Division of Infectious DiseasesDepartment of MedicineUniversity of California, San DiegoLa JollaCA.
Center for Convergent Research of Emerging Virus InfectionKorea Research Institute of Chemical TechnologyDaejeonSouth Korea.
Hepatology. 2021 Feb;73(2):533-547. doi: 10.1002/hep.31313. Epub 2020 Nov 7.
Epitranscriptomic modification of RNA has emerged as the most prevalent form of regulation of gene expression that affects development, differentiation, metabolism, viral infections, and most notably cancer. We have previously shown that hepatitis B virus (HBV) transcripts are modified by N6 methyladenosine (m A) addition. HBV also affects m A modification of several host RNAs, including phosphatase and tensin homolog (PTEN), a well-known tumor suppressor. PTEN plays a critical role in antiviral innate immunity and the development of hepatocellular carcinoma (HCC). Reports have shown that PTEN controlled interferon regulatory factor 3 (IRF-3) nuclear localization by negative phosphorylation of IRF-3 at Ser97, and PTEN reduced carcinogenesis by inhibiting the phosphatidylinositol-3-kinase (PI3K)/AKT pathway.
Here, we show that HBV significantly increases the m A modification of PTEN RNA, which contributes to its instability with a corresponding decrease in PTEN protein levels. This is reversed in cells in which the expression of m A methyltransferases is silenced. PTEN expression directly increases activated IRF-3 nuclear import and subsequent interferon synthesis. In the absence of PTEN, IRF-3 dephosphorylation at the Ser97 site is decreased and interferon synthesis is crippled. In chronic HBV patient biopsy samples, m A-modified PTEN mRNA levels were uniformly up-regulated with a concomitant decrease of PTEN mRNA levels. HBV gene expression also activated the PI3K/AKT pathway by regulating PTEN mRNA stability in HCC cell lines.
The m A epitranscriptomic regulation of PTEN by HBV affects innate immunity by inhibiting IRF-3 nuclear import and the development of HCC by activating the PI3K/AKT pathway. Our studies collectively provide new insights into the mechanisms of HBV-directed immune evasion and HBV-associated hepatocarcinogenesis through m A modification of the host PTEN mRNAs.
RNA 的转录后修饰已成为影响基因表达调控的最普遍形式，这种调控可影响发育、分化、代谢、病毒感染，尤其是癌症。我们之前已经证明乙型肝炎病毒 (HBV) 转录本可通过 N6 甲基腺苷 (m A) 修饰。HBV 还会影响包括磷酸酶和张力蛋白同源物 (PTEN) 在内的几种宿主 RNA 的 m A 修饰，PTEN 是一种众所周知的肿瘤抑制因子。PTEN 在抗病毒先天免疫和肝细胞癌 (HCC) 的发生发展中发挥着关键作用。有报道表明，PTEN 通过对干扰素调节因子 3 (IRF-3) 的 Ser97 进行负磷酸化来控制 IRF-3 的核定位，PTEN 通过抑制磷脂酰肌醇-3-激酶 (PI3K)/AKT 通路来减少致癌作用。
在此，我们发现 HBV 可显著增加 PTEN RNA 的 m A 修饰，这导致其不稳定性增加，相应的 PTEN 蛋白水平降低。在沉默 m A 甲基转移酶表达的细胞中，这种情况会得到逆转。PTEN 的表达直接增加了激活的 IRF-3 核内输入以及随后的干扰素合成。在缺乏 PTEN 的情况下，IRF-3 在 Ser97 位点的去磷酸化减少，干扰素的合成受到阻碍。在慢性 HBV 患者活检样本中，m A 修饰的 PTEN mRNA 水平普遍上调，同时 PTEN mRNA 水平降低。HBV 基因表达还通过调节 PTEN mRNA 稳定性在 HCC 细胞系中激活了 PI3K/AKT 通路。
HBV 通过 HBV 对 PTEN 的 m A 转录后调控，通过抑制 IRF-3 的核内输入以及激活 PI3K/AKT 通路，影响先天免疫并促进 HCC 的发生。我们的研究共同为 HBV 介导的免疫逃避和 HBV 相关肝癌发生的机制提供了新的见解，这些机制涉及宿主 PTEN mRNA 的 m A 修饰。
