Cytokines and growth factors induce activation of the family of signal transducers and activators of transcription (Stats) that directly activate gene expression. Recently, constitutively activated Stat1, Stat3, and Stat5 were identified in nuclear extracts of acute myeloid leukemia (AML) patients, suggesting involvement of constitutive Stat activity in the events of leukemogenesis. In the present study, blasts of nine AML cases were investigated for the constitutive binding activity of the recently identified transcription factor LIL-Stat (LPS- and IL-1-inducible Stat). Band-shift assays were performed using the LPS-and IL-1-responsive element (LILRE) oligonucleotide, a gamma interferon activation site-like site that is present in the human IL-1beta promoter. Constitutive LIL-Stat binding activity was observed in three leukemic cell lines and in seven out of nine AML cases. Transient transfection studies with a reporter plasmid containing three sequential LIL-Stat binding sites showed distinct transcriptional activity of LIL-Stat only in those AML blasts that constitutively expressed LIL-Stat. In CD34+ cells LIL-Stat also constitutively bound to its consensus sequence. However, when these cells were cultured in the presence of macrophage-colony stimulating factor (M-CSF) and stem cell factor (SCF) for differentiation along the monocytic lineage, the LIL-Stat binding activity disappeared totally. In agreement with these findings neither mature monocytes nor granulocytes showed constitutive or inducible LIL-Stat binding activity. We conclude that the LIL-Stat transcription factor is constitutively activated in undifferentiated and leukemic hematopoietic cells, but not in mature cells. This may suggest a role for this transcription factor in the process of differentiation.
Copyright 1998 by The American Society of Hematology.