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. 2003 Jan;23(2):543–554. doi: 10.1128/MCB.23.2.543-554.2003

FIG. 4.

FIG. 4.

MEK1/2 is essential for production of LIF but is not required for LIF action. (A and B) TT cells were treated for 2 days with LIF in the presence of the MEK1/2 inhibitor U0126 (10 μM) and observed for changes in expression of phosphorylated ERK1/2, RET, and phosphorylated STAT3 by Western blotting (A) and morphology (B). (C) TTRaf cells were treated for 2 days with estradiol in the presence of U0126 and observed for changes in expression of phosphorylated ERK1/2 and LIF by Western blotting. (D and E) TT cells were infected with adenoviruses containing constitutively active Ras V12 or Raf BXB in the presence of U0126. After 2 days, cells were observed for LIF expression by RT-PCR (D) and STAT3 activation (E). The data presented are fold increases of activity upon treatment. P values are <0.005 for Ras, Raf, LIF, and LIF+U0126 compared to the control (one-way analysis of variance). Experiments were repeated at least three times with similar results. GAPDH, glyceraldehyde-3-phosphate dehydrogenase.