Vol. 10, Issue 11, 3959-3970, November 1999

Two Distinct Signaling Pathways Downstream of Janus Kinase 2 Play Redundant Roles for Antiapoptotic Activity of Granulocyte-Macrophage Colony-stimulating Factor

Rui Liu,^* Tohru Itoh,^* Ken-ichi Arai,^* and Sumiko Watanabe^*

 ^*Department of Molecular and Developmental Biology, Institute of Medical Science, University of Tokyo, and  CREST, Japan Science and Technology Corporation, Tokyo 108-8639, Japan

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) induces proliferation and sustains the viability of the mouse interleukin-3-dependent cell line BA/F3 expressing the hGM-CSF receptor. Analysis of the antiapoptosis activity of GM-CSF receptor c mutants showed that box1 but not the C-terminal region containing tyrosine residues is essential for GM-CSF-dependent antiapoptotic activity. Because c mutants, which activate Janus kinase 2 but neither signal transducer and activator of transcription 5 nor the MAPK cascade sustain antiapoptosis activity, involvement of Janus kinase 2, excluding the above molecules, in antiapoptosis activity seems likely. GM-CSF activates phosphoinositide-3-OH kinase as well as Akt, and activation of both was suppressed by addition of wortmannin. Interestingly, wortmannin did not affect GM-CSF-dependent antiapoptosis, thus indicating that the phosphoinositide-3-OH kinase pathway is not essential for cell surivival. Analysis using the tyrosine kinase inhibitor genistein and a MAPK/extracellular signal-regulated kinase (ERK) kinase 1 inhibitor, PD98059, indicates that activation of either the genistein-sensitive signaling pathway or the PD98059-sensitive signaling pathway from c may be sufficient to suppress apoptosis. Wild-type and a c mutant lacking tyrosine residues can induce expression of c-myc and bcl-x_L genes; however, drug sensitivities for activation of these genes differ from those for antiapoptosis activity of GM-CSF, which means that these gene products may be involved yet are inadequate to promote cell survival.