Lyn enhances expression of a Stat5-responsive reporter plasmid. (A) COS7 cells were cotransfected with either pcDNA3 (Cont.), pcDNA-Jak2 (Jak2), or pXM-LynA and pXM-LynB (Lyn), as indicated, along with the Stat5-responsive luciferase reporter pZZ1 plasmid, the control Renilla luciferase pRL-TK plasmid, pRK5-Stat5, and pXM-EpoR-Wt. Two days after transfection, cells were either left unstimulated or stimulated with 5 U/mL for 5 hours, as indicated, and harvested for the dual-luciferase assay. The luciferase activity was normalized by the Renilla luciferase activity and expressed in arbitrary units. The data represent averages ± standard deviations of three independent experiments. (B) 32D/EpoR-Wt cells were transiently transfected with either pcDNA3 (Cont.), pcDNA-Jak2 (Jak2), or pXM-LynA and pXM-LynB (Lyn), as indicated, along with pZZ1 and pRL-SV40. One day after transfection, cells were starved overnight, incubated for 5 hours in medium with or without 4 U/mL of Epo (as indicated), and harvested for the dual-luciferase assay.