BackgroundErythropoietin receptor (EPOR) is a functional membrane-bound cytokine receptor. Erythropoietin (EPO) represents an important hematopoietic factor for production, maturation and differentiation of erythroid progenitors. In non-hematopoietic tissue, EPO/EPOR signalization could also play cytoprotective and anti-apoptotic role. Several studies identified pro-stimulating EPO/EPOR effects in tumor cells; however, numerous studies opposed this fact due to the usage of unspecific EPOR antibodies and thus potential absence or very low levels of EPOR in tumor cells. It seems that this problem is more complex and therefore we have decided to focus on EPOR expression at several levels such as the role of methylation in the regulation of EPOR expression, identification of possible EPOR transcripts and the presence of EPOR protein in selected tumor cells.MethodsMethylation status was analysed by bisulfite conversion reaction, PCR and sequencing. The expression of EPOR was monitored by quantitative RT-PCR and western blot analysis.ResultsIn this study we investigated the methylation status of exon 1 of EPOR gene in selected human cancer cell lines. Our results indicated that CpGs methylation in exon 1 do not play a significant role in the regulation of EPOR transcription. However, methylation status of EPOR exon 1 was cell type dependent. We also observed the existence of two EPOR splice variants in human ovarian adenocarcinoma cell line - A2780 and confirmed the expression of EPOR protein in these cells using specific A82 anti-EPOR antibody.ConclusionWe outlined the methylation status of all selected cancer cell lines in exon 1 of EPOR gene and these results could benefit future investigations. Moreover, A82 antibody confirmed our previous results demonstrating the presence of functional EPOR in human ovarian adenocarcinoma A2780 cells.

Erythropoietin (EPO) is the main regulator of erythropoiesis, and its receptor (EPOR) is expressed in various tissues, including tumors. Expression of EPOR in breast cancer tissue has been shown to correlate with expression of the estrogen receptor (ER). However, EPOR promotes proliferation in an EPO-independent manner. In patients with breast cancer, EPOR is associated with impaired tamoxifen response in ER-positive tumors, but not in ER-negative tumors. Furthermore, a positive correlation between EPOR/ER status and increased local cancer recurrence has been demonstrated, and EPOR expression is associated with G-protein coupled ER (GPER). Herein, we assessed the effects of EPOR on cell physiology and tamoxifen response in the absence of EPO stimulation using two cell lines that differ only in their EPOR expression status: RAMA 37 cells (low EPOR expression) and RAMA 37-28 cells (high EPOR expression). Alterations in cell growth, morphology, response to tamoxifen cytotoxicity, and EPOR-activated signal transduction were observed. RAMA 37 cells showed higher proliferation capacity without tamoxifen treatment, while RAMA 37-28 cells were more resistant to tamoxifen and proliferated more rapidly in the presence of tamoxifen. EPOR overexpression induced cell-morphology changes upon tamoxifen treatment, which resulted in the production of cell protrusions and subsequent cell death. Short-term treatment with tamoxifen (6 h) prompted RAMA 37 cells to acquired longer protrusions than RAMA 37-28 cells, which indicated a pre-apoptotic stage. Furthermore, prolonged treatment with tamoxifen (72 h) caused a greater reduction in RAMA 37 cell numbers, which indicated a higher rate of cell death. RAMA 37-28 cells showed prolonged activation of AKT signaling. We propose sustained AKT phosphorylation in EPOR-overexpressing cells as a mechanism that can lead to EPOR-induced tamoxifen resistance.

Abstract. The erythropoietin receptor (EpoR) is a member of the cytokine receptor family. The interaction between erythropoietin (Epo) and EpoR is important for the production and maturation of erythroid cells, resulting in the stimulation of hematopoiesis. The fact that EpoR was also detected in neoplastic cells has opened the question about the relevance of anemia treatment with recombinant Epo in cancer patients. Numerous studies have reported pro-stimulating and anti-apoptotic effects of Epo in cancer cells, thus demonstrating EpoR functionality in these cells. By contrast, a previous study claims the absence of EpoR in tumor cells. This apparent discrepancy is based, according to certain authors, on the use of non-specific anti-EpoR antibodies. With the aim of bypassing the direct detection of EpoR with an anti-EpoR antibody, the present authors propose a far-western blot methodology, which in addition, confirms the interaction of Epo with EpoR. Applying this technique, the presence of EpoR and its interaction with Epo in human ovarian adenocarcinoma A2780 and normal human umbilical vein endothelial cells was confirmed. Furthermore, modified immunoprecipitation of EpoR followed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry analysis confirmed a 57 kDa protein as a human Epo-interacting protein in both cell lines. IntroductionErythropoietin (Epo) is a low-molecular weight glycoprotein produced in the kidney by neural peritubular fibroblasts and by the outer medulla (1,2), depending on the amount of oxygen available (3). The Epo hormone facilitates the creation and maturation of erythroid precursors, and stimulates erythropoiesis upon binding to its receptor, known as erythropoietin receptor (EpoR) (4). Recombinant human Epo (rhEpo) is currently available for the treatment of anemia resulted from chronic liver diseases (5) or chronic renal failure (6), and is a good alternative to blood transfusion in cancer-related anemia (7), a frequent symptom of cancer (8) due to chemotherapy (9).The presence of EpoR has been confirmed in numerous tumor cells, with or without the stimulatory effect of Epo on these cells (10-16). While Epo/EpoR signaling in hematopoietic cells is associated with increased cell proliferation and/or survival, the Epo/EpoR signaling pathway in tumor cells does not always lead to increased cell proliferation, but may alter the sensitivity of cancer cells to therapy (17). The role of Epo and EpoR on growth, survival and therapeutic response in human cancer cells has been previously reviewed by Szenajch et al (17) and Debeljak et al (18).In this regard, although certain studies did not confirm a direct stimulatory effect of Epo on tumor cells, there is sufficient evidence of this effect on endothelial cell proliferation and/or tumor angiogenesis. Epo induced angiogenesis in murine hepatic tumors (19)

We have recently shown that erythropoietin receptor (EPOR) protects cancer cells from tamoxifen (TAM)-induced cell death in the absence of erythropoietin (EPO). In this study, we analyzed the effect of EPOR silencing and EPO treatment on the response to TAM in human ovarian adenocarcinoma cells A2780. We demonstrated that the EPOR siRNA silencing decreases cell proliferation and sensitizes and/or potentiates the anti-proliferative effect of TAM on A2780 cells. Similarly, the combined effect of EPO and TAM treatment significantly reduced cell proliferation compared to TAM alone. Our in vitro results indicated the need for further investigation of EPO effects on a similar in vivo model.