title: Phosphorylation of the Rex protein of human T-cell leukemia virus type I.
abstract: Rex protein, the posttranscriptional regulator of human T-cell leukemia virus type I (HTLV-I), is required for the control of viral structural protein expression and virus replication. Rex is a phosphoprotein found predominantly in the cell nucleolus, whose function is thought to be regulated by its nucleolar localization and phosphorylation. Therefore, we investigated the in vivo phosphorylation of Rex protein in more detail. Phosphorylation of Rex occurred in all HTLV-I-infected cell lines examined in vivo, primarily at serine residues and to a very small extent at threonine residues. Treatment of cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) led to significant but transient enhancement of the incorporation of [32P]orthophosphate into Rex protein. N-terminal truncation of Rex protein abolished TPA-dependent phosphorylation. Chymotryptic digestion of phosphorylated Rex yielded two phosphopeptides. In vivo phosphorylation sites were identified as serine residues 70 and 177 and threonine residue 174. Serine 70 was a TPA-dependent phosphorylation site within a regulatory domain. We have already shown that the protein kinase C inhibitor H-7 (1-(5-isoquinolinylsulfonyl)-2-methylpiperazine) specifically blocked accumulation of viral unspliced gag-pol mRNA. Therefore, the phosphorylation at serine 70 may be involved in the regulation of Rex function in response to extracellular stimuli.
authors.affiliation: Institute for Virus Research, Kyoto University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Adachi
authors.forename: T D
authors.initials: TD
authors.lastname: Copeland
authors.forename: C
authors.initials: C
authors.lastname: Takahashi
authors.forename: T
authors.initials: T
authors.lastname: Nosaka
authors.forename: A
authors.initials: A
authors.lastname: Ahmed
authors.forename: S
authors.initials: S
authors.lastname: Oroszlan
authors.forename: M
authors.initials: M
authors.lastname: Hatanaka
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D015536:Down-Regulation; D016370:Gene Products, rex / Q000235:genetics / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1 / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010957:Plasmids; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D016370:Gene Products, rex; D010710:Phosphates; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate