EGF promotes neuroendocrine-like differentiation of prostate cancer cells in the presence of LY294002 through increased ErbB2 expression independent of the phosphatidylinositol 3-kinase-AKT pathway.

An increased neuroendocrine (NE) cell population in prostate cancer is associated with more aggressive disease and recurrence after androgen-deprivation therapy, although the mechanism responsible is unknown. In this study, we report that the treatment of LNCaP cells with epidermal growth factor (EGF) in the presence of LY294002, an inhibitor of the phosphoinositol 3'-kinase (PI3K)-AKT pathway, induced an increase of levels and activity of ErbB2. Under these conditions, we also observed cell survival and NE differentiation. When we treated with wortmannin, another PI3K inhibitor, or we knocked down PI3K or AKT isoforms in the presence of EGF, ErbB2 up-regulation was not observed, suggesting that the increase of ErbB2 induced by EGF plus LY294002 is not mediated by the PI3K-Akt pathway. Other targets of LY294002 were also discounted. We also show that ErbB2 up-regulation is directly involved in neuroendocine differentiation but not in cell survival as ErbB2 levels increased in parallel with NE differentiation marker levels, whereas ErbB2 knockdown reduced them; other NE differentiation inducers also increased the ErbB2 levels and the immunohistochemical analysis of prostate cancer samples showed colocalization of ErbB2 and chromogranin A. We found that, in LNCaP cells, EGF in combination with LY294002 increased ErbB2 levels by a PI3K/AKT-independent mechanism and that this increase was associated with the acquisition of a NE phenotype. These results suggest that is worth reconsidering ErbB2 as a drug target in prostate cancer and this should be kept in mind when designing new clinical schedules for the treatment of this disease.