Transcriptional repression of IRF7 by MYC is critical for antiviral immune response in human pDC [pDC]

Type I interferons (IFN) are crucial mediators of human innate and adaptive immunity and are massively produced from plasmacytoid dendritic cells (pDC). IRF7 is a critical regulator of type I IFN production when pathogens are detected by TLR7/9 in pDC. However, hyperactivation of pDC can cause life-threatening autoimmune diseases. To avoid the deleterious effects of aberrant pDC activation, tight regulation of IRF7 is required. Nonetheless, the detailed mechanisms of how IRF7 transcription is regulated in pDC are still elusive. To this end, we identified the global gene expression changes after stimulation of human primary pDC with the TLR9 agonist CpGB. We identified that the transcription factor MYC is prominently upregulated upon CpGB engagement in pDC. Moreover, when we knocked down MYC in the pDC-like cell line GEN2.2, production of interferon-stimulated genes (ISGs) was dramatically increased and was further enhanced by CpGB. Interestingly, MYC is shown to be recruited to the IRF7 promoter region through interaction with NCOR2/HDAC3 for its repression, and HDAC3 inhibition enhanced IRF7 expression and IFNβ production. Interestingly, activation of TLR9-mediated NF-kB and MAPK and nuclear translocation of IRF7 were greatly enhanced by MYC depletion. Pharmaceutical inhibition of MYC recovered IRF7 expression, further confirming the negative role of MYC in the antiviral response by pDC. Furthermore, the inverse correlation of MYC and IRF7 was validated in psoriasis skin sample datasets. Therefore, our results identify the novel immunomodulatory role of MYC in human pDC and may add to our understanding of aberrant pDC function in autoimmune diseases. 12 total pDC samples assayed at 4 time points post CpGB stimulation (3 replicates of 0hrs; 3 replicates of 4 hrs; 3 replicates of 8 hrs; 3 replicates of 12 hrs).I型干扰素（Type I interferons, IFN）是人类固有免疫与适应性免疫的关键介导分子，主要由浆细胞样树突状细胞（plasmacytoid dendritic cells, pDC）大量分泌。当pDC通过Toll样受体7/9（TLR7/9）识别病原体时，干扰素调节因子7（IRF7）是调控I型干扰素产生的关键因子。然而，pDC的过度激活可引发危及生命的自身免疫性疾病。为避免pDC异常激活带来的有害效应，需要对IRF7进行严格调控，但目前学界对pDC中IRF7转录调控的具体机制仍尚不明确。为此，我们对经Toll样受体9（TLR9）激动剂CpGB刺激后的人原代pDC进行了全局基因表达谱变化分析，发现转录因子MYC在pDC结合CpGB后显著上调。此外，在类pDC细胞系GEN2.2中敲低MYC后，干扰素刺激基因（ISGs）的表达显著升高，且经CpGB刺激后这一现象进一步增强。研究发现，MYC可通过与核受体辅抑制因子2/组蛋白去乙酰化酶3（NCOR2/HDAC3）结合被招募至IRF7启动子区域以抑制其转录；HDAC3抑制剂处理可增强IRF7的表达及干扰素β（IFNβ）的产生。值得注意的是，MYC敲低可显著增强TLR9介导的核因子κB（NF-κB）、丝裂原活化蛋白激酶（MAPK）通路激活以及IRF7的核转位。通过药物抑制MYC可恢复IRF7的表达，进一步证实了MYC在pDC抗病毒应答中的负调控作用。此外，我们在银屑病皮肤样本数据集中验证了MYC与IRF7的负相关关系。综上，本研究揭示了MYC在人pDC中全新的免疫调控功能，有助于加深学界对自身免疫性疾病中pDC异常功能的理解。本数据集共包含12份pDC样本，在经CpGB刺激后的4个时间点（0小时、4小时、8小时、12小时各3次生物学重复）完成了检测。