title: APOBEC3G: an intracellular centurion.
abstract: The intrinsic antiretroviral factor APOBEC3G (A3G) is highly active against HIV-1 and other retroviruses. In different cell types, A3G is expressed in high-molecular-mass (HMM) RNA- protein complexes or low-molecular-mass (LMM) forms displaying different biological activities. In resting CD4 T cells, a LMM form of A3G potently restricts HIV-1 infection soon after virion entry. However, when T cells are activated, LMM A3G is recruited into HMM complexes that include Staufen-containing RNA granules. These complexes are probably nucleated by the induced expression of Alu/hY retroelement RNAs that accompany T-cell activation. HMM A3G sequesters these retroelement RNAs away from the nuclear long interspersed nuclear element-derived enzymes required for Alu/hY retrotransposition. Human immunodeficiency virus (HIV) exploits this 'window of opportunity' provided by the loss of LMM A3G in activated CD4 T cells to productively infect these cells. During HIV virion formation, newly synthesized LMM A3G is preferentially encapsidated but only under conditions where Vif is absent and thus not able to target A3G for proteasome-mediated degradation. Together, these findings highlight the discrete functions of the different forms of A3G. LMM A3G opposes the external threat posed by exogenous retroviruses, while HMM A3G complexes oppose the internal threat posed by the retrotransposition of select types of retroelements.
authors.affiliation: Gladstone Institute of Virology and Immunology, San Francisco, CA 94158, USA.
authors.forename: Ya-Lin
authors.initials: YL
authors.lastname: Chiu
authors.forename: Warner C
authors.initials: WC
authors.lastname: Greene
mesh_terms: D000071480:APOBEC-3G Deaminase; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000821:virology*; D003564:Cytidine Deaminase / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D015658:HIV Infections / Q000235:genetics / Q000276:immunology*; D015497:HIV-1 / Q000276:immunology*; D006801:Humans; D008954:Models, Biological; D016601:RNA-Binding Proteins / Q000378:metabolism; D018626:Retroelements / Q000235:genetics / Q000276:immunology; D012261:Ribonucleoproteins / Q000378:metabolism; D014771:Virion / Q000378:metabolism; D054320:vif Gene Products, Human Immunodeficiency Virus / Q000276:immunology / Q000378:metabolism
chemical_list: D003598:Cytoskeletal Proteins; D016601:RNA-Binding Proteins; D018626:Retroelements; D012261:Ribonucleoproteins; C492185:STAU1 protein, human; D054320:vif Gene Products, Human Immunodeficiency Virus; C514847:vif protein, Human immunodeficiency virus 1; D000071480:APOBEC-3G Deaminase; C464924:APOBEC3G protein, human; D003564:Cytidine Deaminase