Mitochondrial DNA Depletion Reduces PARP-1 Levels and Promotes Progression of the Neoplastic Phenotype in Prostate Carcinoma

Mitochondrial dysfunction resulting from mitochondrial DNA (mtDNA) mutations and/or depletion has been correlated with cancer progression and drug resistance. To investigate the role of mtDNA in prostate cancer progression, we used LNCaP and PC-3 prostate carcinoma cells as experimental model. Compared to minimally invasive androgen-dependent LNCaP cells, highly invasive androgen-independent PC-3 cells, as well as androgen-independent DU145 and C4-2 cells, exhibited significantly reduced mtDNA content. In PC-3 cells, reduction of mtDNA was accompanied by decreased mitochondrial membrane potential (ΔΨm), increased migration onto the basement membrane protein laminin-1, reduced chemosensitivity to paclitaxel (IC50=110 nM vs. 22 nM) and decreased expression of poly(ADP-ribose) polymerase (PARP)-1. To investigate the relationship between mtDNA depletion and these phenotypic characteristics, we established mtDNA-depleted LNCaP cells [Rho(−)] by long-term exposure to ethidium bromide or treated wild-type LNCaP cells with a mitochondrial ionophore, carbonyl cyanide m-chlorophenylhydrazone. Both manipulations resulted in ΔΨm loss, acquisition of invasive cytology, increased motility onto laminin-1, reduced sensitivity to paclitaxel (IC50=~100 nM) and ~75% reduction in PARP-1 protein levels, resembling PC-3 cells. Overall, these results provide novel evidence demonstrating that mtDNA depletion in early prostate carcinoma may contribute to the acquisition of a more invasive phenotype that is less sensitive to paclitaxel-induced apoptosis.