In vivo interaction of MgcRacGAP with STAT3 and Rac GTPases. (A) Coprecipitation of STAT3, MgcRacGAP, and Rac2. M1 cells were incubated in the presence or absence of 50 ng/mL for 15 minutes, and the cell lysates were subjected to immunoprecipitation with anti-STAT3, anti-Rac2, and a control Ab, followed by the immunoblotting with anti-MgcRacGAP, anti-STAT3, or anti-Rac2 Ab. (B) (i) Coprecipitation of MgcRacGAP with STAT3 in 293T cells transfected with Flag-tagged MgcRacGAP and either the empty vector or HA-tagged STAT3. Cell lysates were immunoprecipitated with anti-HA, and immunoblotted with anti-Flag (top panel). Levels of transfected STAT3-HA and MgcRacGAP-Flag were assayed by blotting with anti-HA and anti-Flag (middle and bottom panels). Cells transfected with the empty vectors alone were used as a negative control. (ii) Coprecipitation of STAT3 with MgcRacGAP in 293T cells transfected with STAT3-HA and either the empty vector or MgcRacGAP-Flag. Cell lysates were immunoprecipitated with anti-Flag and immunoblotted with anti-HA (top panel). Levels of transfected MgcRacGAP-Flag and STAT3-HA were assayed by blotting with anti-Flag and anti-HA (middle and bottom panels). Cells transfected with the empty vector alone were also used as a negative control.