Sheikh Sana Mumtaz, Staab Julia, Bleyer Martina, Ivetic Aleksandar, Lühder Fred, Wirths Oliver, Meyer Thomas
Department of Psychosomatic Medicine and Psychotherapy, University Medical Center Göttingen, Göttingen, Germany.
Institute of Pathology, University Medical Center Düsseldorf, Düsseldorf, Germany.
Cell Commun Signal. 2025 Apr 26;23(1):201. doi: 10.1186/s12964-025-02183-2.
The cytokine-driven transcription factor STAT1 (signal transducer and activator of transcription 1) executes anti-microbial and pro-apoptotic functions, and loss-of-function mutations are associated with increased susceptibility to various infections and the development of tumors. A targeted mutation in mice expressing an N-terminally truncated STAT1 protein (STAT1-ΔN) typically develops splenomegaly in animals older than 6 months due to the formation of splenic non-Hodgkin lymphomas. The expression of the STAT1-ΔN variant resulted in the disruption of normal spleen architecture by malignant CD3- and CD20-negative tumor cells, which stained positively for both tyrosine-phosphorylated STAT1 and STAT3. Immunoblotting of lysates from isolated tumor cells revealed the cytokine-independent hyperphosphorylation of both STAT proteins, whereas the expression level of NF-κB was significantly reduced. Gel-shift assays showed that the DNA-binding activity of STAT1-ΔN was increased compared to the wild-type protein. This elevated level of tyrosine-phosphorylated STAT1-ΔN did not further increase upon stimulation of isolated tumor cells with either interferon-γ (IFNγ), lipopolysaccharide (LPS), or the combination of both. Since the truncation mutant was unable to accumulate in the nucleus upon cytokine stimulation, real-time PCR data from tumor tissue as well as from isolated, IFNγ/LPS-treated lymphoma cells demonstrated significantly reduced STAT1-regulated target gene expression despite its observed hyperphosphorylation. The nuclear import defect of tyrosine-phosphorylated STAT1-ΔN was associated with an elevated tyrosine-phosphorylation level of its antagonistic homolog STAT3, which is a known oncogene. These data demonstrate that the lack of STAT1 nuclear accumulation interferes with the functional balance between the two STAT proteins and, thereby, promotes the formation of phospho-STAT3-expressing CD3 CD20 non-Hodgkin lymphomas in the spleens of the diseased animals.
细胞因子驱动的转录因子STAT1（信号转导及转录激活因子1）执行抗菌和促凋亡功能，功能丧失突变与对各种感染的易感性增加及肿瘤发生相关。在表达N端截短的STAT1蛋白（STAT1-ΔN）的小鼠中，由于脾非霍奇金淋巴瘤的形成，6个月以上的动物通常会出现脾肿大。STAT1-ΔN变体的表达导致正常脾脏结构被恶性CD3和CD20阴性肿瘤细胞破坏，这些肿瘤细胞酪氨酸磷酸化的STAT1和STAT3均呈阳性染色。对分离的肿瘤细胞裂解物进行免疫印迹分析显示，两种STAT蛋白均存在不依赖细胞因子的过度磷酸化，而NF-κB的表达水平显著降低。凝胶迁移试验表明，与野生型蛋白相比，STAT1-ΔN的DNA结合活性增加。在用干扰素-γ（IFNγ）、脂多糖（LPS）或两者组合刺激分离的肿瘤细胞后，酪氨酸磷酸化的STAT1-ΔN的这种升高水平并未进一步增加。由于截短突变体在细胞因子刺激后无法在细胞核中积累，来自肿瘤组织以及分离的、经IFNγ/LPS处理的淋巴瘤细胞的实时PCR数据显示，尽管观察到其过度磷酸化，但STAT1调节的靶基因表达显著降低。酪氨酸磷酸化的STAT1-ΔN的核输入缺陷与其拮抗同源物STAT3（一种已知的癌基因）酪氨酸磷酸化水平升高有关。这些数据表明，STAT1核积累的缺乏干扰了两种STAT蛋白之间的功能平衡，从而促进了患病动物脾脏中表达磷酸化STAT3的CD3 CD20非霍奇金淋巴瘤的形成。
