Molecular analysis of signaling events mediated by the cytoplasmic domain of leukemia inhibitory factor receptor alpha subunit.

A chimeric receptor (130/190) containing the cytoplasmic region of leukemia inhibitory factor receptor alpha subunit (LIFRalpha, or gp190) and the extracellular transmembrane region of gp130 was generated. Expressed of the 130/190 chimera in HL-60 cells to induced the homodimerization of the cytoplasmic domains (190cyt-190cyt) with whole LIFRalpha subunit on HL-60 cells in response to LIF. Expression and activation of the signal transducer and activator of transcription factor-3 (Stat3) and inhibition of leukemia cell proliferation were evaluated in cells transfected with this chimeric molecule. Increased tyrosyl phosphorylation of Stat3 at Tyr705 was detected after 10 min LIF treatment in cells transfected with either the 130/190 or the wild type receptor. Cell proliferation was decreased upon LIF treatment in both cell types. However, expression of the C-terminal region of the cytoplasmic region of LIFRalpha subunit (190CT) in HL-60 cells resulted in lower levels of Stat3 phosphorylation induction by LIF and cell proliferation was unaffected. Immunohistochemical staining indicated an inverse correlation between Cdc25B expression and the levels of phospho-Stat3 in 190CT and 130/190 cells. Expression of CD15, a cell differentiation marker, was lower in 190CT than in 130/190 cells. Together, these results suggest that homodimerization of the 190 cytoplasmic region promotes the Tyr 705 phosphorylation, which correlates with the inhibition of proliferation and stimulation of differentiation in HL-60 cells. Our results also suggest a signal link between Stat3 and Cdc25B.