Liao Shengjie, Du Rong, Wang Lei, Qu Zhen, Cui Xiukun, Li Chang, Liu Fei, Huang Mi, Wang Jiuxiang, Chen Jiaxiang, Gao Meng, Yu Shanshan, Tang Zhaohui, Li David Wan-Cheng, Jiang Tao, Liu Mugen
Key Laboratory of Molecular Biophysics of the Ministry of Education, Center for Human Genome Research, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, PR China.
Union Hospital, Huazhong University of Science and Technology, Wuhan, Hubei 430022, PR China.
Int J Biochem Cell Biol. 2015 Nov;68:78-86. doi: 10.1016/j.biocel.2015.08.016. Epub 2015 Aug 28.
Heat shock factor 4 (HSF4) is an important transcriptional factor that plays a vital role in lens development and differentiation, but the mechanism underlying the regulation of HSF4 is ambiguous. BCAS2 was reported to be an essential subunit of pre-mRNA splicing complex. Here, we identified BCAS2 as a novel HSF4 interacting partner. High expression of BCAS2 in the lens epithelium cells and the bow region of mouse lens was detected by immunohistochemistry. In human lens epithelial cells, BCAS2 negatively regulates HSF4 protein level and transcriptional activity, whereas in BCAS2 knockdown cells, HSF4 protein stability was increased significantly. We further demonstrated that the prolonged protein half-time of HSF4 in BCAS2 knockdown cells was due to reduced ubiquitination. Moreover, we have identified the lysine 206 of HSF4 as the key residue for ubiquitination. The HSF4-K206R mutant blocked the impact of BCAS2 on HSF4 protein stability. Taken together, we identified a pathway for HSF4 degradation through the ubiquitin-proteasome system, and a novel function for BCAS2 that may act as a negative regulatory factor for modulating HSF4 protein homeostasis.
热休克因子4（HSF4）是一种重要的转录因子，在晶状体发育和分化中起着至关重要的作用，但其调节HSF4的机制尚不清楚。据报道，BCAS2是前体mRNA剪接复合体的一个必需亚基。在此，我们鉴定出BCAS2是一种新的与HSF4相互作用的蛋白。通过免疫组织化学检测到BCAS2在小鼠晶状体上皮细胞和晶状体弓区高表达。在人晶状体上皮细胞中，BCAS2负向调节HSF4蛋白水平和转录活性，而在BCAS2敲低的细胞中，HSF4蛋白稳定性显著增加。我们进一步证明，BCAS2敲低细胞中HSF4蛋白半衰期延长是由于泛素化减少所致。此外，我们已确定HSF4的赖氨酸206是泛素化的关键残基。HSF4-K206R突变体阻断了BCAS2对HSF4蛋白稳定性的影响。综上所述，我们确定了一条通过泛素-蛋白酶体系统降解HSF4的途径，以及BCAS2的一种新功能，即其可能作为调节HSF4蛋白稳态的负调控因子。
