Abdelmohsen Kotb, Srikantan Subramanya, Yang Xiaoling, Lal Ashish, Kim Hyeon Ho, Kuwano Yuki, Galban Stefanie, Becker Kevin G, Kamara Davida, de Cabo Rafael, Gorospe Myriam
Laboratory of Cellular and Molecular Biology, NIA-IRP, NIH, Baltimore, MD 21224, USA.
EMBO J. 2009 May 6;28(9):1271-82. doi: 10.1038/emboj.2009.67. Epub 2009 Mar 26.
The RNA-binding protein HuR regulates the stability and translation of numerous mRNAs encoding stress-response and proliferative proteins. Although its post-transcriptional influence has been linked primarily to its cytoplasmic translocation, here we report that moderate heat shock (HS) potently reduces HuR levels, thereby altering the expression of HuR target mRNAs. HS did not change HuR mRNA levels or de novo translation, but instead reduced HuR protein stability. Supporting the involvement of the ubiquitin-proteasome system in this process were results showing that (1) HuR was ubiquitinated in vitro and in intact cells, (2) proteasome inhibition increased HuR abundance after HS, and (3) the HuR kinase checkpoint kinase 2 protected against the loss of HuR by HS. Within a central, HS-labile approximately 110-amino-acid region, K182 was found to be essential for HuR ubiquitination and proteolysis as mutant HuR(K182R) was left virtually unubiquitinated and was refractory to HS-triggered degradation. Our findings reveal that HS transiently lowers HuR by proteolysis linked to K182 ubiquitination and that HuR reduction enhances cell survival following HS.
RNA 结合蛋白 HuR 可调节众多编码应激反应蛋白和增殖蛋白的 mRNA 的稳定性及翻译过程。尽管其转录后影响主要与其胞质转位有关，但我们在此报告，适度热休克（HS）能有效降低 HuR 水平，从而改变 HuR 靶 mRNA 的表达。热休克并未改变 HuR mRNA 水平或从头翻译，而是降低了 HuR 蛋白的稳定性。以下结果表明泛素 - 蛋白酶体系统参与了这一过程：（1）HuR 在体外和完整细胞中均被泛素化；（2）蛋白酶体抑制可增加热休克后 HuR 的丰度；（3）HuR 激酶检查点激酶 2 可防止热休克导致的 HuR 丢失。在一个位于中心的、对热休克敏感的约 110 个氨基酸的区域内，发现 K182 对于 HuR 的泛素化和蛋白水解至关重要，因为突变型 HuR(K182R)几乎未被泛素化，且对热休克引发的降解具有抗性。我们的研究结果表明，热休克通过与 K182 泛素化相关的蛋白水解作用短暂降低 HuR 水平，且 HuR 水平降低可增强热休克后的细胞存活能力。
