侣CAIR-1功能的客户端泛素化的远端。此外，多聚泛素化不足以有效靶向Hsp客户蛋白的蛋白酶体。
BAG family proteins are regulatory co-chaperones for heat shock protein (Hsp) 70. Hsp70 facilitates the removal of injured proteins by ubiquitin-mediated proteasomal degradation. This process can be driven by geldanamycin, an irreversible blocker of Hsp90. We hypothesize that CAIR-1/BAG-3 inhibits Hsp-mediated proteasomal degradation. Human breast cancer cells were engineered to overexpress either full-length CAIR-1 (FL), which binds Hsp70, or a BAG domain-deletion mutant (dBAG) that cannot bind Hsp70. FL overexpression prevented geldanamycin-mediated loss of total and phospho-Akt and other Hsp client proteins. dBAG provided no protection, indicating a requirement for Hsp70 binding. Ubiquitinated Akt accumulated in FL-expressing cells, mimicking the effect of lactacystin proteasomal inhibition, indicating that CAIR-1 inhibits proteasomal degradation distal to protein ubiquitination in a BAG domain-dependent manner. Protein protection in FL cells was generalizable to downstream Akt targets, GSK3beta, P70S6 kinase, CREB, and other Hsp client proteins, including Raf-1, cyclin-dependent kinase 4, and epidermal growth factor receptor. These findings suggest that Hsp70 is a chaperone driving a multiprotein degradation complex and that the inhibitory co-chaperone CAIR-1 functions distal to client ubiquitination. Furthermore, poly-ubiquitination is not sufficient for efficient proteasomal targeting of Hsp client proteins.