Autocrine erythropoietin signaling inhibits hypoxia-induced apoptosis in human breast carcinoma cells.

Disordered perfusion and the resulting hypoxia are important features conferring tumor heterogeneity, which may contribute to relapse. Hypoxic tumor cells have been associated with resistance both to radiation and to cytotoxic drugs. Hypoxia may also serve as a selection pressure in tumors by promoting apoptosis of some cells and expanding variants with decreased apoptotic potential, and thus play a role in the development of a more aggressive phenotype. Erythropoietin (Epo), induced by hypoxia, controls erythropoiesis and plays a role in protection of neurons from hypoxic damage. We have recently demonstrated hypoxia-stimulated expression of Epo and Epo receptor (EpoR) in human breast and cervix cancers, suggesting a role for autocrine Epo signaling in the hypoxic adaptations of carcinomas. In the current study we provide evidence that increased autocrine Epo signaling induced by moderate levels of hypoxia inhibits hypoxia-induced apoptosis and promotes survival in MCF-7 human breast cancer cells. The anti-apoptotic effect of Epo correlates with upregulation of bcl-2 and bcl-XL, suggesting a mechanism similar to those described in hematopoietic cells. The resulting decreased apoptotic potential of hypoxic tumor cells may contribute to increased aggressiveness and therapy resistance of breast cancers.