17β-estradiol (E2) treatment of cells results in an upregulation of SIRT1 and a down-regulation of PPARγ. The decrease in PPARγ expression is mediated by increased degradation of PPARγ. Here we report that PPARγ is ubiquitinated by HECT E3 ubiquitin ligase NEDD4-1 and degraded, along with PPARγ, in response to E2 stimulation. The PPARγ interacts with ubiquitin ligase NEDD4-1 through a conserved PPXY-WW binding motif. The WW3 domain in NEDD4-1 is critical for binding to PPARΓ. NEDD4-1 overexpression leads to PPARγ ubiquitination and reduced expression of PPARγ. Conversely, knockdown of NEDD4-1 by specific siRNAs abolishes PPARΓ ubiquitination. These data indicate that NEDD4-1 is the E3 ubiquitin ligase responsible for PPARγ ubiquitination. Here, we show that NEDD4-1 delays cellular senescence by degrading PPARΓ expression. Taken together, our data show that E2 could upregulate SIRT1 expression via promoting the PPARΓ ubiquitination-proteasome degradation pathway to delay the process of cell senescence.
Nucleostemin(NS)作为核仁蛋白,在神经干细胞、胚胎干细胞以及某些肿瘤细胞中均高表达,在多种肿瘤细胞增殖和凋亡调控中具有重要作用.本文通过瞬时转染NS siRNA降低NS的表达,以探究NS对HepG2细胞增殖和凋亡的影响.结果显示,下调NS表达使HepG2细胞增殖加快,G1期细胞减少,S期及G2/M期细胞增加,凋亡减少.激光共聚焦实验表明,NS与S期激酶相关蛋白2(S-phase kinase-associated protein 2,Skp2)在HepG2细胞中存在共定位现象;Co-IP实验证明,NS与Skp2能相互作用;NS下调后,Skp2出核仁的数量增加,p27和p53表达降低.总之,下调NS可促进HepG2细胞中Skp2从核仁逸出,p27降解增强,同时p53表达下降,或由此促进HepG2细胞增殖,抑制其凋亡.
