Fetal hemoglobin modulation during human erythropoiesis: stem cell factor has “late” effects related to the expression pattern of CD117

Abstract

A cytokine-screening assay of cultured peripheral blood cells obtained using immune rosetting and separation of progenitors was developed to identify determinants of fetal hemoglobin (HbF) modulation during adult erythropoiesis. Among the 12 erythroid growth-promoting cytokines tested, stem cell factor (SCF) at a concentration of 50 ng/mL resulted in the most significant increase in cell proliferation and HbF content. The average HbF/hemoglobin A (HbA) ratio was 30.9% ؎ 18.7% in cultures containing SCF compared with 4.1% ؎ 2.2% in those grown with erythropoietin (EPO) alone (P ‫؍‬ 8.5E-8). To further investigate the hemoglobin-modulating effects of SCF, we examined the surface expression pattern of the SCF receptor, CD117, among maturing erythroblasts. CD117 expression increased during the first week of culture and peaked on culture days 7 to 9. After culture day 9, the level of CD117 declined to lower levels. The rise in CD117 expression to high levels mirrored that of the transferrin receptor (CD71), and the subsequent reduction in CD117 was inversely related to increases in expression of glycophorin A. SCF-related increases in the HbF/HbA ratio correlated with the expression pattern of CD117. SCF added during days 7 to 14 resulted in a more pancellular distribution of HbF on day 14 compared with the heterocellular distribution present in cultures supplemented with SCF on days 0 to 7. A significant SCF-mediated increase in HbF was also measured using progenitors derived from cord blood. These results suggest that the HbF response to SCF is greatest at the late progenitor stage as a function of surface CD117 expression. (Blood. 2003;

A signaling mechanism for growth-related expression of fetal hemoglobin

“…We have previously shown that supplementing SCF to the growth medium resulted in proliferation and increased HbF to levels greater than those achieved in EPO alone. 15 In the present study, a 10-fold increase in the number of erythroblasts was detected in the presence of SCF. The HbF/HbAϩHbF ratio averaged 27.4% Ϯ 7.9% in EPOϩSCF compared with 1.26% Ϯ 1.7% in EPO alone (P ϭ .02).…”

“…We examined cells in this context after 6 days in culture, based on the high levels of CD117 and related SCF effects identified at the proerythroblast stage of erythroid development. 15 Phosphorylation analyses were performed on cell extracts obtained 0, 10, and 30 minutes after addition of SCF. Western blot analyses were performed using antibodies for phosphorylated and total proteins.…”

“…[11][12][13][14] Among cultured human cells from cord blood and adults, SCF has considerable HbF-inducing ability at the proerythroblast stage of differentiation that correlates well with the expression of CD117. 15 SCF binding results in the autophosphorylation of its receptor (CD117) and creates binding sites for SH2 domaincontaining proteins, including those of the Ras/Raf/mitogenactivated protein kinase (MAPK) pathway. SCF-and EPOmediated signals interact at various points along the Ras/Raf1/ MAPK and PI3K pathways to affect specific biologic responses.…”

Fetal hemoglobin chemical inducers for treatment of hemoglobinopathies

“…Wojda et al [216] comparatively analyzed 12 cytokines able to act on erythropoiesis and confirmed that, among them, only SCF was able to significantly enhance HbF synthesis. The capacity of SCF to induce HbF synthesis in adult erythroid cells was correlated to the presence of c-kit on erythroid progenitors/precursors: in fact, the delayed addition of SCF to erythroid cultures was active in inducing a marked enhancement of HbF synthesis at the condition that was added on erythroid cell progeny c-kit + [216].…”

“…The capacity of SCF to induce HbF synthesis in adult erythroid cells was correlated to the presence of c-kit on erythroid progenitors/precursors: in fact, the delayed addition of SCF to erythroid cultures was active in inducing a marked enhancement of HbF synthesis at the condition that was added on erythroid cell progeny c-kit + [216]. Other subsequent studies have shown the possible synergistic effect between SCF and other agents to stimulate HbF synthesis.…”