Threonine phosphorylation of STAT1 restricts interferon signaling and promotes innate inflammatory responses.

Since its discovery over three decades ago, signal transducer and activator of transcription 1 (STAT1) has been extensively studied as a central mediator for interferons (IFNs) signaling and antiviral defense. Here, using genetic and biochemical assays, we unveil Thr748 as a conserved IFN-independent phosphorylation switch in Stat1, which restricts IFN signaling and promotes innate inflammatory responses following the recognition of the bacterial-derived toxin lipopolysaccharide (LPS). Genetically engineered mice expressing phospho-deficient threonine748-to-alanine (T748A) mutant Stat1 are resistant to LPS-induced lethality. Of note, T748A mice exhibited undisturbed IFN signaling, as well as total expression of Stat1. Further, the T748A point mutation of Stat1 recapitulates the safeguard effect of the genetic ablation of Stat1 following LPS-induced lethality, indicating that the Thr748 phosphorylation contributes inflammatory functionalities of Stat1. Mechanistically, LPS-induced Toll-like receptor 4 endocytosis activates a cell-intrinsic IκB kinase-mediated Thr748 phosphorylation of Stat1, which promotes macrophage inflammatory response while restricting the IFN and anti-inflammatory responses. Depletion of macrophages restores the sensitivity of the T748A mice to LPS-induced lethality. Together, our study indicates a phosphorylation-dependent modular functionality of Stat1 in innate immune responses: IFN phospho-tyrosine dependent and inflammatory phospho-threonine dependent. Better understanding of the Thr748 phosphorylation of Stat1 may uncover advanced pharmacologically targetable molecules and offer better treatment modalities for sepsis, a disease that claims millions of lives annually.

Analysis of Protein Interactions in Patient-Derived Xenografts Using Immunoprecipitation.

Proteins are large, complex molecules that regulate multiple functions within the cell. The protein rarely functions as a single molecule, but rather interacts with one or more other proteins forming a dynamic network. Protein-protein interactions are critical for regulating the cell's response toward various stimuli from outside and inside the cell. Identification of protein-protein interactions enhanced our understanding of various biological processes in the living cell. Immunoprecipitation (IP) has been one of the standard and most commonly used biochemical methods to identify and confirm protein-protein interactions. IP uses a target protein-specific antibody conjugated with protein A/G affinity beads to identify molecules interacting with the target protein. Here, we describe the principle, procedure and challenges of the IP assay.

Threonine Phosphorylation and the Yin and Yang of STAT1: Phosphorylation-Dependent Spectrum of STAT1 Functionality in Inflammatory Contexts.

Threonine phosphorylation promotes inflammatory functions of STAT1 while restricting its interferon (IFN) signaling in innate immune responses. However, it remains unclear whether the restriction of STAT1-mediated IFN signaling conferred by threonine phosphorylation is a ubiquitous mechanism or one that is context-dependent. To address this, we utilized pristane-induced lupus, a prototype IFN-driven systemic autoimmune disease model characterized by the production of high-titer autoantibodies against nucleic acid-associated antigens. Through genetic and biochemical assays, we demonstrate that Thr748 phosphorylation is dispensable for STAT1 functionality in pristane-induced lupus. Genetically engineered mice expressing the phospho-deficient threonine 748-to-alanine (T748A) mutant STAT1 exhibited similar survival rates, high titers of anti-dsDNA IgG, and nephritis compared to their wild-type littermates. In sharp contrast, STAT1 deficiency protected mice against pristane-induced lupus, as evidenced by increased survival, low titers of anti-dsDNA IgG, and less severe nephritis in the STAT1 knockout mice compared to their T748A littermates. Our study suggests a phosphorylation-dependent modularity that governs the spectrum of STAT1 functionality in inflammatory contexts: IFN phospho-tyrosine-dependent and inflammatory phospho-threonine-dependent, with Thr748 phosphorylation driving selective inflammatory activities, particularly those not driven by the canonical JAK pathway. From a broader perspective, our findings provide deeper insights into how distinct phosphorylation events shape the combinatorial logic of signaling cassettes, thereby regulating context-dependent responses.

Evaluation of Biomarkers in Egyptian Patients with Different Grades of Nonalcoholic Fatty Liver Disease.

Background and Aims: Nonalcoholic fatty liver disease (NAFLD) is a silent disease; its spectrum includes simple steatosis, nonalcoholic steatohepatitis and fibrosis. Pro- and anti-inflammatory cytokines play roles in the pathogenesis of NAFLD and insulin resistance (IR). Moreover, plasma cell antigen-1 (PC-1) is related to IR and associated with NAFLD progression. Therefore, we aimed to detect biomarkers, ultrasonographic and anthropometric findings capable of differentiating NAFLD grades, since most previous investigators were concerned more with NAFLD patients without classifying them into grades. Methods: A total of 87 NAFLD patients (31 with grade 1 (mild NAFLD), 26 with grade 2 (moderate NAFLD) and 30 with grade 3 (severe NAFLD) were included in the study, in addition to 47 controls (grade 0). All subjects underwent ultrasonographic examination for NAFLD diagnosis. Serum interleukin-10 (IL-10), plasma interleukin-18 (IL-18) and plasma PC-1 levels were determined using enzyme-linked immunosorbent assay. Results: Homoeostasis model assessment (HOMA)-IR was higher in different NAFLD grades than in controls. Ultrasonographic and anthropometric findings and lipid profile indices (except for high-density lipoprotein cholesterol, which was decreased) were increased with NAFLD progression. Grade 3 patients showed significant increase in levels of IL-18 and significant decrease in IL-10 and PC-1 levels when compared to grade 1 patients. Conclusion: Anthropometric and ultrasonographic findings were valuable in differentiating NAFLD grades. IR is very important in NAFLD pathogenesis. IL-18, HOMA-index and PC-1 levels could be used to differentiate between NAFLD grades, together with other measurements.