title: Negative regulation of HIV-1 transcription by a heterodimeric NF-κB1/p50 and C-terminally truncated STAT5 complex.
abstract: Signal transducers and activator of transcription (STAT) proteins are often constitutively activated in leukocytes of HIV-1(+) individuals, which frequently show a dominant expression of a C-terminally truncated isoform of STAT5 (STAT5Δ). STAT5Δ can act as a negative regulator of human immunodeficiency virus type 1 (HIV-1) expression in both CD8-depleted primary leukocytes and chronically infected promonocytic U1 cells stimulated with granulocyte-macrophage colony-stimulating factor (GM-CSF). Activated STAT5Δ can directly bind to two consensus sequences in the HIV-1 long terminal repeat (LTR) promoter; binding impairs recruitment of RNA polymerase II (Crotti, A., Lusic, M., Lupo, R., Lievens, P. M., Liboi, E., Della Chiara, G., et al. (2007). Naturally occurring C-terminally truncated STAT5 is a negative regulator of HIV-1 expression. Blood, 109, 5380-5389). One of the STAT consensus sequences overlaps with one nuclear factor κB (NF-κB) binding site; interestingly, NF-κB1/p50 homodimers, frequently detected in monocytic cells, are negative regulators of HIV transcription. Here, we show that GM-CSF stimulation of U1 cells, while not inducing NF-κB activation, leads to STAT5Δ phosphorylation and binding to the NF-κB/STAT target sequence in the HIV LTR promoter, which already associates with p50 under unstimulated conditions. STAT5Δ was found to associate with p50, but not with RelA/p65, in both U1 cells expressing endogenous proteins and 293T cells overexpressing these factors. Furthermore, GM-CSF stimulation promoted concurrent binding of STAT5Δ and p50 at the HIV LTR promoter in U1 cells. Immunoprecipitation of chromatin from GM-CSF-stimulated U1 cells confirmed in vivo binding of p50 to the viral promoter together with STAT5Δ. Thus, cytokine-activated STAT5Δ/p50 complexes can contribute to the maintenance of HIV-1 latency in monocytic cells.
authors.affiliation: AIDS Immunopathogenesis Unit, Division of Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific Institute, 20132 Milano, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Della Chiara
authors.forename: Andrea
authors.initials: A
authors.lastname: Crotti
authors.forename: Elio
authors.initials: E
authors.lastname: Liboi
authors.forename: Mauro
authors.initials: M
authors.lastname: Giacca
authors.forename: Guido
authors.initials: G
authors.lastname: Poli
authors.forename: Marina
authors.initials: M
authors.lastname: Lusic
mesh_terms: D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D015658:HIV Infections / Q000378:metabolism; D016325:HIV Long Terminal Repeat / Q000235:genetics; D015497:HIV-1 / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D047468:Immunoprecipitation; D050505:Mutant Proteins / Q000378:metabolism*; D052002:NF-kappa B p50 Subunit / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D017384:Sequence Deletion / Q000235:genetics*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D050505:Mutant Proteins; D052002:NF-kappa B p50 Subunit; D050799:STAT5 Transcription Factor; D016178:Granulocyte-Macrophage Colony-Stimulating Factor