Activation of STAT5 during EPO-directed suppression of apoptosis

Allelic burden of Janus kinase 2 in a 6-month course of therapy for myeloproliferative neoplasms

BACKGROUND

Janus kinase 2 (JAK2) V617F gene mutation is an important marker for the diagnosis of Philadelphia negative Myeloproliferative neoplasms (MPN) which is subdivided into Polycythemia Vera (PV), Primary Myelofibrosis (PMF), and Essential Thrombocythemia (ET). The aim here is to investigate the JAK2 allele burden of the patients diagnosed with the subgroups of MPN and to demonstrate the alterations of hematological parameters and spleen size between diagnosis and 6 months of treatment.

METHODS

A total of 107 patients with the diagnosis of MPN and negative Philadelphia chromosome, 51 males and 56 females with a mean age of 59,74 ± 16,41 years, were included in the study. Diagnosis of MPN was based on the World Health Organization (WHO) criteria. Subgroups of MPN distributed as 49,5% ET, 46,7% PV, and 3,8% PMF. Findings such as the age of the patients, JAK-2 allele burden, and laboratory findings of splenomegaly were examined at the time of diagnosis, 3rd month, and 6th month. JAK2 allele burden and spleen size were re-evaluated in 6th month.

RESULTS

Our study confirmed the findings of high Hb, HCT, and RBC but low platelet values in PV patients with high JAK2 allele burden with respect to other groups, a positive correlation between JAK2 allele burden and LDH.

CONCLUSIONS

A novel finding of our study is, that there is not any reducing effect of the phlebotomy on JAK2 allele burden in PV patients whether they receive phlebotomy or not. Evaluation of the spleen size alteration during 6 months within the subgroups demonstrated a decrease in PV and ET groups whereas no statistically significant difference was found in the PMF group.

STAT5 as a Key Protein of Erythropoietin Signalization

Erythropoietin (EPO) acts on multiple tissues through its receptor EPOR, a member of a cytokine class I receptor superfamily with pleiotropic effects. The interaction of EPO and EPOR triggers the activation of several signaling pathways that induce erythropoiesis, including JAK2/STAT5, PI3K/AKT, and MAPK. The canonical EPOR/JAK2/STAT5 pathway is a known regulator of differentiation, proliferation, and cell survival of erythroid progenitors. In addition, its role in the protection of other cells, including cancer cells, is under intense investigation. The involvement of EPOR/JAK2/STAT5 in other processes such as mRNA splicing, cytoskeleton reorganization, and cell metabolism has been recently described. The transcriptomics, proteomics, and epigenetic studies reviewed in this article provide a detailed understanding of EPO signalization. Advances in this area of research may be useful for improving the efficacy of EPO therapy in hematologic disorders, as well as in cancer treatment.

Erythropoietin in Lupus: Unanticipated Immune Modulating Effects of a Kidney Hormone

Systemic lupus erythematosus (SLE) is a multiorgan autoimmune disease with variable clinical presentation, typically characterized by a relapsing-remitting course. SLE has a multifactorial pathogenesis including genetic, environmental, and hormonal factors that lead to loss of tolerance against self-antigens and autoantibody production. Mortality in SLE patients remains significantly higher than in the general population, in part because of the limited efficacy of available treatments and the associated toxicities. Therefore, novel targeted therapies are urgently needed to improve the outcomes of affected individuals. Erythropoietin (EPO), a kidney-produced hormone that promotes red blood cell production in response to hypoxia, has lately been shown to also possess non-erythropoietic properties, including immunomodulatory effects. In various models of autoimmune diseases, EPO limits cell apoptosis and favors cell clearance, while reducing proinflammatory cytokines and promoting the induction of regulatory T cells. Notably, EPO has been shown to reduce autoimmune response and decrease disease severity in mouse models of SLE. Herein, we review EPO's non-erythropoietic effects, with a special focus on immune modulating effects in SLE and its potential clinical utility.

Role of Erythropoietin in Cerebral Glioma: An Innovative Target in Neuro-Oncology

BACKGROUND

Erythropoietin (EPO) is a cytokine primarily involved in the regulation of erythropoiesis. In response to hypoxia-ischemia, hypoxia-inducible factor 1 induces EPO production, which, in turn, inhibits apoptosis of erythroid progenitor cells. By the same mechanism and acting through other signaling pathways, EPO exerts neuroprotective effects. Increased resistance to hypoxia and decreased apoptosis are thought to be important mechanisms for tumor progression, including malignant glioma. Because recent studies have demonstrated that EPO and its receptor (EPOR) are expressed in several tumors and can promote tumor growth, in the present study, we investigated EPO and EPOR expression in human glioma and the effect of EPO administration in a rat model of glioma implantation.

METHODS

Using Western blotting and immunohistochemical analysis, we examined the expression of EPO, EPOR, platelet endothelial cell adhesion molecule, and Ki-67 in human glioma specimens and experimentally induced glioma in rats. In the experimental setting, a daily dose of recombinant human EPO (rHuEPO) or saline solution were administered for 21 days in Fischer rats subjected to 9L cell line implantation.

RESULTS

In both human and animal specimens, we found an increase in EPOR expression as long as the lesion presented with an increasing malignant pattern. A significant direct correlation was found between the expression of EPOR and Ki-67 and EPOR and platelet endothelial cell adhesion molecule in low- and high-grade gliomas. The rats treated with rHuEPO presented with significantly larger tumor spread compared with the saline-treated rats.

CONCLUSIONS

The results of our study have shown that the EPO/EPOR complex might play a significant role in the aggressive behavior of high-grade gliomas. The larger tumor spread in rHuEPO-treated rats suggests a feasible role for EPO in the aggressiveness and progression of malignant glioma.

Cibinetide dampens innate immune cell functions thus ameliorating the course of experimental colitis

Two distinct forms of the erythropoietin receptor (EPOR) mediate the cellular responses to erythropoietin (EPO) in different tissues. EPOR homodimers signal to promote the maturation of erythroid progenitor cells. In other cell types, including immune cells, EPOR and the ß-common receptor (CD131) form heteromers (the innate repair receptor; IRR), and exert tissue protective effects. We used dextran sulphate sodium (DSS) to induce colitis in C57BL/6 N mice. Once colitis was established, mice were treated with solvent, EPO or the selective IRR agonist cibinetide. We found that both cibinetide and EPO ameliorated the clinical course of experimental colitis in mice, resulting in improved weight gain and survival. Correspondingly, DSS-exposed mice treated with cibinetide or EPO displayed preserved tissue integrity due to reduced infiltration of myeloid cells and diminished production of pro-inflammatory disease mediators including cytokines, chemokines and nitric oxide synthase-2. Experiments using LPS-activated primary macrophages revealed that the anti-inflammatory effects of cibinetide were dependent on CD131 and JAK2 functionality and were mediated via inhibition of NF-κB subunit p65 activity. Cibinetide activation of the IRR exerts potent anti-inflammatory effects, especially within the myeloid population, reduces disease activity and mortality in mice. Cibinetide thus holds promise as novel disease-modifying therapeutic of inflammatory bowel disease.

A Nonhematopoietic Erythropoietin Analogue, ARA 290, Inhibits Macrophage Activation and Prevents Damage to Transplanted Islets

BACKGROUND

Erythropoietin exerts anti-inflammatory, antiapoptotic, and cytoprotective effects in addition to its hematopoietic action. A nonhematopoietic erythropoietin analogue, ARA 290, has similar properties. The efficacy of pancreatic islet transplantation (PITx) is reduced due to islet damage that occurs during isolation and from the severe inflammatory reactions caused by the transplantation procedure. We investigated whether ARA 290 protects islets and ameliorates inflammatory responses following PITx thus improving engraftment.

METHODS

The effects of ARA 290 on pancreatic islets of C57BL/6J (H-2) mice and on murine macrophages were investigated using an in vitro culture model. As a marginal PITx, 185 islets were transplanted into the liver of streptozotocin-induced diabetic mice (H-2) via the portal vein. Recipients were given ARA 290 (120 μg/kg) intraperitoneally just before and at 0, 6, and 24 hours after PITx. Liver samples were obtained at 12 hours after PITx, and expression levels of proinflammatory cytokines were assessed.

RESULTS

ARA 290 protected islets from cytokine-induced damage and apoptosis. Secretion of pro-inflammatory cytokines (IL-6, IL-12, and TNF-α) from macrophages was significantly inhibited by ARA 290. After the marginal PITx, ARA 290 treatment significantly improved the blood glucose levels when compared to those of control animals (P < 0.001). Upregulation of monocyte chemoattractant protein-1, macrophage inflammatory protein-1β, IL-1β, and IL-6 messenger RNA expression within the liver was suppressed by ARA 290 treatment.

CONCLUSIONS

ARA 290 protected pancreatic islets from cytokine-induced damage and apoptosis and ameliorated the inflammatory response after PITx. ARA 290 appears to be a promising candidate for improvement of PITx.

AG490 suppresses EPO-mediated activation of JAK2-STAT but enhances blood flow recovery in rats with critical limb ischemia

Background

Erythropoietin (EPO) has been demonstrated to enhance recovery in ischemic organs through enhancing angiogenesis. In this study, we used an experimental critical limb ischemia (CLI) rat model to reveal the underlying mechanisms and directly examine the benefits of the anti-apoptotic capacity of EPO in the acute phase of limb ischemia and following blood flow recovery.

Methods

To determine the role of the JAK2/STAT pathway in EPO-enhanced recovery after CLI, male Sprague-Dawley rats (n = 8 for each group) were divided into group 1 (normal control), group 2 (CLI treated with normal saline), group 3 (CLI treated with EPO), group 4 (CLI treated with AG490, a JAK2 inhibitor), and group 5 (CLI treated with EPO and AG490). Animals were sacrificed either at day 1 or day 14 and biochemical and histopathological examination of ischemic quadriceps were conducted.

Results

At day 1, EPO administration reduced expression levels of apoptotic indices and activated the JAK2/STAT pathway; this activation was inhibited by additional AG490 treatment. Furthermore, the decrease in the size of the infarcted area, as well as activation of ERK1/2 and JNK showed similar regulatory trends with EPO or AG490 treatment. Of Interest, EPO and AG490 in combination showed a synergistic effect, increasing expression levels of antioxidants (GR, GPx, NQO-1) and decreasing transcriptional levels of pro-inflammatory factors (TNF-α, NF-kB). At day 14, laser Doppler analysis showed that the blood flow recovery was enhanced by EPO, AG490, or combined treatment.

Conclusion

Although inhibition of the JAK2/STAT pathways reduces the anti-apoptotic effects of EPO in the early phase of CLI, the benefits of AG490 in anti-inflammation and anti-oxidation still play a positive role in enhancing blood flow recovery after CLI.

Recombinant Human Erythropoietin Protects Myocardial Cells from Apoptosis via the Janus-Activated Kinase 2/Signal Transducer and Activator of Transcription 5 Pathway in Rats with Epilepsy

OBJECTIVE

To investigate the potential mechanisms underlying the protective effects of recombinant human erythropoietin (rhEPO) and carbamylated EPO (CEPO) against myocardial cell apoptosis in epilepsy.

METHODS

Rats were given an intra-amygdala injection of kainic acid to induce epilepsy. Groups of rats were treated with rhEPO or CEPO before induction of epilepsy, whereas additional rats were given a caudal vein injection of AG490, a selective inhibitor of Janus kinase 2 (JAK2). At different time points after seizure onset, electroencephalogram changes were recorded, and myocardium samples were taken for the detection of myocardial cell apoptosis and expression of JAK2, signal transducer and activator of transcription 5 (STAT5), caspase-3, and bcl-xl mRNAs and proteins.

RESULTS

Induction of epilepsy significantly enhanced myocardial cell apoptosis and upregulated the expression of caspase-3 and bcl-xl proteins and JAK2 and STAT5a at both the mRNA and protein levels. Pretreatment with either rhEPO or CEPO reduced the number of apoptotic cells, upregulated bcl-xl expression, and downregulated caspase-3 expression in the myocardium of epileptic rats. Both myocardial JAK2 and STAT5a mRNAs, as well as phosphorylated species of JAK2 and STAT5a, were upregulated in epileptic rats in response to rhEPO-but not to CEPO-pretreatment. AG490 treatment increased apoptosis, upregulated caspase-3 protein expression, and downregulated bcl-xl protein expression in the myocardium of epileptic rats.

CONCLUSIONS

These results indicate that myocardial cell apoptosis may contribute to myocardial injury in epilepsy. EPO protects myocardial cells from apoptosis via the JAK2/STAT5 pathway in rats with experimental epilepsy, whereas CEPO exerts antiapoptotic activity perhaps via a pathway independent of JAK2/STAT5 signaling.

Erythropoietin acts as an anti-inflammatory signal on murine mast cells

Recently it was found that the erythropoietin receptor (EpoR) is expressed on innate immune cells, such as dendritic cells and macrophages. We found that murine bone marrow-derived mast cells express the EpoR and that its expression is increased under hypoxic conditions. Interestingly, Epo stimulation of the cells did not activate signal transducer and activator of transcription molecules, nor did we find differences in the expression of typical STAT-dependent genes, the proliferation rate, and the ability to differentiate or to protect the cells from apoptosis. Instead, we demonstrate that stimulation of mast cells with Epo leads to phosphorylation of the receptor tyrosine kinase c-kit. We hypothesize that this is due to the formation of a receptor complex between the EpoR and c-kit. The common beta chain of the IL-3 receptor family, which was described as part of the tissue protective receptor (TPR) on other non-erythroid cells, however is not activated. To investigate whether the EpoR/c-kit complex has tissue protective properties, cells were treated with the Toll-like receptor ligand LPS. Combined Epo and LPS treatment downregulated the inflammatory response of the cells as detected by a decrease in IL-6 and TNF-α secretion.

Erythropoietin protects against diabetes through direct effects on pancreatic beta cells

In mouse models of type 1 and type 2 diabetes, administration of human erythropoietin protects against disease by acting directly on pancreatic β cells.

A common feature among all forms of diabetes mellitus is a functional β-cell mass insufficient to maintain euglycemia; therefore, the promotion of β-cell growth and survival is a fundamental goal for diabetes prevention and treatment. Evidence has suggested that erythropoietin (EPO) exerts cytoprotective effects on nonerythroid cells. However, the influence of EPO on pancreatic β cells and diabetes has not been evaluated to date. In this study, we report that recombinant human EPO treatment can protect against diabetes development in streptozotocin-induced and db/db mouse models of type 1 and type 2 diabetes, respectively. EPO exerts antiapoptotic, proliferative, antiinflammatory, and angiogenic effects within the islets. Using β-cell–specific EPO receptor and JAK2 knockout mice, we show that these effects of EPO result from direct biological effects on β cells and that JAK2 is an essential intracellular mediator. Thus, promotion of EPO signaling in β cells may be a novel therapeutic strategy for diabetes prevention and treatment.

Scavenger receptor class BI mediates the anti-apoptotic effect of erythropoietin

A scavenger receptor of the B class (SR-BI)/human homolog of SR-BI, CD36, and LIMP II analogous-1 (CLA-1), has been identified as a receptor for high-density lipoprotein (HDL). Mice lacking SR-B1 develop anemia, plausibly explained by the observation that the erythrocyte life-span in these animals is reduced. Erythropoietin (EPO) is known to promote survival of erythroid cells, in large part through protection from apoptosis. We have examined the role of EPO on hSR-BI/CLA-1 expression and erythrocyte apoptosis. Endogenous expression of hSR-BI/CLA-1 was increased by exposure to EPO. EPO increased transcriptional activity of hSR-BI/CLA-1 promoter. The stimulatory effect of EPO on hSR-BI/CLA-1 promoter activity was abrogated by LY294002, specific inhibitor of phosphatidylinositol-3 kinase (PI3K). Constitutively active Akt stimulates the activity of the hSR-BI/CLA-1 promoter and a dominant-negative mutant of Akt abolished the ability of EPO to stimulate promoter activity. Finally, EPO in combination with HDL protected the cell from apoptosis, which suggests that hSR-BI/CLA-1 induced by EPO might contribute to the erythrocyte life-span.

Antiapoptotic properties of erythropoiesis-stimulating proteins in models of cisplatin-induced acute kidney injury

Erythropoietin (Epo) induces erythrocytosis by suppressing erythroid progenitor cell apoptosis through the Janus-activated kinase-signal transducers and activators of transcription (JAK-STAT) pathway. Since apoptosis contributes to cisplatin (CP)-induced nephrotoxicity and Epo receptors (EpoR) are expressed in the kidney, we examined the role of antiapoptosis in recombinant human erythropoietin (rHuEpo)-mediated renal protection. In human renal proximal tubular epithelial (RPTE) cells in culture, rHuEpo, but not inactive rHuEpo (I-rHuEpo), the receptor-binding sites of which are mutated, caused a significant reduction in CP-induced apoptosis at > or = 100 U/ml. rHuEpo, but not I-rHuEpo, increased STAT5 and Akt/PKB phosphorylation, demonstrating functional EpoR expression on RPTE cells. Furthermore, the JAK2 inhibitor tyrphostin AG-490 attenuated rHuEpo protection, suggesting a role of the JAK-STAT pathway in rHuEpo-mediated antiapoptosis. In rats, intravenous administration of 5,000 U/kg rHuEpo, but not an equivalent peptide mass of I-rHuEpo, before a single 5.5 mg/kg iv injection of CP, significantly increased hematocrit (Hct) and reduced the CP-induced increase in serum creatinine. Serum creatinine on day 4 was 3.4 +/- 0.3, 1.9 +/- 0.3, and 3.5 +/- 0.4 mg/dl in the CP, CP + rHuEpo, and CP + I-rHuEpo groups, respectively. Similarly, darbepoietin-alpha (DA), a hyperglycosylated analog of rHuEpo with prolonged in vivo activity when injected at 25 microg/kg iv before CP, significantly increased Hct and reduced serum creatinine. Renal clearance studies based on glomerular filtration rate and renal blood flow confirmed the significant renal protection by DA against CP. Tubular apoptosis and necrosis were significantly reduced in the kidneys of the CP + DA vs. the CP + saline group. Moreover, the equalization of Hct by venesection did not abrogate the DA-mediated renal protection. Administration of DA 48 h after CP injection also conferred significant renal protection. Thus our experiments confirm a role for erythropoiesis-stimulating proteins, including the new analog DA, in limiting CP-induced nephrotoxicity and suggest that antiapoptosis via the Epo-EpoR interaction is an important mechanism for renal protection.

Protective effect of erythropoietin against radiocontrast-induced renal tubular epithelial cell injury

BACKGROUND/AIMS

Recombinant human erythropoietin (rhEpo) has been shown to reduce tissue injury following ischemia-reperfusion. We examined whether rhEpo protects in vitro renal tubular epithelial cells against radiocontrast media-induced injury.

METHODS

LLC-PK1 renal tubular epithelial cells were exposed to non-ionic radiocontrast agent iohexol (low-osmolar) or iodixanol (iso-osmolar), with or without rhEpo (200 U/ml). Following a 6-hour exposure, cells were incubated for 24 h in radiocontrast-free culture medium. Cell viability was then assessed by the MTT assay. We also assessed cell apoptosis by the TUNEL assay, and activities of caspase-3, caspase-8, and caspase-9 were determined by a luminescence assay.

RESULTS

rhEpo improved viability of iohexol-treated LLC-PK1 cells by 27 +/- 6% (88.1 +/- 1.5 vs. 70.8 +/- 3.3%, p = 0.008). Similarly, rhEpo improved the viability of iodixanol-treated LLC-PK1 cells by 26 +/- 4% (82.5 +/- 2.1vs. 65.7 +/- 1.7%, p = 0.028). rhEpo also decreased apoptosis rates of iohexol-treated LLC-PK1 cells (6.4 +/- 0.9/1,000 cells vs. 14.8 +/- 2.4/1,000 cells, p = 0.028), and iodixanol-treated LLC-PK1 cells (8.0 +/- 1.2/1,000 cells vs. 13.5 +/- 1.9/1,000 cells, p = 0.028). In iohexol-treated LLC-PK1 cells, rhEpo attenuated activation of caspase-3 (p = 0.003), caspase-8 (p = 0.033) and caspase-9 (p = 0.055).

CONCLUSION

rhEpo attenuates in vitro renal tubular epithelial cell injury induced by low- and iso-osmolar radiocontrast media, possibly by reduction of caspases activation and apoptosis rates.

EPO modulation of cell-cycle regulatory genes, and cell division, in primary bone marrow erythroblasts

Erythropoietin (EPO's) actions on erythroblasts are ascribed largely to survival effects. Certain studies, however, point to EPO-regulated proliferation. To investigate this problem in a primary system, Kit(pos)CD71(high) erythroblasts were prepared from murine bone marrow, and were first used in the array-based discovery of EPO-modulated cell-cycle regulators. Five cell-cycle progression factors were rapidly up-modulated: nuclear protein 1 (Nupr1), G1 to S phase transition 1 (Gspt1), early growth response 1 (Egr1), Ngfi-A binding protein 2 (Nab2), and cyclin D2. In contrast, inhibitory cyclin G2, p27/Cdkn1b, and B-cell leukemia/lymphoma 6 (Bcl6) were sharply down-modulated. For CYCLIN G2, ectopic expression also proved to selectively attenuate EPO-dependent UT7epo cell-cycle progression at S-phase. As analyzed in primary erythroblasts expressing minimal EPO receptor alleles, EPO repression of cyclin G2 and Bcl6, and induction of cyclin D2, were determined to depend on PY343 (and Stat5) signals. Furthermore, erythroblasts expressing a on PY-null EPOR-HM allele were abnormally distributed in G0/G1. During differentiation divisions, EPOR-HM Ter119(pos) erythroblasts conversely accumulated in S-phase and faltered in an apparent EPO-directed transition to G0/G1. EPO/EPOR signals therefore control the expression of select cell-cycle regulatory genes that are proposed to modulate stage-specific decisions for erythroblast cell-cycle progression.

Erythropoietin fails to interfere with the antiproliferative and cytotoxic effects of antitumor drugs

PURPOSE

Erythropoietin (EPO) therapy is widely used for the prevention and treatment of anemia resulting from cancer chemotherapy. Native EPO regulates erythropoiesis, at least in part, by protecting erythroid progenitor cells from apoptotic cell death. The recent discovery of the EPO receptor (EPOR) on cancer cells raises the concern that EPO therapy might stimulate tumor growth and/or protect cancer cells from drug-induced apoptosis. Therefore, the capacity of EPO to interfere with the effects of conventional chemotherapeutic drugs on proliferation, apoptosis, and the induction of senescence was investigated in MCF-7 and MDA-MB231 breast tumor cells, which express the EPOR as well as in F-MEL erythroleukemia cells.

EXPERIMENTAL DESIGN

Breast cancer cells and F-MEL leukemic cells were cultured in the presence or absence of EPO and then exposed to antitumor drugs. Cell proliferation was assessed by a standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide dye reduction assay 72 hours after drug exposure. Cytotoxicity was monitored by clonogenic survival. Apoptosis was evaluated either by the terminal deoxyribonucleotide transferase-mediated nick-end labeling assay or fluorescence-activated cell sorting analysis, and senescence was monitored by beta-galactosidase staining. EPO signaling was assessed by monitoring the phosphorylation/activation of specific signaling proteins.

RESULTS

EPO failed to stimulate the proliferation of MCF-7 or MDA-MB231 breast tumor cells or F-MEL leukemic cells. EPO treatment also failed to interfere with the antiproliferative and/or cytotoxic effects of Adriamycin, Taxol, and tamoxifen in breast tumor cells (or of cytarabine and daunorubicin in F-MEL cells). EPO failed to prevent apoptosis induced by Taxol or senescence induced by Adriamycin in MCF-7 cells. EPO stimulated the activation of extracellular signal-regulated kinase, p38, and c-Jun-NH(2)-kinase in MCF-7 cells but did not activate Akt or signal transducers and activators of transcription 5 (STAT5). EPO failed to activate any of these signaling pathways in MDA-MB231 cells. Cytarabine and daunorubicin interfered with EPO signaling in F-MEL cells.

CONCLUSIONS

These findings suggest that EPO is unlikely to directly counteract the effectiveness of cancer chemotherapeutic drugs. This may be a consequence of either ineffective signaling through the EPOR or drug-mediated suppression of EPO signaling.

Erythropoietin stimulates growth and STAT5 phosphorylation in human prostate epithelial and prostate cancer cells

BACKGROUND

Erythropoietin (Epo), the principal regulator of erythroid progenitor survival, growth, and differentiation, initiates its action by binding to its cognate cell surface receptor (EpoR). EpoR have been identified on a variety of non-hematopoietic cells, both normal and malignant, however, little is known about the function of EpoR on malignant cells.

METHODS

RT-PCR, Western blotting, and immunohistochemistry were used to demonstrate that prostate cancer cells express EpoR at both the gene and protein level. Cell proliferation assays and STAT5 phosphorylation were used to demonstrate Epo's mitogenic action and intracellular signaling, respectively.

RESULTS

We have demonstrated that transformed prostate epithelial and prostate cancer cell lines, as well as primary prostate tissue, express the EpoR. Importantly, the EpoR on prostate cells are functional, as demonstrated by the observation that each of the cell lines exhibited a dose-dependent proliferative response to Epo, and that Epo triggered STAT5b phosphorylation in the cells.

CONCLUSION

Human prostatic epithelial cells and prostate cancer cells express functional EpoR, and Epo serves as a growth factor for these cells. These results have implications for our understanding of normal prostatic growth and development and of the pathobiology of human prostate cancer.

Schwann cells express erythropoietin receptor and represent a major target for Epo in peripheral nerve injury

Erythropoietin (Epo) expresses potent neuroprotective activity in the peripheral nervous system; however, the underlying mechanism remains incompletely understood. In this study, we demonstrate that Epo is upregulated in sciatic nerve after chronic constriction injury (CCI) and crush injury in rats, largely due to local Schwann cell production. In uninjured and injured nerves, Schwann cells also express Epo receptor (EpoR), and its expression is increased during Wallerian degeneration. CCI increased the number of Schwann cells at the injury site and the number was further increased by exogenously administered recombinant human Epo (rhEpo). To explore the activity of Epo in Schwann cells, primary cultures were established. These cells expressed cell-surface Epo receptors, with masses of 71 and 62 kDa, as determined by surface protein biotinylation and affinity precipitation. The 71-kDa species was rapidly but transiently tyrosine-phosphorylated in response to rhEpo. ERK/MAP kinase was also activated in rhEpo-treated Schwann cells; this response was blocked by pharmacologic antagonism of JAK-2. RhEpo promoted Schwann cell proliferation, as determined by BrdU incorporation. Cell proliferation was ERK/MAP kinase-dependent. These results support a model in which Schwann cells are a major target for Epo in injured peripheral nerves, perhaps within the context of an autocrine signaling pathway. EpoR-induced cell signaling and Schwann cell proliferation may protect injured peripheral nerves and promote regeneration.

Timing of Erythropoietin Treatment for Cardioprotection in Ischemia/Reperfusion

Erythropoietin (EPO) is a hormone known to stimulate hematopoiesis. However, recent research suggests additional properties of EPO, such as protection against ischemia/reperfusion (I/R) injury in various tissues. We studied the effect of timing of EPO administration on cardioprotection during I/R in the heart. Male Sprague-Dawley rats were subjected to 45 minutes of coronary occlusion, followed by 24 hours of reperfusion. Animals were randomized to receive saline or single dose of EPO (5,000 IU/kg) either 2 hours before I/R, at the start of ischemia, or after the onset of reperfusion. The ratio of infarct area/area at risk (planimetry), left ventricular (LV) function (pressure development), and apoptosis (number of active caspase-3 positive cells) were determined after 24-hour reperfusion. Administration of EPO during different time points resulted in a 19 to 23% (P < 0.05) reduction in the infarct area/area at risk, which was accompanied by a trend toward better LV hemodynamic parameters. Apoptosis was significantly attenuated in groups treated with EPO at the start of ischemia (29% reduction) and after the onset of reperfusion (38%), and to a lesser extent (16%) in the group pre-treated with EPO. Thus, in vivo administration of EPO at different time points protects the myocardial structure and preserves cardiac function during I/R. Cardioprotective effect of EPO is associated with inhibition of apoptosis.

Adenoviral gene transfer of erythropoietin confers cytoprotection to isolated pancreatic islets

BACKGROUND

The transfer of cytoprotective genes to isolated pancreatic islets may contribute to their enhanced survival in the transplant setting. Our laboratory established the expression of functional erythropoietin (EPO) receptors throughout pancreatic islets. Because EPO is a cytokine that promotes survival, we examined whether adenovirus-mediated gene transfer of EPO would result in cytoprotection of human pancreatic islets in culture and in the transplant setting.

METHODS

Isolated human islets were transduced using an adenoviral vector coding for human EPO or green fluorescent protein. Comparison of cell death in culture was measured using annexin V-phycoerythrin and propidium iodide. Transplantation of transduced islets into diabetic nude mice was used to assess the effect of EPO on islet function and in vivo survival.

RESULTS

Adenoviral delivery of EPO to pancreatic islets resulted in high-level EPO synthesis and secretion, which did not affect islet function in vitro or in vivo. Islets transduced with EPO were protected from apoptosis in culture and were at a functional advantage in vivo when compared with islets transduced with green fluorescent protein or untransduced islets. The high level of EPO had a negative effect on the blood chemistry of the animals that underwent transplantation.

CONCLUSIONS

Overexpression of EPO protects islets from destruction and does not compromise islet function. Genetic engineering with EPO may be a viable approach for improving islet survival and engraftment in the transplant setting, but regulation of the gene's expression will be an important prerequisite to this strategy.

Transgenic bcl-2 is not sufficient to rescue all hematolymphoid defects in STAT5A/5B-deficient mice

OBJECTIVE

Cytokines bind high-affinity receptors expressed on hematopoietic cells to initiate signaling cascades that regulate differentiation, proliferation, and survival. Previous studies have established a role for STAT5 in transducing survival signals for hematopoietic progenitor cells in response to cytokines.

MATERIALS AND METHODS

To determine if constitutive expression of a member of the bcl-2 family of anti-apoptotic proteins could compensate for the loss of STAT5, we utilized combinatorial genetics to generate STAT5A/5B-deficient mice expressing a bcl-2 transgene.

RESULTS

Although bcl-2 expression restored peripheral blood counts to normal in STAT5A/5B(-/-) mice, we noted a striking failure of this transgene to correct defects in hematopoietic stem and progenitor cells.

CONCLUSION

These data imply important effects of STAT5 in modulating hematopoietic cells in addition to promoting survival per se.

Human, nonhuman primate, and rat pancreatic islets express erythropoietin receptors

BACKGROUND

Erythropoietin (EPO) promotes survival in a variety of cells by mediating antiapoptotic signals through the EPO receptor (R). The authors examined pancreatic islets for the presence of EPO-R to determine whether these cells are protected by EPO from cytokine-induced apoptosis.

METHODS

Reverse-transcriptase polymerase chain reaction, immunohistology, and Western blots were used to establish the presence and localization of EPO-R on rat, nonhuman primate, and human islets. Islets were exposed to cytokines in the presence and absence of recombinant EPO and apoptosis was measured using a terminal deoxynucleotide transferase-mediated dUTP nick-end labeling assay followed by fluorescence-activated cell sorter analysis. Glucose stimulation indices were measured to assess the effect of EPO on islet function.

RESULTS

The presence of EPO-R was demonstrated on islets regardless of species. Recombinant EPO protected islets in culture from cytokine-induced apoptosis in a dose-dependent manner. Furthermore, the presence of EPO in the media does not adversely affect islet function.

CONCLUSIONS

This is the first demonstration that pancreatic islets express EPO-R and that EPO may prevent islet-cell apoptosis in culture. In vivo trials to evaluate the potential of long-term expression of EPO to augment islet survival in transplantation are underway.

Naturally occurring dominant-negative Stat5 suppresses transcriptional activity of estrogen receptors and induces apoptosis in T47D breast cancer cells

Signal transducer and activator of transcription (Stat) 5 regulates growth, differentiation, and survival of mammary and hematopoietic cells. The role of Stat5 in breast cancer has not been established, although Stat5 is critical for some hematopoietic malignancies. We detected for the first time that Stat5b is constitutively activated in human breast cancer cell lines, and analysed the role of Stat5 in estrogen receptor(ER)-positive breast cancer cell lines using dominant-negative variants of Stat5. Two distinct carboxyl-truncated Stat5a derivatives were generated. Stat5aDelta740 corresponded to a naturally occurring alternative splice variant, and Stat5aDelta713 was analogous to an 80 kDa Stat5a product of a nuclear protease. Stat5aDelta740 and Stat5aDelta713 displayed comparable dominant-negative properties and suppressed transcriptional activity of wild-type Stat5a and Stat5b equally well. Cotransfection experiments revealed that Stat5aDelta740 completely blocked transcriptional activity of endogenous estrogen receptor in T47D and MCF7 cells, and of both ER alpha and ER beta in COS-7 cells. Stat5aDelta740 was selected for adenoviral delivery, and high-efficiency expression of tyrosine phosphorylated Stat5aDelta740 was achieved in infected cells. Adenoviral-mediated Stat5aDelta740 induced apoptosis in T47D cells but not in caspase-3-negative MCF7 cells. The present study indicates that overexpression of a dominant-negative variant of Stat5 suppresses ER transcriptional activity and induces apoptosis in estrogen-responsive breast cancer tissue culture cells.

Recombinant human erythropoietin counteracts secondary injury and markedly enhances neurological recovery from experimental spinal cord trauma

Erythropoietin (EPO) functions as a tissue-protective cytokine in addition to its crucial hormonal role in red cell production. In the brain, for example, EPO and its receptor are locally produced, are modulated by metabolic stressors, and provide neuroprotective and antiinflammatory functions. We have previously shown that recombinant human EPO (rhEPO) administered within the systemic circulation enters the brain and is neuroprotective. At present, it is unknown whether rhEPO can also improve recovery after traumatic injury of the spinal cord. To evaluate whether rhEPO improves functional outcome if administered after cord injury, two rodent models were evaluated. First, a moderate compression of 0.6 N was produced by application of an aneurysm clip at level T3 for 1 min. RhEPO (1,000 units per kg of body weight i.p.) administered immediately after release of compression was associated with partial recovery of motor function within 12 h after injury, which was nearly complete by 28 days. In contrast, saline-treated animals exhibited only poor recovery. In the second model used, rhEPO administration (5,000 units per kg of body weight i.p. given once 1 h after injury) also produced a superior recovery of function compared with saline-treated controls after a contusion of 1 N at level T9. In this model of more severe spinal cord injury, secondary inflammation was also markedly attenuated by rhEPO administration and associated with reduced cavitation within the cord. These observations suggest that rhEPO provides early recovery of function, especially after spinal cord compression, as well as longer-latency neuroprotective, antiinflammatory and antiapoptotic functions.

Activation of Raf/ERK1/2 MAP kinase pathway is involved in GM-CSF-induced proliferation and survival but not in erythropoietin-induced differentiation of TF-1 cells

The involvement of MAPK pathways in differentiation, proliferation and survival was investigated by comparing Epo and GM-CSF signalling in human factor-dependent myeloerythroid TF-1 cells with abnormal Epo-R. GM-CSF withdrawal induced cell-cycle arrest and apoptosis accompanied by increased caspase-3 activity, DNA degradation and reduced expression of the antiapoptotic Bcl-2 and Bcl-xl proteins. Readministration of GM-CSF but not Epo reversed these processes and induced proliferation. The GM-CSF promoted cell survival and proliferation correlated with MEK-1 dependent ERK1/2, Elk-1 and CREB phosphorylation and Egr-1, c-Fos expression as well as with increased STAT-5, AP-1, c-Myb and NF-kappaB DNA-binding. In contrast, Epo failed to activate the Raf-1/ERK1/2 MAPK pathway or to induce Egr-1 and/or c-Fos expression, while it induced erythroid differentiation in GM-CSF-deprived cells. In addition, the Epo-induced haemoglobin production was inhibited in the presence of GM-CSF. These results demonstrate that the activation of MAPK cascade is not necessary for Epo-induced haemoglobin production in TF-1 cells and suggest a negative cross-talk between the signalling of GM-CSF-stimulated cell proliferation and Epo-induced erythroid differentiation.

Activation of the transcription factor NF-kappaB by the erythropoietin receptor: structural requirements and biological significance

The transcription factor nuclear factor kappa B (NF-kappaB) has been implicated in the regulation of genes mainly involved in inflammation and immune response. We analysed the role of NF-kappaB in signalling pathways induced by the hematopoietic growth factor erythropoietin (EPO). Our data, obtained by electrophoretic mobility shift assays (EMSA) and reporter gene assays, show that the intracellular domain of the EPO receptor (EPOR) transmits signals leading to the activation of NF-kappaB. Studies employing an inhibitor specific for the EPOR-associated tyrosine kinase JAK2 suggest that JAK2-dependent pathways are not involved. The induction of an NF-kappaB-triggered reporter gene construct was inhibited by cotransfection of dominant negative forms of the src kinase Lyn, but not by dominant negative JAK2. Using epidermal growth factor (EGF)/EPOR hybrids containing mutant forms of the EPOR intracellular domain, we were able to further define the critical structures for the induction of NF-kappaB. The data show that although the activity of JAK2 seems to be dispensable, its association to the receptor, as well as the phosphorylation of membrane proximal tyrosine residues, are essential. Furthermore, the functional analysis of different receptor forms revealed a correlation of the abilities to induce NF-kappaB activity and to generate antiapoptotic signals.

The biology of erythropoietin in the central nervous system and its neurotrophic and neuroprotective potential

This review summarizes published as well as preliminary data on the biology of erythropoietin (Epo) in the developing and mature human central nervous system (CNS). Both Epo receptor (Epo-R) and Epo gene expression underlie developmental changes and a brain-specific regulation. These features suggest a different role of Epo in normal brain development than in neuroprotection and neuronal tissue repair after brain injury. Epo concentrations in the cerebrospinal fluid may have primary paracrine effects. While the transport of Epo across the intact blood brain barrier (BBB) is generally limited in humans, systemically produced or administrated Epo may cross during BBB dysfunction. Summarized data of the in vivo and in vitro effects of Epo in the CNS show significant neuroprotective and neurotrophic effects of this molecule. These effects are mediated by several mechanisms, including the activation of a variety of genes and their consecutive protein production. Therapeutic strategies involving activation of the CNS Epo-R are discussed, including the potential use of Epo mimetic peptides.

The granulocyte colony-stimulating factor receptor supports erythroid differentiation in the absence of the erythropoietin receptor or Stat5

To evaluate the functional conservation of signal transduction mechanisms between haematopoietic receptors and to characterize the molecules activated in this phenomenon, we introduced granulocyte colony-stimulating factor receptor (G-CSFR) cDNA into mouse fetal liver cells using a retroviral vector. In semi-solid medium assays, G-CSFR-infected cells gave rise to all types of colonies [granulocyte-macrophage (GM), megakaryocyte (MK) and mixed lineage (GEMM) colony-forming units (CFU) and erythroid burst-forming units (BFU-E)] in the presence of G-CSF alone. The direct effect of G-CSF on erythroid differentiation of G-CSFR-transduced erythroid progenitors was demonstrated by the development of erythroid colonies using G-CSFR-expressing Lin- cells cloned at one cell per well in liquid culture in the presence of G-CSF. Interestingly, while Stat5, but not Stat3, was activated in erythroid cells in response to erythropoietin (EPO), both were activated in erythroid and granulocytic cells stimulated by G-CSF. Furthermore, G-CSF induced the growth of erythroid colonies from G-CSFR-expressing fetal liver cells from EPO receptor-/- (EPO-R-/-) or Stat5a-/- Stat5b-/- mice, demonstrating that erythroid differentiation can occur in the absence of EPO-R or Stat5. These data show that forced expression of G-CSFR allows G-CSF-dependent multilineage proliferation and differentiation of haematopoietic progenitors and rescues EPO-R-/- erythroid cells. While G-CSF induces Stat5 activation in G-CSFR-expressing erythroid cells, this activation is not necessary for the terminal erythroid differentiation induced by G-CSF.