Expression and function of Flt3/flk2 in human tumor cell lines

The receptor tyrosine kinase Flt3 is expressed on the blasts of a high prop ortion of AML cases. We were interested in the expression and function of F lt3 on various human tumors. Human tumor cell lines were tested for FID exp ression by Northern blot analysis and RT-PCR using head/neck (n=3), breast (n=4), ovarian (n=4), small cell lung (n=2), non-small cell lung (n=2), gas tric (n=1), colon (n=3), pancreatic (n=1) and prostate carcinoma (n=1), cho riocarcinoma (n=1), glioblastoma (n=5), neuroblastoma (n=1), melanoma (n=3) , lymphoma (n=1), Hodgkin's disease (n=2), and leukemic (n=6) cell lines. W ith no expression on the other cell samples, 3 of 6 leukemic cell lines sho wed expression of Flt3 mRNA. The cDNA region corresponding to the juxtamemb rane domain did not show any mutation as determined by sequence analysis. I n all 3 positive cell lines, protein expression was verified by immunopreci pitation followed by immunoblot analysis. Although Flt3 is functional in th ese cell lines, as judged by ligand-dependent receptor autophosphorylation, it only mediates a proliferative response in 2 of the 3 cell lines. In con clusion, Flt3 is expressed exclusively in hematopoietic malignancies. Altho ugh early signalling events are detectable in all Flt3-positive cell lines tested, the expression of Flt3 does not predict a proliferative response of the cell lines. No internal tandem duplication of the juxtamembrane domain can be observed.