Erythropoietin stimulates cancer cell migration and activates RhoA protein through a mitogen-activated protein kinase/extracellular signal-regulated kinase-dependent mechanism

Biomolecules-releasing click chemistry-based bioadhesives for repairing acetabular labrum tears

Currently, there are no effective clinical or experimental treatments to fully restore the function of the torn acetabular labrum. To fill the gap, here, we report the finding of progenitor cells in labral tissue, which can be recruited and stimulated to repair torn acetabular labral tissue. This study aimed to develop a biomolecule releasing bioadhesive which can speed up labral tissue healing by eliciting autologous labral progenitor cellular responses. A click chemistry-based bioadhesive, capable of releasing biomolecules, was synthesized to exert ~3× adhesion strength compared with fibrin glue. Via the release of platelet-derived growth factor (PDGF), the adhesive was shown to actively recruit and stimulate the proliferation of labral progenitor cells to the tear sites and within the adhesive. Finally, the ability of this biomolecules-releasing adhesive designed to promote labral tissue regeneration was evaluated using discarded human acetabular labrum tissue compared with surgical suture ex vivo. Histological analysis shows that PDGF-releasing bioadhesive yielded significantly more labrum cell responses and extracellular matrix protein (proteoglycan and collagen) production at the tear tissue site than surgical suture controls. The results confirm that the new PDGF-releasing bioadhesive can activate the responses of autologous labral progenitor cells to significantly improve labral tissue regeneration. Clinical significance: These PDGF-releasing bioadhesives may serve as a new and effective tool for repairing and regenerating acetabular labrum tears.

The Role of PI3K/AKT and MAPK Signaling Pathways in Erythropoietin Signalization

Erythropoietin (EPO) is a glycoprotein cytokine known for its pleiotropic effects on various types of cells and tissues. EPO and its receptor EPOR trigger signaling cascades JAK2/STAT5, MAPK, and PI3K/AKT that are interconnected and irreplaceable for cell survival. In this article, we describe the role of the MAPK and PI3K/AKT signaling pathways during red blood cell formation as well as in non-hematopoietic tissues and tumor cells. Although the central framework of these pathways is similar for most of cell types, there are some stage-specific, tissue, and cell-lineage differences. We summarize the current state of research in this field, highlight the novel members of EPO-induced PI3K and MAPK signaling, and in this respect also the differences between erythroid and non-erythroid cells.

BRIP1 inhibits the tumorigenic properties of cervical cancer by regulating RhoA GTPase activity

Breast cancer 1, early onset (BRCA1)-interacting protein 1 (BRIP1), a DNA-dependent adenosine triphosphatase and DNA helicase, is required for BRCA-associated DNA damage repair functions, and may be associated with the tumorigenesis and aggressiveness of various cancers. The present study investigated the expression of BRIP1 in normal cervix tissues and cervical carcinoma via reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry assays. BRIP1 expression was observed to be reduced in squamous cancer tissue and adenocarcinoma compared with normal cervix tissue, and there were significant correlations between the reduction in BRIP1 expression and unfavorable variables, including the International Federation of Gynecologists and Obstetricians stage and presence of lymph node metastases. In order to elucidate the role of BRIP1 in cervical cancer, a BRIP1 recombinant plasmid was constructed and overexpressed in a cervical cancer cell line (HeLa). The ectopic expression of BRIP1 markedly inhibited the tumorigenic properties of HeLa cells in vitro, as demonstrated by decreased cell growth, invasion and adhesion, and increased cell apoptosis. In addition, it was identified that the inhibitory tumorigenic properties of BRIP1 may be partly attributed to the attenuation of RhoA GTPase activity. The present study provides a novel insight into the essential role of BRIP1 in cervical cancer, and suggests that BRIP1 may be a useful therapeutic target for the treatment of this common malignancy.

Early activation of MAP kinases by influenza A virus X-31 in murine macrophage cell lines

Early molecular responses to Influenza A (FLUA) virus strain A/X-31 H3N2 in macrophages were explored using J774.A1 and RAW 264.7 murine cell lines. NF-kappa B (NFκB) was reported to be central to FLUA host-response in other cell types. Our data showed that FLUA activation of the classical NFκB dependent pathway in these macrophages was minimal. Regulator proteins, IkappaB-alpha and -beta (IκBα, IκBβ), showed limited degradation peaking at 2 h post FLUA exposure and p65 was not observed to translocate from the cytoplasm to the nucleus. Additionally, the non-canonical NFκB pathway was not activated in response to FLUA. The cells did display early increases in TNFα and other inflammatory cytokine and chemokine production. Mitogen activated phosphokinase (MAPK) signaling pathways are also reported to control production of inflammatory cytokines in response to FLUA. The activation of the MAPKs, cJun kinases 1 and 2 (JNK 1/2), extracellular regulated kinases 1 and 2 (ERK 1/2), and p38 were investigated in both cell lines between 0.25 and 3 h post-infection. Each of these kinases showed increased phosphorylation post FLUA exposure. JNK phosphorylation occurred early while p38 phosphorylation appeared later. Phosphorylation of ERK 1/2 occurred earlier in J774.A1 cells compared to RAW 264.7 cells. Inhibition of MAPK activation resulted in decreased production of most FLUA responsive cytokines and chemokines in these cells. The results suggest that in these monocytic cells the MAPK pathways are important in the early response to FLUA.

Overexpression of RhoA promotes the proliferation and migration of cervical cancer cells

The pro-oncogenic role of RhoA has been well identified in other cancers, but rarely in cervical cancer (CC), one of the main causes of cancer-related death in women. In the present study, we identified the overexpression of RhoA and its downstream effectors, ROCK-1 and ROCK-II, in CC specimens using western blotting. Then, we determined the effect of RhoA on the proliferation and migration of Hela cells, one of CC cell lines, by upregulating or downregulating the RhoA expression in Hela cells. We found that there was an overexpression of RhoA, ROCK-I/II in CC, which was associated with the progression of CC. And we confirmed that RhoA promoted the proliferation and migration of CC cells. In conclusion, we found a positive correlation among RhoA with the progression of CC by in vivo and in vitro evidences. A high RhoA expression in CC may predict a high metastatic potential of CC.

Co-stimulation with stem cell factor and erythropoietin enhances migration of c-Kit expressing cervical cancer cells through the sustained activation of ERK1/2

The cytokines erythropoietin (Epo) and stem cell factor (SCF), coupled with the cooperation between their receptors (EpoR and c-Kit), are essential components of normal physiological erythropoiesis. In earlier studies, we demonstrated the expression of c-Kit and EpoR in cervical cancer cells. It was identified that SCF is a survival factor, whereas Epo promotes cell proliferation. Cooperation between EpoR and SCF in cervical cancer has rarely been studied, despite the fact that cell migration and anchorage independent growth are considered initial steps in metastasis. Thus, the aim of this study was to analyse the effect of SCF and Epo alone, or in combination, on the migration and anchorage independent growth of two cervical cancer-derived cell lines. First, we demonstrated the expression of EpoR and c-Kit in the cell lines. Next, we evaluated anchorage independent growth, and identified that Epo and SCF produced a modest number of colonies, whereas the combination Epo/SCF induced a significantly higher number of colonies. Migration was then evaluated in Boyden chambers. Co-stimulation with Epo/SCF induced a significantly higher number of migrating cells than either cytokine alone. SCF-, Epo- and Epo/SCF-induced migration was inhibited by blocking phosphorylation of Janus kinase 2 (JAK2). Accordingly, western blot analysis demonstrated that the JAK2/signal transducer and activator of transcription-5 (STAT5) axis was activated in all cases. By contrast, inhibition of extracellular signal-related kinase (ERK) 1/2 abrogated migration induced by SCF and Epo/SCF only. Concurrently, Epo induced a modest, transient activation of ERK1/2, whereas SCF and Epo/SCF prompted a strong, sustained phosphorylation of ERK1/2. The results from this study have revealed that co-stimulation with Epo/SCF promotes migration and anchorage independent cell growth, and that co-signalling from EpoR and c-Kit converge on JAK2/STAT5 activation. Furthermore, SCF- and Epo/SCF-induced migration depends on the sustained activation of ERK1/2. These results indicate that co-signalling from different cytokine receptors induces migration, and this suggests that migratory behaviour may be regulated by the cooperative activity of Epo and SCF in cells expressing their cognate receptors.

ROCKing the JAKs

The endocrine cytokine leptin is mainly secreted by white adipose tissue and plasma leptin levels positively correlate with body fat mass. Via its action on neurons in the hypothalamic arcuate nucleus (ARC), leptin regulates body weight by stimulating energy expenditure and inhibiting food intake. The main signaling pathway of the leptin receptor is the JAK2-STAT3 pathway. A recent publication of Huang et al. in Nature Neuroscience shows that leptin’s hypothalamic signaling via JAK2 requires the kinase ROCK1 (Rho-associated coiled-coil-containing protein kinase 1). ROCK1 directly phosphorylates JAK2, and this phosphorylation is required for the JAK2-STAT3 pathway of the leptin receptor. Gene deletion of ROCK1 in ARC neurons targeted by leptin makes these neurons less sensitive to leptin. This is reflected by a pronounced weight gain with hyperphagia, reduced locomotor activity, and increased fat accumulation. In this article we comment on the article of Huang et al. While the mechanism of ROCK1 activation in the neurons remains uncharacterized for the moment, a literature survey suggests that the interplay between ROCK1 and a JAK kinase may be a common theme for receptors that function via a JAK2 and even for other members of the JAK kinase family.

A new mechanism of RhoA ubiquitination and degradation: roles of SCF(FBXL19) E3 ligase and Erk2

RhoA is a small GTPase multifunctional protein that regulates cell proliferation and cytoskeletal reorganization. Regulation of its protein stability plays an important role in its biological functions. We have shown that a Skp1-Cul1-F-box (SCF) FBXL19 E3 ubiquitin ligase targets Rac1, a related member of the Rho family for ubiquitination and degradation. Here, SCF(FBXL19) mediates RhoA ubiquitination and proteasomal degradation in lung epithelial cells. Ectopically expressed FBXL19 decreased RhoA wild type, active, and inactive forms. Cellular depletion of FBXL19 increased RhoA protein levels and extended its half-life. FBXL19 bound the small GTPase in the cytoplasm leading to RhoA ubiquitination at Lys(135). A RhoA(K135R) mutant protein was resistant to SCF(FBXL19)-mediated ubiquitination and degradation and exhibited a longer lifespan. Protein kinase Erk2-mediated phosphorylation of RhoA was both sufficient and required for SCF(FBXL19)-mediated RhoA ubiquitination and degradation. Thus, SCF(FBXL19) targets RhoA for its disposal, a process regulated by Erk2. Ectopically expressed FBXL19 reduced phosphorylation of p27 and cell proliferation, a process mediated by RhoA. Further, FBXL19 cellular expression diminished lysophosphatidic acid (LPA)-induced phosphorylation of myosin light chain (MLC) and stress fiber formation. Hence, SCF(FBXL19) functions as a RhoA antagonist during cell proliferation and cytoskeleton rearrangement. These results provide the first evidence of an F-box protein targeting RhoA thereby modulating its cellular lifespan that impacts cell proliferation and cytoskeleton rearrangement.

Erythropoietin-driven signalling and cell migration mediated by polyADP-ribosylation

Background:

Recombinant human erythropoietin (EPO) is the leading biotechnology engineered hormone for treatment of anaemia associated with chronic conditions including kidney failure and cancer. The finding of EPO receptors on cancer cells has raised the concern that in addition to its action in erythropoiesis, EPO may promote tumour cell growth. We questioned whether EPO-induced signalling and consequent malignant cell manifestation is mediated by polyADP-ribosylation.

Methods:

Erythropoietin-mediated PARP (polyADP-ribose polymerase-1) activation, gene expression and core histone H4 acetylation were examined in UT7 cells, using western blot analysis, RT–PCR and immunofluorescence. Erythropoietin-driven migration of the human breast epithelial cell line MDA-MB-435 was determined by the scratch assay and in migration chambers.

Results:

We have found that EPO treatment induced PARP activation. Moreover, EPO-driven c-fos and Egr-1 gene expression as well as histone H4 acetylation were mediated via polyADP-ribosylation. Erythropoietin-induced cell migration was blocked by the PARP inhibitor, ABT-888, indicating an essential role for polyADP-ribosylation in this process.

Conclusions:

We have identified a novel pathway by which EPO-induced gene expression and breast cancer cell migration are regulated by polyADP-ribosylation. This study introduces new possibilities regarding EPO treatment for cancer-associated anaemia where combining systemic EPO treatment with targeted administration of PARP inhibitors to the tumour may allow safe treatment with EPO, minimising its possible undesirable proliferative effects on the tumour.

The effect of erythropoietin on normal and neoplastic cells

Erythropoietin (Epo) is an essential hormone that binds and activates the Epo receptor (EpoR) resident on the surface of erythroid progenitor cells, thereby promoting erythropoiesis. Recombinant human erythropoietin has been used successfully for over 20 years to treat anemia in millions of patients. In addition to erythropoiesis, Epo has also been reported to have other effects, such as tissue protection and promotion of tumor cell growth or survival. This became of significant concern in 2003, when some clinical trials in cancer patients reported increased tumor progression and worse survival outcomes in patients treated with erythropoiesis-stimulating agents (ESAs). One of the potential mechanisms proffered to explain the observed safety issues was that functional EpoR was expressed in tumors and/or endothelial cells, and that ESAs directly stimulated tumor growth and/or antagonized tumor ablative therapies. Since then, numerous groups have performed further research evaluating this potential mechanism with conflicting data and conclusions. Here, we review the biology of endogenous Epo and EpoR expression and function in erythropoiesis, and evaluate the evidence pertaining to the expression of EpoR on normal nonhematopoietic and tumor cells.

Erythropoietin Increases Expression and Function of Transient Receptor Potential Canonical 5 Channels

Hypertension is a common complication in hemodialysis patients during erythropoietin (EPO) treatment. The underlying mechanisms of EPO-induced hypertension still remain to be determined. Increased transient receptor potential canonical (TRPC) channels have been associated with hypertension. Now, TRPC gene expression was investigated using quantitative real-time RT-PCR and immunoblotting in cultured human endothelial cells and in monocytes from hemodialysis patients. EPO dose-dependently increased TRPC5 mRNA in endothelial cells. EPO increased TRPC5 mRNA stability, that is, EPO prolonged the half-life period for TRPC5 mRNA from 16 hours (control) to 24 hours ( P <0.05). The poly(A) tail length was measured by rapid amplification of cDNA ends-poly(A) test. Increased TRPC5 mRNA stability was attributed to longer 3′ poly(A) tail lengths after EPO administration. EPO also significantly increased TRPC5 channel protein abundance by 70% ( P <0.05). Whole-cell patch clamp showed that angiotensin II–induced, TRPC5-mediated currents were dramatically increased in endothelial cells treated with EPO. Fluorescent dye techniques confirmed that increased calcium influx after EPO treatment was abolished after TRPC5 knockdown ( P <0.05). EPO also significantly increased intracellular reactive oxygen species production. Knockdown of TRPC5 alleviated EPO-induced reactive oxygen species generation in endothelial cells ( P <0.05). In vivo, EPO-treated hemodialysis patients showed significantly increased amounts of TRPC5 mRNA in monocytes compared with EPO-free hemodialysis patients (6.0±2.4 [n=12] versus 1.0±0.5 [n=9]; P <0.01). Patients undergoing EPO treatment also showed significantly elevated systolic blood pressure (160±7 versus 139±6 mm Hg; P <0.05). Our findings suggest that upregulated functional TRPC5 gene may be one cause of EPO-induced hypertension in patients with chronic kidney disease.

Association between pharmaceutical support and basic science research on erythropoiesis-stimulating agents

BACKGROUND

To our knowledge, no prior research has evaluated the association between pharmaceutical industry funding and basic science research results. When erythropoiesis-stimulating agents (ESAs) were licensed to treat chemotherapy-associated anemia, basic science concerns related to potential cancer stimulation were raised. We evaluated associations between pharmaceutical industry support and reported findings evaluating ESA effects on cancer cells.

METHODS

Articles identified in MEDLINE and EMBASE databases (1988-2008) investigating basic science findings related to ESA administration in the solid tumor setting were reviewed. Outcomes included information on erythropoietin receptors (EpoRs), Epo-induced signaling events, cellular function, and qualitative conclusions. Information on study funding (academic investigators with no reported funding from ESA manufacturers [64 studies], academic investigators with grant funding from ESA manufacturers [7 studies], and investigators employed by the ESA manufacturers [3 studies]) was evaluated. Some studies did not include information on each outcome.

RESULTS

Investigators without funding from ESA manufacturers were more likely than academic investigators with such funding or investigators employed by ESA manufacturers to identify EpoRs on solid tumor cells (100%, 60%, and 67%, respectively; P = .009), Epo-induced signaling events (94%, 0%, and 0%, respectively; P = .001), or changes in cellular function (57%, 0%, and 0%, respectively; P = .007) and to conclude that ESAs had potentially harmful effects on cancer cells (57%, 0%, and 0%, respectively; P = .008).

CONCLUSIONS

Researchers who do not have pharmaceutical industry support are more likely than those with pharmaceutical support to identify detrimental in vitro effects of ESAs. The potential for conflicts of interest to affect basic science research should be considered.

Erythropoietin-induced activation of the JAK2/STAT5, PI3K/Akt, and Ras/ERK pathways promotes malignant cell behavior in a modified breast cancer cell line

Erythropoietin (Epo), the major regulator of erythropoiesis, and its cognate receptor (EpoR) are also expressed in nonerythroid tissues, including tumors. Clinical studies have highlighted the potential adverse effects of erythropoiesis-stimulating agents when used to treat cancer-related anemia. We assessed the ability of EpoR to enhance tumor growth and invasiveness following Epo stimulation. A benign noninvasive rat mammary cell line, Rama 37, was used as a model system. Cell signaling and malignant cell behavior were compared between parental Rama 37 cells, which express few or no endogenous EpoRs, and a modified cell line stably transfected with human EpoR (Rama 37-28). The incubation of Rama 37-28 cells with pharmacologic levels of Epo led to the rapid and sustained increases in phosphorylation of signal transducers and activators of transcription 5, Akt, and extracellular signal-regulated kinase. The activation of these signaling pathways significantly increased invasion, migration, adhesion, and colony formation. The Epo-induced invasion capacity of Rama 37-28 cells was reduced by the small interfering RNA-mediated knockdown of EpoR mRNA levels and by inhibitors of the phosphoinositide 3-kinase/Akt and Ras/extracellular signal-regulated kinase signaling pathways with adhesion also reduced by Janus-activated kinase 2/signal transducers and activators of transcription 5 inhibition. These data show that Epo induces phenotypic changes in the behavior of breast cancer cell lines and establishes links between individual cell signaling pathways and the potential for cancer spread.

Anaemia: a rare but neglected problem among Finnish patients receiving chemotherapy for solid tumours

GOALS OF THE WORK

Anaemia is very frequently diagnosed among cancer patients. Use of erythropoietins has proved to be effective in reducing the need of transfusions and enhancing patients' quality of life, but may also have detrimental effects in treating nonanemic asymptomatic patients. We assessed the frequency of anaemia and the frequency with which it was diagnosed and treated in different types of solid tumours treated at outpatient chemotherapy policlinics.

MATERIALS AND METHODS

During the study period, altogether 733 consecutive subjects received chemotherapy at the five Finnish University Hospitals. Their data were collected. The physician who was responsible for the chemotherapy treatment was unaware of the survey. The response to anaemia (treated or not, the modality of treatment) were established from patients records; 69% were females, mean age was 61 years (range, 24-92).

RESULTS

The median haemoglobin level was 12.7 g/dL (range, 8.9-15.5 g/dL). About one third of the patients (200/733, 27%) had a value less than 12 g/dL. In only 15% of these cases was there any documentation of response or a possible treatment option for anaemia. On the other hand, only 12% of all patients (N=91) had a haemoglobin value less than 11 g/dL. However, in most of them anaemia had not been considered; in only 25% of cases was an active treatment option selected.

CONCLUSIONS

According to our survey, anaemia was less common in our patients than in the European Cancer Anaemia Survey. Only a minority of chemotherapy patients receiving their treatments as outpatients would need active treatment for their anaemia.

Anti-glycophorin single-chain Fv fusion to low-affinity mutant erythropoietin improves red blood cell-lineage specificity

The presence of erythropoietin (Epo) receptors on cells besides red blood cell precursors, such as cancer cells or megakaryocyte precursors, can lead to side effects during Epo therapy including enhanced tumor growth and platelet production. It would be ideal if the action of Epo could be limited to erythroid precursors. To address this issue, we constructed single-chain variable fragment (scFv)-Epo fusion proteins that used the anti-glycophorin 10F7 scFv amino-terminal to Epo analogues that would have minimal activity alone. We introduced the Epo mutations N147A, R150A and R150E, which progressively weakened receptor affinity in the context of Epo alone, as defined by cell proliferation assays using TF-1 or UT-7 cells. Fusion of these mutant proteins to the 10F7 scFv significantly rescued the activity of the mutant proteins, but had a relatively small effect on wild-type Epo. For example, fusion to the 10F7 scFv enhanced the activity of Epo(R150A) by 10- to 27-fold, while a corresponding fusion to wild-type Epo enhanced its activity only up to 2.7-fold. When glycophorin was blocked by antibody competition or reduced by siRNA-mediated inhibition of expression, the activity of 10F7 scFv-Epo(R150A) was correspondingly reduced, while such inhibition had essentially no effect on the activity of 10F7 scFv-Epo(wild-type). In addition, potent stimulation of Epo receptors by 10F7 scFv-Epo(R150A) was observed in long-term proliferation and viability assays. Taken together, these results indicate that a combination of targeting and affinity modulation can be used to engineer forms of Epo with enhanced cell-type specificity.

Anemia management in oncology and hematology

Anemia is frequent in cancer patients and its incidence increases with chemotherapy. The probability of requiring transfusions also increases with chemotherapy. Anemia negatively impacts survival and accentuates fatigue in cancer patients. Cancer promotes inflammatory cytokine production, which suppresses erythropoiesis and erythropoietin (EPO) production. Erythropoiesis-stimulating agents (ESAs) improve erythropoiesis and reduce transfusion needs in anemic cancer patients receiving chemotherapy. However, meta-analyses have shown an increased risk of thromboembolic (TE) events with ESA use during chemotherapy, but not increased on-study mortality or reduced overall survival. Three reasons have been proposed to explain why ESAs might have adverse effects in anemic cancer patients: tumor progression due to stimulation of tumor cell EPO receptors; increased risk of TE; and reduced survival. However, erythropoietin is not an oncogene, nor is the EPO receptor. It has also been demonstrated that erythropoietin does not stimulate tumor proliferation. Increased TE risk associated with ESAs is probably a consequence of increased blood viscosity due to excessive RBC mass elevation with concomitant plasma volume contraction, nitric oxide scavenging, and endothelial cell activation. Increased ESA dosing may also impact survival negatively because EPO contracts the plasma volume and stimulates inflammatory cytokine production independently of increasing erythropoiesis. Furthermore, transfusions themselves are associated with an increase in TE and plasma volume contraction, and these events are potentiated when ESAs are given with transfusions. An update on the management of anemia in oncology, the potential adverse events of ESAs, the benefits and risks of transfusions, and QoL are discussed in this paper.

Sphingosine kinase as an oncogene: autocrine sphingosine 1-phosphate modulates ML-1 thyroid carcinoma cell migration by a mechanism dependent on protein kinase C-alpha and ERK1/2

Sphingosine 1-phosphate (S1P) induces migration of the human thyroid follicular carcinoma cell line ML-1 by activation of S1P(1) and S1P(3) receptors, G(i) proteins, and the phosphatidylinositol 3-kinase-Akt pathway. Because sphingosine kinase isoform 1 (SK) recently has been implicated as an oncogene in various cancer cell systems, we investigated the functions of SK in the migration, proliferation and adhesion of the ML-1 cell line. SK overexpressing ML-1 cells show an enhanced secretion of S1P, which can be attenuated, by inhibiting SK activity and a multidrug-resistant transport protein (ATP-binding cassette transporter). Furthermore, overexpression of SK enhances serum-induced migration of ML-1 cells, which can be attenuated by blocking ATP-binding cassette transporter and SK, suggesting that the migration is mediated by autocrine signaling through secretion of S1P. Inhibition of protein kinase C alpha, with both small interfering RNA (siRNA) and small molecular inhibitors attenuates migration in SK overexpressing cells. In addition, SK-overexpressing cells show an impaired adhesion, slower cell growth, and an up-regulation of ERK1/2 phosphorylation, as compared with cells expressing a dominant-negative SK. Taken together, we present evidence suggesting that SK enhances migration of ML-1 cells by an autocrine mechanism and that the S1P-evoked migration is dependent on protein kinase C alpha, ERK1/2, and SK.

Biological functions and therapeutic use of erythropoiesis-stimulating agents: perplexities and perspectives

Randomized clinical studies, carried out in patients with haematological malignancies and with solid tumours, have consistently demonstrated that treatment with recombinant human erythropoietin (Epo) increases haemoglobin levels, reduces blood transfusion requirements, and improves the quality of life. In addition, identification of erythropoietin receptor (EpoR) expression on many types of non-erythroid and cancer cells has spurred an interest in the extra-haematological activities of Epo itself and other erythropoiesis-stimulating agents (ESAs). Epo and its derivatives have emerged as major tissue-protective cytokines in ischaemic and degenerative damage of cardiovascular, neurological and renal diseases, while their angiogenetic and immunomodulatory properties indicate that their therapeutic potential may extend well beyond erythropoiesis alone. Both preclinical and clinical data, however, have suggested that they may contribute to tumour progression and prejudice survival when administered to anaemic cancer patients, though the results are equivocal and the assumed mechanisms by which tumour growth could be promoted are not fully understood. While these findings offer new perspectives, they nonetheless demand caution in the employment of ESAs. Further, well-designed experimental and clinical studies are warranted.

The role of erythropoietin as an inhibitor of tissue ischemia

Erythropoietin is a hypoxia-induced cytokine that stimulates erythropoiesis through the promotion of erythroid precursor cell proliferation and differentiation. Recent evidence supports that erythropoietin has a broad spectrum of tissue protecting actions affecting other systems than hemopoietic. Lately, research has focused on the nonhemopoietic effects of erythropoietin against tissue ischemia due to the unexpected observations of erythropoietin receptor expression by various cells, such as endothelial cells, neuronal cells, cardiac myocytes, and vascular smooth muscle cells. It has been shown that erythropoietin exerts its cardioprotective action during cardiac ischemic injury through reducing the infract size and enhancing new vessel formation over a longer time frame. Erythropoietin plays a crucial role in neuroprotection in many types of ischemic injury in the central and the peripheral nervous system. It is also strongly believed that erythropoietin exhibits a critical role in many other disorders that are pathogenetically related to acute tissue ischemia. This article reviews the proposed implications of erythropoietin in tissue ischemia and discusses the possible mechanisms for this action along with its potential therapeutic applications.