Université Paris Cité, CNRS, INSERM, Institut Cochin, 22 Rue Méchain, 75014, Paris, France.
Center for Immunology of Viral, Auto-Immune, Hematological and Bacterial Diseases, Université Paris-Saclay, Inserm, CEA, IMVA-HB/IDMIT), Fontenay-Aux-Roses, France.
Retrovirology. 2022 Oct 29;19(1):23. doi: 10.1186/s12977-022-00610-7.
TASOR, a component of the HUSH repressor epigenetic complex, and SAMHD1, a cellular triphosphohydrolase (dNTPase), are both anti-HIV proteins antagonized by HIV-2/SIVsmm Viral protein X. As a result, the same viral protein is able to relieve two different blocks along the viral life cell cycle, one at the level of reverse transcription, by degrading SAMHD1, the other one at the level of proviral expression, by degrading TASOR. Phosphorylation of SAMHD1 at T592 has been shown to downregulate its antiviral activity. The discovery that T819 in TASOR was lying within a SAMHD1 T592-like motif led us to ask whether TASOR is phosphorylated on this residue and whether this post-translational modification could regulate its repressive activity.
Using a specific anti-phospho-antibody, we found that TASOR is phosphorylated at T819, especially in cells arrested in early mitosis by nocodazole. We provide evidence that the phosphorylation is conducted by a Cyclin/CDK1 complex, like that of SAMHD1 at T592. While we could not detect TASOR in quiescent CD4 + T cells, TASOR and its phosphorylated form are present in activated primary CD4 + T lymphocytes. In addition, TASOR phosphorylation appears to be independent from TASOR repressive activity. Indeed, on the one hand, nocodazole barely reactivates HIV-1 in the J-Lat A1 HIV-1 latency model despite TASOR T819 phosphorylation. On the other hand, etoposide, a second cell cycle arresting drug, reactivates latent HIV-1, without concomitant TASOR phosphorylation. Furthermore, overexpression of wt TASOR or T819A or T819E similarly represses gene expression driven by an HIV-1-derived LTR promoter. Finally, while TASOR is degraded by HIV-2 Vpx, TASOR phosphorylation is prevented by HIV-1 Vpr, likely as a consequence of HIV-1 Vpr-mediated-G2 arrest.
Altogether, we show that TASOR phosphorylation occurs in vivo on T819. This event does not appear to correlate with TASOR-mediated HIV-1 silencing. We speculate that TASOR phosphorylation is related to a role of TASOR during cell cycle progression.
TASOR 是 HUSH 抑制物表观遗传复合物的一个组成部分，SAMHD1 是一种细胞三磷酸水解酶（dNTPase），它们都是 HIV-2/SIVsmm 病毒蛋白 X 拮抗的抗 HIV 蛋白。因此，同一种病毒蛋白能够通过降解 SAMHD1 在逆转录水平和通过降解 TASOR 在原病毒表达水平上解除两种不同的病毒生命周期阻断。SAMHD1 的 T592 磷酸化已被证明可下调其抗病毒活性。TASOR 中的 T819 位于 SAMHD1 的 T592 样基序内的发现促使我们提出问题：TASOR 是否在该残基上发生磷酸化，以及这种翻译后修饰是否可以调节其抑制活性。
使用特异性的磷酸化抗体，我们发现 TASOR 在 T819 处发生磷酸化，尤其是在被长春花碱阻滞于早期有丝分裂的细胞中。我们提供的证据表明，磷酸化是由细胞周期蛋白/CDK1 复合物进行的，就像 SAMHD1 的 T592 那样。虽然我们在静止的 CD4+T 细胞中检测不到 TASOR，但 TASOR 和其磷酸化形式存在于激活的原发性 CD4+T 淋巴细胞中。此外，TASOR 磷酸化似乎独立于 TASOR 的抑制活性。事实上，一方面，尽管 TASOR 的 T819 磷酸化，但长春花碱几乎不能在 J-Lat A1 HIV-1 潜伏期模型中重新激活 HIV-1。另一方面，另一种细胞周期阻滞药物依托泊苷可重新激活潜伏的 HIV-1，而不伴随 TASOR 磷酸化。此外，wt TASOR 或 T819A 或 T819E 的过表达同样可抑制由 HIV-1 衍生的 LTR 启动子驱动的基因表达。最后，虽然 HIV-2 Vpx 可降解 TASOR，但 HIV-1 Vpr 可阻止 TASOR 磷酸化，这可能是 HIV-1 Vpr 介导的 G2 阻滞的结果。
总之，我们证明 TASOR 在体内发生 T819 磷酸化。这一事件似乎与 TASOR 介导的 HIV-1 沉默无关。我们推测 TASOR 磷酸化与 TASOR 在细胞周期进程中的作用有关。
