AIDS Immunopathogenesis Unit, Division of Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific Institute, 20132 Milano, Italy.
J Mol Biol. 2011 Jul 29;410(5):933-43. doi: 10.1016/j.jmb.2011.03.044.
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.
信号转导子和转录激活子（STAT）蛋白在 HIV-1（+）个体的白细胞中经常被持续激活，这些白细胞通常表现出 STAT5 羧基端截断异构体（STAT5Δ）的优势表达。STAT5Δ 可以作为 CD8 耗尽的原代白细胞和被粒细胞-巨噬细胞集落刺激因子（GM-CSF）刺激的慢性感染的单核细胞 U1 细胞中人类免疫缺陷病毒 1（HIV-1）表达的负调节剂。激活的 STAT5Δ 可以直接与 HIV-1 长末端重复（LTR）启动子中的两个共有序列结合；结合会损害 RNA 聚合酶 II（Crotti，A.，Lusic，M.，Lupo，R.，Lievens，P. M.，Liboi，E.，Della Chiara，G.，等人（2007 年）。天然存在的羧基端截断 STAT5 是 HIV-1 表达的负调节剂。血液，109，5380-5389）的募集。STAT 共有序列之一与核因子 κB（NF-κB）结合位点重叠；有趣的是，在单核细胞中经常检测到的 NF-κB1/p50 同源二聚体是 HIV 转录的负调节剂。在这里，我们表明 GM-CSF 刺激 U1 细胞虽然不会诱导 NF-κB 激活，但会导致 STAT5Δ 磷酸化并与 HIV LTR 启动子中的 NF-κB/STAT 靶序列结合，在未受刺激的条件下，该序列已经与 p50 结合。在表达内源性蛋白的 U1 细胞和过表达这些因子的 293T 细胞中，发现 STAT5Δ 与 p50 而不是 RelA/p65 结合。此外，GM-CSF 刺激促进了 U1 细胞中 HIV LTR 启动子处 STAT5Δ 和 p50 的同时结合。GM-CSF 刺激的 U1 细胞染色质免疫沉淀证实了 p50 与病毒启动子的体内结合以及 STAT5Δ。因此，细胞因子激活的 STAT5Δ/p50 复合物可以有助于单核细胞中 HIV-1 的潜伏维持。
