WCU Department of Cogno-Mechatronics Engineering, Pusan National University, Busan 609-735, Republic of Korea.
Int J Mol Med. 2012 Apr;29(4):581-6. doi: 10.3892/ijmm.2012.879. Epub 2012 Jan 3.
We have previously shown that hepatitis B virus (HBV) protein X (HBX), a regulatory protein of HBV, activates Stat1, leading to type I interferon (IFN) production. Type I IFN secreted from HBX-expressing hepatic cells enforces antiviral signals through its binding to the cognate type I IFN receptor. We therefore investigated how cells handle this detrimental situation. Interestingly, compared to Chang cells stably expressing an empty vector (Chang-Vec), Chang cells stably expressing HBX (Chang-HBX) showed lower levels of IFN-α receptor 1 (IFNAR1) protein, a subunit of type I IFN receptor. The levels of IFNAR1 transcripts detected in Chang-HBX cells were lower than the levels in Chang-Vec cells, indicating that HBX regulates IFNAR1 at the transcriptional level. Moreover, we observed that HBX induced the translocation of IFNAR1 to the cytoplasm. Consistent with these observations, HBX also downregulated Tyk2, which is required for the stable expression of IFNAR1 on the cell surface. Eventually, Chang-HBX cells consistently maintained a lower level of IFNAR1 expression and displayed no proper response to IFN-α, while Chang-Vec cells exhibited a proper response to IFN-α treatment. Taken together, we propose that HBX downregulates IFNAR1, leading to the avoidance of extracellular IFN-α signal transduction.
我们之前已经证明,乙型肝炎病毒 (HBV) 蛋白 X (HBX) 是 HBV 的一种调节蛋白,可激活 Stat1,导致 I 型干扰素 (IFN) 的产生。从表达 HBX 的肝细胞中分泌的 I 型 IFN 通过与其同源 I 型 IFN 受体结合来强制发挥抗病毒信号。因此,我们研究了细胞如何处理这种有害情况。有趣的是,与稳定表达空载体 (Chang-Vec) 的 Chang 细胞相比,稳定表达 HBX (Chang-HBX) 的 Chang 细胞的 I 型 IFN 受体亚单位 IFN-α受体 1 (IFNAR1) 蛋白水平较低。在 Chang-HBX 细胞中检测到的 IFNAR1 转录本水平低于 Chang-Vec 细胞中的水平,表明 HBX 在转录水平上调节 IFNAR1。此外,我们观察到 HBX 诱导 IFNAR1 向细胞质易位。与这些观察结果一致,HBX 还下调了 Tyk2,后者是 IFNAR1 在细胞表面稳定表达所必需的。最终,Chang-HBX 细胞始终保持较低水平的 IFNAR1 表达,对 IFN-α没有适当的反应,而 Chang-Vec 细胞对 IFN-α 治疗表现出适当的反应。总之,我们提出 HBX 下调 IFNAR1,从而避免了细胞外 IFN-α信号转导。