Division of Infectious Diseases, Department of Internal Medicine, University of Texas Health Science Center at Houston, Houston, TX, 77030, USA.
Department of Molecular Virology & Microbiology, Baylor College of Medicine, Houston, TX, USA.
Virol J. 2019 Feb 20;16(1):22. doi: 10.1186/s12985-019-1128-6.
The regulatory cyclin, Cyclin T1 (CycT1), is a host factor essential for HIV-1 replication in CD4 T cells and macrophages. The importance of CycT1 and the Positive Transcription Elongation Factor b (P-TEFb) complex for HIV replication is well-established, but regulation of CycT1 expression and protein levels during HIV replication and latency establishment in CD4 T cells is less characterized.
To better define the regulation of CycT1 levels during HIV replication in CD4 T cells, multiparameter flow cytometry was utilized to study the interaction between HIV replication (intracellular p24) and CycT1 of human peripheral blood memory CD4 T cells infected with HIV in vitro. CycT1 was further examined in CD4 T cells of human lymph nodes.
In activated (CD3+CD28 costimulation) uninfected blood memory CD4 T cells, CycT1 was most significantly upregulated in maximally activated (CD69+CD25+ and HLA.DR+CD38+) cells. In memory CD4 T cells infected with HIV in vitro, two distinct infected populations of p24+CycT1+ and p24+CycT1- cells were observed during 7 days infection, suggestive of different phases of productive HIV replication and subsequent latency establishment. Intriguingly, p24+CycT1- cells were the predominant infected population in activated CD4 T cells, raising the possibility that productively infected cells may transition into latency subsequent to CycT1 downregulation. Additionally, when comparing infected p24+ cells to bystander uninfected p24- cells (after bulk HIV infections), HIV replication significantly increased T cell activation (CD69, CD25, HLA.DR, CD38, and Ki67) without concomitantly increasing CycT1 protein levels, possibly due to hijacking of P-TEFb by the viral Tat protein. Lastly, CycT1 was constitutively expressed at higher levels in lymph node CD4 T cells compared to blood T cells, potentially enhancing latency generation in lymphoid tissues.
CycT1 is most highly upregulated in maximally activated memory CD4 T cells as expected, but may become less associated with T cell activation during HIV replication. The progression into latency may further be predicated by substantial generation of p24+CycT1- cells during HIV replication.
调节细胞周期蛋白 Cyclin T1（CycT1）是 HIV-1 在 CD4 T 细胞和巨噬细胞中复制所必需的宿主因子。CycT1 和正向转录伸长因子 b（P-TEFb）复合物对 HIV 复制的重要性已得到充分证实，但在 HIV 复制和潜伏期建立过程中 CD4 T 细胞中 CycT1 的表达和蛋白水平的调节仍知之甚少。
为了更好地定义 HIV 在体外感染的 CD4 T 细胞中复制过程中 CycT1 水平的调节，我们利用多参数流式细胞术研究了 HIV 复制（细胞内 p24）与人类外周血记忆 CD4 T 细胞中 HIV 感染的 CycT1 之间的相互作用。进一步在人类淋巴结的 CD4 T 细胞中检查了 CycT1。
在激活的（CD3+CD28 共刺激）未感染的血液记忆 CD4 T 细胞中，在最大激活（CD69+CD25+和 HLA.DR+CD38+）细胞中，CycT1 被显著上调。在体外感染 HIV 的记忆 CD4 T 细胞中，在 7 天的感染过程中观察到两种不同的感染 p24+CycT1+和 p24+CycT1-细胞群体，提示存在不同的 HIV 复制阶段和随后的潜伏期建立。有趣的是，p24+CycT1-细胞是激活的 CD4 T 细胞中主要的感染群体，这表明感染的细胞可能在 CycT1 下调后进入潜伏期。此外，当将感染的 p24+细胞与旁观者未感染的 p24-细胞（在批量 HIV 感染后）进行比较时，HIV 复制会显著增加 T 细胞的激活（CD69、CD25、HLA.DR、CD38 和 Ki67），而不会同时增加 CycT1 蛋白水平，这可能是由于病毒 Tat 蛋白劫持了 P-TEFb。最后，与血液 T 细胞相比，淋巴结 CD4 T 细胞中 CycT1 的表达水平始终较高，这可能会增强淋巴组织中的潜伏生成。
CycT1 在最大激活的记忆 CD4 T 细胞中被高度上调，这是意料之中的，但在 HIV 复制过程中，它与 T 细胞的激活可能不再相关。在 HIV 复制过程中，大量生成 p24+CycT1-细胞可能进一步预示着潜伏期的进展。
