The identification of erythropoietin receptors (EpoR) on cancer cells has caused concern, since it implies the possibility that treatment of cancer patients with erythropoietin (Epo) and related agents with demonstrable antiapoptotic activity could enhance cancer growth and progression. However, the function and even the validity of the identification of these receptors have been called into question. We now report the characterization of EpoR and Epo expression by 4 human ovarian cancer cell lines: A2780, CaOV, SKOV and OVCAR-3. Using semiquantitative RT-PCR, restriction digestion of the PCR products and DNA sequence analysis, we determined that each of the lines expresses the EpoR and Epo at the mRNA level. A2780 cells were the highest expressers of both genes. We demonstrated EpoR protein both by western blotting and by immunofluorescence and biologically active Epo protein by quantitative in vitro bioassay. The EpoR on A2780 cells was shown to be functional, since Epo stimulation resulted in phosphorylation of Erk1/2, an important EpoR mitogenic signaling intermediate. None of the cell lines exhibited a growth response in culture to exogenous Epo. However, addition of a neutralizing anti-Epo antibody to A2780 cells resulted in partial growth inhibition that was reversed by the addition of excess Epo, providing evidence for an autocrine/paracrine mechanism of growth enhancement in these cells.
Copyright 2007 Wiley-Liss, Inc.