Abstract 2998: The effect of Erythropoietin on telomerase activity and regulation in non-erythroid and cancer cells
Authors: Uziel Orit , Kanfer Gil , Beery Einat , Nordenberg Jardena , Lahav Meir 
Published: June 2012

Abstract
Background: Erythropoietin (EPO), an erythropoiesis regulating growth factor, is widely used to treat anemia in cancer patients. However clinical studies recently reported that EPO treatment was associated with decreased survival of patients due to cancer progression and aggressiveness. In the light of the major importance of telomerase in cancer biology we assumed that the effects of EPO may be mediated through its effect on telomerase. In this aim we explored the possible effects of EPO on telomerase activation and regulation in non-erythroid and in cancer cells. In addition, we studied the role of telomerase in the effects of EPO on cell migration, sensitivity to cytotoxic drugs and changes in the cell cycle status.
Methods: The experimental system consisted of non-erythroid benign and cancer cell lines: Ba/F3, WTEPO (Ba/F3 expressing the wild type Epo-R), NPVY (WTEPO containing NPVY insertion into Epo-R, increasing its maturation and surface expression). The cells were deprived from growth factors for 16 hours and then grown for additional 24-48 hours in the presence of these factors. The effect of EPO on telomerase activity (TA) was assessed by the TRAP assay and its regulation was evaluated on the transcriptional (by real time PCR) and the post-translational (by Western blot) levels. Cancer cell proliferation was evaluated by the WST-1 and SRB assays, migration by the Boyden chamber and wound healing assays, and response to chemotherapy by assessing proliferation.
Results: EPO (and IL3) increased TA in all four cell lines. TA was correlated with the levels of Epo-R, (NPVY cells). This increase was post-translationally mediated while the transcription of hTERT was not affected. This effect was mediated by Src Lyn phosphorylating AKT and subsequent phosphorylation of telomerase. The cell proliferation also increased concomitantly with telomerase activation. EPO promoted Ewing sarcoma cell migration in both assays. EPO had no effect on the cells sensitivity to cytotoxic drugs and on the cell cycle status.
The inhibition of telomerase modestly repressed the proliferative effect of EPO. However, telomere shortening caused by long term inhibition of the enzyme totally abolished that effect.
Conclusions: This is the first report regarding the effect of EPO on TA and its regulation in non-erythroid and cancer cells. This regulation is not mediated by the major signaling pathway of EPO-R, involving mainly Jak2. Telomerase and intact telomeres may be the mediators of the proliferative effects induced by EPO. In the view of these findings, we propose that the safety of EPO administration in cancer patients requires a better understanding of EPO effect on cancer cell in general and on telomerase activity in particular. Therefore, the effect of EPO on this enzyme may be of clinical importance with translational applications.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2998. doi:10.1158/1538-7445.AM2011-2998