Molecular mechanisms of NF-κB mediated T-cell acitivation induced by HTLV-I Tax

我们研究了NF-κB在人类t细胞白血病病毒I型（HTLV-I）癌基因产物Tax诱导的t细胞活化中的作用。gp34是一种细胞表面分子，在抗原刺激的t细胞和HTLV-I感染的t细胞上表达，但在丝裂原刺激的t细胞上不表达。与此一致的是，gp34启动子中的NF-κB样序列可被HTLV-I Tax激活，但与典型的NF-κB可被TPA激活不同，它不被TPA激活。为了充分了解HTLV-I Tax活化t细胞的分子机制，我们试图寻找除TPA治疗外激活NF-κB样序列所需的刺激。我们将gp34启动子驱动的荧光素酶质粒转染到人t细胞系Jurkat中，并检测与TPA单独处理相比，加入离子霉素或针对细胞表面分子（CD2, CD3, CD4， CD26和CD28）的抗体是否增强了报告细胞活性。离子霉素和抗CD28抗体的加入分别使报告蛋白活性提高了8倍和9倍，表明Ca浓度升高和CD28产生的信号通路可以激活gp34 NF-κB样序列。然而，其激活率比Tax低（40倍），这表明Tax可能激活了这两种途径之外的其他途径。此外，我们使用表达Tax的重组腺病毒和IL-2依赖的人t细胞系Kit 225证明了Tax可以诱导静止的人t细胞的细胞周期进展。税收突变体诱导细胞周期进展的能力与激活NF-κB转录途径的能力相似，表明NF-κB途径对税收介导的细胞周期进展很重要。然而，过表达NF-κB不诱导细胞周期进展。这些结果表明，除了典型的NF-κB外，Tax还可以激活其他途径。

We examined the role of NF-κB in T-cell activation induced by the oncogene product Tax of human T-cell leukemia virus type I (HTLV-I).gp34 is a cell surface molecule which is expressed on antigen stimulated T-cells and HTLV-I infected T-cells, but not on mitogen stimulated T-cells. Consistent with this, NF-κB like sequence in gp34 promoter is activated by HTLV-I Tax, however it is not activated by TPA treatment unlike typical NF-κB which is activated by TPA treatment. For full understanding of molecular mechanism of T-cell activation by HTLV-I Tax, we have attempted to search for stimulation required for the activation of the NF-κB like sequence in addition to TPA treatment. We transfected gp34 promoter-driven luciferase plasmids into a human T-cell line Jurkat and examined whether the addition of ionomycin or antibodies against cell surface molecules (CD2, CD3, CD4, CD26 and CD28) enhanced reporter activity as compared to TPA treatment alone. Addition of ionomycin and anti-CD28 antibodies enhanced the reporter activity by 8 and 9 folds, respectively, indicating that the signaling pathways originated from increase in Ca concentration and CD28 can activate the gp34 NF-κB like sequence. However, the activation was lower than that by Tax (40 folds), indicating the possibility that Tax activates other pathways than these two.In addition, we showed that Tax can induce cell cycle progression in resting human T-cells using a Tax-expessing recombinant adenovirus and an IL-2 dependent human T-cell line Kit 225. The ability of Tax mutants to induce cell cycle progression paralleled those to activate the NF-κB transcription pathway, indicating that the NF-κB pathway is important for Tax-mediated cell cycle progression. However, overexpression of NF-κB did not induce cell cycle progression. These results indicate that Tax can activate other pathway (s) than typical NF-κB.