Karim Md Fazlul, Yoshizawa Tatsuya, Sobuz Shihab U, Sato Yoshifumi, Yamagata Kazuya
Department of Medical Biochemistry, Faculty of Life Sciences, Kumamoto University, Kumamoto 860-8556, Japan.
Department of Medical Biochemistry, Faculty of Life Sciences, Kumamoto University, Kumamoto 860-8556, Japan.
Biochem Biophys Res Commun. 2017 Aug 19;490(2):423-428. doi: 10.1016/j.bbrc.2017.06.057. Epub 2017 Jun 14.
Sirtuin 7 (SIRT7) is an NAD-dependent deacetylase/deacylase, but only a limited number of SIRT7 substrates have been identified. Recently, we found that Sirt7 knockout mice are resistant to high-fat diet-induced fatty liver, and that SIRT7 positively regulates the protein level of TR4, a nuclear receptor involved in lipid metabolism, by inhibiting the CUL4B/DDB1/DCAF1 E3 ubiquitin ligase complex. However, the mechanism by which SIRT7 inhibits the E3 ubiquitin ligase complex was not identified. Here, we demonstrate that SIRT7 binds directly to DDB1 and deacetylates DDB1 at Lys1121. K1121R-DDB1 (a deacetylation-mimicking mutant) displayed reduced binding with DCAF1. The expression of TR4 protein and TR4 target genes, including Cd36, Cidea, Cidec and Pparg1, was increased in K1121R-DDB1-overexpressing Hepa1-6 cells compared to WT-DDB1-overexpressing cells. Our results indicate that the SIRT7-mediated deacetylation of K1121 attenuates the activity of the CUL4B/DDB1/DCAF1 E3 ubiquitin ligase complex by reducing binding between DDB1 and DCAF1, leading to the increased expression of TR4.
沉默调节蛋白7（SIRT7）是一种依赖烟酰胺腺嘌呤二核苷酸（NAD）的去乙酰化酶/脱酰基酶，但目前仅鉴定出有限数量的SIRT7底物。最近，我们发现Sirt7基因敲除小鼠对高脂饮食诱导的脂肪肝具有抗性，并且SIRT7通过抑制CUL4B/DDB1/DCAF1 E3泛素连接酶复合物来正向调节TR4（一种参与脂质代谢的核受体）的蛋白质水平。然而，SIRT7抑制E3泛素连接酶复合物的机制尚未明确。在此，我们证明SIRT7直接与DDB1结合，并使DDB1的赖氨酸1121位点去乙酰化。K1121R-DDB1（一种模拟去乙酰化的突变体）与DCAF1的结合减少。与过表达野生型DDB1的Hepa1-6细胞相比，过表达K1121R-DDB1的Hepa1-6细胞中TR4蛋白及其靶基因（包括Cd36、Cidea、Cidec和Pparg1）的表达增加。我们的结果表明，SIRT7介导的赖氨酸1121位点去乙酰化通过减少DDB1与DCAF1之间的结合来减弱CUL4B/DDB1/DCAF1 E3泛素连接酶复合物的活性，从而导致TR4表达增加。
