JAK1

JAK1 is an essential Janus kinase that mediates biologic responses downstream of class II cytokine receptors, γc-containing receptors, and gp130-dependent receptors^[1]. Mechanistically, the JAK/STAT pathway provides a rapid membrane-to-nucleus signaling module that drives transcriptional programs linked to inflammation, immunity, cancer, and autoimmune disease^[2]. In inflammatory contexts, JAK1 transduces signals from γc cytokines, IL-6, interferons, and IL-10, connecting cytokine receptor activation to immune-cell regulation and synovial inflammation^[3]. Disease models and human genetics support this role, because JAK1 gain-of-function variants drive immune dysregulation with atopic dermatitis, allergy, eosinophilia, and gastrointestinal inflammation^[4][5]. Compared with related isoforms, JAK1 shows nonredundant signaling, and Jak1 has a dominant role over Jak3 in γc receptor signaling^[1][6]. JAK2 more directly supports hematopoietic growth-factor pathways, whereas JAK3 is mainly linked to common γc receptor biology^[3][6]. For experimental applications, selective JAK1 inhibitors help separate cytokine-driven inflammatory signaling from broader JAK blockade^[7]. Chemical proteomics identified an allosteric cysteine in JAK1 C817, absent from JAK2 and JAK3, enabling inhibitors that block JAK1-dependent trans-phosphorylation and cytokine signaling^[8].