Loss of mitochondrial membrane potential is inhibited by bombesin in etoposide-induced apoptosis in PC-3 prostate carcinoma cells

Abstract

Neuroendocrine secretory products and their interactions with epithelial prostate cells are currently under investigation in order to understand their significance in the pathogenesis, prognosis, and therapy of prostate carcinoma. These neuropeptides have the potential to disrupt the balance between cell death and cell growth in the tumor. Our research was based on the role of bombesin in modulating the mitochondrial membrane potential (Delta psi(m)) in cell death induced by etoposide on PC-3 cells. Cells were cultured and stained with 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1). At low membrane potentials, JC-1 produces a green fluorescence, and at high membrane potentials, it forms "J aggregates" with red fluorescence. Cells were examined in a confocal microscope. For quantitative analyses, regions of interest were selected. The size, number of pixels, and ratios between fluorescence intensity in the red and green channels in each region of interest were calculated. The loss of Delta psi(m) in etoposide-treated PC-3 cells was prevented by bombesin. The quantitative analysis of JC-1-stained cells revealed a significant decrease in the red (high Delta psi(m)) to green (low Delta psi(m)) ratio in etoposide-treated cells when compared with control cells, which was restored in the presence of bombesin (P < 0.00001). The interaction between treatments and area (P = 0.0002) was highly significant, and confirms that PC-3 cells keep their apoptosis machinery, showing an apoptotic volume decrease in response to etoposide. The protection by bombesin occurs by inhibition of apoptosis and maintenance of mitochondrial integrity. New therapeutic protocols and trials need to be developed to test drugs acting through the neutralization of antiapoptotic intracellular pathways mediated by neuroendocrine hormones.