Synergistic roles for Pim-1 and c-Myc in STAT3-mediated cell cycle progression and antiapoptosis.

The activation of STAT3 by the cytokine receptor gp130 is required for both the G1 to S cell cycle transition and antiapoptosis. We found that Pim-1 and Pim-2 are targets for the gp130-mediated STAT3 signal. Expression of a kinase-defective Pim-1 mutant attenuated gp130-mediated cell proliferation. Constitutive expression of Pim-1 together with c-myc, another STAT3 target, fully compensated for loss of the STAT3-mediated cell cycle progression, antiapoptosis, and bcl-2 expression. We also identified valosine-containing protein (VCP) as a target gene for the Pim-1-mediated signal. Expression of a mutant VCP led cells to undergo apoptosis. These results indicate that Pim-family proteins play crucial roles in gp130-mediated cell proliferation and explain the synergy between Pim and c-Myc proteins in cell proliferation and lymphomagenesis.