Erythropoietin signaling promotes invasiveness of human head and neck squamous cell carcinoma

RNA interference-mediated inhibition of erythropoietin receptor expression suppresses tumor growth and invasiveness in A2780 human ovarian carcinoma cells

Although recombinant human erythropoietin (rHuEpo) has revolutionized the treatment of anemia, recent clinical trials suggested that rHuEpo use may be associated with decreased survival in cancer patients. Although the expression of erythropoietin (Epo) receptor (EpoR) has been demonstrated in various human cancers, the effect of exogenous Epo on the growth and therapy resistance of EpoR-bearing tumor cells is unclear at present. In the current study, we examined the hypothesis that EpoR may contribute to tumor growth independent of Epo in A2780 human ovarian carcinoma cells. A2780 human ovarian carcinoma cells showed high levels of EpoR expression, but lacked expression of Epo mRNA and biologically active Epo protein under both normoxic and hypoxic conditions. Exogenous Epo did not stimulate EpoR-mediated signaling, proliferation, invasiveness, or resistance to cytotoxic drugs in A2780 cells. In contrast, specific inhibition of EpoR expression using a short hairpin RNA (shRNA) expression plasmid resulted in markedly reduced proliferation and invasiveness in vitro. In addition, inhibition of EpoR expression led to abrogated in vivo ovarian cancer cell growth in a tumor xenograft system and resulted in decreased EpoR signaling. Our findings suggest that EpoR may be constitutively active in some cancer cells in the absence of Epo and provide the first evidence for a potential role of an Epo-independent, EpoR-mediated pathway in the growth of some human cancers.

Erythropoietin receptor is expressed in meningiomas and lower levels are associated with tumour recurrence

AIMS

The Epo-EpoR pathway plays a role in tumour growth, metastasis and treatment resistance and is a potential target in oncological treatment. As the EpoR status in human meningiomas is unknown, our aim was to characterize EpoR expression in these tumours.

METHODS

We examined 131 meningioma samples of all WHO grades from 116 patients by immunohistochemistry for EpoR. Among these, 25 meningiomas showed brain invasion and 29 patients had a further tumour recurrence. A group of 20 patients without tumour recurrence served as controls. In 12 cases we were able to compare both the primary and the following recurrent tumours. The presence of EpoR in meningiomas was confirmed by RT-PCR and Western blot.

RESULTS

EpoR was expressed in all meningiomas. Statistical analysis revealed that the mean expression levels of EpoR were significantly lower in primary tumours with known recurrence compared with a recurrence-free control group. Additional matched pair analysis in individual cases showed no significant differences between primary and recurrent tumours. No significant correlation between EpoR expression and WHO grade, age, sex or brain invasion was detected. Using specific primer pairs for RT-PCR, we were able to detect all three known isoforms of EpoR: the full-length isoform EpoR-F, the truncated isoform EpoR-T and the soluble isoform EpoR-S.

CONCLUSIONS

Our results demonstrate the expression of EpoR in meningiomas. Lower EpoR mean levels might be a useful marker for a higher recurrence risk, but further studies are needed to clarify the influence of EpoR on recurrences and the role of the different isoforms.

Constitutively active erythropoietin receptor expression in breast cancer cells promotes cellular proliferation and migration through a MAP-kinase dependent pathway

The role of erythropoietin receptor (EpoR) expression in tumor cells and the potential of EpoR-mediated signaling to contribute to cellular proliferation and invasiveness require further characterization. To determine whether EpoR expression and activation in tumor cells modulates intracellular signal transduction to promote cellular proliferation and migration, we employed a novel experimental model using human breast cancer cells engineered to stably express a constitutively active EpoR-R129C variant. EpoR-R129C expression resulted in increased cellular proliferation and migration of breast cancer cells and these effects were associated with significantly increased Epo-induced phosphorylation of ERK1/2, AKT and c-Jun-NH2-kinase (SAPK/JNK) proteins. Expression of the constitutively active EpoR-R129C receptor promoted the proliferation and migration of breast cancer cells via activation of ERK- and SAPK/JNK-dependent signaling pathways, respectively. These findings suggest that EpoR over-expression and activation in breast cancer cells has the potential to contribute to tumor progression by promoting the proliferation and invasiveness of the neoplastic cells.

Differential up-regulation of erythropoietin and its receptor in benign and malignant prostatic tissue

PURPOSE

To investigate differential up-regulation of erythropoietin and its receptor in benign and malignant prostatic tissue.

MATERIALS AND METHODS

An immunohistochemical analysis of EPO and EPOR expression was performed on 30 cases of prostate carcinoma (PCa) with 16 high-grade prostate intraepithelial neoplasia (PIN), 50 cases of benign prostatic hyperplasia (BPH) lesions, and 30 normal prostatic tissue samples as control.

RESULTS

Over-expression of EPOR was only shown in PCa and high-grade PIN tissue but over-expression of EPO was also shown in BPH tissue. There was significant relationship between EPO and EPOR score in BPH, high-grade PIN, and PCa but no association between EPOR or EPO score and Gleason score in PCa.

CONCLUSIONS

Up-regulation of EPOR has a more important role in comparison with EPO in prostate carcinogenesis. Differential over-expression of EPOR and EPO in benign and malignant prostatic tissue is ascribed to different mechanisms involved in up-regulation between EPO and EPOR.

EPO-R expression patterns in resected gastric adenocarcinoma followed by adjuvant chemoradiation treatment

The primary aim was to determine whether Epo-R immunohistochemical expression is related to disease free survival (DFS) in specimens of GC from patients who underwent adjuvant chemoradiation. Specimens of gastric adenocarcinomas obtained from 44 patients who had undergone curative gastrectomy and adjuvant treatment were investigated immunohistochemically expression of Epo-R. Three patterns for Epo-R staining were defined: Pattern A (secretory cells-like staining), Pattern B (parietal-like staining) and Pattern C (chief-like staining). Median DFS was 38 months (CI 95%: 33-43) and 15 months (IC 95%: 3-27) in the pattern B and C, respectively, but it was not reached in the pattern A (p = 0.06). Our findings suggest that there may be a relationship between Epo-R expression and DFS in the patients with GC resected.

Secondary analysis of the CHOIR trial epoetin-alpha dose and achieved hemoglobin outcomes

Trials of anemia correction in chronic kidney disease have found either no benefit or detrimental outcomes of higher targets. We did a secondary analysis of patients with chronic kidney disease enrolled in the Correction of Hemoglobin in the Outcomes in Renal Insufficiency trial to measure the potential for competing benefit and harm from achieved hemoglobin and epoetin dose trials. In the 4 month analysis, significantly more patients in the high-hemoglobin compared to the low-hemoglobin arm were unable to achieve target hemoglobin and required high-dose epoetin-alpha. In unadjusted analyses, the inability to achieve a target hemoglobin and high-dose epoetin-alpha were each significantly associated with increased risk of a primary endpoint (death, myocardial infarction, congestive heart failure or stroke). In adjusted models, high-dose epoetin-alpha was associated with a significant increased hazard of a primary endpoint but the risk associated with randomization to the high hemoglobin arm did not suggest a possible mediating effect of higher target via dose. Similar results were seen in the 9 month analysis. Our study demonstrates that patients achieving their target had better outcomes than those who did not; and among subjects who achieved their randomized target, no increased risk associated with the higher hemoglobin goal was detected. Prospective studies are needed to confirm this relationship and determine safe dosing algorithms for patients unable to achieve target hemoglobin.

Unraveling the Mystery of Erythropoietin-Stimulating Agents in Cancer Promotion

Erythropoietin-stimulating agents (ESA) are approved for use in treating chemotherapy-induced anemia in patients with nonmyeloid malignancies. However, recent clinical trials have shown evidence of inferior overall survival and/or locoregional control of tumors in patients receiving ESAs. Given these concerning data, current studies are focused on elucidating the biological mechanisms by which ESAs may contribute to cancer promotion. Evidence suggests that ESAs activate several signaling pathways that are important in altering tumor behavior and response to treatment. Although further research is needed to more precisely elucidate these mechanisms, caution should be exercised in the use of ESAs beyond their approved indication in cancer patients. [Cancer Res 2008;68(11):4013–7]

STAT3: a critical transcription activator in angiogenesis

Angiogenesis, the formation of new blood vessels from the pre-existing vasculature, is a complex multistage process regulated by a number of signal transduction pathways. Accumulating evidence suggests that signal transducer and activator of transcription (STATs), mainly STAT3, play an important role in angiogenesis under both physiological and pathological conditions in addition to cell survival, proliferation, differentiation, and oncogenesis. STAT3, as a critical multifunctional mediator, regulates many aspects of angiogenesis at the transcriptional level. This review will highlight the pivotal role of STAT3 in well-studied tumorous angiogenesis and cardiac angiogenesis, and summarize various potential mechanisms utilized by STAT3 to regulate the transcriptional activation of VEGF.

Erythropoietin and erythropoietin receptor in colorectal cancer

Erythropoietin via erythropoietin receptor effectively prevents anemia, giving reasons for a clinical use of erythropoietin in patients with colorectal cancers. However, erythropoietin seems to promote survival of the neoplastic cells in hypoxic environment. The aim of this study was to evaluate immunohistochemically the expression of erythropoietin and erythropoietin receptor in 136 primary colorectal cancers with a correlation to different anatomo-clinical features. Erythropoietin correlated with erythropoietin receptor in colorectal cancers (r = 0.547, P < .00001). Erythropoietin and erythropoietin receptor expressions were statistically higher in adenocarcinomas versus mucinous carcinomas (P = .05 and P = .03, respectively) and in moderately (G2) versus poorly differentiated (G3) tumors (P = .001 and P = .02, respectively). This in vivo study is the first study that provides evidences for the presence of erythropoietin and erythropoietin receptor in human colorectal cancer. The expressions of these proteins strictly depended on grading because the better histological differentiation probably comes from trophic influence of erythropoietin and erythropoietin receptor.

The erythropoietin receptor in normal and cancer tissues

The hormone erythropoietin (EPO) is essential for the survival, proliferation and differentiation of the erythrocytic progenitors. The EPO receptor (EPO-R) of erythrocytic cells belongs to the cytokine class I receptor family and signals through various protein kinases and STAT transcription factors. The EPO-R is also expressed in many organs outside the bone marrow, suggesting that EPO is a pleiotropic anti-apoptotic factor. The controversial issue as to whether the EPO-R is functional in tumor tissue is critically reviewed. Importantly, most studies of EPO-R detection in tumor tissue have provided falsely positive results because of the lack of EPO-R specific antibodies. However, endogenous EPO appears to be necessary to maintain the viability of endothelial cells and to promote tumor angiogenesis. Although there is no clinical proof that the administration of erythropoiesis stimulating agents (ESAs) promotes tumor growth and mortality, present recommendations are that (i) ESAs should be administered at the lowest dose sufficient to avoid the need for red blood cell transfusions, (ii) ESAs should not be used in patients with active malignant disease not receiving chemotherapy or radiotherapy, (iii) ESAs should be discontinued following the completion of a chemotherapy course, (iv) the target Hb should be 12 g/dL and not higher and (v) the risks of shortened survival and tumor progression have not been excluded when ESAs are dosed to target Hb <12 g/dL.

Role of erythropoietin in cancer-related anaemia: a double-edged sword?

Anaemia often occurs in cancer patients and its origin is multifactorial, resulting from either bone marrow infiltration of cancer cells or cytotoxic effects produced by chemotherapy and radiotherapy. Anaemia impacts significantly on quality of life and appears markedly to limit disease control. Erythropoietin stimulates erythrocyte formation and the human recombinant form is useful in treating anaemia in cancer patients. Over the past decade erythropoietin has been associated with amelioration of anaemia and reduced need for blood transfusions. Nevertheless, several pre-clinical and clinical trials, employing relatively high doses of erythropoietin, have been halted recently following increased mortality and morbidity, primarily due to thrombotic events and possible tumour growth stimulation. It is, therefore, too early to know whether erythropoietin is useful in controlling morbidity and mortality in cancer-related anaemia. The risk-benefit of erythropoietic agents should be studied in carefully controlled trials. This review discusses prevalent issues and addresses key questions concerning the use of erythropoietic agents for the treatment of cancer-related anaemia.

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

Erythropoietin (Epo) receptor (EpoR) is expressed in several cancer cell lines, and the functional consequence of this expression is under extensive study. In this study, we used a cervical cancer cell line in which EpoR was first found to be expressed and to correlate with the severity of the disease. We demonstrate that Epo is a chemoattractant for these cancer cells, enhancing their migration under serum-starved conditions. Using a Transwell migration system, we show that Epo enhances cancer cell migration in a dose- and time-dependent manner. The effect of Epo is dependent on the activity of two signaling pathways: the mitogen-activated protein kinase (MAPK) pathway and the RhoA GTPase pathway. We show that Epo activates both pathways in a Janus kinase-dependent manner and that this activation is required for Epo effects on cell migration. Furthermore, we use both pharmacological and genetic inhibitors to demonstrate that the activation of RhoA GTPase is dependent on the activity of the MAPK pathway, providing the first evidence for interaction between these two signaling cascades.

Expression of erythropoietin receptor and in vitro functional effects of epoetins in B-cell malignancies

PURPOSE

Erythropoietin (EPO) and EPO receptor (EPO-R) expression have been reported in solid tumors and are claimed to regulate tumor growth; however, no data have been published on this issue in B-cell malignancies or normal lymphoid cells. This report describes genomic/protein EPO-R expression and in vitro effects of recombinant human EPO (epoetin) in B-cell chronic lymphocytic leukemia (B-CLL), mantle-cell lymphoma (MCL), and multiple myeloma (MM).

EXPERIMENTAL DESIGN

Blood samples were obtained from patients with B-CLL, MCL, and healthy volunteers, and bone marrow was obtained from MM patients. EPO-R mRNA was detected by reverse transcription-PCR. EPO-R surface expression was investigated by flow cytometry using digoxigenin-labeled epoetin and polyclonal rabbit anti-EPO-R antibody for intracellular receptor. Tumor cell stimulation was determined in vitro using [(3)H]thymidine incorporation and CD69 expression after exposure to epoetin alpha or beta or darbepoetin alpha.

RESULTS

EPO-R mRNA was detected in mononuclear cells from 32 of 41 (78%) B-CLL and 5 of 7 (71%) MCL patients, and 21 of 21 (100%) MM samples. Expression was also detected in highly purified T cells from six of eight B-CLL patients, four of four MM patients, and normal donor B and T cells. Surface EPO-R protein was not detected. Intracellular EPO-R staining with anti-EPO-R antibodies was unspecific. No tumor-stimulatory effect was observed with high epoetin concentrations.

CONCLUSIONS

EPO-R gene is frequently expressed in lymphoid malignancies and normal B and T cells. However, there was no surface protein expression and no epoetin-induced in vitro stimulation of tumor B cells, indicating that epoetin therapy in vivo is likely to be safe in patients with lymphoid malignancies.

Erythropoietin and erythropoietin receptor coexpression is associated with poor survival in stage I non-small cell lung cancer

PURPOSE

This study was designed to evaluate the prognostic effect of erythropoietin (EPO) and EPO receptor (EPO-R) expression in stage I non-small cell lung cancer (NSCLC) patients.

EXPERIMENTAL DESIGN

EPO and EPO-R expression in 158 tumor samples from resected stage I NSCLC was evaluated using immunohistochemistry and tissue array technology.

RESULTS

EPO-R and EPO were highly expressed in 20.9% and 35.4% of tumors, respectively. High EPO-R expression compared with negative or low-level expression was associated with a poor 5-year disease-specific survival (60.6% versus 80.8%; P = 0.01, log-rank test). High EPO expression compared with negative and low-level expression was associated with a trend toward a poor 5-year disease-specific survival (69.6% versus 80.4%; P = 0.13, log-rank test). A high level of EPO-R and EPO coexpression was associated with a poor 5-year disease-specific survival compared with other groups of patients (50.0% versus 80.0% survival at the end of follow-up; P = 0.005, log-rank test). In multivariate analysis for disease-specific survival, high-level EPO-R and EPO coexpression was an independent prognostic factor for disease-specific survival (hazard ratio, 2.214; 95% confidence interval, 1.012-4.848; P = 0.046).

CONCLUSION

These results establish the pejorative prognostic value of EPO and EPO-R expression in early-stage resected NSCLC and suggest a potential paracrine and/or autocrine role of endogenous EPO in NSCLC aggressiveness.

Does erythropoietin have a dark side? Epo signaling and cancer cells

Erythropoietin (Epo) stimulates red blood cell production by docking with its cognate receptor on the erythroid progenitor cell and triggering an array of signaling pathways that inhibit apoptosis and promote cell proliferation and differentiation. In its pharmaceutical forms, epoetin and darbepoetin, Epo is widely used to treat various anemias, including those associated with cancer. The Epo receptor is also expressed by nonhematopoietic cells, including cancer cells, and Epo exhibits a "tissue-protective" effect on nonhematopoietic tissues, possibly mediated through a novel heteroreceptor, blocking apoptosis induced by a variety of insults. The unexpected results of several clinical studies in which Epo was used to treat cancer patients have now raised the question of a potential direct growth-promoting action of Epo on cancer cells.

Survival and invasiveness of astrocytomas promoted by erythropoietin

OBJECT

The hypoxia-inducible pleiotropic hormone, erythropoietin (EPO), has recently been found to promote the development and survival of neurons and astrocytes. Since hypoxia has been implicated in the malignant progression of some human cancers, the authors investigated whether EPO signaling influenced the malignant properties of human astrocytoma cells.

METHODS

Reverse transcriptase-polymerase chain reaction, Western blot analysis, and immunohistochemical studies were used to measure EPO and its receptor (EPOR). Cell viability, Matrigel invasion assays, metalloprotease assays, EPO neutralizing antibodies, and EPOR overexpression were used to study the biological actions of EPO. Expression of both EPO and EPOR was observed in the hypoxic regions and invasive margins of glioma specimens obtained at biopsy, and expression of EPOR correlated with the stage of the tumor. The EPOR was also functionally upregulated by hypoxia in cultured glioblastoma multiforme (GBM) cells. Both hypoxia and EPO protected cultured GBM cells from cisplatin cytotoxicity and promoted the invasiveness of GBM cells through Matrigel by potentiating metalloprotease activity. Hypoxia-enhanced cell invasion was attenuated in cells that overexpressed a nonfunctional EPOR.

CONCLUSIONS

Hypoxia-inducible autocrine and paracrine EPO signaling participates in the malignant progression of GBMs.

Interrelation of directly measured oxygenation levels, erythropoietin and erythropoietin receptor expression in spontaneous canine tumours

The expression of the hypoxia-inducible protein erythropoietin in tumour cells correlates with levels of tumour hypoxia. Our aim was to look for an interrelation of directly measured oxygenation levels, the presence of tissue erythropoietin and its receptor. Data of tumour oxygenation status, plasma and tissue erythropoietin and its receptor in a group of spontaneously occurring tumours in 15 dogs were collected. Polarographic tumour oxygen partial pressure measurements were obtained and data were correlated. Significant positive correlations were found between tissue erythropoietin and the percentages of pO2 values < or = 10 mmHg. Multivariate analysis revealed no parameters influencing plasma erythropoietin levels. Our results show that a co-expression of erythropoietin receptor and its ligand in spontaneous canine tumours exists, that the level of hypoxia in tumour cells correlates with the level of tissue erythropoietin and suggest the need to be quantitatively and functionally tested as novel prognostic biological parameters in neoplastic tissues.

Erythropoietin activates the phosphoinositide 3-kinase/Akt pathway in human melanoma cells

Erythropoietin (Epo) is used commonly to treat cancer and/or therapy-related anemia. Until recently, Epo was considered to be a specific stimulator of erythropoiesis, acting via its receptor, EpoR. It becomes clear, however, that EpoR is expressed in a variety of cell types other than hematopoietic cells, and that Epo is a potent cytoprotective cytokine increasing cell survival under hypoxic conditions. Epo and EpoR are also expressed in various malignant tumors, and EpoR expression shows association with tumor invasion and progression. Recently, a functional Epo autocrine signaling mechanism was also detected in human melanoma cells. In this study, we examined the hypothesis that Epo activates the Akt signaling pathway in human melanoma cells and thus promotes the survival of tumor cells. The Akt signaling pathway in response to Epo was examined in melanoma. Similar to Epo, the expression of EpoR was up-regulated in response to hypoxia and Epo stimulation in melanoma cells. Melanoma cells constitutively expressed Akt with variable expression of mammalian target of rapamycin, and Epo dose-dependently induced their activity. Epo increased Akt kinase activity, which was abrogated by co-treatment with LY294002, a specific blocker of phosphoinositide 3-kinase. LY294002 also inhibited the cytoprotective effects of Epo in melanoma cells under both normoxic and hypoxic conditions. Our results suggest that Epo promotes melanoma cell survival by activating an Akt-dependent signaling pathway.

Recombinant erythropoietin beta enhances growth of xenografted human squamous cell carcinoma of the head and neck after surgical trauma

CONCLUSION

Treatment of anaemia with recombinant human erythropoietin beta (rHuEpo) in patients with squamous cell carcinoma of the head and neck (HNSCC) undergoing curative radiotherapy does not improve cancer control. In fact, incompletely resected patients with HNSCC receiving radiation in combination with rHuEpo showed poorer loco-regional progression-free survival than patients receiving radiation in combination with placebo. It could be hypothesized that the effects of rHuEpo on tumour cell growth might only be manifested in vivo and after cell trauma, and that treating anaemia with rHuEpo might contribute to poor outcome after incomplete surgical resection.

OBJECTIVE

The aim of the present study was to examine the effect of rHuEpo alone and in combination with surgical trauma on the growth of human squamous cell carcinoma in vivo, xenografted onto nude mice.

MATERIALS AND METHODS

The surgical trauma was inflicted through subcutaneous transection of the tumour with a needle. Immunohistochemical staining verified expression of the EPO receptor in tumour cells.

RESULTS

rHuEpo alone had no effect on the growth of xenografted HNSCC. However, a significant increase in tumour growth was observed after surgical trauma in combination with rHuEpo compared with surgery alone (p = 0.0008).

Relation of erythropoietin and erythropoietin receptor expression to hypoxia and anemia in head and neck squamous cell carcinoma

PURPOSE

The use of erythropoietin in head and neck squamous cell carcinoma (HNSCC) has been associated with poor survival. This study examines the protein and mRNA expression of erythropoietin and erythropoietin receptor in HNSCC and their relation to hypoxia, hemoglobin (Hb), and clinical outcome.

EXPERIMENTAL DESIGN

The immunohistochemical expression of erythropoietin and erythropoietin receptor was assessed in 151 cases of HNSCC. Expression was compared with the hypoxia-dependent proteins hypoxia-inducible factor-1alpha (HIF-1alpha) and carbonic anhydrase-9 (CA-9) and correlated with clinical outcome. The mRNA expression of erythropoietin and erythropoietin receptor was measured in paired samples of HNSCC.

RESULTS

Erythropoietin and erythropoietin receptor were expressed in 95% and 99% of tumors, respectively. Using a weighed expression score, there was a positive correlation between erythropoietin and erythropoietin receptor expression (r = 0.18, P = 0.03). HIF-1alpha (r = 0.38, P < 0.01) and CA-9 (r = 0.26, P = 0.002) correlated with erythropoietin expression, but there was no correlation with erythropoietin receptor. No correlation was found between Hb and erythropoietin (r = 0.07, P = 0.36) or erythropoietin receptor (r = -0.02, P = 0.8), and no survival difference between high and low erythropoietin or erythropoietin receptor expression (P = 0.59 and P = 0.98, respectively). The mRNA expression of erythropoietin (P = 0.03) but not erythropoietin receptor (P = 0.62) was significantly increased in 11 paired samples of HNSCC.

CONCLUSION

In vivo, the HIF pathway regulates erythropoietin at the mRNA level but not erythropoietin receptor expression in HNSCC. Anemia does not seem to influence the hypoxic microenvironment of tumors sufficiently to alter the expression of erythropoietin. The effects of exogenous erythropoietin may be acting via receptors expressed on tumor cells in vivo, or on vascular cells, which also express the pathway.

The role of the phosphatidylinositide 3-kinase–protein kinase B pathway in schizophrenia

Neuroanatomical studies of brains from schizophrenic patients report evidence for neuronal dystrophy, while in genetic studies in schizophrenia there is evidence for mutations in growth factors and the downstream enzymes phosphatidylinositide 3-kinase (PI3K) and protein kinase B (PKB). Since the PI3K-PKB pathway is involved in cellular growth and proliferation, reduced activity of this cascade in schizophrenia could at least partly explain the neuronal dystrophy. Risk factors for schizophrenia, such as corticosteroids and cannabis, suppress the activity of the PI3K-PKB pathway. Conversely, estrogen and vitamin D, 2 factors with a moderate protective activity in schizophrenia, electroconvulsive shock therapy, and chronic treatment with antipsychotic compounds stimulate the pathway. Reduced activity of the PI3K-PKB pathway makes the brain more susceptible to virus infections, anoxia, and obstetric complications (recognized risk factors for schizophrenia), whereas a diminution of growth factor levels towards the end of puberty could contribute to an increase in schizophrenia symptoms observed around that time. On the other hand, constitutive (over)activation of the PI3K-PKB pathway increases cancer risk. Consequently, the presumed hypoactivity of the PI3K-PKB cascade might provide a partial explanation for the remarkable epidemiological finding of a reduced cancer rate in schizophrenic patients. Recognition of the role of a dysfunctional PI3K-PKB pathway in schizophrenia might help in the discovery of hitherto undetected causative gene mutations and could also lead to novel therapeutic approaches. However, a major challenge that remains to be solved is how the PI3K-PKB pathway can be activated without increasing the risk of cancer.

Erythropoietin biology in cancer

Erythropoietin (Epo) has long been known to be the principal hematopoietic growth factor that regulates cellular proliferation and differentiation along the erythroid lineage. Recent studies have shown that Epo is a pleiotropic cytokine that is proangiogenic and exerts broad tissue-protective effects in diverse nonhematopoietic organs. Recombinant Epo (rEpo) has been widely used in the clinic to prevent or treat malignancy-associated anemia. A series of clinical trials have documented the efficacy of rEpo in reducing RBC transfusion requirements and improving quality of life in cancer patients, and a recent meta-analysis suggested a positive effect on survival. However, two randomized trials reported negative outcomes with rEpo, as patients in the rEpo arm fared worse than their placebo-treated counterparts with respect to progression-free survival. The expression of Epo receptor (EpoR) in cancer cells has raised the possibility that exogenous rEpo may exert direct effects on tumor cells associated with the potential for stimulation of proliferation, inhibition of apoptosis, or modulation of sensitivity to chemoradiation therapy. The presence of an autocrine-paracrine Epo-EpoR system in tumors and potential effects of Epo on tumor microenvironment and angiogenesis are consistent with a complex biology for Epo-EpoR signaling in cancer that requires further research. This review describes Epo and EpoR biology, focusing on the pleiotropic effects of Epo on nonhematopoietic tissues as well as the expression and function of EpoR in cancer cells.