Table_1_Effect of Different Nuclear Localization Signals on the Subcellular Localization and Anti-HIV-1 Function of the MxB Protein.DOCX

Interferon exerts its antiviral activity by stimulating the expression of antiviral proteins. These interferon stimulate genes (ISGs) often target a group of viruses with unique molecular mechanisms. One such ISG is myxovirus resistance B (MxB) that has been reported to inhibit human immunodeficiency virus type 1 (HIV-1) by targeting viral capsid and impairing nuclear import of viral DNA. The antiviral specificity of MxB is determined by its N-terminal 25 amino acids sequence which has the nuclear localization activity, therefore functions as a nuclear localization signal (NLS). In this study, we report that the bipartite NLS, but not the classic NLS, the PY-NLS, nor the arginine-rich NLS, when used to replace the N-terminal sequence of MxB, drastically suppress HIV-1 gene expression and virus production, thus creates a new anti-HIV-1 mechanism. MxB preserves its anti-HIV-1 activity when its N-terminal sequence is replaced by the arginine-rich NLS. Interestingly, the arginine-rich NLS allows MxB to inhibit HIV-1 CA mutants that are otherwise resistant to wild type MxB, which suggests sequence specific targeting of viral capsid. Together, these data implicate that it is not the nuclear import function itself, but rather the sequence and the mechanism of action of the NLS which define the antiviral property of MxB.

干扰素通过诱导抗病毒蛋白的表达发挥抗病毒活性。干扰素刺激基因（ISGs）往往通过独特的分子机制靶向多类病毒。其中一种干扰素刺激基因即为黏液病毒抗性蛋白B（MxB），已有研究证实其可通过靶向病毒衣壳并干扰病毒DNA的核输入过程，抑制1型人类免疫缺陷病毒（HIV-1）。MxB的抗病毒特异性由其N端25个氨基酸序列决定，该序列具备核定位活性，因此可作为核定位信号（NLS）发挥功能。本研究表明，将MxB的N端序列替换为双分型核定位信号（bipartite NLS），而非经典型核定位信号、PY型核定位信号或富含精氨酸的核定位信号时，可显著抑制HIV-1的基因表达与病毒生成，由此建立了全新的抗HIV-1机制。当MxB的N端序列被富含精氨酸的核定位信号替换后，其仍保留抗HIV-1活性。值得注意的是，富含精氨酸的核定位信号可使MxB抑制对野生型MxB产生耐药性的HIV-1衣壳突变体，这提示MxB对病毒衣壳存在序列特异性靶向作用。综上，本研究结果显示，决定MxB抗病毒特性的并非核输入功能本身，而是核定位信号的序列及其作用机制。