The E3 ligase TRIM56 is a host restriction factor of Zika virus and depends on its RNA-binding activity but not miRNA regulation, for antiviral function

Yang, Darong; Li, Nan L.; Wei, Dahai; Liu, Baoming; Guo, Fang; Elbahesh, Husni; Zhang, Yunzhi; Zhou, Zhi; Chen, Guo-Yun; Li, Kui

To investigate if TRIM56 expression changes in neural cell types following ZIKV infection, we first examined the abundance of endogenous TRIM56 protein in SVGA cells by immunoblotting (Fig 9A) . At 72 h.p.i, cells infected with increasing doses of ZIKV-MR766 all exhibited ã 3-fold increase in TRIM56 protein, compared with mock-infected cells (compare lanes 2-6 vs lane 1). This was not secondary to an overt IFN response, as minimal induction of IFIT3, a well-characterized ISG and sensitive marker of IFN production, was merely observed at high MOIs (lanes 5 and 6), and high concentration IFN treatment (lane 7) did not give rise to more robust uptick of TRIM56 expression than ZIKV, despite being a much stronger inducer of IFIT3 expression. Subsequently, qPCR of TRIM56 and ISG56 mRNA expression confirmed the protein data and indicated that the ZIKV upregulation of TRIM56 occurred at mRNA level (Fig 9B and 9C) . To determine whether this is the case in primary cells of neural origin, we examined Trim56 expression in primary mouse cortical neurons. Because it was challenging to obtain large number of neurons for immunoblotting, we utilized qPCR assay to quantify the mRNA levels of Trim56 prior to and at 24 and 48 h.p.i., respectively, of ZIKV-PRVABC59 (MOI = 1). As shown in Fig 9D, these cells were found to have basal expression of Trim56. In line with the expression pattern of TRIM56 transcript in SVGA cells, Trim56 mRNA abundance was upregulated by~2-fold at 48 h.p.i. In aggregate, the experiments show that TRIM56 is expressed in human and mouse neural cell types, which moderately upregulate the expression of this antiviral protein in response to ZIKV infection.