LYN ASSOCIATES WITH THE JUXTAMEMBRANE REGION OF C-KIT AND IS ACTIVATED BY STEM-CELL FACTOR IN HEMATOPOIETIC-CELL LINES AND NORMAL PROGENITOR CELLS

Stem cell factor (SCF) is a cytokine critical for normal hematopoiesis . The receptor for SCF is c-Kit, a receptor tyrosine kinase. Our labor atory is interested in delineating critical components of the SCF sign al transduction pathway in hematopoietic tissue. The present study exa mines activation of Src family members in response to SCF. Stimulation of cell lines as well as normal progenitor cells with SCF rapidly inc reased tyrosine phosphorylation of the Src family member Lyn. Peak res ponses were noted 10-20 min after SCF treatment, and phosphorylation o f Lyn returned to basal levels 60-90 min after stimulation, SCF also i nduced increases in Lyn kinase activity in, vitro. Lyn coimmunoprecipi tated with c-Kit, and studies with GST fusion proteins demonstrated th at Lyn readily associated with the juxtamembrane region of c-Kit. Trea tment of cells with either Lyn antisense oligonucleotides or PPI, a Sr c family inhibitor, resulted in dramatic inhibition of SCF-induced pro liferation. These data demonstrate that SCF rapidly activates Lyn and suggest that Lyn is critical in SCF-induced proliferation in hematopoi etic cells.