title: An intronic G run within HIV-1 intron 2 is critical for splicing regulation of vif mRNA.
abstract: Within target T lymphocytes, human immunodeficiency virus type I (HIV-1) encounters the retroviral restriction factor APOBEC3G (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G; A3G), which is counteracted by the HIV-1 accessory protein Vif. Vif is encoded by intron-containing viral RNAs that are generated by splicing at 3' splice site (3'ss) A1 but lack splicing at 5'ss D2, which results in the retention of a large downstream intron. Hence, the extents of activation of 3'ss A1 and repression of D2, respectively, determine the levels of vif mRNA and thus the ability to evade A3G-mediated antiviral effects. The use of 3'ss A1 can be enhanced or repressed by splicing regulatory elements that control the recognition of downstream 5'ss D2. Here we show that an intronic G run (G(I2)-1) represses the use of a second 5'ss, termed D2b, that is embedded within intron 2 and, as determined by RNA deep-sequencing analysis, is normally inefficiently used. Mutations of G(I2)-1 and activation of D2b led to the generation of transcripts coding for Gp41 and Rev protein isoforms but primarily led to considerable upregulation of vif mRNA expression. We further demonstrate, however, that higher levels of Vif protein are actually detrimental to viral replication in A3G-expressing T cell lines but not in A3G-deficient cells. These observations suggest that an appropriate ratio of Vif-to-A3G protein levels is required for optimal virus replication and that part of Vif level regulation is effected by the novel G run identified here.
authors.affiliation: Institute for Virology, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
authors.forename: Marek
authors.initials: M
authors.lastname: Widera
authors.forename: Steffen
authors.initials: S
authors.lastname: Erkelenz
authors.forename: Frank
authors.initials: F
authors.lastname: Hillebrand
authors.forename: Aikaterini
authors.initials: A
authors.lastname: Krikoni
authors.forename: Darius
authors.initials: D
authors.lastname: Widera
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kaisers
authors.forename: René
authors.initials: R
authors.lastname: Deenen
authors.forename: Michael
authors.initials: M
authors.lastname: Gombert
authors.forename: Rafael
authors.initials: R
authors.lastname: Dellen
authors.forename: Tanya
authors.initials: T
authors.lastname: Pfeiffer
authors.forename: Barbara
authors.initials: B
authors.lastname: Kaltschmidt
authors.forename: Carsten
authors.initials: C
authors.lastname: Münk
authors.forename: Valerie
authors.initials: V
authors.lastname: Bosch
authors.forename: Karl
authors.initials: K
authors.lastname: Köhrer
authors.forename: Heiner
authors.initials: H
authors.lastname: Schaal
mesh_terms: D000071480:APOBEC-3G Deaminase; D000595:Amino Acid Sequence; D002460:Cell Line; D003564:Cytidine Deaminase / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D015700:HIV Envelope Protein gp41 / Q000737:chemistry / Q000235:genetics; D015497:HIV-1 / Q000235:genetics* / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D007438:Introns / Q000235:genetics*; D019169:Jurkat Cells; D008969:Molecular Sequence Data; D009154:Mutation; D022821:RNA Splice Sites; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics; D016415:Sequence Alignment; D017423:Sequence Analysis, RNA; D013601:T-Lymphocytes / Q000276:immunology / Q000821:virology; D015854:Up-Regulation; D014779:Virus Replication; D054321:rev Gene Products, Human Immunodeficiency Virus / Q000235:genetics / Q000378:metabolism; D054320:vif Gene Products, Human Immunodeficiency Virus / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D015700:HIV Envelope Protein gp41; D022821:RNA Splice Sites; D012333:RNA, Messenger; D012367:RNA, Viral; D054321:rev Gene Products, Human Immunodeficiency Virus; C514860:rev protein, Human Immunodeficiency Virus-1; D054320:vif Gene Products, Human Immunodeficiency Virus; D000071480:APOBEC-3G Deaminase; C464924:APOBEC3G protein, human; D003564:Cytidine Deaminase