JAK1^A634D, JAK1^R724H, and JAK1^R879C differentially favor IFN-β and IL-9 signaling. (A-B) BW5147 cells (12 × 10⁶) stably transduced by JAK1^WT or JAK1^A634D were electroporated with 15 μg of the ISGF-3 responsive pIRF7-luc (A) or the STAT3 responsive pGL3-pap1-luc (B) luciferase reporter plasmid 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 pIRF7-luc) and by 100 U/mL hIL-9 (for pGL3-pap1) for 2 hours before luciferase assay was performed. Results are mean ± SD of biologic triplicates. Similar results were obtained in 3 independent experiments. (C-D) BW5147 cells (10⁶) stably transduced by JAK1 wild-type (WT) or different JAK1 mutants were stimulated with 1% IFN-β or mock/control HEK293 supernatants (C) and stimulated with 100 U/mL hIL-9 (D) for 3 hours, lysed, and used for total RNA extraction. Real-time PCR was performed to quantify transcripts of mIRF-7 and mBcl-3 genes. Gene expressions 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.