Coexpression of stem cell factor and its receptor c-Kit in human malignant glioma cell lines

Stem cell factor (SCF), a hematopoietic growth factor, is the ligand of the tyrosine kinase receptor encoded by the c-kit proto-oncogene. Beside the important role of this receptor-ligand complex in hematopoiesis, gametogenesis and melanogenesis, SCF and its receptor have been shown to be expressed in the brain. We have studied the expression of SCF and c-kit in 20 human malignant glioma cell lines at the mRNA as well as at the protein level. In addition, recombinant human (rh) SCF was tested in [3H]thymidine uptake assays for a mitogenic effect on these cells. SCF and c-Kit proteins were detected in the cytoplasm of glioma cells by alkaline phosphatase-monoclonal anti-alkaline phosphatase immunostaining and Western blot analysis. However, neither SCF nor c-Kit were seen on the cell surface by flow cytometry. Furthermore, none of the proliferation assays showed a mitogenic effect for exogenously added rhSCF. Blocking studies using an anti-SCF antibody failed to demonstrate modulating effects on the growth of selected cell lines. These results suggest that SCF and c-Kit may mediate non-proliferative signals or may employ intracellular mechanisms for autocrine growth regulation of glioma cells.