Ca2+ homeostasis and apoptotic resistance of neuroendocrine-differentiated prostate cancer cells

Abstract

Neuroendocrine (NE) differentiation is a hallmark of advanced, androgen-independent prostate cancer, for which there is no successful therapy. NE tumor cells are nonproliferating and escape apoptotic cell death; therefore, an understanding of the apoptotic status of the NE phenotype is imperative for the development of new therapies for prostate cancer. Here, we report for the first time on alterations in intracellular Ca²⁺ homeostasis, which is a key factor in apoptosis, caused by NE differentiation of androgen-dependent prostate cancer epithelial cells. NE-differentiating regimens, either cAMP elevation or androgen deprivation, resulted in a reduced endoplasmic reticulum Ca²⁺-store content due to both SERCA 2b Ca²⁺ ATPase and luminal Ca²⁺ binding/storage chaperone calreticulin underexpression, and to a downregulated store-operated Ca²⁺ current. NE-differentiated cells showed enhanced resistance to thapsigargin- and TNF--induced apoptosis, unrelated to antiapoptotic Bcl-2 protein overexpression. Our results suggest that targeting the key players determining Ca²⁺ homeostasis in an attempt to enhance the proapoptotic potential of malignant cells may prove to be a useful strategy in the treatment of advanced prostate cancer.