THROMBOPOIETIN INDUCES TYROSINE PHOSPHORYLATION OF A COMMON BETA-SUBUNIT OF GM-CSF RECEPTOR AND ITS ASSOCIATION WITH STAT5 IN TF-1 TPO CELLS/

TF-1/TPO cells are derived from an erythroleukemia cell line, TF-1, an d are absolutely dependent on either TPO or granulocyte-macrophage col ony-stimulating factor (GM-CSF)/interleukin-3 (IL3) for their continuo us growth and survival. To gain insight into the molecular basis of he mopoietic activities shared by TPO and GM-CSF/IL3 in TF-1/TPO cells, a re studied the cross-talk between signal transduction pathways elicite d by these cytokines. Stimulation of TF-1/TPO cells with TPO resulted in tyrosine phosphorylation of the TPO receptor (c-Mpl) as well as the common beta subunit (beta c) of GM-CSF/IL3 receptor complex. GM-CSF, however, induced tyrosine phosphorylation of beta c but not cMpl. TPO- imduced tyrosine phosphorylation of beta c was time- and dose-dependen t. We next examined whether or not TPO-induced tyrosine phosphorylatio n of beta c led to recruitment of SH2-containing molecules such as Sta t5 and Shc. While GM-CSF caused association of Stat5 and Shc with beta c, TPO caused association of Stat5, but not Shc, with beta c, suggest ing that TPO and GM-CSF may not induce phosphorylation of the same set s of tyrosine residues in pc. These results suggest that activation of c-Mpl affects the signaling pathway of GM-CSF/IL3 but not vice versa. (C) Academic Press.