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
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