Erythropoietin Can Induce the Expression of Bcl-xLthrough Stat5 in Erythropoietin-dependent Progenitor Cell Lines

Abstract

Erythropoietin (Epo) initiates its cellular response by binding to the Epo receptor, which triggers the activation of signal transducer and activator of transcription (Stat) 5 protein. Cell culture studies of erythroid progenitors have suggested that Epo functions as a survival factor by repressing apoptosis at least in part through Bcl-xL, an anti-apoptotic protein of the Bcl-2 family. In this report, we examine whether Stat5 can induce transactivation of the bcl-x gene in response to Epo. Two Epo-responsive progenitor cell lines, HCD-57 and Bcl-2-transfected Ba/F3-Epo receptor (Ba/F3-EpoR-Bcl-2), were used in this study. After Epo stimulation, we observed a correlation between expression ofbcl-x L and activation of Stat5 as assessed by the expression of oncostatin M, a direct target of Stat5, and the phosphorylation and nuclear translocation of Stat5. Moreover, a Stat binding element in the bcl-x promoter was found to be active in response to Epo, a finding that was further confirmed because mutagenesis of this sequence motif abrogated its promoter activity and overexpression of a dominant negative Stat5 protein blocked transactivation. When DNA-protein binding analyses were performed, we found that Stat5, not Stat1 or Stat3, was the protein bound to the bcl-x promoter in response to Epo. These data suggest that Epo-dependent activation of Stat5 is a transcriptional pathway that can be used by Epo-responsive progenitor cells to induce the expression of bcl-xLand consequently to inhibit apoptosis. Erythropoietin (Epo) initiates its cellular response by binding to the Epo receptor, which triggers the activation of signal transducer and activator of transcription (Stat) 5 protein. Cell culture studies of erythroid progenitors have suggested that Epo functions as a survival factor by repressing apoptosis at least in part through Bcl-xL, an anti-apoptotic protein of the Bcl-2 family. In this report, we examine whether Stat5 can induce transactivation of the bcl-x gene in response to Epo. Two Epo-responsive progenitor cell lines, HCD-57 and Bcl-2-transfected Ba/F3-Epo receptor (Ba/F3-EpoR-Bcl-2), were used in this study. After Epo stimulation, we observed a correlation between expression ofbcl-x L and activation of Stat5 as assessed by the expression of oncostatin M, a direct target of Stat5, and the phosphorylation and nuclear translocation of Stat5. Moreover, a Stat binding element in the bcl-x promoter was found to be active in response to Epo, a finding that was further confirmed because mutagenesis of this sequence motif abrogated its promoter activity and overexpression of a dominant negative Stat5 protein blocked transactivation. When DNA-protein binding analyses were performed, we found that Stat5, not Stat1 or Stat3, was the protein bound to the bcl-x promoter in response to Epo. These data suggest that Epo-dependent activation of Stat5 is a transcriptional pathway that can be used by Epo-responsive progenitor cells to induce the expression of bcl-xLand consequently to inhibit apoptosis. The intracellular molecular pathways that regulate the survival of primitive erythroid progenitors are still poorly understood. Erythropoietin (Epo) 1The abbreviations used are: Epo, erythropoietin; Stat, signal transducer and activator of transcription; EpoR, erythropoietin receptor; ATA, aurintricarboxylic acid; GAS, interferon-γ activation site; PCR, polymerase chain reaction; kb, kilobase(s) 1The abbreviations used are: Epo, erythropoietin; Stat, signal transducer and activator of transcription; EpoR, erythropoietin receptor; ATA, aurintricarboxylic acid; GAS, interferon-γ activation site; PCR, polymerase chain reaction; kb, kilobase(s) is necessary for erythroid progenitor proliferation and to prevent the apoptotic cell death of immature erythroblasts (1Koury M.J. Bondurant M.C. J. Cell. Physiol. 1988; 137: 65-74Crossref PubMed Scopus (144) Google Scholar, 2Koury M.J. Bondurant M.C. Science. 1990; 248: 378-381Crossref PubMed Scopus (710) Google Scholar). Epo binds to a specific cell surface receptor that is expressed on erythroid progenitors (3Wognum A.W. Lansdorp P.M. Humphries R.K. Krystal G. Blood. 1990; 76: 697-705Crossref PubMed Google Scholar, 4Sawyer S.T. Krantz S.B. Goldwasser E. J. Biol. Chem. 1987; 262: 5554-5562Abstract Full Text PDF PubMed Google Scholar). The Epo receptor associates with Jak2, a member of a subfamily of protein tyrosine kinases, which plays an important role in cytokine-dependent gene regulation. Activated Jak2, in turn, converts a latent cytoplasmic transcription factor, Stat5, into its active form by tyrosine phosphorylation. The activated Stat5 translocates into the nucleus, where it binds to specific DNA response elements in the promoter region of target genes and activates transcription (5Darnell J.E. Kerr I.M. Stark G.M. Science. 1994; 264: 1415-1421Crossref PubMed Scopus (4912) Google Scholar, 6Ihle J.N. Nature. 1995; 377: 591-594Crossref PubMed Scopus (1136) Google Scholar, 7Ihle J.N. Cell. 1996; 84: 331-334Abstract Full Text Full Text PDF PubMed Scopus (1258) Google Scholar). It has been shown that the ability of interleukin-2 to signal activation of Stat5 in 32D lymphocytes is directly related to its ability to promote protection from apoptosis and long-term cell growth (8Zamorano J. Wang H.Y. Wang R. Shi Y. Longmore G.D. Keegan A.D. J. Immunol. 1998; 160: 3502-3512PubMed Google Scholar). Furthermore, growth factor-independent activation of the Jak2-Stat5 pathway in Nb2 lymphocytes protects these cells against apoptosis induced in the absence of growth factor (9Rui H. Xu J. Mehta S. Fang H. Williams J. Dong F. Grimley P.M. J. Biol. Chem. 1998; 273: 28-32Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar). We have recently shown that a member of the Bcl-2 family of apoptosis-regulatory proteins, Bcl-xL (10Boise L.H. Gonzalez-Garcia M. Postema C.E. Ding L. Lindsten T. Turka L.A. Mao X. Nuñez G. Thompson C.B. Cell. 1993; 74: 597-608Abstract Full Text PDF PubMed Scopus (2908) Google Scholar), but not Bcl-2, is highly expressed in the erythroleukemic cell lines HEL and K562 (11Benito A. Silva M. Grillot D. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 87: 3837-3843Crossref PubMed Google Scholar) and that the constitutive expression of Bcl-xL protects cells from apoptosis induced by differentiation inducer agents. Furthermore, Epo maintains survival and represses apoptosis of HCD-57 erythroid progenitor cells through the expression of Bcl-xL(12Silva M. Grillot D. Benito A. Richard C. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 88: 1576-1582Crossref PubMed Google Scholar). This anti-apoptotic protein is down-regulated after Epo withdrawal in HCD-57 cells, and the cells undergo apoptotic cell death. Interestingly, when HCD-57 cells transduced with a retroviral vector encoding Bcl-xL are cultured in the absence of Epo, the endogenous level of Bcl-xL is down-regulated, but the cells remain viable, further indicating that the expression of Bcl-xL is mediated by Epo and that this is an important mechanism to repress apoptosis in erythroid progenitors. The relevance of this association has been suggested in patients with polycythemia vera, in whom autonomous Epo-independent erythroid cells arise from monoclonal progenitors. These abnormal progenitor cells exhibit a deregulated expression of Bcl-xL that may contribute to bypass the need for the growth factor and may consequently explain their Epo-independent survival (13Silva M. Richard C. Benito A. Sanz C. Olalla Y. Fernandez-Luna J.L. N. Engl. J. Med. 1998; 338: 564-571Crossref PubMed Scopus (183) Google Scholar). The genomic organization and promoter region of the bcl-xgene have recently been determined (14Grillot D. Gonzalez-Garcia M. Ekhterae D. Duan L. Inohara N. Ohta S. Seldin M.F. Nuñez G. J. Immunol. 1997; 158: 4750-4757PubMed Google Scholar), which facilitates the analysis of the transcriptional factors involved in the expression ofbcl-x. In the present study, we have examined whether Epo induces the expression of bcl-xL through activation of Stat5 to better understand the molecular basis for the survival of erythroid progenitor cells. We have identified an Epo-responsive motif for the binding of a Stat protein (Stat binding element) in the untranslated 5′ region of the mouse bcl-xgene. Furthermore, we have shown that Stat5 binds to the Epo-responsive motif and that this motif is active in response to Epo because transient transfection experiments showed activity of a reporter gene in the presence of Epo that can be abrogated by mutagenesis of the Stat binding element or overexpression of a dominant negative Stat5 protein. These findings suggest that at least one of the molecular pathways that maintains the survival of erythroid progenitors may be triggered by the interaction of Epo with its specific receptor, which induces the expression of Bcl-xL through the binding of Stat5 to thebcl-x promoter. The murine Epo-dependent HCD-57 cell line was maintained in Iscove's modified Dulbecco's medium (Life Technologies, Inc.) as described previously (12Silva M. Grillot D. Benito A. Richard C. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 88: 1576-1582Crossref PubMed Google Scholar). Ba/F3 cells stably expressing the Epo receptor (15Liboi E. Carroll M. D'Andrea A.D. Mathey-Prevot B. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 11351-11355Crossref PubMed Scopus (82) Google Scholar) were transfected by electroporation (960 microfarads; 250 V) with 20 μg of the pSFFV-Neo plasmid containing bcl-2. Individual cell clones were selected for growth in the presence of G418 (1 mg/ml) and hygromycin B (1 μg/ml) by limiting dilution. Three individual clones expressing high levels of Bcl-2 were randomly selected and used by virtue of resistance to apoptosis. Ba/F3-EpoR-Bcl-2 clones were grown in RPMI 1640 medium (Seromed Biochrom KG, Berlin, Germany) supplemented with 10% fetal calf serum (Flow Laboratories, Irvine, CA), 2 × 10−5m 2-mercaptoethanol, 2 mm glutamine, 100 units/ml penicillin, 100 μg/ml streptomycin, and 0.1 unit/ml recombinant murine Epo (Roche Molecular Biochemicals). In some experiments, Ba/F3-EpoR-Bcl-2 cells were starved of Epo for 20 h and then treated with 100 μm aurintricarboxylic acid (ATA) (Sigma) for 12 h. Total RNA was prepared using Trizol reagent (Life Technologies, Inc.). To assess mRNA expression, a semiquantitative reverse transcription-PCR method was used as described previously (12Silva M. Grillot D. Benito A. Richard C. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 88: 1576-1582Crossref PubMed Google Scholar). The generated cDNA was by using for murine (12Silva M. Grillot D. Benito A. Richard C. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 88: 1576-1582Crossref PubMed Google Scholar), and The was as for for 20 and for After the for for and for oncostatin were a and with were cultured in the absence of Epo for h and then for with Epo. of nuclear cells were for on in 20 mm mm 5 mm 10% mm μg/ml μm and were in mm mm mm 2 mm 5 mm 0.1 mm 5 mm and mm and After the were the were used as nuclear The expression of Stat5 and in the nuclear was determined by as described previously (11Benito A. Silva M. Grillot D. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 87: 3837-3843Crossref PubMed Google Scholar). were with mouse Laboratories, or and then with or to was by a were cultured in the absence of Epo for h and then for with Epo and in mm 0.1 mm mm and and were of and the were with to which and from the were and to as described previously (11Benito A. Silva M. Grillot D. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 87: 3837-3843Crossref PubMed Google Scholar). were with mouse or mouse and bound were by Ba/F3-EpoR-Bcl-2 cells were cultured in the absence of serum and Epo for h and then with 100 units/ml Epo for were in mm 0.1 mm 0.1 mm mm mm mm and mm and cell were and the nuclear were in 20 mm mm mm mm mm and mm and described R. A. R. T. R. Cell 1997; Google Scholar), nuclear μg of were with a DNA from the promoter region of the mouse bcl-x gene (14Grillot D. Gonzalez-Garcia M. Ekhterae D. Duan L. Inohara N. Ohta S. Seldin M.F. Nuñez G. J. Immunol. 1997; 158: 4750-4757PubMed Google Scholar), thebcl-x a Stat binding or which a binding for Stat5 were on a in mm and 2 mm were and by were using specific for Stat5, or nuclear containing of protein were with a of bcl-x or DNA Ba/F3-EpoR-Bcl-2 cells were cultured in the absence of Epo for 20 h and then transfected by electroporation with μg of a reporter vector containing a of the or (14Grillot D. Gonzalez-Garcia M. Ekhterae D. Duan L. Inohara N. Ohta S. Seldin M.F. Nuñez G. J. Immunol. 1997; 158: 4750-4757PubMed Google Scholar) and μg of the vector used to the expression of the reporter When cells were with and μg of a vector containing a form of Stat5 that the transactivation The cDNA by B. for Germany) S. R. F. C. E. M. E. B. J. Biol. Chem. 1997; PubMed Scopus Google Scholar) was into the of the pSFFV-Neo vector (11Benito A. Silva M. Grillot D. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 87: 3837-3843Crossref PubMed Google Scholar). cells were with or 2 units/ml Epo for and the activity was by using the reporter mutagenesis of the vector was by using the mutagenesis with and The DNA was to the We have previously shown that Epo can as a survival factor by repressing apoptosis through the expression of Bcl-xL (12Silva M. Grillot D. Benito A. Richard C. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 88: 1576-1582Crossref PubMed Google Scholar). Epo induces the expression of a of genes through activation of the Jak2-Stat5 pathway J.E. Krystal G. 1996; Google Scholar), we whether the expression of with the expression of oncostatin M, a member of the subfamily induced by Epo and a direct target of Stat5 A. M. M. T. A. J. 1996; PubMed Scopus Google Scholar). When Epo-responsive cell lines, HCD-57 and were cultured in the absence of Epo, the levels of oncostatin and were down-regulated by h after Epo withdrawal as assessed by semiquantitative reverse transcription-PCR analysis of Epo to growth cells the expression of and oncostatin M. shown in the mRNA levels h after the of Epo and to the expression of bcl-x L was to that of cells. The levels of oncostatin mRNA to and a level of expression at to to To whether the of bcl-xL protein cells were with 20 μg/ml for a that blocked of protein as determined by analysis not shown in oncostatin mRNA levels were further in cells treated with Epo to cells treated with Epo In a of bcl-x L mRNA was observed in cells treated with Epo. Epo induces the expression of bcl-x L and oncostatin in HCD-57 and Ba/F3-EpoR-Bcl-2 cells, and L a to the of oncostatin M, genes are induced in a protein In the mRNA levels of member that apoptosis Cell. 1993; 74: Full Text PDF PubMed Scopus Google Scholar), were not by Epo or by with Epo. The activation of a Jak2-Stat5 pathway by ATA, a with anti-apoptotic has been recently described in Nb2 lymphocytes (9Rui H. Xu J. Mehta S. Fang H. Williams J. Dong F. Grimley P.M. J. Biol. Chem. 1998; 273: 28-32Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar). When Ba/F3-EpoR-Bcl-2 cells were starved of Epo for 20 h and then treated with in the absence of Epo for a 12 the expression of bcl-x L was the as that of cells with Epo indicating that the activation of the Jak2-Stat5 pathway with the expression ofbcl-x L. To further that of Ba/F3-EpoR-Bcl-2 cells with Epo triggers the activation of Stat5, we the phosphorylation level and nuclear translocation of this transcription shown in in the absence of Epo, Stat5 after of Epo stimulation, Stat5 was tyrosine and this level of phosphorylation was maintained or in some experiments by after Epo Furthermore, the expression of Stat5 was the at indicating that the of Stat5 with Epo tyrosine phosphorylation of Stat5 is by and nuclear we examined the presence of Stat5 in the of Ba/F3-EpoR-Bcl-2 cells. shown in Stat5 was to the in response to Epo, as assessed by with an the and with against the nuclear factor showed that protein was in the the in nuclear expression of Stat5 were to the with Epo. the shown in were with a Ba/F3-EpoR-Bcl-2 were with clones not of bcl-x L and oncostatin in Ba/F3-EpoR-Bcl-2 cells treated with reverse transcription-PCR analysis of oncostatin and mRNA after 12 h of Epo by 12 h of Epo or In cells were for h. After were a and with phosphorylation and nuclear of Stat5 in Ba/F3-EpoR-Bcl-2 cells. cells were cultured in the absence of Epo for h and then for with Epo. Cell were by with an which and and by with an monoclonal The were and with a monoclonal cells were cultured in the absence of Epo for h and then for with Epo or The expression of Stat5 and in the nuclear was determined by using specific monoclonal The promoter region of the mouse bcl-x gene has recently been (14Grillot D. Gonzalez-Garcia M. Ekhterae D. Duan L. Inohara N. Ohta S. Seldin M.F. Nuñez G. J. Immunol. 1997; 158: 4750-4757PubMed Google Scholar). This region a sequence of the in 2 with a Stat binding element as the interferon-γ activation J.N. Cell. 1996; 84: 331-334Abstract Full Text Full Text PDF PubMed Scopus (1258) Google Scholar). shown by transfection with reporter the constitutive activity induced by a genomic of 2 was a sequence L.H. Gonzalez-Garcia M. Postema C.E. Ding L. Lindsten T. Turka L.A. Mao X. Nuñez G. Thompson C.B. Cell. 1993; 74: 597-608Abstract Full Text PDF PubMed Scopus (2908) Google To the promoter activity of this which the Stat binding a vector was transfected into Ba/F3-EpoR-Bcl-2 cells. The constitutive expression of Bcl-2 these cells to in the absence of Epo a which was a the with Epo that the activation of factors involved in signal The analysis was in Ba/F3-EpoR-Bcl-2 which not a with one of these The levels of activity in the cells were observed in cells a containing a 5′ of the was for activity in response to Epo. shown in the activity in Ba/F3-EpoR-Bcl-2 cells transfected with a vector was in the and cell When we examined the and we found that the activity was to that with the not To further the of the Stat binding element in the a mutagenesis analysis was We this sequence motif and transfected Ba/F3-EpoR-Bcl-2 cells with a shown in the levels of activity were observed with Ba/F3-EpoR-Bcl-2 cells transfected with the Furthermore, were between the cells and the cells, indicating the of the Stat binding element in transactivation of the bcl-x promoter. Interestingly, this activation is on endogenous Stat5, as by the ability of which the transactivation and a dominant negative R. R. S. C. X. L. A. B. F. Cell. Biol. 1996; PubMed Scopus Google Scholar), to this Stat5 has been shown to be the factor that the of Epo on the transcription of genes in erythroid cells J.E. Krystal G. 1996; Google Scholar). To whether Stat5 the of Epo L we DNA-protein binding analyses to whether Stat5 can to thebcl-x promoter. with one of the Ba/F3-EpoR-Bcl-2 clones is shown in Ba/F3-EpoR-Bcl-2 cells starved of serum and Epo for h and then with Epo for were in an were prepared and used in a binding with We showed that of cells with Epo in the of a DNA-protein when using a from the a target of Stat5, further indicating that Stat5 was activated in response to Epo. were with a sequence of thebcl-x promoter of the was observed in cells. In a DNA-protein binding was induced by Epo Furthermore, a of an the of this In was observed when nuclear were with a of a of the and as the bcl-x To further the for an we the ability of the DNA a sequence to form a binding shown in DNA-protein was observed in response to Epo. These be for by in nuclear protein because an bound the of in nuclear not To the Stat family member bound to the element of the bcl-x promoter in Ba/F3-EpoR-Bcl-2 cells, experiments were using specific for Stat5, and shown in of the DNA-protein induced by Epo. Epo initiates its cellular response by binding to the Epo receptor expressed on the surface of immature erythroblasts (3Wognum A.W. Lansdorp P.M. Humphries R.K. Krystal G. Blood. 1990; 76: 697-705Crossref PubMed Google Scholar, 4Sawyer S.T. Krantz S.B. Goldwasser E. J. Biol. Chem. 1987; 262: 5554-5562Abstract Full Text PDF PubMed Google Scholar). After is to a cytoplasmic protein tyrosine Jak2, which in activates a transcription factor, Stat5, a signal that to the of erythroid progenitors into cells S.T. J. Biol. Chem. 1995; PubMed Scopus Google Scholar). In the absence of Epo, erythroid progenitors and their genomic DNA is into a of apoptotic cell death (1Koury M.J. Bondurant M.C. J. Cell. Physiol. 1988; 137: 65-74Crossref PubMed Scopus (144) Google Scholar, 2Koury M.J. Bondurant M.C. Science. 1990; 248: 378-381Crossref PubMed Scopus (710) Google Scholar). of the family of apoptosis-regulatory genes that as of apoptosis in cells have been identified (10Boise L.H. Gonzalez-Garcia M. Postema C.E. Ding L. Lindsten T. Turka L.A. Mao X. Nuñez G. Thompson C.B. Cell. 1993; 74: 597-608Abstract Full Text PDF PubMed Scopus (2908) Google Scholar, G. M.F. Cell Biol. 1994; Full Text PDF PubMed Scopus Google Scholar). We have recently that when the Epo-dependent erythroid progenitor cell line HCD-57 is cultured in the absence of Epo, the expression of Bcl-xL is down-regulated, and this is by the activation of an apoptotic (12Silva M. Grillot D. Benito A. Richard C. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 88: 1576-1582Crossref PubMed Google Scholar). The constitutive expression of Bcl-xL erythroid progenitors from apoptosis induced by Epo that Epo can as a survival factor by repressing apoptosis through Bcl-xL in erythroid progenitor cells. In an to the pathway involved in the transactivation of thebcl-x promoter in erythroid cells, we Epo-dependent cell lines, HCD-57 and HCD-57 is a murine erythroid progenitor cell line that erythroid differentiation in the presence of (12Silva M. Grillot D. Benito A. Richard C. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 88: 1576-1582Crossref PubMed Google Scholar). is a murine progenitor cell line stably transfected with the Epo receptor that and erythroid differentiation in Epo (15Liboi E. Carroll M. D'Andrea A.D. Mathey-Prevot B. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 11351-11355Crossref PubMed Scopus (82) Google Scholar, T. Y. A. A. M. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: PubMed Scopus Google Scholar). We have transfected this cell line with to apoptosis when cultured in the absence of Epo. The of bcl-x L mRNA after Epo an that was maintained or in the presence of protein was shown M, an response gene induced by Epo through the Jak2-Stat5 It has been previously N. J. 1997; Google Scholar) that bcl-x L as a response gene in that it protein it is important to that thebcl-x promoter for the binding of transcription and (14Grillot D. Gonzalez-Garcia M. Ekhterae D. Duan L. Inohara N. Ohta S. Seldin M.F. Nuñez G. J. Immunol. 1997; 158: 4750-4757PubMed Google Scholar), which L may be induced by transcriptional pathways by their for a Stat binding element has been found in the promoter region of the bcl-x gene Y. H. T. J. 1997; PubMed Scopus Google Scholar), we the promoter activity of this sequence motif in response to Epo in Ba/F3-EpoR-Bcl-2 cells. We found that the Stat binding element to Epo by the expression of a reporter gene and that this sequence bound Stat5 as assessed by DNA-protein binding The that the pathway to be necessary to prevent apoptosis in erythroid progenitors in response to Epo A. S.T. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar) is with this It has been shown that the Epo-dependent of apoptosis is blocked by the expression of dominant negative of Jak2, an role for this tyrosine in the apoptotic pathway H. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). We have activated the pathway by Ba/F3-EpoR-Bcl-2 cells with This growth tyrosine phosphorylation of and activation of Stat5, in the of genes (9Rui H. Xu J. Mehta S. Fang H. Williams J. Dong F. Grimley P.M. J. Biol. Chem. 1998; 273: 28-32Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar). Interestingly, not to regulate of the Stat it with this we found that expression of oncostatin M, a direct target of Stat5 A. M. M. T. A. J. 1996; PubMed Scopus Google Scholar), and bcl-x L. These data suggest a in which Epo triggers the activation of the Jak2-Stat5 and Stat5 induces the expression of bcl-x the apoptotic of Epo-responsive progenitor cell it has been shown that the of that have the Stat5 genes an role for these in with growth and the to a of Epo, are S. C. E. D. Wang D. M. S. G. J.N. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). the expression of Bcl-xL was not in cellular It is that in these the expression ofbcl-x or and of the promote erythroid progenitor with this it has been shown that HCD-57 erythroid cells Bcl-xL and Bcl-2, which are down-regulated after Epo withdrawal (12Silva M. Grillot D. Benito A. Richard C. Nuñez G. Fernandez-Luna J.L. Blood. 1996; 88: 1576-1582Crossref PubMed Google Scholar), and that Bcl-xL to be the anti-apoptotic protein in this cell Bcl-2 may contribute to cell transcription factors Stat5 may induce the expression of survival genes in response to Epo. it is that transcription factors may induce the expression of In it has been shown that Stat1 the expression of bcl-x in after with factor Y. H. T. J. 1997; PubMed Scopus Google we have shown that Stat1 was to the element from the bcl-x promoter. with these it has been described that in erythroid Stat5, not Stat1 or Stat3, is activated after with Epo A. H. Y. M. T. Y. Blood. 1998; PubMed Google Scholar), which it that Stat in erythroid cells. be because a motif for transcription factors of the family has been identified in the promoter region of D. Gonzalez-Garcia M. Ekhterae D. Duan L. Inohara N. Ohta S. Seldin M.F. Nuñez G. J. Immunol. 1997; 158: 4750-4757PubMed Google Scholar). has been shown to be involved in the of erythroid progenitor survival and differentiation by apoptosis M.J. Proc. Natl. Acad. Sci. U. S. A. 1995; PubMed Scopus Google Scholar). In data that activation of Stat5 can induce the expression ofbcl-x L in Epo-responsive progenitor cell may be transcriptional pathways involved in this we for the a transactivation mechanism of thebcl-x promoter induced by Epo, which may at least in part for the anti-apoptotic activity of Epo in erythroid cells.