Erythropoietin (Epo) is a glycoprotein hormone essential for erythroid progenitor cell survival, proliferation and differentia-

Erythropoietin (Epo) is a critical regulator of erythroid cell proliferation, differentiation and apoptosis. In the form of a recombinant protein, it is widely used to treat various forms of anemia, including that associated with cancer and with the myelosuppressive effects of chemotherapy. Studies of ovarian cancer cell lines have demonstrated the presence of the Epo receptor (EpoR), but there are disagreements regarding its localization and functionality in these cells. Using fluorescence microscopy, we were not able to identify the EpoR on the surface of A2780 cells, in contrast to the positive control K562 cells. Flow cytometry did reveal a weak surface EpoR signal in A2780 cells. Interestingly, most of the EpoR in A2780 cells was found in the cytoplasm, more abundantly as an intracellular membraneassociated protein than a soluble one. Silencing EpoR expression by lentiviral-mediated shRNA resulted in reduced A2780 proliferation as well as reduction in Epo-induced phosphorylation of Erk1/2. Our findings provide important insights into the biology of the EpoR in ovarian cancer cells.