Pim-1 cooperates with SOCS1 and SOCS3 to inhibit STAT5-dependent transcription in IL-3–stimulated FDCP1 cells. FD/Neo and FD/Pim44 cells were transfected with the Spi-LUC2 reporter with or without expression vectors for SOCS1, SOCS2, or SOCS3. Cells were left unstimulated or stimulated with IL-3 as indicated.