Upregulation of erythropoietin and erythropoietin receptor in castration-resistant progression of prostate cancer

Hypoxia-induced erythropoietin signaling plays an important role in tumor growth and invasion.In the present study,we investigated the contribution of erythropoietin signaling pathway to castration-resistant prostate cancer and the development of a neuroendocrine phenotype.Immunohistochemical staining showed that the erythropoietin and erythropoietin receptor scores in castration-resistant prostate cancer and androgen-dependent prostate cancer were 7.55 versus 4.5 and 7.45 versus 5.9,respectively(P<0.001).Furthermore,a cell proliferation assay was conducted,and the differential expression of erythropoietin and erythropoietin receptor in LNCaP cells and hypoxia-induced LNCaP cells was evaluated using western blot and quantitative real-time PCR.The proliferation capacity of hypoxia-induced LNCaP cells was similar in cultures of both fetal bovine serum and charcoal-stripped fetal bovine serum,suggesting that LNCaP cells acquired hypoxia-induced androgen-independent growth.After 2 weeks of hypoxic culture,LNCaP cells showed a neuroendocrine cell change and increased expression of neuron-specific enolase,erythropoietin,and erythropoietin receptor;knockdown of erythropoietin receptor reversed the hypoxia-induced upregulation of neuron-specific enolase in the LNCaP cells.In conclusion,the concurrent upregulation of erythropoietin and erythropoietin receptor in castration-resistant prostate cancer suggests that the erythropoietin/erythropoietin receptor autocrine loop plays an important role in the progression of castration resistance and is responsible for the development of a neuroendocrine phenotype.