H. Wu et al., FUNCTIONAL INTERACTION OF ERYTHROPOIETIN AND STEM-CELL FACTOR RECEPTORS IS ESSENTIAL FOR ERYTHROID COLONY FORMATION, Proceedings of the National Academy of Sciences of the United Statesof America, 94(5), 1997, pp. 1806-1810
Production of mature erythrocytes requires multiple growth factors, bu
t we do not know how their actions are coordinated, Here we show that
erythroid progenitors from erythropoietin receptor (Epo-R)(-/-) fetal
livers, infected in vitro with a retrovirus expressing the wild-type E
po-R, require addition of both Epo and stem cell factor (SCF) to form
colony-forming unit erythroid (CFU-E) colonies. Thus, a functional int
eraction between KIT and the Epo-R, similar to what we reported in cul
tured cells, is essential for the function of CFU-E progenitors, In co
ntrast, CFU-E colony formation in vitro by normal fetal liver progenit
ors requires only Epo; the essential interaction between activated KIT
and the Epo-R must have occurred in vivo before or at the CFU-E proge
nitor stage, Using truncated dominant-negative mutant Epo-Rs, me show
that KIT does not activate the Epo-R by inducing its dimerization, but
presumably does so by phosphorylating tyrosine residue(s) in its cyto
solic domain, By expressing mutant Epo-Rs containing only one of eight
cytosolic tyrosines, we show that either tyrosine residue Y464 or Y47
9 suffices for Epo-dependent cell proliferation, However, only Epo-R F
7Y479 is capable of supporting erythroid colony formation when express
ed in Epo-R(-/-) fetal liver cells, indicating that Y464 either cannot
send a differentiation signal or fails to respond to SCF/KIT activati
on, This work employs a novel experimental system to study the functio
n of growth factors and their receptors in normal hematopoiesis.