The role of autophagy in human cytomegalovirus IE2 expression
TL;DR: Whether autophagy regulates the expression of human cytomegalovirus immediately early two viral protein (IE2) is investigated to find one way for autophagic to restrict HCMV replication.
Abstract: The purpose of this study was to determine whether autophagy regulates the expression of human cytomegalovirus (HCMV) immediately early two viral protein (IE2). Rapamycin and 3-methyladenine (3-MA) were used to stimulate or suppress autophagy during HCMV infection. UL122 recombinant plasmid was transfected to overexpress IE2 and small interference RNA against autophagy-related protein 3 (ATG3) was used to knockdown ATG3. Western blot was performed to measure the expression of viral proteins and autophagy levels. Immunofluorescence was used to detect the immediately early 1 viral protein (IE1) expression. In human embryonic lung fibroblasts, infection of HCMV promotes the lipidation of light chain 3 (LC3) at 6 and 24 hours post infection (hpi), which was accompanied by the increased expression of viral protein IE2. When only IE2 was overexpressed via UL122 recombinant plasmid transfection without HCMV infection, the autophagy hallmarks LC3II and ATG3 were upregulated. Furthermore, viral protein IE2 expression was reduced at 24 and 48 hpi either by the treatment of autophagy inducer rapamycin or by the inhibitor 3-MA before HCMV infection. At the same time, small interference ATG3 transient transfection, used to suppress autophagy, significantly inhibited IE2 expression. However, when 3-MA was used to regulate autophagy levels after HCMV infection, expression of IE2 and IE1 were both decreased, while autophagy inducer rapamycin treatment after HCMV infection increased IE2 expression slightly. IE2 was involved in autophagy induced by HCMV infection and blocking autophagy could inhibit the expression of HCMV viral protein IE2, which might be one way for autophagy to restrict HCMV replication.
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TL;DR: Autophagy is a complex degradative process by which eukaryotic cells capture cytoplasmic components for subsequent degradation through lysosomal hydrolases as mentioned in this paper.
Abstract: Autophagy is a complex degradative process by which eukaryotic cells capture cytoplasmic components for subsequent degradation through lysosomal hydrolases. Although this catabolic process can be triggered by a great variety of stimuli, action in cells varies according to cellular context. Autophagy has been previously linked to disease development modulation, including cancer. Autophagy helps suppress cancer cell advancement in tumor transformation early stages, while promoting proliferation and metastasis in advanced settings. Oncoviruses are a particular type of virus that directly contribute to cell transformation and tumor development. Extensive molecular studies have revealed complex ways in which autophagy can suppress or improve oncovirus fitness while still regulating viral replication and determining host cell fate. This review includes recent advances in autophagic cellular function and emphasizes its antagonistic role in cancer cells.
13 citations
TL;DR: In this paper , the roles of viruses, exosomes, and microRNAs in the autophagy process are highlighted, and a variety of cellular and molecular pathways that are activated and inhibited by several factors (e.g., genetics, epigenetics, and environment factors) are related to the beginning and development of autophagia.
Abstract: Autophagy is known as a conserved self-eating mechanism that contributes to cells to degrade different intracellular components (i.e., macromolecular complexes, aggregated proteins, soluble proteins, organelles, and foreign bodies). Autophagy needs formation of a double-membrane structure, which is composed of the sequestered cytoplasmic contents, called autophagosome. There are a variety of internal and external factors involved in initiation and progression of autophagy process. Viruses as external factors are one of the particles that could be associated with different stages of this process. Viruses exert their functions via activation and/or inhibition of a wide range of cellular and molecular targets, which are involved in autophagy process. Besides viruses, a variety of cellular and molecular pathways that are activated and inhibited by several factors (e.g., genetics, epigenetics, and environment factors) are related to beginning and developing of autophagy mechanism. Exosomes and microRNAs have been emerged as novel and effective players anticipated in various stages of autophagy. More knowledge in these pathways and identification of accurate roles of them could help to provide better therapeutic approaches in several diseases such as cancer. We highlighted the roles of viruses, exosomes, and microRNAs in the autophagy processes.
7 citations
TL;DR: The role of human cytomegalovirus (HCMV) DNA and proteins are often detected in malignant tumors, warranting studies of the role that HCMV plays in carcinogenesis and tumor progression as discussed by the authors .
Abstract: Human cytomegalovirus (HCMV) DNA and proteins are often detected in malignant tumors, warranting studies of the role that HCMV plays in carcinogenesis and tumor progression. HCMV proteins were shown to regulate the key processes involved in tumorigenesis. While HCMV as an oncogenic factor just came into focus, its ability to promote tumor progression is generally recognized. The review discusses the viral factors and cell molecular pathways that affect the resistance of cancer cells to therapy. CMV inhibits apoptosis of tumor cells, that not only promotes tumor progression, but also reduces the sensitivity of cells to antitumor therapy. Autophagy was found to facilitate either cell survival or cell death in different tumor cells. In leukemia cells, HCMV induces a "protective" autophagy that suppresses apoptosis. Viral factors that mediate drug resistance and their interactions with key cell death pathways are necessary to further investigate in order to develop agents that can restore the tumor sensitivity to anticancer drugs.
05 Oct 2022
TL;DR: Viral factors that mediate drug resistance and their interactions with key cell death pathways are necessary to further investigate in order to develop agents that can restore the tumor sensitivity to anticancer drugs.
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TL;DR: It is demonstrated that the rat microtubule‐associated protein 1 light chain 3 (LC3), a homologue of Apg8p essential for autophagy in yeast, is associated to the autophagosome membranes after processing.
Abstract: Little is known about the protein constituents of autophagosome membranes in mammalian cells. Here we demonstrate that the rat microtubule-associated protein 1 light chain 3 (LC3), a homologue of Apg8p essential for autophagy in yeast, is associated to the autophagosome membranes after processing. Two forms of LC3, called LC3-I and -II, were produced post-translationally in various cells. LC3-I is cytosolic, whereas LC3-II is membrane bound. The autophagic vacuole fraction prepared from starved rat liver was enriched with LC3-II. Immunoelectron microscopy on LC3 revealed specific labelling of autophagosome membranes in addition to the cytoplasmic labelling. LC3-II was present both inside and outside of autophagosomes. Mutational analyses suggest that LC3-I is formed by the removal of the C-terminal 22 amino acids from newly synthesized LC3, followed by the conversion of a fraction of LC3-I into LC3-II. The amount of LC3-II is correlated with the extent of autophagosome formation. LC3-II is the first mammalian protein identified that specifically associates with autophagosome membranes.
6,244 citations
"The role of autophagy in human cyto..." refers background in this paper
...The modification of the microtubule‐ associated protein 1 LC3I by lipidation (LC3II) and the abundance of SQSTM1/p62 (sequestosome 1), an autophagic substrate located within autophagosomes, were detected as hallmarks of autophagy.(22) As shown in Figure 1B, compared with controls (lane 2, 4, and 6), HCMV infection decreased the LC3I/II ratio (lane 1, 3, and 5) at 6, 12, and 24 hours post infection (hpi); while at 48 hpi (lane 7), HCMV infection increased the LC3I/II ratio....
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TL;DR: It is shown that the herpes simplex virus type 1 (HSV-1)-encoded neurovirulence protein ICP34.5 binds to the mammalian autophagy protein Beclin 1 and inhibits its Autophagy function, which is essential for viral Neurovirulence.
756 citations
"The role of autophagy in human cyto..." refers background in this paper
...5 could inhibit autophagy to counter the pathogenicity of HSV‐1 by interacting with Beclin‐1.(34,35) Virus FLICE‐like inhibitor protein encoded by Kaposi's sarcoma‐associated herpesvirus could inhibit autophagy through its interaction with the E2 ligase ATG3....
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...5 could inhibit autophagy to counter the pathogenicity of HSV‐1 by interacting with Beclin‐1.34,35 Virus FLICE‐like inhibitor protein encoded by Kaposi's sarcoma‐associated herpesvirus could inhibit autophagy through its interaction with the E2 ligase ATG3....
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TL;DR: 71 HCMV-encoded proteins that included 12 proteins encoded by known viral open reading frames previously not associated with virions and 12 proteins from novel viral ORFs are identified.
Abstract: Human cytomegalovirus (HCMV), a member of the herpesvirus family, is a large complex enveloped virus composed of both viral and cellular gene products. While the sequence of the HCMV genome has been known for over a decade, the full set of viral and cellular proteins that compose the HCMV virion are unknown. To approach this problem we have utilized gel-free two-dimensional capillary liquid chromatography-tandem mass spectrometry (MS/MS) and Fourier transform ion cyclotron resonance MS to identify and determine the relative abundances of viral and cellular proteins in purified HCMV AD169 virions and dense bodies. Analysis of the proteins from purified HCMV virion preparations has indicated that the particle contains significantly more viral proteins than previously known. In this study, we identified 71 HCMV-encoded proteins that included 12 proteins encoded by known viral open reading frames (ORFs) previously not associated with virions and 12 proteins from novel viral ORFs. Analysis of the relative abundance of HCMV proteins indicated that the predominant virion protein was the pp65 tegument protein and that gM rather than gB was the most abundant glycoprotein. We have also identified over 70 host cellular proteins in HCMV virions, which include cellular structural proteins, enzymes, and chaperones. In addition, analysis of HCMV dense bodies indicated that these viral particles are composed of 29 viral proteins with a reduced quantity of cellular proteins in comparison to HCMV virions. This study provides the first comprehensive quantitative analysis of the viral and cellular proteins that compose infectious particles of a large complex virus.
602 citations
"The role of autophagy in human cyto..." refers background in this paper
...The major tegument protein pUL83 (phosphoprotein pp65) of HCMV is the most abundant protein in the virion, which is involved in virus transcription and replication.(9,10) It is deposited into infected cells immediately after entry, which then plays important roles in immune evasion to promote the formation of latent infection....
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TL;DR: The results indicate the essential role of the Atg8 system in the proper development of autophagic isolation membranes in mice.
Abstract: Autophagy is an evolutionarily conserved bulk-protein degradation pathway in which isolation membranes engulf the cytoplasmic constituents, and the resulting autophagosomes transport them to lysoso...
453 citations
"The role of autophagy in human cyto..." refers background in this paper
...ATG3 deficient mice display severe defects in autophagosome formation and die within 1 day after birth.(20) During viral infection, autophagy can play a host monitoring mechanism in the transmission of viral antigens into the endosomal and lysosomal compartments, where the immune sensors are stimulated to activate autophagy after their enrichment....
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TL;DR: This study identifies a checkpoint of the autophagy pathway where cellular and viral FLIPs limit the Atg3-mediated step of LC3 conjugation to regulate autophagosome biogenesis, and the FLIP-derived short peptides induce growth suppression and cell death with autphagy, representing biologically active molecules for potential anti-cancer therapies.
Abstract: Autophagy is an active homeostatic degradation process for the removal or turnover of cytoplasmic components wherein the LC3 ubiquitin-like protein undergoes an Atg7 E1-like enzyme/Atg3 E2-like enzyme-mediated conjugation process to induce autophagosome biogenesis. Besides its cytoprotective role, autophagy acts on cell death when it is abnormally upregulated. Thus, the autophagy pathway requires tight regulation to ensure that this degradative process is well balanced. Two death effector domains (DED1/2) containing cellular FLICE-like inhibitor protein (cFLIP) and viral FLIP (vFLIP) of Kaposi's sarcoma-associated herpesvirus (KSHV), Herpesvirus saimiri (HVS), and Molluscum contagiosum virus (MCV) protect cells from apoptosis mediated by death receptors. Here, we report that cellular and viral FLIPs suppress autophagy by preventing Atg3 from binding and processing LC3. Consequently, FLIP expression effectively represses cell death with autophagy, as induced by rapamycin, an mTor inhibitor and an effective anti-tumour drug against KSHV-induced Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). Remarkably, either a DED1 alpha2-helix ten amino-acid (alpha2) peptide or a DED2 alpha4-helix twelve amino-acid (alpha4) peptide of FLIP is individually sufficient for binding FLIP itself and Atg3, with the peptide interactions effectively suppressing Atg3-FLIP interaction without affecting Atg3-LC3 interaction, resulting in robust cell death with autophagy. Our study thus identifies a checkpoint of the autophagy pathway where cellular and viral FLIPs limit the Atg3-mediated step of LC3 conjugation to regulate autophagosome biogenesis. Furthermore, the FLIP-derived short peptides induce growth suppression and cell death with autophagy, representing biologically active molecules for potential anti-cancer therapies.
398 citations
"The role of autophagy in human cyto..." refers background in this paper
...UL122 recombinant plasmid was transfected to overexpress IE2 and small interference RNA against autophagy‐related protein 3 (ATG3) was used to knockdown ATG3....
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...Virus FLICE‐like inhibitor protein encoded by Kaposi's sarcoma‐associated herpesvirus could inhibit autophagy through its interaction with the E2 ligase ATG3.(36) On the other hand, there's controversial studies about how autophagy effects viral replication and viral protein expression....
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...5 could inhibit autophagy to counter the pathogenicity of HSV‐1 by interacting with Beclin‐1.34,35 Virus FLICE‐like inhibitor protein encoded by Kaposi's sarcoma‐associated herpesvirus could inhibit autophagy through its interaction with the E2 ligase ATG3....
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