T Cells Contain an RNase-Insensitive Inhibitor of APOBEC3G Deaminase Activity

The deoxycytidine deaminase APOBEC3G (A3G) is expressed in human T cells and inhibits HIV-1 replication. When transfected into A3G-deficient epithelial cell lines, A3G induces catastrophic hypermutation by deaminating the HIV-1 genome. Interestingly, studies suggest that endogenous A3G in T cells induces less hypermutation than would be expected. However, to date, the specific deaminase activity of endogenous A3G in human CD4+ T cells has not been examined directly. Here, we compared deaminase activity of endogenous and exogenous A3G in various human cell lines using a standard assay and a novel, quantitative, high-throughput assay. Exogenous A3G in epithelial cell lysates displayed deaminase activity only following RNase treatment, as expected given that A3G is known to form an enzymatically inactive RNA-containing complex. Surprisingly, comparable amounts of endogenous A3G from T cell lines or from resting or activated primary CD4+ T cells exhibited minimal deaminase activity, despite RNase treatment. Specific deaminase activity of endogenous A3G in H9, CEM, and other T cell lines was up to 36-fold lower than specific activity of exogenous A3G in epithelial-derived cell lines. Furthermore, RNase-treated T cell lysates conferred a dose-dependent inhibition to epithelial cell lysates expressing enzymatically active A3G. These studies suggest that T cells, unlike epithelial-derived cell lines, express an unidentified RNase-resistant factor that inhibits A3G deaminase activity. This factor could be responsible for reduced levels of hypermutation in T cells, and its identification and blockade could offer a means for increasing antiretroviral intrinsic immunity of T cells

Technique [Volume 87, Issue 20]

Are we really safe?Beyond the White and GoldBig Sky experiments (with mixed success) with new release By DesignCaldwell residents move to new campus homesCouncil Clippings: SenateCount yourself in for 'Monte Cristo'Faces at Georgia TechFresh start for young, talented baseball squadGuitarist bringing good Laugh to Atlanta in FebruaryHoopster excitement from a losing seasonIntramural Notebook with Jack B. NimbleKing Week Ecumenical Service brings message to campusLetters to the EditorNaval ROTC celebrates 75 yearsNews BriefsOUR VIEWS: Consensus OpinionReady to leap tall buildings in a single bound?SGA budget set for vote next TuesdaySports BriefsSTAFF EDITORIAL: Atlanta a city with many flaws, not worth living inSTAFF EDITORIAL: Students helping students does not constitute cheatingTech cagers look to break goose eggTech rower paddles his way to 2004 OlympicsTechs and the CityThe Live List: Jan. 25-Feb. 2'This is neither a success nor a failure'...Two BitsTwo Tech students named scholarsWith Starsailor, Love is Here but good music isn'

Technique [Volume 87, Issue 29]

All-American Ayalon, senior Laitala make waves with school-record marksAmendments ruled invalidAmendments to the SGA ConstitutionAn Untitled PerspectiveAthletes struggle to find study timeBaseball Notebook: Jackets building steamBeyond the White and GoldCampus gets green for springClough names director, changes Ferst Center structureCouncil Clippings: HouseCouncil Clippings: SenateDaytime Emmys select surprising nomineesDennis Quaid hits home run in 'The Rookie'Drinking stats inconclusiveFaces at Georgia TechGolf, softball facilities could become home for aquariumGreek Sing event showcases fraternities' and sororities' vocal talents at Ferst CenterHangin' with Jason WilliamsHeadstrong music fails to push possible creative limitsIntramural NotebookLetters to the EditorMusic Midtown artist Harcourt to bring Monsters in MayNews BriefsOUR VIEWS: Consensus OpinionSports BriefsSTAFF EDITORIALTechs and the CityThe BuzzThe Live List: April 5th onward...Two Bit