Novel Regulatory Mechanism of STAT1 through Redox Post-translational Modification of Cysteines

STAT1 plays a central role in the immune system, in which it mediates signaling induced by different cytokines, including type I (α/β) and type II Interferon (IFN), and regulates expression of genes involved in many physiological processes, including antiviral and antibacterial defense, immune tolerance, suppression of cell proliferation, and induction of apoptosis. Dysregulation or mutation of STAT1 causes life threatening conditions resulting from inefficient defense against pathogens, autoimmunity or cancer development. Single nucleotide polymorphisms of STAT1 Cys residues are associated with chronic mucocutaneous candidiasis disease (CMCD), suggesting a role of Cys in the capacity of STAT1 to drive an appropriate anti-pathogen response. Regulation of STAT1 activity through different post-translational modifications is well-characterized. However, the role of Reactive Oxygen species (ROS) and Cys reversible oxidative post-translational modifications (ox-PTMs) on STAT1 function remained to be investigated. Using maleimide-derivative switch methods to label Cys ox-PTMs, we found that Diamide, a thiol-oxidizing agent, and the myeloperoxidase-generated HOCl induce ox-PTMs of STAT1 Cys in epithelial cells (A549), monocytes (THP-1) and ectopically expressed STAT1 in STAT1 deficient fibroblasts (U3A). Analysis of Cys/Ala (C/A) mutants of STAT1 in response to IFNγ and IFNβ revealed gain of function phenotype of mutations in two different functional domains of STAT1. Altogether, our data supports a model in which previously unrecognized ox-PTMs of STAT1 Cys residues are essential to dampen STAT1 activity. Current studies are aimed at further characterizing the specific Cys ox-PTMs and their consequences on STAT1-dependent transcriptional program induction and antiviral immune response.