title: Granulin and granulin repeats interact with the Tat.P-TEFb complex and inhibit Tat transactivation.
abstract: The cellular positive transcription elongation factor b (P-TEFb), containing cyclin T1 and cyclin-dependent kinase 9 (CDK9), interacts with the human immunodeficiency virus, type 1 (HIV-1) regulatory protein Tat to enable viral transcription and replication. Cyclin T1 is an unusually long cyclin and is engaged by cellular regulatory proteins. Previous studies showed that the granulin/epithelin precursor (GEP) binds the histidine-rich region of cyclin T1 and inhibits P-TEFb function. GEP is composed of repeats that vary in sequence and properties. GEP also binds directly to Tat. Here we show that GEP and some of its constituent granulin repeats can inhibit HIV-1 transcription via Tat without directly binding to cyclin T1. The interactions of granulins with Tat and cyclin T1 differ with respect to their binding sites and divalent cation requirements, and we identified granulin repeats that bind differentially to Tat and cyclin T1. Granulins DE and E bind Tat but do not interact directly with cyclin T1. These granulins are present in complexes with Tat and P-TEFb in which Tat forms a bridge between the cellular proteins. Granulins DE and E repress transcription from the HIV-1 LTR and gene expression from the viral genome, raising the possibility of developing granulin-based inhibitors of viral infection.
authors.affiliation: Department of Biochemistry and Molecular Biology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103-2714, USA.
authors.forename: Mainul
authors.initials: M
authors.lastname: Hoque
authors.forename: Bin
authors.initials: B
authors.lastname: Tian
authors.forename: Michael B
authors.initials: MB
authors.lastname: Mathews
authors.forename: Tsafi
authors.initials: T
authors.lastname: Pe'ery
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism; D056906:Cyclin T; D042863:Cyclin-Dependent Kinase 9 / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D015696:Gene Products, tat / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D042925:Positive Transcriptional Elongation Factor B / Q000378:metabolism*; D000077153:Progranulins; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques; D054322:tat Gene Products, Human Immunodeficiency Virus
chemical_list: C503684:CCNT1 protein, human; C503685:Ccnt1 protein, mouse; C503686:Ccnt1 protein, rat; D056906:Cyclin T; D016213:Cyclins; D015696:Gene Products, tat; D036341:Intercellular Signaling Peptides and Proteins; D046912:Multiprotein Complexes; D000077153:Progranulins; D020033:Protein Isoforms; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; D054322:tat Gene Products, Human Immunodeficiency Virus; D042925:Positive Transcriptional Elongation Factor B; D042863:Cyclin-Dependent Kinase 9