Department of Immunotherapeutics, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8519, Japan.
Retrovirology. 2013 May 20;10:52. doi: 10.1186/1742-4690-10-52.
Human T-cell leukemia virus type-1 (HTLV-1) is the causative retrovirus of adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-1 gene expression is maintained at low levels in vivo by unknown mechanisms. A combination therapy of interferon-α (IFN-α) and zidovudin (AZT) shows therapeutic effects in ATL patients, although its mechanism is also obscure. We previously found that viral gene expression in IL-2-dependent HTLV-1-infected T-cells (ILTs) derived from ATL patients was markedly suppressed by stromal cells through a type I IFN response. Here, we investigated the effects of IFN-α with or without AZT on viral gene expression and cell growth in ILTs.
ILTs expressed variable but lower amounts of HTLV-1 Tax protein than HTLV-1-transformed HUT102 cells. Following the addition of IFN-α, the amounts of HTLV-1 p19 in the supernatants of these cells decreased in three days, while HTLV-1 gene expression decreased only in ILTs but not HUT102 cells. IFN-α also suppressed the spontaneous HTLV-1 induction in primary ATL cells cultured for 24 h. A time course study using ILTs revealed that the levels of intracellular Tax proteins decreased in the first 24 h after addition of IFN-α, before the reduction in HTLV-1 mRNA levels. The initial decreases of Tax protein following IFN-α treatment were observed in 6 of 7 ILT lines tested, although the reduction rates varied among ILT lines. An RNA-dependent protein kinase (PKR)-inhibitor reversed IFN-mediated suppression of Tax in ILTs. IFN-α also induced cell cycle arrest at the G0/G1 phase and suppressed NF-κB activities in these cells. AZT alone did not affect HTLV-1 gene expression, cell viability or NF-κB activities. AZT combined with IFN-α markedly induced cell apoptosis associated with phosphorylation of p53 and induction of p53-responsive genes in ILTs.
IFN-α suppressed HTLV-1 gene expression at least through a PKR-mediated mechanism, and also induced cell cycle arrest in ILTs. In combination with AZT, IFN-α further induced p53 signaling and cell apoptosis in these cells. These findings suggest that HTLV-1-infected cells at an IL-2-dependent stage retain susceptibility to type I IFN-mediated regulation of viral expression, and partly explain how AZT/IFN-α produces therapeutic effects in ATL.
人类 T 细胞白血病病毒 1 型（HTLV-1）是成人 T 细胞白血病/淋巴瘤（ATL）和 HTLV-1 相关脊髓病/热带痉挛性截瘫（HAM/TSP）的致病逆转录病毒。HTLV-1 基因的表达在体内通过未知机制维持在低水平。干扰素-α（IFN-α）和齐多夫定（AZT）的联合治疗对 ATL 患者具有治疗效果，尽管其机制也不清楚。我们之前发现，源自 ATL 患者的 IL-2 依赖性 HTLV-1 感染 T 细胞（ILTs）中的病毒基因表达通过 I 型 IFN 反应被基质细胞显著抑制。在这里，我们研究了 IFN-α联合或不联合 AZT 对 ILTs 中病毒基因表达和细胞生长的影响。
ILTs 表达的 HTLV-1 Tax 蛋白量比 HTLV-1 转化的 HUT102 细胞少，但变异较大。加入 IFN-α后，这些细胞上清液中的 HTLV-1 p19 在 3 天内减少，而 HTLV-1 基因表达仅在 ILTs 中减少，而不在 HUT102 细胞中减少。IFN-α 还抑制了培养 24 小时的原发性 ATL 细胞中 HTLV-1 的自发诱导。使用 ILTs 的时间过程研究表明，在加入 IFN-α后的前 24 小时内，细胞内 Tax 蛋白水平下降，然后 HTLV-1 mRNA 水平下降。在测试的 7 个 ILT 系中的 6 个中观察到 IFN 处理后 Tax 蛋白的初始减少，尽管减少率在 ILT 系之间有所不同。RNA 依赖性蛋白激酶（PKR）抑制剂逆转了 IFN 对 ILTs 中 Tax 的抑制作用。IFN-α 还诱导这些细胞在 G0/G1 期的细胞周期停滞，并抑制 NF-κB 活性。AZT 单独不影响 HTLV-1 基因表达、细胞活力或 NF-κB 活性。AZT 联合 IFN-α 可显著诱导 ILTs 中的细胞凋亡，与 p53 磷酸化和 p53 反应性基因的诱导有关。
IFN-α 通过 PKR 介导的机制抑制 HTLV-1 基因表达，还诱导 ILTs 中的细胞周期停滞。与 AZT 联合使用时，IFN-α 进一步诱导这些细胞中的 p53 信号和细胞凋亡。这些发现表明，处于 IL-2 依赖性阶段的 HTLV-1 感染细胞仍然容易受到 I 型 IFN 介导的病毒表达调控，部分解释了 AZT/IFN-α 如何在 ATL 中产生治疗效果。
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