JAK1^A634D up-regulates ligand-induced signaling through the type I IFN receptor. (A) BW5147 cells (10⁶) stably transduced with JAK1^WT or JAK^A634D, with intact or mutated Y107A FERM domain (JAK1^A634D/Y107A), were stimulated for 3 hours with 1% IFN-β or mock/control HEK293 supernatant, lysed, and used for total RNA extraction. To quantify ligand-induced expression of type I IFN–induced genes, quantitative RT-PCR was performed with primers for mIRF-7 and mOasl-2 genes. Transcripts were normalized to the level of the murine β-actin transcripts. Results are mean ± SD of biologic triplicates. Similar results were obtained in 3 independent experiments in BW5147 and BaF3 cell lines. (B) BW5147 cells (12 × 10⁶) stably transduced by JAK1^WT or JAK1^A634D were electroporated with 15 μg of pIRF7-luc luciferase reporter plasmid, which contains the promoter of the murine IRF-7, and 1 μg of internal control pRL-TK plasmid. Cells were seeded in 96-well plates at 5 × 10⁵ cells/well and stimulated with 1% IFN-β or mock/control HEK293 supernatants for 2 hours before luciferase assay was performed. Results are mean ± SD of biologic triplicates. Similar results were obtained in 3 independent experiments. WT indicates wild-type.