Mitochondrial DNA and MitomiR Variations in Pancreatic Cancer: Potential Diagnostic and Prognostic Biomarkers.

Pancreatic cancer is an aggressive disease with poor prognosis. Only about 15-20% of patients diagnosed with pancreatic cancer can undergo surgical resection, while the remaining 80% are diagnosed with locally advanced or metastatic pancreatic ductal adenocarcinoma (PDAC). In these cases, chemotherapy and radiotherapy only confer marginal survival benefit. Recent progress has been made in understanding the pathobiology of pancreatic cancer, with a particular effort in discovering new diagnostic and prognostic biomarkers, novel therapeutic targets, and biomarkers that can predict response to chemo- and/or radiotherapy. Mitochondria have become a focus in pancreatic cancer research due to their roles as powerhouses of the cell, important subcellular biosynthetic factories, and crucial determinants of cell survival and response to chemotherapy. Changes in the mitochondrial genome (mtDNA) have been implicated in chemoresistance and metastatic progression in some cancer types. There is also growing evidence that changes in microRNAs that regulate the expression of mtDNA-encoded mitochondrial proteins (mitomiRs) or nuclear-encoded mitochondrial proteins (mitochondria-related miRs) could serve as diagnostic and prognostic cancer biomarkers. This review discusses the current knowledge on the clinical significance of changes of mtDNA, mitomiRs, and mitochondria-related miRs in pancreatic cancer and their potential role as predictors of cancer risk, as diagnostic and prognostic biomarkers, and as molecular targets for personalized cancer therapy.

Mitochondria Can Cross Cell Boundaries: An Overview of the Biological Relevance, Pathophysiological Implications and Therapeutic Perspectives of Intercellular Mitochondrial Transfer.

Mitochondria are complex intracellular organelles traditionally identified as the powerhouses of eukaryotic cells due to their central role in bioenergetic metabolism. In recent decades, the growing interest in mitochondria research has revealed that these multifunctional organelles are more than just the cell powerhouses, playing many other key roles as signaling platforms that regulate cell metabolism, proliferation, death and immunological response. As key regulators, mitochondria, when dysfunctional, are involved in the pathogenesis of a wide range of metabolic, neurodegenerative, immune and neoplastic disorders. Far more recently, mitochondria attracted renewed attention from the scientific community for their ability of intercellular translocation that can involve whole mitochondria, mitochondrial genome or other mitochondrial components. The intercellular transport of mitochondria, defined as horizontal mitochondrial transfer, can occur in mammalian cells both in vitro and in vivo, and in physiological and pathological conditions. Mitochondrial transfer can provide an exogenous mitochondrial source, replenishing dysfunctional mitochondria, thereby improving mitochondrial faults or, as in in the case of tumor cells, changing their functional skills and response to chemotherapy. In this review, we will provide an overview of the state of the art of the up-to-date knowledge on intercellular trafficking of mitochondria by discussing its biological relevance, mode and mechanisms underlying the process and its involvement in different pathophysiological contexts, highlighting its therapeutic potential for diseases with mitochondrial dysfunction primarily involved in their pathogenesis.

Integrin-Linked Kinase Links Integrin Activation to Invadopodia Function and Invasion via the p(T567)-Ezrin/NHERF1/NHE1 Pathway.

Tumor cell invasion depends largely on degradation of the extracellular matrix (ECM) by protease-rich structures called invadopodia, whose formation and activity requires the convergence of signaling pathways engaged in cell adhesion, actin assembly, membrane regulation and ECM proteolysis. It is known that ß1-integrin stimulates invadopodia function through an invadopodial p(T567)-ezrin/NHERF1/NHE1 signal complex that regulates NHE1-driven invadopodia proteolytic activity and invasion. However, the link between ß1-integrin and this signaling complex is unknown. In this study, in metastatic breast (MDA-MB-231) and prostate (PC-3) cancer cells, we report that integrin-linked kinase (ILK) integrates ß1-integrin with this signaling complex to regulate invadopodia activity and invasion. Proximity ligation assay experiments demonstrate that, in invadopodia, ILK associates with ß1-integrin, NHE1 and the scaffold proteins p(T567)-ezrin and NHERF1. Activation of ß1-integrin increased both invasion and invadopodia activity, which were specifically blocked by inhibition of either NHE1 or ILK. We conclude that ILK integrates ß1-integrin with the ECM proteolytic/invasion signal module to induce NHE1-driven invadopodial ECM proteolysis and cell invasion.

Mitochondria and cancer chemoresistance.

Mitochondria, known for more than a century as the energy powerhouse of a cell, represent key intracellular signaling hub that are emerging as important determinants of several aspects of cancer development and progression, including metabolic reprogramming, acquisition of metastatic capability, and response to chemotherapeutic drugs. The majority of cancer cells harbors somatic mutations in the mitochondrial genome (mtDNA) and/or alterations in the mtDNA content, leading to mitochondrial dysfunction. Decreased mtDNA content is also detected in tumor-initiating cells, a subpopulation of cancer cells that are believed to play an integral role in cancer recurrence following chemotherapy. Although mutations in mitochondrial genes are common in cancer cells, they do not shut down completely the mitochondrial energy metabolism and functionality. Instead, they promote rewiring of the bioenergetics and biosynthetic profile of a cancer cell through a mitochondria-to-nucleus signaling activated by "dysfunctional" mitochondria that results in changes in transcription and/or activity of cancer-related genes and signaling pathways. Different cancer cell types may undergo different bioenergetic changes, some to more glycolytic and some to more oxidative. These different metabolic signatures may coexist within the same tumor mass (intra-tumor heterogeneity). In this review we describe the current understanding of mitochondrial dysfunction in the context of cancer chemoresistance with special attention to the role of mtDNA alterations. We put emphasis on potential therapeutic strategies targeting different metabolic events specific to cancer cells, including glycolysis, glutaminolysis, oxidative phosphorylation, and the retrograde signaling, to prevent chemoresistance. We also highlight novel genome-editing strategies aimed at "correcting" mtDNA defects in cancer cells. We conclude on the importance of considering intratumor metabolic heterogeneity to develop effective metabolism-based cancer therapy that can overcome chemoresistance. This article is part of a Special Issue entitled Mitochondria in Cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

Silencing of BRCA2 decreases anoikis and its heterologous expression sensitizes yeast cells to acetic acid-induced programmed cell death.

Adhesion of normal epithelial cells to the extracellular matrix (ECM) is essential for survival. Cell detachment from ECM induces a specific form of programmed cell death (PCD) termed anoikis. BRCA2, a tumor suppressor gene whose mutations confer predisposition to cancer, has been implicated in the regulation of DNA repair, transcription, cell proliferation, and apoptosis. However, the potential role of BRCA2 in the regulation of anoikis has not been investigated. Here, we found that suppression of BRCA2 expression by short hairpin RNA promoted resistance to anoikis in prostate, breast and thyroid normal epithelial cells, which was accompanied by reduced caspases 3/7 levels and activity. Using yeast as a model, we assessed that expression of human BRCA2 does not induce cell death by itself but it can promote acetic acid-induced PCD (AA-PCD). Induction of BRCA2 expression decreased cell survival and increased the number of cells positive to different apoptotic markers, including DNA fragmentation and phosphatidylserine externalization en route to AA-PCD. A higher increase in ROS levels occurred in the early phase of AA-PCD in BRCA2-expressing yeast cells compared with non-expressing cells. Accordingly, a delay in the initial burst of ROS levels was observed in BRCA2-knockdown anoikis-resistant human cells. Treatment with the antioxidants N-acetylcysteine or ascorbic acid reduced sensitivity to anoikis in human cells and inhibited AA-PCD in yeast cells expressing BRCA2. Taken together, these results show a new function of BRCA2 protein as modulator of anoikis sensitivity through an evolutionarily-conserved molecular mechanism involving regulation of ROS production and/or detoxification by BRCA2 during PCD processes.

The expanding role of yeast in cancer research and diagnosis: insights into the function of the oncosuppressors p53 and BRCA1/2.

When the glucose supply is high, despite the presence of oxygen, Saccharomyces cerevisiae uses fermentation as its main metabolic pathway and switches to oxidative metabolism only when this carbon source is limited. There are similarities between glucose-induced repression of oxidative metabolism of yeast and metabolic reprogramming of tumor cells. The glucose-induced repression of oxidative metabolism is regulated by oncogene homologues in yeast, such as RAS and Sch9p, the yeast homologue of Akt. Yeast also undergoes an apoptosis-like programmed cell death process sharing several features with mammalian apoptosis, including oxidative stress and a major role played by mitochondria. Evasion of apoptosis and sustained proliferative signaling are hallmarks of cancer. This, together with the possibility of heterologous expression of human genes in yeast, has allowed new insights to be obtained into the function of mammalian oncogenes/oncosuppressors. Here, we elaborate on the similarities between tumor and yeast cells underpinning the use of this model organism in cancer research. We also review the achievements obtained through heterologous expression in yeast of p53, BRCA1, and BRCA2, which are among the best-known cancer-susceptibility genes, with the aim of understanding their role in tumorigenesis. Yeast-cell-based functional assays for cancer genetic testing will also be dealt with.

Skp2 overexpression is associated with loss of BRCA2 protein in human prostate cancer.

BRCA2 (breast cancer 2, early onset) is a tumor suppressor gene that confers increased susceptibility for prostate cancer (PCa). Previous in vitro experiments demonstrated that Skp2, an E3 ubiquitin ligase aberrantly overexpressed in PCa, is involved in the proteolytic degradation of BRCA2 in PCa cells, suggesting that the BRCA2-Skp2 interaction may play a role in prostate tumorigenesis. Herein, we investigated BRCA2 and Skp2 expression during PCa development using a prostate TMA. Although luminal and basal benign prostate epithelium exhibited moderate to strong nuclear BRCA2 immunostaining, the intensity and number of positive nuclei decreased significantly in high-grade prostatic intraepithelial neoplasia and PCa. Decreased frequency and intensity of nuclear BRCA2 labeling were inversely correlated with Skp2 expression in high-grade prostatic intraepithelial neoplasia and PCa. To functionally assess the effects of BRCA2 and Skp2 expression on prostate malignant transformation, we overexpressed Skp2 in normal immortalized prostate cells. Skp2 overexpression reduced BRCA2 protein and promoted cell growth and migration. A similar phenotype was observed after reduction of BRCA2 protein levels using specific BRCA2 small-interfering RNA. Forced BRCA2 expression in Skp2-overexpressing stable transfectants inhibited the migratory and growth properties by >60%. These results show that loss of BRCA2 expression during prostate tumor development is strongly correlated with both migratory behavior and cancer growth and include Skp2 as a BRCA2 proteolytic partner in vivo.

Programmed Cell Death in Health and Disease.

Programmed cell death is a conserved evolutionary process of cell suicide that is central to the development and integrity of eukaryotic organisms [...].

Extracellular Vesicles and Pancreatic Cancer: Insights on the Roles of miRNA, lncRNA, and Protein Cargos in Cancer Progression.

Pancreatic cancer (PC) is among the most devastating digestive tract cancers worldwide. This cancer is characterized by poor diagnostic detection, lack of therapy, and difficulty in predicting tumorigenesis progression. Although mutations of key oncogenes and oncosuppressor involved in tumor growth and in immunosurveillance escape are known, the underlying mechanisms that orchestrate PC initiation and progression are poorly understood or still under debate. In recent years, the attention of many researchers has been concentrated on the role of extracellular vesicles and of a particular subset of extracellular vesicles, known as exosomes. Literature data report that these nanovesicles are able to deliver their cargos to recipient cells playing key roles in the pathogenesis and progression of many pancreatic precancerous conditions. In this review, we have summarized and discussed principal cargos of extracellular vesicles characterized in PC, such as miRNAs, lncRNAs, and several proteins, to offer a systematic overview of their function in PC progression. The study of extracellular vesicles is allowing to understand that investigation of their secretion and analysis of their content might represent a new and potential diagnostic and prognostic tools for PC.

Loss of FBXO31-mediated degradation of DUSP6 dysregulates ERK and PI3K-AKT signaling and promotes prostate tumorigenesis.

FBXO31 is the substrate receptor of one of many CUL1-RING ubiquitin ligase (CRL1) complexes. Here, we show that low FBXO31 mRNA levels are associated with high pre-operative prostate-specific antigen (PSA) levels and Gleason grade in human prostate cancer. Mechanistically, the ubiquitin ligase CRL1FBXO31 promotes the ubiquitylation-mediated degradation of DUSP6, a dual specificity phosphatase that dephosphorylates and inactivates the extracellular-signal-regulated kinase-1 and -2 (ERK1/2). Depletion of FBXO31 stabilizes DUSP6, suppresses ERK signaling, and activates the PI3K-AKT signaling cascade. Moreover, deletion of FBXO31 promotes tumor development in a mouse orthotopic model of prostate cancer. Treatment with BCI, a small molecule inhibitor of DUSP6, suppresses AKT activation and prevents tumor formation, suggesting that the FBXO31 tumor suppressor activity is dependent on DUSP6. Taken together, our studies highlight the relevance of the FBXO31-DUSP6 axis in the regulation of ERK- and PI3K-AKT-mediated signaling pathways, as well as its therapeutic potential in prostate cancer.

The Mitochondrial Proteome of Tumor Cells: A SnapShot on Methodological Approaches and New Biomarkers.

Mitochondria are highly dynamic and regulated organelles implicated in a variety of important functions in the cell, including energy production, fatty acid metabolism, iron homeostasis, programmed cell death, and cell signaling. Changes in mitochondrial metabolism, signaling and dynamics are hallmarks of cancer. Understanding whether these modifications are associated with alterations of the mitochondrial proteome is particularly relevant from a translational point of view because it may contribute to better understanding the molecular bases of cancer development and progression and may provide new potential prognostic and diagnostic biomarkers as well as novel molecular targets for anti-cancer treatment. Making an inventory of the mitochondrial proteins has been particularly challenging given that there is no unique consensus targeting sequence that directs protein import into mitochondria, some proteins are present at very low levels, while other proteins are expressed only in some cell types, in a particular developmental stage or under specific stress conditions. This review aims at providing the state-of-the-art on methodologies used to characterize the mitochondrial proteome in tumors and highlighting the biological relevance of changes in expression and delocalization of proteins in and out the mitochondria in cancer biology.

Mitochondria at the Crossroads of Physiology and Pathology.

Mitochondria play a crucial role in cell life and death by regulating bioenergetic and biosynthetic pathways. They are able to adapt rapidly to different microenvironmental stressors by accommodating the metabolic and biosynthetic needs of the cell. Mounting evidence places mitochondrial dysfunction at the core of several diseases, notably in the context of pathologies of the cardiovascular and central nervous system. In addition, mutations in some mitochondrial proteins are bona fide cancer drivers. Better understanding of the functions of these multifaceted organelles and their components may finetune our knowledge on the molecular bases of certain diseases and suggest new therapeutic avenues.

Epigenetic suppression of FBXL7 promotes metastasis.

Epigenetic reprogramming is emerging as a key mechanism for metastasis development. Our study identified a novel regulatory mechanism whereby promoter methylation-mediated epigenetic silencing of the gene encoding the ubiquitin ligase subunit F-box/LRR-repeat protein 7 (FBXL7) induces accumulation of active c-SRC, which, in turn, activates epithelial-to-mesenchymal transition and supports cancer cell invasion and metastasis.

Epigenetic silencing of the ubiquitin ligase subunit FBXL7 impairs c-SRC degradation and promotes epithelial-to-mesenchymal transition and metastasis.

Epigenetic plasticity is a pivotal factor that drives metastasis. Here, we show that the promoter of the gene that encodes the ubiquitin ligase subunit FBXL7 is hypermethylated in advanced prostate and pancreatic cancers, correlating with decreased FBXL7 mRNA and protein levels. Low FBXL7 mRNA levels are predictive of poor survival in patients with pancreatic and prostatic cancers. FBXL7 mediates the ubiquitylation and proteasomal degradation of active c-SRC after its phosphorylation at Ser 104. The DNA-demethylating agent decitabine recovers FBXL7 expression and limits epithelial-to-mesenchymal transition and cell invasion in a c-SRC-dependent manner. In vivo, FBXL7-depleted cancer cells form tumours with a high metastatic burden. Silencing of c-SRC or treatment with the c-SRC inhibitor dasatinib together with FBXL7 depletion prevents metastases. Furthermore, decitabine reduces metastases derived from prostate and pancreatic cancer cells in a FBXL7-dependent manner. Collectively, this research implicates FBXL7 as a metastasis-suppressor gene and suggests therapeutic strategies to counteract metastatic dissemination of pancreatic and prostatic cancer cells.

Selective modulation of type 1 insulin-like growth factor receptor signaling and functions by beta1 integrins.

We show here that beta1 integrins selectively modulate insulin-like growth factor type I receptor (IGF-IR) signaling in response to IGF stimulation. The beta1A integrin forms a complex with the IGF-IR and insulin receptor substrate-1 (IRS-1); this complex does not promote IGF-I mediated cell adhesion to laminin (LN), although it does support IGF-mediated cell proliferation. In contrast, beta1C, an integrin cytoplasmic variant, increases cell adhesion to LN in response to IGF-I and its down-regulation by a ribozyme prevents IGF-mediated adhesion to LN. Moreover, beta1C completely prevents IGF-mediated cell proliferation and tumor growth by inhibiting IGF-IR auto-phosphorylation in response to IGF-I stimulation. Evidence is provided that the beta1 cytodomain plays an important role in mediating beta1 integrin association with either IRS-1 or Grb2-associated binder1 (Gab1)/SH2-containing protein-tyrosine phosphate 2 (Shp2), downstream effectors of IGF-IR: specifically, beta1A associates with IRS-1 and beta1C with Gab1/Shp2. This study unravels a novel mechanism mediated by the integrin cytoplasmic domain that differentially regulates cell adhesion to LN and cell proliferation in response to IGF.

Mitochondrial Dysfunction in Aging and Cancer.

Aging is a major risk factor for developing cancer, suggesting that these two events may represent two sides of the same coin. It is becoming clear that some mechanisms involved in the aging process are shared with tumorigenesis, through convergent or divergent pathways. Increasing evidence supports a role for mitochondrial dysfunction in promoting aging and in supporting tumorigenesis and cancer progression to a metastatic phenotype. Here, a summary of the current knowledge of three aspects of mitochondrial biology that link mitochondria to aging and cancer is presented. In particular, the focus is on mutations and changes in content of the mitochondrial genome, activation of mitochondria-to-nucleus signaling and the newly discovered mitochondria-telomere communication.

6-Thioguanine and Its Analogs Promote Apoptosis of Castration-Resistant Prostate Cancer Cells in a BRCA2-Dependent Manner.

Background: Mutations in the oncosuppressor gene BReast CAncer susceptibility gene 2 (BRCA2) predispose to aggressive forms of prostate cancer which show poor response to taxane-based therapy, the standard treatment for castration-resistant, aggressive prostate cancer. Herein, we addressed the question whether changes in BRCA2 expression, a potential surrogate marker for BRCA2 activity, may affect the response of castration-resistant prostate cancer cells to 6-thioguanine (6-TG), a thiopurine used in the treatment of haematological malignancies. Methods: Yeast, normal prostate cells and castration-resistant prostate cancer cells were treated with 6-TG or its analogues, in presence or absence of paclitaxel, or with olaparib, a poly-(ADP-ribose) polymerase (PARP) inhibitor currently in clinical trials for treatment of metastatic castration-resistant prostate cancer, and cell proliferation, apoptosis and androgen receptor (AR) levels were measured. Results: 6-TG inhibited cell proliferation in yeast, normal and castration-resistant prostate cancer cells but promoted apoptosis only in cancer cells. Suppression of BRCA2 expression by siRNA or shRNA increased the sensitivity to 6-TG- and olaparib-induced apoptosis but did not affect cancer cell response to taxane. Intriguingly, 6-TG reduced AR expression levels independently on BRCA2 expression. Instead, olaparib decreased AR levels only in BRCA2-knockdown prostate cancer cells. Notably, overexpression of BRCA2 resulted in resistance of castration-resistant prostate cancer cells to 6-TG-, taxane- and olaparib-based treatment but promoted sensitivity to apoptosis induced by 2-amino-6-bromopurine and 2,6-dithiopurine, two 6-TG analogues. Conclusions: Our results provide a pre-clinical rationale for the use of 6-TG in the treatment of BRCA2-deficient castration-resistant prostate cancers, and of certain 6-TG analogues for treatment of BRCA2-proficient prostate cancers.

IFNγ-Induced IFIT5 Promotes Epithelial-to-Mesenchymal Transition in Prostate Cancer via miRNA Processing.

IFNγ, a potent cytokine known to modulate tumor immunity and tumoricidal effects, is highly elevated in patients with prostate cancer after radiation. In this study, we demonstrate that IFNγ can induce epithelial-to-mesenchymal transition (EMT) in prostate cancer cells via the JAK-STAT signaling pathway, leading to the transcription of IFN-stimulated genes (ISG) such as IFN-induced tetratricopeptide repeat 5 (IFIT5). We unveil a new function of IFIT5 complex in degrading precursor miRNAs (pre-miRNA) that includes pre-miR-363 from the miR-106a-363 cluster as well as pre-miR-101 and pre-miR-128, who share a similar 5'-end structure with pre-miR-363. These suppressive miRNAs exerted a similar function by targeting EMT transcription factors in prostate cancer cells. Depletion of IFIT5 decreased IFNγ-induced cell invasiveness in vitro and lung metastasis in vivo. IFIT5 was highly elevated in high-grade prostate cancer and its expression inversely correlated with these suppressive miRNAs. Altogether, this study unveils a prometastatic role of the IFNγ pathway via a new mechanism of action, which raises concerns about its clinical application.Significance: A unique IFIT5-XRN1 complex involved in the turnover of specific tumor suppressive microRNAs is the underlying mechanism of IFNγ-induced epithelial-to-mesenchymal transition in prostate cancer.See related commentary by Liu and Gao, p. 1032.

Loss of BRCA2 promotes prostate cancer cell invasion through up-regulation of matrix metalloproteinase-9.

BRCA2 is a multifunctional tumor suppressor protein which plays critical roles in DNA repair, transcription, and cell proliferation, and the loss of which has been linked to the biology of several types of cancers. Here, on prostate adenocarcinoma specimens from 80 patients, we demonstrate that BRCA2 protein is lost in carcinoma cells compared to normal and hyperplastic prostate epithelium. Using highly metastatic prostate cancer PC-3 cells, we show that while BRCA2 depletion by small-interfering RNA promoted migration onto the extracellular matrix proteins fibronectin, laminin, and collagens, as well as invasion through the reconstituted basement membrane matrix Matrigel by more than 140%, recombinant BRCA2 overexpression decreased both phenomena by 57-80% and changed cell morphology from angular and spindle to round and compact. The BRCA2 inhibitory effect on cancer cell migration and invasion resulted from down-regulation of matrix metalloproteinase (MMP)-9 protein levels due to increased MMP-9 proteolysis, and was signaled through inhibition of PI3-kinase/AKT and activation of MAPK/ERK pathway. In BRCA2-overexpressing PC-3 cells, transient transfection with a constitutively active PI3-kinase mutant or treatment with the MAPK/ERK inhibitor PD98059 rescued MMP-9 levels and restored the migratory and invasive capabilities. Consistently, PI3-kinase inhibition with a dominant-negative mutant or MAPK/ERK activation with a gain-of-function mutant reduced MMP-9 levels and prevented migration and invasion in wild-type PC-3 cells. These results provide novel evidence showing that a functional BRCA2 protein may limit the metastatic potential of neoplastic cells by down-regulating MMP-9 production through inhibition of PI3-kinase/AKT and activation of MAPK/ERK, effectively hindering cancer cell migration and invasion.

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 (DeltaPsi(m)), increased migration onto the basement membrane protein laminin-1, reduced chemosensitivity to paclitaxel (IC(50)=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 DeltaPsi(m) loss, acquisition of invasive cytology, increased motility onto laminin-1, reduced sensitivity to paclitaxel (IC(50)= approximately 100 nM) and approximately 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.