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Delviks-Frankenberry KA, Desimmie BA, Pathak VK. Structural Insights into APOBEC3-Mediated Lentiviral Restriction. Viruses 2020; 12:E587. [PMID: 32471198 PMCID: PMC7354603 DOI: 10.3390/v12060587] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 05/22/2020] [Accepted: 05/24/2020] [Indexed: 01/18/2023] Open
Abstract
Mammals have developed clever adaptive and innate immune defense mechanisms to protect against invading bacterial and viral pathogens. Human innate immunity is continuously evolving to expand the repertoire of restriction factors and one such family of intrinsic restriction factors is the APOBEC3 (A3) family of cytidine deaminases. The coordinated expression of seven members of the A3 family of cytidine deaminases provides intrinsic immunity against numerous foreign infectious agents and protects the host from exogenous retroviruses and endogenous retroelements. Four members of the A3 proteins-A3G, A3F, A3H, and A3D-restrict HIV-1 in the absence of virion infectivity factor (Vif); their incorporation into progeny virions is a prerequisite for cytidine deaminase-dependent and -independent activities that inhibit viral replication in the host target cell. HIV-1 encodes Vif, an accessory protein that antagonizes A3 proteins by targeting them for polyubiquitination and subsequent proteasomal degradation in the virus producing cells. In this review, we summarize our current understanding of the role of human A3 proteins as barriers against HIV-1 infection, how Vif overcomes their antiviral activity, and highlight recent structural and functional insights into A3-mediated restriction of lentiviruses.
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Affiliation(s)
| | | | - Vinay K. Pathak
- Viral Mutation Section, HIV Dynamics and Replication Program, National Cancer Institute at Frederick, Frederick, MD 21702, USA; (K.A.D.-F.); (B.A.D.)
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Madison MN, Roller RJ, Okeoma CM. Human semen contains exosomes with potent anti-HIV-1 activity. Retrovirology 2014; 11:102. [PMID: 25407601 PMCID: PMC4245725 DOI: 10.1186/s12977-014-0102-z] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Accepted: 10/31/2014] [Indexed: 11/16/2022] Open
Abstract
Background Exosomes are membranous nanovesicles secreted into the extracellular milieu by diverse cell types. Exosomes facilitate intercellular communication, modulate cellular pheno/genotype, and regulate microbial pathogenesis. Although human semen contains exosomes, their role in regulating infection with viruses that are sexually transmitted remains unknown. In this study, we used semen exosomes purified from healthy human donors to evaluate the role of exosomes on the infectivity of different strains of HIV-1 in a variety of cell lines. Results We show that human semen contains a heterologous population of exosomes, enriched in mRNA encoding tetraspanin exosomal markers and various antiviral factors. Semen exosomes are internalized by recipient cells and upon internalization, inhibit replication of a broad array of HIV-1 strains. Remarkably, the anti-HIV-1 activity of semen exosomes is specific to retroviruses because semen exosomes blocked replication of the murine AIDS (mAIDS) virus complex (LP-BM5). However, exosomes from blood had no effect on HIV-1 or LP-BM5 replication. Additionally, semen and blood exosomes had no effect on replication of herpes simplex virus; types 1 and 2 (HSV1 and HSV2). Mechanistic studies indicate that semen exosomes exert a post-entry block on HIV-1 replication by orchestrating deleterious effects on particle-associated reverse transcriptase activity and infectivity. Conclusions These illuminating findings i) improve our knowledge of the cargo of semen exosomes, ii) reveal that semen exosomes possess anti-retroviral activity, and iii) suggest that semen exosome-mediated inhibition of HIV-1 replication may provide novel opportunities for the development of new therapeutics for HIV-1.
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Affiliation(s)
- Marisa N Madison
- Department of Microbiology, Carver College of Medicine, University of Iowa, 51 Newton Road, Iowa City, IA 52242-1109, USA.
| | - Richard J Roller
- Department of Microbiology, Carver College of Medicine, University of Iowa, 51 Newton Road, Iowa City, IA 52242-1109, USA.
| | - Chioma M Okeoma
- Department of Microbiology, Carver College of Medicine, University of Iowa, 51 Newton Road, Iowa City, IA 52242-1109, USA. .,Interdisciplinary Program in Molecular and Cellular Biology, University of Iowa, Iowa City, IA 52242, USA.
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Click RE. Dietary supplemented 2-mercaptoethanol prevents spontaneous and delays virally-induced murine mammary tumorigenesis. Cancer Biol Ther 2014; 14:521-6. [PMID: 23760494 DOI: 10.4161/cbt.24347] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
There seems to be little doubt that organosulfur compounds have enormous benefits for biological processes, especially those of diseases like cancer. The preliminary results herein define a cancer model in which benefits/mechanisms of multitudes of xenobiotic and nature's organosulfurs could easily be compared. Mice from three strains with a high incidence for naturally occurring tumors were treated daily with 2-mercaptoethanol (2-Me) starting at weaning. The 100% tumor incidence of undefined etiology in untreated BXSB-Yaa (+) males was completely prevented by 2-Me. In contrast, 2-Me treatment of female and male C3H.OL and C3H.OH congenic strains, did not change the 100% tumor incidence due to milk-borne retrovirus, MMTV(S), but did: (1) delay the appearance of tumors by 42%; (2) increase longevity 56%; and (3) increase longevity, post-tumor detection, 95%. The addition of these results to the increasingly impressive anti-cancer benefits of simple xenobiotic organosulfurs raise the question: Can they be adapted for use as a preventive modality for human cancer?
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Watanabe J, Kaneko Y, Kurosumi M, Kobayashi Y, Sakamoto M, Yoshida MA, Akiyama M, Matsushima Y. High-incidence spontaneous tumors in JF1/Ms mice: relevance of hypomorphic germline mutation and subsequent promoter methylation of Ednrb. J Cancer Res Clin Oncol 2013; 140:99-107. [DOI: 10.1007/s00432-013-1546-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Accepted: 10/24/2013] [Indexed: 10/26/2022]
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Jones PH, Okeoma CM. Phosphatidylinositol 3-kinase is involved in Toll-like receptor 4-mediated BST-2/tetherin regulation. Cell Signal 2013; 25:2752-61. [PMID: 24036213 DOI: 10.1016/j.cellsig.2013.08.042] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Accepted: 08/30/2013] [Indexed: 10/26/2022]
Abstract
BST-2 is a virus restriction factor whose expression is principally induced by IFNα through the type I IFN receptor. However, expression of BST-2 is modulated by mitogens, notably the TLR4 agonist - LPS, via mechanisms that are poorly understood. In this study, the role of TLR4 pathway on BST-2 expression was examined. We demonstrate that the TLR4/PI3K signaling pathway regulates both constitutive and LPS-induced BST-2 expression. LPS stimulation induces BST-2 expression in a manner dependent on TLR4/TRIF/IRF3 pathway. Genetic deletion or pharmacological inhibition of signaling through TLR4, as well as, the deletion of the TRIF and IRF3 genes blunts BST-2 induction by LPS. However, MYD88-/- cells have enhanced BST-2 levels and respond to LPS-mediated induction of BST-2. High level of BST-2 in MYD88 null cells is dependent on IFNβ since antibody-mediated neutralization of IFNβ synthesis results in reduced BST-2 levels in these cells. Similar to the effect of MYD88, inhibition of PI3K activity elevates basal BST-2 level and augments LPS-induced BST-2 expression. Importantly, BST-2 regulation via TLR4 and PI3K is transcriptionally controlled. We discovered that actinomycin D-mediated blocking of gene transcription and inhibition of protein synthesis with cycloheximide result in impairment of BST-2 mRNA expression. Taken together, our results demonstrate that activation of TLR4 results in TRIF/IRF3-mediated positive regulation of BST-2 or MYD88/PI3K-directed negative regulation of BST-2. Thus, our findings enlist BST-2 as one of the genes regulated by PI3K downstream of TLR4 and identify the TLR4/PI3K signaling as a novel pathway that controls BST-2 expression.
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Affiliation(s)
- Philip H Jones
- Department of Microbiology, University of Iowa, Carver College of Medicine, Iowa City, IA, United States
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Jones PH, Mahauad-Fernandez WD, Madison MN, Okeoma CM. BST-2/tetherin is overexpressed in mammary gland and tumor tissues in MMTV-induced mammary cancer. Virology 2013; 444:124-39. [PMID: 23806386 DOI: 10.1016/j.virol.2013.05.042] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Revised: 05/03/2013] [Accepted: 05/31/2013] [Indexed: 11/26/2022]
Abstract
BST-2 restricts MMTV replication, but once infection has established, MMTV modulates BST-2 levels. MMTV-directed BST-2 modulation is tissue-specific and dependent on infection and neoplastic transformation status of cells. In the lymphoid compartment of infected mice, BST-2 expression is first upregulated and then significantly downregulated regardless of absence or presence of mammary tumors. However, in mammary gland tissues, upregulation of BST-2 expression is dependent on the presence of mammary tumors and tumor tissues themselves have high BST-2 levels. Elevated BST-2 expression in these tissues is not attributable to IFN since levels of IFNα and IFNγ negatively correlate with BST-2. Importantly, soluble factors released by tumor cells suppress IFNα and IFNγ but induce BST-2. These data suggest that overexpression of BST-2 in carcinoma tissues could not be attributed to IFNs but to a yet to be determined factor that upregulates BST-2 once oncogenesis is initiated.
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Affiliation(s)
- Philip H Jones
- Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242-1109, USA.
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Jones PH, Maric M, Madison MN, Maury W, Roller RJ, Okeoma CM. BST-2/tetherin-mediated restriction of chikungunya (CHIKV) VLP budding is counteracted by CHIKV non-structural protein 1 (nsP1). Virology 2013; 438:37-49. [PMID: 23411007 DOI: 10.1016/j.virol.2013.01.010] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 11/28/2012] [Accepted: 01/16/2013] [Indexed: 12/17/2022]
Abstract
Chikungunya virus (CHIKV) is a re-emerging alphavirus transmitted by Aedes mosquitoes. Infection with CHIKV elicits a type I interferon response that facilities virus clearance, probably through the action of down-stream effectors such as antiviral IFN-stimulated genes (ISGs). Bone marrow stromal antigen 2 (BST-2) is an ISG shown to restrict HIV-1 replication by preventing the infection of bystander cells by tethering progeny virions on the surface of infected cells. Here we show that enrichment of cell surface BST-2 results in retention of CHIKV virus like particles (VLPs) on the cell membrane. BST-2 was found to co-localize with CHIKV structural protein E1 in the context of VLPs without any noticeable effect on BST-2 level. However, CHIKV nonstructural protein 1 (nsP1) overcomes BST-2-mediated VLPs tethering by down-regulating BST-2 expression. We conclude that BST-2 tethers CHIKV VLPs on the host cell plasma membrane and identify CHIKV nsP1 as a novel BST-2 antagonist.
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Affiliation(s)
- Philip H Jones
- Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
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Mehta HV, Jones PH, Weiss JP, Okeoma CM. IFN-α and lipopolysaccharide upregulate APOBEC3 mRNA through different signaling pathways. THE JOURNAL OF IMMUNOLOGY 2012; 189:4088-103. [PMID: 22972924 DOI: 10.4049/jimmunol.1200777] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
APOBEC3 (A3) proteins are virus-restriction factors that provide intrinsic immunity against infections by viruses like HIV-1 and mouse mammary tumor virus. A3 proteins are inducible by inflammatory stimuli, such as LPS and IFN-α, via mechanisms that are not fully defined. Using genetic and pharmacological studies on C57BL/6 mice and cells, we show that IFN-α and LPS induce A3 via different pathways, independently of each other. IFN-α positively regulates mouse APOBEC3 (mA3) mRNA expression through IFN-αR/PKC/STAT1 and negatively regulates mA3 mRNA expression via IFN-αR/MAPKs-signaling pathways. Interestingly, LPS shows some variation in its regulatory behavior. Although LPS-mediated positive regulation of mA3 mRNA occurs through TLR4/TRIF/IRF3/PKC, it negatively modulates mA3 mRNA via TLR4/MyD88/MAPK-signaling pathways. Additional studies on human peripheral blood mononuclear cells reveal that PKC differentially regulates IFN-α and LPS induction of human A3A, A3F, and A3G mRNA expression. In summary, we identified important signaling targets downstream of IFN-αR and TLR4 that mediate A3 mRNA induction by both LPS and IFN-α. Our results provide new insights into the signaling targets that could be manipulated to enhance the intracellular store of A3 and potentially enhance A3 antiviral function in the host.
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Affiliation(s)
- Harshini V Mehta
- Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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Jones PH, Mehta HV, Okeoma CM. A novel role for APOBEC3: susceptibility to sexual transmission of murine acquired immunodeficiency virus (mAIDS) is aggravated in APOBEC3 deficient mice. Retrovirology 2012; 9:50. [PMID: 22691411 PMCID: PMC3418182 DOI: 10.1186/1742-4690-9-50] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Accepted: 05/16/2012] [Indexed: 01/28/2023] Open
Abstract
Background APOBEC3 proteins are host factors that restrict infection by retroviruses like HIV, MMTV, and MLV and are variably expressed in hematopoietic and non-hematopoietic cells, such as macrophages, lymphocytes, dendritic, and epithelia cells. Previously, we showed that APOBEC3 expressed in mammary epithelia cells function to limit milk-borne transmission of the beta-retrovirus, mouse mammary tumor virus. In this present study, we used APOBEC3 knockout mice and their wild type counterpart to query the role of APOBEC3 in sexual transmission of LP-BM5 MLV – the etiological agent of murine AIDs (mAIDs). Results We show that mouse APOBEC3 is expressed in murine genital tract tissues and gametes and that genital tract tissue of APOBEC3-deficient mice are more susceptible to infection by LP-BM5 virus. APOBEC3 expressed in genital tract tissues most likely plays a role in decreasing virus transmission via the sexual route, since mice deficient in APOBEC3 gene have higher genitalia and seminal plasma virus load and sexually transmit the virus more efficiently to their partners compared to APOBEC3+ mice. Moreover, we show that female mice sexually infected with LP-BM5 virus transmit the virus to their off-spring in APOBEC3-dependent manner. Conclusion Our data indicate that genital tissue intrinsic APOBEC3 restricts genital tract infection and limits sexual transmission of LP-BM5 virus.
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Affiliation(s)
- Philip H Jones
- Department of Microbiology, Carver College of Medicine, University of Iowa, 51 Newton Road, Iowa City, IA 52242-1109, USA
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Jones PH, Mehta HV, Maric M, Roller RJ, Okeoma CM. Bone marrow stromal cell antigen 2 (BST-2) restricts mouse mammary tumor virus (MMTV) replication in vivo. Retrovirology 2012; 9:10. [PMID: 22284121 PMCID: PMC3283513 DOI: 10.1186/1742-4690-9-10] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2011] [Accepted: 01/27/2012] [Indexed: 11/10/2022] Open
Abstract
Background Bone marrow stromal cell antigen 2 (BST-2) is a cellular factor that restricts the egress of viruses such as human immunodeficiency virus (HIV-1) from the surface of infected cells, preventing infection of new cells. BST-2 is variably expressed in most cell types, and its expression is enhanced by cytokines such as type I interferon alpha (IFN-α). In this present study, we used the beta-retrovirus, mouse mammary tumor virus (MMTV) as a model to examine the role of mouse BST-2 in host infection in vivo. Results By using RNA interference, we show that loss of BST-2 enhances MMTV replication in cultured mammary tumor cells and in vivo. In cultured cells, BST-2 inhibits virus accumulation in the culture medium, and co-localizes at the cell surface with virus structural proteins. Furthermore, both scanning electron micrograph (SEM) and transmission electron micrograph (TEM) show that MMTV accumulates on the surface of IFNα-stimulated cells. Conclusions Our data provide evidence that BST-2 restricts MMTV release from naturally infected cells and that BST-2 is an antiviral factor in vivo.
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Affiliation(s)
- Philip H Jones
- Department of Microbiology, University of Iowa, Carver College of Medicine, Iowa City, IA, USA
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Expression of murine APOBEC3 alleles in different mouse strains and their effect on mouse mammary tumor virus infection. J Virol 2009; 83:3029-38. [PMID: 19153233 DOI: 10.1128/jvi.02536-08] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recent work has shown that mouse APOBEC3 restricts infection by mouse mammary tumor virus (MMTV) and murine leukemia virus (MLV) and that there are polymorphic APOBEC3 alleles found in different inbred mouse strains. For example, C57BL/6 mice, which are resistant to Friend MLV (F-MLV), encode a APOBEC3 gene different from that encoded by F-MLV-susceptible BALB/c mice; the predominant RNA produced in C57BL/6 mice lacks exon 5 (mA3(-5)) and encodes a protein with 15 polymorphic amino acids. It has also been reported that BALB/c mice produce only a variant RNA that lacks exon 2 (mA3(-2)). In this study, we examined the effect of these polymorphic APOBEC3 proteins on MMTV infection. We found that the major RNA made in C57BL/6 and B10.BR mice lacks exon 5 but that BALB/c and C3H/HeN mice predominantly express an RNA that contains all nine exons. In addition to producing the splice variant, C57BL/6 and B10.BR cells and tissues had levels of mA3 RNA fivefold higher than those from BALB/c and C3H/HeN mice. A cloned C57BL/6-derived mA3 protein lacking exon 5 inhibited MMTV infection better than a cloned full-length protein derived from 129/Ola RNA when packaged into MMTV virions. We also tested dendritic cells derived from different inbred mouse strains for their abilities to be infected by MMTV and showed that susceptibility to infection correlated with the presence of the exon 5-encoding allele. In vivo susceptibility to infection cosegregated with the inherited mA3 allele in a C57BL/6 x BALB/c backcross analysis. Moreover, virus produced in vivo in the mammary tissue of mA3 knockout and BALB/c mice was more infectious than that produced in the tissue of C57BL/6 mice. These data indicate that mA3 plays a role in the genetics of susceptibility and resistance to MMTV infection.
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Ross SR. MMTV infectious cycle and the contribution of virus-encoded proteins to transformation of mammary tissue. J Mammary Gland Biol Neoplasia 2008; 13:299-307. [PMID: 18661104 PMCID: PMC2715138 DOI: 10.1007/s10911-008-9090-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/10/2008] [Accepted: 07/04/2008] [Indexed: 02/08/2023] Open
Abstract
Mouse mammary tumor virus has served as a major model for the study of breast cancer since its discovery 1920's as a milk-transmitted agent. Much is known about in vivo infection by this virus, which initially occurs in lymphocytes that then carry virus to mammary tissue. In addition to the virion proteins, MMTV encodes a number of accessory proteins that facilitate high level in vivo infection. High level infection of lymphoid and mammary epithelial cells ensures efficient passage of virus to the next generation. Since MMTV causes mammary tumors by insertional activation of oncogenes, which is thought to be a stochastic process, mammary epithelial cell transformation is a by-product of the infectious cycle. The envelope protein may also participate in transformation. Although there have been several reports of a similar virus in human breast cancer, the existence of a human MTV has not been definitely established.
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Affiliation(s)
- Susan R Ross
- Department of Microbiology/Abramson Family Cancer Center, University of Pennsylvania, 421 Curie Blvd., Philadelphia, PA 1914, USA.
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