PTP1B dephosphorylates IL-4–induced STAT6. (A,B) HEK293 cells were transfected with PTP1B (A) or PTP-PEST (B) plasmids and either STAT6 plasmid or empty vector. Forty-eight hours after transfection, cells were stimulated with IL-4 (100 U/mL) for 30 minutes. As a control, nontransfected HEK293 cells were similarly stimulated (A). Cellular proteins from unstimulated and IL-4–stimulated cells were resolved by SDS-PAGE and immunoblotted for tyrosine-phosphorylated STAT6 (pSTAT6), STAT6, PTP1B, or PTP-PEST and actin. The result is representative of 3 independent experiments.