EXPRESSION OF FLT3 RECEPTOR AND FLT3-LIGAND IN HUMAN LEUKEMIA-LYMPHOMA CELL-LINES

The FLT3 gene encodes a receptor tyrosine kinase that is closely relat ed to two well-known receptors, KIT and FMS, that regulate with their respective ligands, stem cell factor (SCF) and macrophage colony-stimu lating factor (M-CSF), proliferation and differentiation of hematopoie tic cells. The ligand for FLT3, FL, is active in both soluble and memb rane-bound forms. We examined expression of FL and FLT3 mRNA in a pane l of some 110 continuous human leukemia-lymphoma cell lines from all m ajor hematopoietic cell lineages by Northern blot analysis. FLT3 mRNA is expressed primarily in pre-B cell lines, myeloid and monocytic cell lines whereas FL mRNA was detected in most cell lines from all cell l ineages. Analysis of FLT3 receptor protein expression examined with a specific anti-FLT3 monoclonal antibody and flow cytometry in 17 cell l ines confirmed the results obtained at the mRNA level. Forty of 110 ce ll lines displayed both receptor and ligand mRNA suggesting a possible autocrine or intracrine stimulation. In normal hematopoietic cells ex pression of FLT3 was reported to be associated with CD34 positivity, a cell surface marker of immature and precursor cells. No correlation b etween FLT3 and CD34 expression was found in the cell lines analyzed. These studies served to illustrate further the importance of the FL-FL T3 ligand-receptor system in the regulation of hematopoietic cells.