Abnormal response to granulocyte colony-stimulating factor (G-CSF) in
canine cyclic hematopoiesis is not caused by altered G-CSF receptor
expression
BR Avalos, VC Broudy, SK Ceselski, BJ Druker, JD Griffin and WP Hammond
Department of Internal Medicine, Ohio State University, Columbus 43210.
A decrease in responsiveness to granulocyte colony-stimulating factor
(G-CSF) has been implicated in the pathophysiology of cyclic hematopoiesis.
Using the canine model of cyclic neutropenia, we examined the response of
neutrophil precursors to G-CSF in vitro and G- CSF receptor expression in
neutrophils from grey collie dogs to determine whether the abnormal
response observed to G-CSF in vivo in this disorder is present at the level
of the progenitor cell and is caused by defective G-CSF receptor
expression. Bone marrow mononuclear cells from grey collie dogs required
sevenfold higher G-CSF concentrations than normal dog cells to achieve
half-maximal colony growth [56 pmol/L v 8 pmol/L). Receptor binding assays
with 125I- labeled G-CSF and Scatchard analyses of the equilibrium binding
data were consistent with expression of a single class of high-affinity
receptors for G-CSF on neutrophils from both normal dogs and grey collies
with similar receptor numbers (56 to 446 sites/cell v 78 to 199 sites/cell)
and binding affinities (28 to 206 pmol/L v 84 to 195 pmol/L). Chemical
cross-linking studies identified a G-CSF binding protein of approximately
120 kD on neutrophils from grey collies, similar in size to that on normal
dog neutrophils. No abnormal G-CSF receptor mRNA transcripts were detected
in neutrophils from grey collie dogs by Northern blot analysis. Treatment
of both normal and grey collie neutrophils with G-CSF rapidly induced
tyrosine phosphorylation of an 80-kD protein that behaved like canine
c-rel. These results demonstrate that the abnormal responsiveness to G-CSF
in canine cyclic hematopoiesis is present in neutrophil precursors and is
not associated with demonstrable alterations in the number, binding
affinity, or overall size of the G-CSF receptor in neutrophils, or with
defective tyrosine phosphorylation of p80. These data suggest that cyclic
hematopoiesis is caused by a defect in the G-CSF signal transduction
pathway at a point distal to G-CSF receptor binding that does not involve
the early biochemical events leading to p80 tyrosine phosphorylation.
Volume 84,
Issue 3,
pp. 789-794,
08/01/1994
Copyright © 1994 by The American Society of Hematology
