Laboratory of Virology, National Institute of Immunology, New Delhi, India.
Blood. 2011 Jun 16;117(24):6600-7. doi: 10.1182/blood-2011-01-333427. Epub 2011 Apr 26.
HIV-1 viral protein U (Vpu) is involved in ubiquitination and degradation of BM stromal cell Ag 2 and surface receptor CD4 through their recruitment to SCF(β-TrcP) (Skp1/Cul1/F-box) ubiquitin ligase (SCF) complex. Here, we show that specific interaction of wild-type Vpu protein with SCF complex leads to inhibition of ubiquitination and proteasomal degradation of p53 protein in a β-TrcP-dependent manner. Successful interaction of SCF(β-TrcP) complex with β-TrcP binding motif (DS(52)GNES(56)) present in Vpu is essential because mutant Vpu possessing specific alanine substitutions (DA(52)GNEA(56)) in the β-TrcP binding motif not only failed to stabilize p53 protein but was also unable to inhibit ubiquitination of p53 protein. Furthermore, Vpu competes efficiently with the interaction of p53 protein with the β-TrcP subunit of the SCF complex and inhibits subsequent ubiquitination of p53 proteins in a dose-dependent manner. We also observed potent apoptotic activity in a p53 null cell line (H-1299) that was cotransfected with p53 and Vpu-expressing plasmids. Furthermore, MOLT-3 (human T-lymphoblast) cells when infected with vesicular stomatitis virus glycoprotein-pseudotypic HIV-1 possessing wild-type vpu gene exhibited maximum activation of p53/Bax proteins and p53-mediated cell death. These findings establish a novel function of Vpu in modulating the stability of p53 protein that correlates positively with apoptosis during late stages of HIV-1 infection.
HIV-1 病毒蛋白 U（Vpu）通过招募到 SCF（β-TrcP）（Skp1/Cul1/F-box）泛素连接酶（SCF）复合物，参与 BM 基质细胞 Ag2 和表面受体 CD4 的泛素化和降解。在这里，我们表明野生型 Vpu 蛋白与 SCF 复合物的特异性相互作用导致 p53 蛋白的泛素化和蛋白酶体降解受到抑制，这是依赖于β-TrcP 的。SCF（β-TrcP）复合物与 Vpu 中存在的β-TrcP 结合基序（DS（52）GNES（56））的成功相互作用是必不可少的，因为具有β-TrcP 结合基序中特定丙氨酸取代（DA（52）GNEA（56））的突变 Vpu 不仅不能稳定 p53 蛋白，而且也不能抑制 p53 蛋白的泛素化。此外，Vpu 有效地与 p53 蛋白与 SCF 复合物的β-TrcP 亚基的相互作用竞争，并以剂量依赖的方式抑制随后的 p53 蛋白的泛素化。我们还观察到在共转染 p53 和 Vpu 表达质粒的 p53 缺失细胞系（H-1299）中具有很强的凋亡活性。此外，感染具有野生型 vpu 基因的水疱性口炎病毒糖蛋白假型 HIV-1 的 MOLT-3（人 T 淋巴细胞白血病）细胞表现出最大的 p53/Bax 蛋白激活和 p53 介导的细胞死亡。这些发现确立了 Vpu 在调节 p53 蛋白稳定性方面的新功能，这与 HIV-1 感染后期的凋亡呈正相关。
