Department of Microbiology and Immunology, The University of Western Ontario, London, ON N6A 3K7, Canada.
Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
Viruses. 2020 Jun 3;12(6):610. doi: 10.3390/v12060610.
Viruses alter a multitude of host-cell processes to create a more optimal environment for viral replication. This includes altering metabolism to provide adequate substrates and energy required for replication. Typically, viral infections induce a metabolic phenotype resembling the Warburg effect, with an upregulation of glycolysis and a concurrent decrease in cellular respiration. Human adenovirus (HAdV) has been observed to induce the Warburg effect, which can be partially attributed to the adenovirus protein early region 4, open reading frame 1 (E4orf1). E4orf1 regulates a multitude of host-cell processes to benefit viral replication and can influence cellular metabolism through the transcription factor avian myelocytomatosis viral oncogene homolog (MYC). However, E4orf1 does not explain the full extent of Warburg-like HAdV metabolic reprogramming, especially the accompanying decrease in cellular respiration. The HAdV protein early region 1A (E1A) also modulates the function of the infected cell to promote viral replication. E1A can interact with a wide variety of host-cell proteins, some of which have been shown to interact with metabolic enzymes independently of an interaction with E1A. To determine if the HAdV E1A proteins are responsible for reprogramming cell metabolism, we measured the extracellular acidification rate and oxygen consumption rate of A549 human lung epithelial cells with constitutive endogenous expression of either of the two major E1A isoforms. This was followed by the characterization of transcript levels for genes involved in glycolysis and cellular respiration, and related metabolic pathways. Cells expressing the 13S encoded E1A isoform had drastically increased baseline glycolysis and lower maximal cellular respiration than cells expressing the 12S encoded E1A isoform. Cells expressing the 13S encoded E1A isoform exhibited upregulated expression of glycolysis genes and downregulated expression of cellular respiration genes. However, tricarboxylic acid cycle genes were upregulated, resembling anaplerotic metabolism employed by certain cancers. Upregulation of glycolysis and tricarboxylic acid cycle genes was also apparent in IMR-90 human primary lung fibroblast cells infected with a HAdV-5 mutant virus that expressed the 13S, but not the 12S encoded E1A isoform. In conclusion, it appears that the two major isoforms of E1A differentially influence cellular glycolysis and oxidative phosphorylation and this is at least partially due to the altered regulation of mRNA expression for the genes in these pathways.
病毒改变了宿主细胞的许多过程，为病毒复制创造了更优的环境。这包括改变代谢以提供复制所需的足够底物和能量。通常，病毒感染会诱导类似于瓦博格效应的代谢表型，即糖酵解上调和细胞呼吸同时下降。已经观察到人类腺病毒（HAdV）诱导瓦博格效应，这部分归因于腺病毒早期区域 4，开放阅读框 1（E4orf1）蛋白。E4orf1 通过转录因子禽髓细胞瘤病毒致癌基因同源物（MYC）调节宿主细胞的许多过程，从而有益于病毒复制，并可以通过转录因子 MYC 影响细胞代谢。然而，E4orf1 并不能解释 HAdV 代谢重编程的全部程度，特别是细胞呼吸的伴随下降。HAdV 早期区域 1A（E1A）蛋白也调节感染细胞的功能以促进病毒复制。E1A 可以与多种宿主细胞蛋白相互作用，其中一些蛋白已被证明可以与代谢酶相互作用，而与 E1A 的相互作用无关。为了确定 HAdV E1A 蛋白是否负责重编程细胞代谢，我们测量了具有两种主要 E1A 同工型之一组成型内源性表达的 A549 人肺上皮细胞的细胞外酸化率和耗氧量。随后，我们对参与糖酵解和细胞呼吸以及相关代谢途径的基因的转录水平进行了表征。表达 13S 编码的 E1A 同工型的细胞的基础糖酵解水平明显升高，最大细胞呼吸水平低于表达 12S 编码的 E1A 同工型的细胞。表达 13S 编码的 E1A 同工型的细胞表现出糖酵解基因的上调表达和细胞呼吸基因的下调表达。然而，三羧酸循环基因上调，类似于某些癌症采用的补料代谢。在感染表达 13S，但不表达 12S 编码的 E1A 同工型的 HAdV-5 突变病毒的 IMR-90 人原代肺成纤维细胞中，也明显上调了糖酵解和三羧酸循环基因的表达。总之，似乎两种主要的 E1A 同工型差异地影响细胞糖酵解和氧化磷酸化，这至少部分归因于这些途径中基因的 mRNA 表达的改变调节。
