A novel mechanism of cooperation between c-Kit and erythropoietin receptor - Stem cell factor induces the expression of Stat5 and erythropoietin receptor, resulting in efficient proliferation and survival by erythropoietin
Optimal production of red cells in vivo requires collaboration between c-Kit, erythropoietin receptor (Epo-R), and GATA-1. However, the mechanism(s) of collaboration remain unclear. Utilizing an embryonic stem cell-derived erythroid progenitor cell line from mice deficient in GATA-1, we have examined the role of c-Kit and Epo-R in erythroid cell proliferation, survival, and differentiation. In the absence of GATA-1, we demonstrate an essential role for c-Kit in survival and proliferation of erythroid progenitors via the regulation of Bcl-2 expression. In addition, we demonstrate that Epo-R and Stat5 are regulated by a second, novel mechanism. We demonstrate that c-Kit stimulation by stem cell factor is essential for the maintenance of Epo-R and Stat5 protein expression, which results in significantly enhanced Bcl-x(L) induction and survival of erythroid progenitors in response to Epo stimulation. Restoration of GATA-1 function results in terminal erythroid maturation and up-regulation of Epo-R and Bcl-x(L) expression, leading also to significantly enhanced survival of terminally differentiating erythroid progenitors in the presence of only Epo. These results demonstrate that c-Kit and Epo-R have unique role(s) during distinct phases of erythroid maturation, and both stem cell factor and Epo contribute to the regulation of the Epo-R-Stat5-Bcl-x(L) pathway to ensure optimal survival, proliferation, and differentiation of erythroid progenitors.
"This result would suggest that the few CFU-E that survive functional SCF deficiency in vivo can still respond normally to exogenous EPO, though their numbers are reduced by limitations imposed on the cellular pathway at more primitive levels. The interaction of SCF and EPO, which is of obvious significance in these earlier populations, has been elegantly examined at the molecular level and shown to result from a subtle interplay of survival, proliferation, and differentiation signals . EPO can also be used to increase hemoglobin, hematocrit values and reduce the requirement of RBC transfusions in ICU patients . "
[Show abstract][Hide abstract] ABSTRACT: Erythropoiesis is a vital process governed through various factors. There is extreme unavailability of suitable donor due to rare phenotypic blood groups and other related complications like hemoglobinopathies, polytransfusion patients, and polyimmunization. Looking at the worldwide scarcity of blood, especially in low income countries and the battlefield, mimicking erythropoiesis using ex vivo methods can provide an efficient answer to various problems associated with present donor derived blood supply system. Fortunately, there are many ex vivo erythropoiesis methodologies being developed by various research groups using stem cells as the major source material for large scale blood production. Most of these ex vivo protocols use a cocktail of similar growth factors under overlapping growth conditions. Erythropoietin (EPO) is a key regulator in most ex vivo protocols along with other growth factors such as SCF, IL-3, IGF-1, and Flt-3. Now transfusable units of blood can be produced by using these protocols with their set of own limitations. The present paper focuses on the molecular mechanism and significance of various growth factors in these protocols that shall remain helpful for large scale production.
"Our previous study revealed that IL-3 induced marked phosphorylation of GATA-1 at serine26
. Given that GATA-1 plays a critical role in erythropoiesis and that EPO is essential for erythroid production by preventing committed erythroid progenitors from undergoing apoptosis and allowing them to proliferate and differentiate , , , , it was of interest to investigate whether phosphorylation of GATA-1 at serine26 could be induced by EPO signaling in erythroid cells. To address this issue, freshly prepared BM cells were stimulated by various cytokines and the phosphorylation of ERK and GATA-1 were examined. "
[Show abstract][Hide abstract] ABSTRACT: We previously reported that IL-3 signaling induces phosphorylation of GATA-1 at the serine(26) position, which contributes to IL-3-mediated anti-apoptotic response. Here, we demonstrate that phosphorylation of GATA-1 at serine(26) is also transiently induced in cells of the erythroid lineage (primary erythroblasts and erythrocyte-committed progenitors [EPs]) by erythropoietin (EPO), the principal cytokine regulating erythropoiesis. To examine whether phosphorylation of GATA-1 at serine(26) would have any impact on erythropoiesis, mutant mice carrying either a glutamic acid (GATA-1(S26E)) or alanine (GATA-1(S26A)) substitution at serine(26) were generated. Neither GATA-1(S26E) nor GATA-1(S26A) mice showed any significant difference from control mice in peripheral blood cell composition under either steady state or stress conditions. The erythroblast differentiation in both mutant mice also appeared to be normal. However, a moderate reduction in the CFU-E progenitor population was consistently observed in the bone marrow of GATA-1(S26E), but not GATA-1(S26A) mice, suggesting that such defect was compensated for within the bone marrow. Surprisingly, reduced CFU-E progenitor population in GATA-1(S26E) mice was mainly due to EPO-induced growth suppression of GATA-1(S26E) EPs, albeit in the absence of EPO these cells manifested a survival advantage. Further analyses revealed that EPO-induced growth suppression of GATA-1(S26E) EPs was largely due to the proliferation block resulted from GATA-1(S26E)-mediated transcriptional activation of the gene encoding the cell cycle inhibitor p21(Waf1/Cip1). Taken together, these results suggest that EPO-induced transient phosphorylation of GATA-1 at serine(26) is dispensable for erythropoiesis. However, failure to dephosphorylate this residue following its transient phosphorylation significantly attenuates the colony-forming activity of EPs.
PLoS ONE 05/2013; 8(5):e64269. DOI:10.1371/journal.pone.0064269 · 3.23 Impact Factor
"One mechanism involves EpoR as a direct downstream effector of Kit signaling through transphosphorylation induced by SCF. More indirectly, Kit signaling contributes to the sustained expression of Stat5 protein which can then be activated by Epo . Target gene products of the EpoR-activated Stat5 axis can also contribute to enhance Kit signaling . "
[Show abstract][Hide abstract] ABSTRACT: Overexpression of the transcription factor Spi-1/PU.1 by transgenesis in mice induces a maturation arrest at the proerythroblastic stage of differentiation. We have previously isolated a panel of spi-1 transgenic erythroleukemic cell lines that proliferated in the presence of either erythropoietin (Epo) or stem cell factor (SCF). Using these cell lines, we observed that EpoR stimulation by Epo down-regulated expression of the SCF receptor Kit and induced expression of the Src kinase Lyn. Furthermore, enforced expression of Lyn in the cell lines increased cell proliferation in response to Epo, but reduced cell growth in response to SCF in accordance with Lyn ability to down-regulate Kit expression. Together, the data suggest that Epo-R/Lyn signaling pathway is essential for extinction of SCF signaling leading the proerythroblast to strict Epo dependency. These results highlight a new role for Lyn as an effector of EpoR in controlling Kit expression. They suggest that Lyn may play a central role in during erythroid differentiation at the switch between proliferation and maturation.
PLoS ONE 02/2009; 4(5):e5721. DOI:10.1371/journal.pone.0005721 · 3.23 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.