BCL3 upregulation by IL-9 in cells expressing mutated hIL-9R. BW5147 cells transfected with the wild-type human IL-9R (BWh9R) or mutants of this receptor partially (BWmut6 and BWmut7) or totally (BWphe116) defective in STAT activation (see text) were stimulated with 500 U/mL human IL-9 for 24 hours. After electrophoresis of 5 μg of total RNA and transfer to nitrocellulose, filters were hybridized with a ³²P-labeled mouse BCL3 cDNA probe. Hybridization with a β-actin probe confirmed the even loading of RNA in each lane.