Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, University of Western Ontario, Dental Sciences Building, Room 3007J, London, ON, N6A 5C1, Canada.
Retrovirology. 2018 Jan 12;15(1):6. doi: 10.1186/s12977-018-0388-3.
The HIV-1 accessory proteins Nef and Vpu alter cell surface levels of multiple host proteins to modify the immune response and increase viral persistence. Nef and Vpu can downregulate cell surface levels of the co-stimulatory molecule CD28, however the mechanism of this function has not been completely elucidated.
Here, we provide evidence that Nef and Vpu decrease cell surface and total cellular levels of CD28. Moreover, using inhibitors we implicate the cellular degradation machinery in the downregulation of CD28. We shed light on the mechanisms of CD28 downregulation by implicating the Nef LL and DD motifs in decreasing cell surface CD28 and Nef DD in decreasing total cellular CD28. Moreover, the Vpu LV and S motifs were required for cell surface CD28 downregulation, while, unlike for CD4 downregulation, Vpu W was dispensable. The Vpu S motif was also critical for Vpu-mediated decreases in total CD28 protein level. Finally, the ability of Vpu to downregulate CD28 is conserved between multiple group M Vpu proteins and infection with viruses encoding or lacking Nef and Vpu have differential effects on activation upon stimulation.
We report that Nef and Vpu downregulate cell surface and total cellular CD28 levels. We identified inhibitors and mutations within Nef and Vpu that disrupt downregulation, shedding light on the mechanisms utilized to downregulate CD28. The conservation and redundancy between the abilities of two HIV-1 proteins to downregulate CD28 highlight the importance of this function, which may contribute to the development of latently infected cells.
HIV-1 的辅助蛋白 Nef 和 Vpu 改变多种宿主蛋白的细胞表面水平，以改变免疫反应并增加病毒的持久性。Nef 和 Vpu 可以下调共刺激分子 CD28 的细胞表面水平，但这一功能的机制尚未完全阐明。
在这里，我们提供的证据表明，Nef 和 Vpu 降低了 CD28 的细胞表面和总细胞水平。此外，我们使用抑制剂表明细胞降解机制参与了 CD28 的下调。我们通过暗示 Nef LL 和 DD 基序在降低细胞表面 CD28 中，以及 Nef DD 在降低总细胞 CD28 中，揭示了 CD28 下调的机制。此外，Vpu LV 和 S 基序是细胞表面 CD28 下调所必需的，而与 CD4 下调不同，Vpu W 是可有可无的。Vpu S 基序对于 Vpu 介导的总 CD28 蛋白水平降低也是至关重要的。最后，Vpu 下调 CD28 的能力在多个 M 组 Vpu 蛋白之间是保守的，并且感染编码或缺乏 Nef 和 Vpu 的病毒对刺激后的激活有不同的影响。
我们报告 Nef 和 Vpu 下调细胞表面和总细胞 CD28 水平。我们确定了 Nef 和 Vpu 内的抑制剂和突变，这些抑制剂和突变破坏了下调，揭示了用于下调 CD28 的机制。两种 HIV-1 蛋白下调 CD28 的能力的保守性和冗余性突出了这一功能的重要性，这可能有助于潜伏感染细胞的发展。
