Figure 3

PTPMeg2 decreases the transcription activity of STAT3. (A) PTPMeg2 inhibits IL-6-stimulated STAT3 transcriptional activity. Luciferase assays were performed using MCF7 cells with transient expression of Myc-PTPMeg2 and Flag-STAT3, transfected with APRE-Luc reporter and pRL-TK (as an internal control). Relative luciferase activities were normalized with the internal control. Results are presented as mean ± SD from three independent experiments. (B) PTPMeg2 inhibits STAT3-mediated transcriptional activity in a dose dependent manner. Different amounts of PTPMeg2 were co-expressed with STAT3 in the presence or absence of IL-6 stimulation. Different amounts of PTPMeg2CS were also co-expressed with STAT3. (C) The PTP domain of PTPMeg2 inhibits the STAT3 transcriptional activity. Different domains and deletions of PTPMeg2 were co-expressed with Flag-STAT3 in the MCF7 cells and luciferase assays were performed as above. (D) Depletion of PTPMeg2 results in an enhanced STAT3 transcriptional activity. An shRNA targeting PTPMeg2 was co-expressed with STAT3 in MCF7 cells transfected with APRE-Luc reporter and pRL-TK under stimulation of IL-6. Luciferase activities were assayed as above. (E) Levels of pSTAT3(Tyr705) and STAT3 were examined in the MCF7 cells overexpressed and depleted PTPMeg2 in separated membranes from the same lysates. (F) PTPMeg2 has no effect on the STAT1 transcriptional activity. M67 luciferase reporters were co-transfected into MCF7 cells with STAT1 and PTPMeg2, in the presence or absence of IFN-gamma. Luciferase activities shown are mean ± SD of three independent experiments.