PTP1B inhibits IL-4–induced gene transcription. (A) Mock or PTP1B encoding plasmids were cotransfected into HEK293 cells with the STAT6-driven luciferase reporter-construct C/EBP-N4 and STAT6 and pRL plasmids. Luciferase activity was determined 48 hours after transfection in either unstimulated cells or cells that had been stimulated with IL-4 (100 U/mL) for 6 hours. Numbers refer to relative luciferase activities, the average value obtained for the reporter without activator being taken as 1. Numbers are means and SD of 3 independent experiments, each performed in triplicate. (B) VAL cells were transiently transfected with either control pIRES-hrGFPII vector or pIRES-hrGFPII PTP1B vectors as described in “Methods” in “Cell transfections.” At 48 hours after transfection, cells were sorted for GFP expression and incubated with or without IL-4 (100 U/mL) for 6 hours. RNA was extracted, and CD23 and PTP1B RNA expression was measured by real-time RT-PCR in triplicate. The result is representative of 3 independent experiments.