Stem cell factor and erythropoietin inhibit apoptosis of human erythroid progenitor cells through different signalling pathways

Abstract

Summary. Erythropoietin (EPO) and stem cell factor (SCF) are two important factors in human erythropoiesis. We have recently demonstrated that SCF and EPO synergistically activate mitogen-activated protein (MAP) kinase, thereby promoting growth of human erythroid colony-forming cells (ECFCs). In the present study, we have examined the intracellular mechanisms by which SCF and EPO maintain survival of these cells. In the absence of SCF and EPO, human ECFCs underwent rapid apoptosis. The process was significantly inhibited by addition of a single factor and was totally prevented in the presence of both factors. Treatment of ECFCs with wortmannin, a specific inhibitor of phosphoinositide 3-kinase (PI3K), inhibited the antiapoptotic effect of SCF but had no effect on that of EPO, indicating that SCF but not EPO inhibits apoptosis through the PI3K pathway. In contrast, treatment of ECFCs with PD98059, a specific inhibitor of MAP kinase/ERK kinase (MEK), inhibited cell growth but had no effect on the antiapoptotic activity of either SCF or EPO, suggesting that SCF and EPO prevent apoptosis of human ECFCs independent of the extracellular signal-regulated kinase (ERK) pathway. Interestingly, both EPO and SCF induced activation of PI3K. However, through PI3K, SCF caused activation of protein kinase B (PKB), an anti-apoptosis signal, whereas EPO led to activation of ERKs. Furthermore, the SCF-and EPO-maintained expression of antiapoptotic protein Bcl-X L was correlated with the activation of ERKs and was inhibited by PD98059, suggesting that Bcl-X L may not have a major role in preventing apoptosis of human ECFCs. Phosphorylated BAD was not affected by SCF, EPO or wortmannin. Taken together with our previous results, the present study indicates that SCF and EPO support survival and growth of human ECFCs through different signalling pathways and that they transduce distinctly different signals through activation of PI3K.

In vitro antiproliferative activity of the farnesyltransferase inhibitor R115777 in hematopoietic progenitors from patients with myelofibrosis with myeloid metaplasia

“…Nonmegakaryocytic progenitors from ET and PV patients were just as sensitive as the MMM progenitors (median IC 50 20 nM, range 5-47 nM, P ¼ 0.17) (Figure 1). In contrast, higher median R115777 IC 50 concentrations were required for inhibition of nonmegakaryocytic progenitors from normal controls (median 46 nM, range 6-118 nM) (Figure 1), although this difference was not statistically In vitro antiproliferative activity of farnesyltransferase RA Mesa et al significant among any of the three groups because of the wide range in sensitivity within each group.…”

“…41 It has been shown that both the PI-3 kinase pathway and the Mek pathway are involved with downstream signaling from a variety of critical hematopoietic growth factors, including erythropoietin and stem cell factor. 50,51 In addition, inhibition of the PI-3 kinase and Mek1 pathways has been shown to inhibit the growth of erythroid progenitors through potentially different mechanisms. 50,51 Since circulating progenitor cells in MMM constitute only a small fraction of the circulating mononuclear cells, it was not feasible to assess the effects of R115777 on these pathways using a biochemical approach.…”

“…50,51 In addition, inhibition of the PI-3 kinase and Mek1 pathways has been shown to inhibit the growth of erythroid progenitors through potentially different mechanisms. 50,51 Since circulating progenitor cells in MMM constitute only a small fraction of the circulating mononuclear cells, it was not feasible to assess the effects of R115777 on these pathways using a biochemical approach. Examination of other inhibitors, however, indicated that MMM progenitors (and normal hematopoietic progenitors) were much more sensitive to the antiproliferative effects of the PI-3 kinase inhibitor LY294004 than the Mek1 inhibitor PD98059.…”

Neuroprotective effects and intracellular signaling pathways of erythropoietin in a rat model of multiple sclerosis

“…In previous studies on hematopoietic progenitors as well as in a study on neuronal cell cultures, an Epo-induced activation of the MEK/MAPK pathway has been demonstrated. 43,[51][52][53] To investigate the functional significance of this part of the Epoinduced signal transduction in vivo, we treated rats with a combination of Epo and PD 98059, a selective and cellpermeable inhibitor of the single upstream kinase MEK. 54 Under this combined treatment, RGC counts were only moderately decreased when compared to Epo monotherapy, indicating that phosphorylation of MAPKs has a smaller impact on Epo-induced RGC survival than activation of PI3-K/ Akt.…”

Vascular Endothelial Growth Factor Receptor-2 Induces Survival of Hematopoietic Progenitor Cells

“…7D) in bone marrow following VEGFR-2 dimerization. Either of these kinases could account, at least in part, for the survival that we observed in response to VEGFR-2 dimerization, since induction of these signaling pathways by other hematopoietic cytokines, such as SCF and erythropoietin, has been implicated in hematopoietic cell survival (35)(36)(37).…”