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The tumor suppressor NDRG2 recruits protein phosphatase 2A to suppress STAT5 phosphorylation in adult T-cell leukemia/lymphoma.

Adult T-cell leukemia/lymphoma (ATL) is an aggressive T-cell malignancy with a poor prognosis that is caused by human T-cell leukemia virus type 1 infection. We previously demonstrated that N-myc downstream-regulated gene 2 (NDRG2) is significantly downregulated in ATL, resulting in aberrant activation of the signal transduction pathways through the dissociation of serine/threonine protein phosphatase 2A. To identify potential targets of NDRG2, we performed comprehensive mass spectrometry of differentially phosphorylated peptides in ATL cells with overexpression of NDRG2 using a TiO2-based enrichment method. Kyoto Encyclopedia of Genes and Genomes and gene ontology analysis revealed that the downregulated phosphopeptides correlated with signaling pathways, T-cell differentiation, and proliferation. Our results identified signal transducer and activator of transcription 5B as a novel NDRG2-regulated protein that is dephosphorylated at serine 193 and tyrosine 699. Although enforced expression of NDRG2 in ATL cell lines does not change the phosphorylation of Janus kinase 3, an upstream regulator of STAT5, phosphorylated STAT5 at tyrosine and serine is significantly suppressed by the direct binding to STAT5 with NDRG2 leading to the inhibition of STAT5 downstream gene expression. Furthermore, NDRG2 binds to STAT5B with alanine replacement of Y699 (Y699A), but only weakly associates with S193A, suggesting that NDRG2 is directly involved in serine phosphorylation through the recruitment of serine/threonine protein phosphatase 2A to STAT5. Because S193 A remarkably induces reduced phosphorylation of Y699 and subsequent transcriptional activity, the induction of serine phosphorylation through the loss of NDRG2 expression is dispensable for STAT5 tyrosine phosphorylation and activity. Since the loss of NDRG2 expression is essential factor to maintenance of ATL cells by STAT5 activity through phosphorylation of serine and tyrosine, targeting STAT5 becomes a feasible and effective strategy in NDRG2-deficient ATL.

Humans

Respiratory viruses activate autophagy via the IFN-STAT1/STAT5B-SOCS1 axis.

Autophagy is an ancient catabolic process that has emerged as part of innate immunity. Upon infection, autophagy is activated but the key factors responsible remained unclear. Here, we show that interferon (IFN) released during viral infections subsequently activates autophagy via STAT1/5B-mediated upregulation of Suppressor of Cytokine Signaling 1 (SOCS1). Our data show that scavenging of IFNs diminishes autophagy induced by several respiratory viruses. All types of IFN (I, II and III) mediated robust autophagic flux activation in both cell lines and primary human lung fibroblasts in a JAK1-3 dependent manner. Depletion or pharmacological inhibition of individual signal transducer and activator of transcription (STAT) transcription factors demonstrated that both STAT1 and STAT5B are required for IFN-induced autophagy. Upon IFN stimulation STAT1 and STAT5B associate and translocate to the nucleus. Transcriptome analyses revealed that most known anti-viral IFN-stimulated genes (ISGs) remain induced to high levels upon inhibition of STAT5 expect for a small subset of ISGs, among them SOCS1. Overexpression of SOCS1 stimulated autophagy, whereas its depletion impaired IFN-induced autophagy. Successful viruses like measles virus (MeV) or respiratory syncytial virus (RSV) evolved strategies to exploit autophagy to promote their own replication. Uncoupling IFN-mediated ISG defenses from autophagy induction by STAT5 inhibition reduced virus-induced autophagy, and inhibited efficient replication of autophagy-dependent MeV and RSV. Overexpression of SOCS1 upon STAT5 inhibition largely rescued both infection-induced autophagy and viral replication. Taken together, our data show that IFN promotes autophagy via STAT1/STAT5B-SOCS1 in viral infections and reveal that targeting of this axis allows inhibition of autophagy-dependent viruses without compromising innate immune defenses.

Humans

Establishment of a STAT6 Reporter Assay for Screening Environmental Toxicants Affecting Allergic Airway Inflammation.

Air pollution-associated allergic airway inflammation is an increasing public health concern. Interleukin‑4 (IL‑4) and interleukin‑13 (IL‑13), which activate the Signal Transducer and Activator of Transcription 6 (STAT6) pathway, a central mediator of allergic airway inflammation, may modulate the respiratory toxicities of pollutants. The present study describes the generation and validation of a stable STAT6 luciferase reporter assay in human airway epithelial cells for evaluating environmental toxicants that modulate STAT6 signaling. Human bronchial epithelial 16HBE14o- cells were transduced with a STAT6-responsive luciferase reporter using a lentiviral vector, followed by optimization of puromycin selection and multiplicity of infection, and monoclonal isolation by limiting dilution. A stable clone with strong and reproducible induction across serial passages was selected. Reporter responsiveness was validated by IL-4/IL-13 stimulation, and STAT6 dependence was confirmed using selective STAT6, STAT5, and STAT3 inhibitors. Assay performance was quantified by Z'-factor analysis, which indicated reproducible signal separation. Furthermore, the assay was applied to individual air-pollution constituents, and benzo[b]fluoranthene and particulate matter significantly increased STAT6 reporter activity. This method provides a scalable approach for measuring STAT6 activity in airway epithelial cells and for prioritizing environmental toxicants that modulate allergic airway signaling.

STAT6 Transcription Factor

PRRSV suppresses FTO-dependent m6A demethylation to reprogram STAT signaling and innate immunity.

RNA viruses have evolved diverse strategies to evade host interferon (IFN)-stimulated gene (ISG) defenses; however, how they exploit host epitranscriptomic regulation remains poorly understood. Here, we identify an immune-evasion mechanism in which porcine reproductive and respiratory syndrome virus (PRRSV) targets the m6A demethylase fat mass and obesity-associated protein (FTO) to suppress antiviral signaling. Mechanistically, the viral endoribonuclease nsp11 inhibits STAT5-dependent transcription through the key residues Q96 and S104, thereby reducing FTO expression. Loss of FTO increases m6A modification of STAT2 and STAT3 transcripts, impairing their translation and phosphorylation, thereby attenuating ISG responses. Reduced STAT3 activity further dampens STAT5 signaling, establishing a feed-forward circuit that amplifies suppression of antiviral immunity. Functionally, disruption of this regulatory region (Q96A and S104A) attenuates viral pathogenicity in vivo and restores ISG induction. These mutations also reduce infection-associated inflammatory responses and the accumulation of reactive oxygen species. Together, these findings define a nsp11-STAT5-FTO-STAT2/3 axis that enables PRRSV to reprogram host epitranscriptomic control of innate immunity. Our work reveals a mechanism of epitranscriptomic hijacking and identifies FTO as a key host factor exploited by RNA viruses, highlighting m6A regulation as a potential target for antiviral intervention.IMPORTANCEViruses must overcome host innate immune defenses to establish infection; however, the mechanisms by which they manipulate host RNA regulation remain incompletely understood. In this study, we show that porcine reproductive and respiratory syndrome virus (PRRSV) suppresses interferon responses by targeting the host m6A demethylase FTO through its endoribonuclease nsp11. This process involves the inhibition of STAT5 phosphorylation, which reduces FTO expression and increases m6A modification of key immune regulators, including STAT2 and STAT3, thereby impairing their activation. Disruption of this pathway attenuates viral pathogenicity in vivo and restores antiviral signaling. These results demonstrate that PRRSV can reprogram host epitranscriptomic regulation to modulate innate immunity and suggest that m6A-related pathways may be potential targets for antiviral intervention.

Immunity, Innate