Reduction of the transcription level of the mitochondrial genome in human glioblastoma

Metabolic dysregulation of tricarboxylic acid cycle and oxidative phosphorylation in glioblastoma

Glioblastoma multiforme (GBM) exhibits genetic alterations that induce the deregulation of oncogenic pathways, thus promoting metabolic adaptation. The modulation of metabolic enzyme activities is necessary to generate nucleotides, amino acids, and fatty acids, which provide energy and metabolic intermediates essential for fulfilling the biosynthetic needs of glioma cells. Moreover, the TCA cycle produces intermediates that play important roles in the metabolism of glucose, fatty acids, or non-essential amino acids, and act as signaling molecules associated with the activation of oncogenic pathways, transcriptional changes, and epigenetic modifications. In this review, we aim to explore how dysregulated metabolic enzymes from the TCA cycle and oxidative phosphorylation, along with their metabolites, modulate both catabolic and anabolic metabolic pathways, as well as pro-oncogenic signaling pathways, transcriptional changes, and epigenetic modifications in GBM cells, contributing to the formation, survival, growth, and invasion of glioma cells. Additionally, we discuss promising therapeutic strategies targeting key players in metabolic regulation. Therefore, understanding metabolic reprogramming is necessary to fully comprehend the biology of malignant gliomas and significantly improve patient survival.

Roles of MT-ND1 in Cancer

The energy shift toward glycolysis is one of the hallmarks of cancer. Complex I is a vital enzyme complex necessary for oxidative phosphorylation. The mitochondrially encoded NADH: ubiquinone oxidoreductase core subunit 1 (MT-ND1) is the largest subunit coded by mitochondria of complex I. The present study summarizes the structure and biological function of MT-ND1. From databases and literature, the expressions and mutations of MT-ND1 in a variety of cancers have been reviewed. MT-ND1 may be a biomarker for cancer diagnosis and prognosis. It is also a potential target for cancer therapy.

Synergistic anti-tumor efficacy of mutant isocitrate dehydrogenase 1 inhibitor SYC-435 with standard therapy in patient-derived xenograft mouse models of glioma

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A novel pair of orthotopic PDX models of glioma bearing IDH1-R132H/R132C mutations.

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New mutant IDH1i (SY-435) with standard therapy led to strong therapeutic efficacy.

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H3K4/K9 methylation/mtDNA-encoded molecules mediate anti-tumor activity of SYC-435.

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Discovered MYO1F, CTC1 and BCL9 as novel genes that mediated SYC-435 resistance.

Clinical outcomes in patients with WHO grade II/III astrocytoma, oligodendroglioma or secondary glioblastoma remain poor. Isocitrate dehydrogenase 1 (IDH1) is mutated in > 70% of these tumors, making it an attractive therapeutic target. To determine the efficacy of our newly developed mutant IDH1 inhibitor, SYC-435 (1-hydroxypyridin-2-one), we treated orthotopic glioma xenograft model (IC-BT142AOA) carrying R132H mutation and our newly established orthotopic patient-derived xenograft (PDX) model of recurrent anaplastic oligoastrocytoma (IC-V0914AOA) bearing R132C mutation. In addition to suppressing IDH1 mutant cell proliferation in vitro, SYC-435 (15 mg/kg, daily x 28 days) synergistically prolonged animal survival times with standard therapies (Temozolomide + fractionated radiation) mediated by reduction of H3K4/H3K9 methylation and expression of mitochondrial DNA (mtDNA)-encoded molecules. Furthermore, RNA-seq of the remnant tumors identified genes (MYO1F, CTC1 and BCL9) and pathways (base excision repair, TCA cycle II, sirtuin signaling, protein kinase A, eukaryotic initiation factor 2 and α-adrenergic signaling) as mediators of therapy resistance. Our data demonstrated the efficacy SYC-435 in targeting IDH1 mutant gliomas when combined with standard therapy and identified a novel set of genes that should be prioritized for future studies to overcome SYC-435 resistance.

YKL-39 as a Potential New Target for Anti-Angiogenic Therapy in Cancer

YKL-39 belongs to the evolutionarily conserved family of Glyco_18-containing proteins composed of chitinases and chitinase-like proteins. Chitinase-like proteins (CLPs) are secreted lectins that lack hydrolytic activity due to the amino acid substitutions in their catalytic domain and combine the functions of cytokines and growth factors. One of the major cellular sources that produce CLPs in various pathologies, including cancer, are macrophages. Monocytes recruited to the tumor site and programmed by tumor cells differentiate into tumor-associated macrophages (TAMs), which are the primary source of pro-angiogenic factors. Tumor angiogenesis is a crucial process for supplying rapidly growing tumors with essential nutrients and oxygen. We recently determined that YKL-39 is produced by tumor-associated macrophages in breast cancer. YKL-39 acts as a strong chemotactic factor for monocytes and stimulates angiogenesis. Chemotherapy is a common strategy to reduce tumor size and aggressiveness before surgical intervention, but chemoresistance, resulting in the relapse of tumors, is a common clinical problem that is critical for survival in cancer patients. Accumulating evidence indicates that TAMs are essential regulators of chemoresistance. We have recently found that elevated levels of YKL-39 expression are indicative of the efficiency of the metastatic process in patients who undergo neoadjuvant chemotherapy. We suggest YKL-39 as a new target for anti-angiogenic therapy that can be combined with neoadjuvant chemotherapy to reduce chemoresistance and inhibit metastasis in breast cancer patients.

Recent advances in the discovery of small molecules targeting glioblastoma

Glioblastoma (GBM) is one of the most common central nervous system cancers. It is characterized as a fast-growing tumor that arises from multiple cell types with neural stem-cell-like properties. Additionally, GBM tumors are highly invasive, which is attributed to the presence of glioblastoma stem cells that makes surgery ineffective in most cases. Currently, temozolomide is the unique chemotherapy option approved by the U.S. Food and Drug Administration for GBM treatment. This review analyzes the emergence and development of new synthetic small molecules discovered as promising anti-glioblastoma agents. A number of compounds were described herein and grouped according to the main chemical class used in the drug discovery process. Importantly, we focused only on synthetic compounds published in the last 10 years, thus excluding natural products. Furthermore, we included in this review only those most biologically active compounds with proven in vitro and/or in vivo efficacy.

Targeting the Warburg effect for cancer treatment: Ketogenic diets for management of glioma

Gliomas are a highly heterogeneous tumor, refractory to treatment and the most frequently diagnosed primary brain tumor. Although the current WHO grading system (2016) demonstrates promise towards identifying novel treatment modalities and better prediction of prognosis over time, to date, existing targeted and mono therapy approaches have failed to elicit a robust impact on disease progression and patient survival. It is possible that tumor heterogeneity as well as specifically targeted agents fail because redundant molecular pathways in the tumor make it refractory to such approaches. Additionally, the underlying metabolic pathology, which is significantly altered during neoplastic transformation and tumor progression, is unaccounted for. With several molecular and metabolic pathways implicated in the carcinogenesis of CNS tumors, including glioma, we postulate that a systemic, broad spectrum approach to produce robust targeting of relevant and multiple molecular and metabolic regulation of growth and survival pathways, critical to the modulation of hallmarks of carcinogenesis, without clinically limiting toxicity, may provide a more sustained impact on clinical outcomes compared to the modalities of treatment evaluated to date. The objective of this review is to examine the emerging hallmark of reprogramming energy metabolism of the tumor cells and the tumor microenvironment during carcinogenesis, and to provide a rationale for exploiting this hallmark and its biological capabilities as a target for secondary chemoprevention and treatment of glioma. This review will primarily focus on interventions to induce ketosis to target the glycolytic phenotype of many cancers, with specific application to secondary chemoprevention of low grade glioma- to halt the progression of lower grade tumors to more aggressive subtypes, as evidenced by reduction in validated intermediate endpoints of disease progression including clinical symptoms.

Decoding Warburg's hypothesis: tumor-related mutations in the mitochondrial respiratory chain

Otto Warburg observed that cancer cells derived their energy from aerobic glycolysis by converting glucose to lactate. This mechanism is in opposition to the higher energy requirements of cancer cells because oxidative phosphorylation (OxPhos) produces more ATP from glucose. Warburg hypothesized that this phenomenon occurs due to the malfunction of mitochondria in cancer cells. The rediscovery of Warburg's hypothesis coincided with the discovery of mitochondrial tumor suppressor genes that may conform to Warburg's hypothesis along with the demonstrated negative impact of HIF-1 on PDH activity and the activation of HIF-1 by oncogenic signals such as activated AKT. This work summarizes the alterations in mitochondrial respiratory chain proteins that have been identified and their involvement in cancer. Also discussed is the fact that most of the mitochondrial mutations have been found in homoplasmy, indicating a positive selection during tumor evolution, thereby supporting their causal role.

Expression of mitochondrial genes MT-ND1, MT-ND6, MT-CYB, MT-COI, MT-ATP6, and 12S/MT-RNR1 in colorectal adenopolyps

Despite improvements in treatment strategies, colorectal cancer (CRC) still has high mortality rates. Most CRCs develop from adenopolyps via the adenoma-carcinoma sequence. A mechanism for inhibition of this sequence in individuals with a high risk of developing CRC is urgently needed. Differential studies of mitochondrial (mt) gene expressions in the progressive stages of CRC with villous architecture are warranted to reveal early risk assessments and new targets for chemoprevention of the disease. In the present study, reverse transcription-quantitative PCR (RT-qPCR) was used to determine the relative amount of the transcripts of six mt genes [MT-RNR1, MT-ND1, MT-COI, MT-ATP6, MT-ND6, and MT-CYB (region 648-15887)] which are involved in the normal metabolism of mitochondria. A total of 42 pairs of tissue samples obtained from colorectal adenopolyps, adenocarcinomas, and their corresponding adjacent normal tissues were examined. Additionally, electron transport chain (ETC), complexes I (NADH: ubiquinone oxidoreductase) and III (CoQH2-cytochrome C reductase), and carbonyl protein group contents were analyzed. Results indicate that there were differential expressions of the six mt genes and elevated carbonyl protein contents among the colorectal adenopolyps compared to their paired adjacent normal tissues (p < 0.05). The levels of complexes I and III were higher in tumor tissues relative to adjacent normal tissues. Noticeably, the expression of MT-COI was overexpressed in late colorectal carcinomas among all studied transcripts. Our data suggest that increased expressions in certain mt genes and elevated levels of ROS may potentially play a critical role in the colorectal tumors evolving from adenopolyps to malignant lesions.

Disruption of Mitochondrion-To-Nucleus Interaction in Deceased Cloned Piglets

Most animals produced by somatic cell nuclear transfer (SCNT) are heteroplasmic for mitochondrial DNA (mtDNA). Oxidative phosphorylation (OXPHOS) in clones therefore requires the coordinated expression of genes encoded by the nuclear DNA and the two sources of mitochondria. Such interaction is rarely studied because most clones are generated using slaughterhouse oocytes of unrecorded origin. Here we traced the maternal lineages of seven diseased and five one-month-old live cloned piglets by sequencing their mtDNA. Additionally by using a 13K oligonucleotide microarray, we compared the expression profiles of nuclear and mtDNA-encoded genes that are involved in mitochondrial functions and regulation between the cloned groups and their age-matched controls (n=5 per group). We found that the oocytes used to generate the cloned piglets were of either the Large White or Duroc background, and oocyte genetic background was not related to the clones’ survival. Expression profiles of mtDNA-encoded genes in clones and controls showed intermixed clustering patterns without treatment or maternal lineage-dependency. In contrast, clones and controls clustered separately for their global and nuclear DNA-encoded mitochondrial genes in the lungs for both the deceased and live groups. Functional annotation of differentially expressed genes encoded by both nuclear and mtDNA revealed abnormal gene expression in the mitochondrial OXPHOS pathway in deceased clones. Among the nine differentially expressed genes of the OXPHOS pathway, seven were down-regulated in deceased clones compared to controls, suggesting deficiencies in mitochondrial functions. Together, these data demonstrate that the coordination of expression of mitochondrial genes encoded by nuclear and mtDNA is disrupted in the lung of diseased clones.

Mitochondrial protein ATPase family, AAA domain containing 3A correlates with radioresistance in glioblastoma

BACKGROUND

ATPase-family, AAA domain containing 3A (ATAD3A) is located on human chromosome 1p36.33, and high endogenous expression may associate with radio- and chemosensitivity. This study was conducted to investigate the significance of ATAD3A in glioblastoma multiforme (GBM).

METHODS

Clinical significance of ATAD3A expression was assessed by immunohistochemistry in 67 GBM specimens, and prognostic value was assessed in 32 GBM patients statistically. To investigate in vitro phenotypic effects of ATAD3A, cell viability was measured using a clonogenic survival assay under either knockdown or ectopic expression of ATAD3A in GBM cell lines. The effects of ATAD3A knockdown on targeted DNA repair-associated proteins in T98G cells were evaluated using immunofluorescence and Western blotting.

RESULTS

Clinically, high expression of ATAD3A was independent of O(6)-DNA methylguanine-methyltransferase methylation status and correlated with worse prognosis. In vitro, high ATAD3A-expressing T98G cells were more resistant to radiation-induced cell death compared with control and low endogenous ATAD3A U87MG cells. After silencing ATAD3A, T98G cells became more sensitive to radiation. On the other hand, enforced ATAD3A expression in U87MG cells exhibited increased radioresistance. ATAD3A may coordinate with aldo-keto reductase genes and participate in bioactivation or detoxication of temozolomide. Surprisingly, deficient DNA repair after irradiation was observed in T98G/ATAD3A knockdown as a result of decreased nuclear ataxia telangiectasia mutated kinase and histones H2AX and H3, which was also evidenced by the sustained elevation of poly (ADP-ribose) polymerase prior to and after radiation treatment.

CONCLUSION

Our data suggest that high expression of ATAD3A is an independent biomarker for radioresistance in GBM. ATAD3A could be a potential target for therapy.

Potential involvement of F0F1-ATP(synth)ase and reactive oxygen species in apoptosis induction by the antineoplastic agent erucylphosphohomocholine in glioblastoma cell lines : a mechanism for induction of apoptosis via the 18 kDa mitochondrial translocator protein

Erucylphosphohomocholine (ErPC3, Erufosine) was reported previously to induce apoptosis in otherwise highly apoptosis-resistant malignant glioma cell lines while sparing their non-tumorigenic counterparts. We also previously found that the mitochondrial 18 kDa Translocator Protein (TSPO) is required for apoptosis induction by ErPC3. These previous studies also suggested involvement of reactive oxygen species (ROS). In the present study we further investigated the potential involvement of ROS generation, the participation of the mitochondrial respiration chain, and the role of the mitochondrial F(O)F(1)-ATP(synth)ase in the pro-apoptotic effects of ErPC3 on U87MG and U118MG human glioblastoma cell lines. For this purpose, cells were treated with the ROS chelator butylated hydroxyanisole (BHA), the mitochondrial respiration chain inhibitors rotenone, antimycin A, myxothiazol, and the uncoupler CCCP. Also oligomycin and piceatannol were studied as inhibitors of the F(O) and F(1) subunits of the mitochondrial F(O)F(1)-ATP(synth)ase, respectively. BHA was able to attenuate apoptosis induction by ErPC3, including mitochondrial ROS generation as determined with cardiolipin oxidation, as well as collapse of the mitochondrial membrane potential (Deltapsi(m)). Similarly, we found that oligomycin attenuated apoptosis and collapse of the Deltapsi(m), normally induced by ErPC3, including the accompanying reductions in cellular ATP levels. Other inhibitors of the mitochondrial respiration chain, as well as piceatannol, did not show such effects. Consequently, our findings strongly point to a role for the F(O) subunit of the mitochondrial F(O)F(1)-ATP(synth)ase in ErPC3-induced apoptosis and dissipation of Deltapsi(m) as well as ROS generation by ErPC3 and TSPO.

HMGA1 levels influence mitochondrial function and mitochondrial DNA repair efficiency

HMGA chromatin proteins, a family of gene regulatory factors found at only low concentrations in normal cells, are almost universally overexpressed in cancer cells. HMGA proteins are located in the nuclei of normal cells except during the late S/G(2) phases of the cell cycle, when HMGA1, one of the members of the family, reversibly migrates to the mitochondria, where it binds to mitochondrial DNA (mtDNA). In many cancer cells, this controlled shuttling is lost and HMGA1 is found in mitochondria throughout the cell cycle. To investigate the effects of HMGA1 on mitochondria, we employed a genetically engineered line of human MCF-7 cells in which the levels of transgenic HMGA1 protein could be reversibly controlled. "Turn-ON" and "turn-OFF" time course experiments were performed with these cells to either increase or decrease intracellular HMGA1 levels, and various mitochondrial changes were monitored. Results demonstrated that changes in both mtDNA levels and mitochondrial mass inversely paralleled changes in HMGA1 concentrations, strongly implicating HMGA1 in the regulation of these parameters. Additionally, the level of cellular reactive oxygen species (ROS) increased and the efficiency of repair of oxidatively damaged mtDNA decreased as consequences of elevated HMGA1 expression. Increased ROS levels and reduced repair efficiency in HMGA1-overexpressing cells likely contribute to the increased occurrence of mutations in mtDNA frequently observed in cancer cells.

Altered expression of 12S/MT-RNR1, MT-CO2/COX2, and MT-ATP6 mitochondrial genes in prostate cancer

BACKGROUND

Prostate cancer is one of the commonest cancers worldwide and is responsible for nearly 6% of all male cancer deaths. Despite this relevance, the mechanisms involved in the development and progression of this malignancy remain unknown. The involvement of polypeptides of the mitochondrial respiratory chain, the Krebs cycle and the glutathione antioxidant system in this type of cancer has been previously described, although no publication has focused on the expression of mitochondrial genes in the prostate of PCa patients.

METHODS

We have determined by reverse transcription-quantitative PCR (RT-qPCR) the relative amount of the transcripts of eight mitochondrial genes (MT-ND2, MT-ND4, MT-ND6, MT-CYB, 12S/MT-RNR1, 16S/MT-RNR2, MT-CO2/COX2, MT-ATP6), and four nuclear genes (COX11, GSR, CS, ACO2), all of them key players in the normal metabolism of mitochondria. Additionally we analyzed the expression of Cyclophilin A (PPIA).

RESULTS

We observed differential expression of mitochondrial 12S/MT-RNR1, MT-CO2/COX2, and MT-ATP6 transcripts in tumor samples when compared to their paired normal samples.

CONCLUSIONS

The amount of mitochondrial 12S/MT-RNR1, MT-CO2/COX2, and MT-ATP6 transcripts is significantly decreased in tumor samples when compared to their paired normal sample, suggesting that mitochondrial gene expression is altered in PCa.

Transcription analysis in the MeLiM swine model identifies RACK1 as a potential marker of malignancy for human melanocytic proliferation

BACKGROUND

Metastatic melanoma is a severe disease. Few experimental animal models of metastatic melanoma exist. MeLiM minipigs exhibit spontaneous melanoma. Cutaneous and metastatic lesions are histologically similar to human's. However, most of them eventually spontaneously regress. Our purpose was to investigate whether the MeLiM model could reveal markers of malignancy in human melanocytic proliferations.

RESULTS

We compared the serial analysis of gene expression (SAGE) between normal pig skin melanocytes and melanoma cells from an early pulmonary metastasis of MeLiM minipigs. Tag identification revealed 55 regulated genes, including GNB2L1 which was found upregulated in the melanoma library. In situ hybridisation confirmed GNB2L1 overexpression in MeLiM melanocytic lesions. GNB2L1 encodes the adaptor protein RACK1, recently shown to influence melanoma cell lines tumorigenicity. We studied the expression of RACK1 by immunofluorescence and confocal microscopy in tissues specimens of normal skin, in cutaneous and metastatic melanoma developped in MeLiM minipigs and in human patients. In pig and human samples, the results were similar. RACK1 protein was not detected in normal epidermal melanocytes. By contrast, RACK1 signal was highly increased in the cytoplasm of all melanocytic cells of superficial spreading melanoma, recurrent dermal lesions and metastatic melanoma. RACK1 partially colocalised with activated PKCalphabeta. In pig metastases, additional nuclear RACK1 did not associate to BDNF expression. In human nevi, the RACK1 signal was low.

CONCLUSION

RACK1 overexpression detected in situ in human melanoma specimens characterized cutaneous and metastatic melanoma raising the possibility that RACK1 can be a potential marker of malignancy in human melanoma. The MeLiM strain provides a relevant model for exploring mechanisms of melanocytic malignant transformation in humans. This study may contribute to a better understanding of melanoma pathophysiology and to progress in diagnosis.

Pyruvate modifies glycolytic and oxidative metabolism of rat embryonic spinal cord astrocyte cell lines and prevents their spontaneous transformation

This study aimed to provide detailed data on mitochondrial respiration of normal astrocyte cell lines derived from rat embryonic spinal cord. Astrocytes in early passages (EP), cultured without pyruvate for more than 35 passages, defined here as late passages (LP), undergo spontaneous transformation. To study initial steps in cell transformation, EP data were compared with those of LP cells. LP cells had reduced glycolysis, fewer mitochondria and extremely low oxidative rates, resulting from a dysfunction of complexes I and II + III of the respiratory chain. Treatment of EP cells with pyruvate until they were, by definition, LP cultures prevented transformation of these cells. Pyruvate-treated EP cells had more mitochondria than normal cells but slightly lower respiratory rates. The increase of mitochondrial content thus appears to act as a compensatory effect to maintain oxidative phosphorylation in these LP 'non-transformed' cells, in which mitochondrial function is reduced. However, pyruvate treatment of transformed LP cells during additional passages did not significantly restore their oxidative metabolism. These data highlight changes accompanying spontaneous astrocyte transformation and suggest potential targets for the control of astrocyte proliferation and reaction to various insults to the central nervous system.

Mitochondrial dysfunction, persistently elevated levels of reactive oxygen species and radiation-induced genomic instability: a review

Radiation-induced genomic instability (RIGI) challenges the long-standing notion that radiation's effects derive solely from nuclear impact. In RIGI it is the unirradiated progeny that can display phenotypic changes at delayed times after irradiation of the parental cell. RIGI might well provide the driving force behind the development of radiation-induced tumorigenesis as most cancer cells even in pre-neoplastic states display multiple genetic alterations. Thus, understanding RIGI may help elucidate the mechanisms underlying radiation-induced carcinogenesis. One characteristic of clones of genetically unstable cells is that many exhibit persistently increased levels of reactive oxygen species (ROS). Furthermore, oxidants enhance and antioxidants diminish radiation-induced instability. However, much about the mechanisms behind the initiation and perpetuation of RIGI remains unknown and we examine the evidence for the hypothesis that oxidative stress and mitochondrial dysfunction may be involved in perpetuating the unstable phenotype in some cell clones surviving ionizing radiation.

Nuclear HMGA1 nonhistone chromatin proteins directly influence mitochondrial transcription, maintenance, and function

We have previously demonstrated that HMGA1 proteins translocate from the nucleus to mitochondria and bind to mitochondrial DNA (mtDNA) at the D-loop control region [G.A. Dement, N.R. Treff, N.S. Magnuson, V. Franceschi, R. Reeves, Dynamic mitochondrial localization of nuclear transcription factor HMGA1, Exp. Cell Res. 307 (2005) 388-401.] [11]. To elucidate possible physiological roles for such binding, we employed methods to analyze mtDNA transcription, mitochondrial maintenance, and other organelle functions in transgenic human MCF-7 cells (HA7C) induced to over-express an HA-tagged HMGA1 protein and control (parental) MCF-7 cells. Quantitative real-time (RT) PCR analyses demonstrated that mtDNA levels were reduced approximately 2-fold in HMGA1 over-expressing HA7C cells and flow cytometric analyses further revealed that mitochondrial mass was significantly reduced in these cells. Cellular ATP levels were also reduced in HA7C cells and survival studies showed an increased sensitivity to killing by 2-deoxy-D-glucose, a glycolysis-specific inhibitor. Flow cytometric analyses revealed additional mitochondrial abnormalities in HA7C cells that are consistent with a cancerous phenotype: namely, increased reactive oxygen species (ROS) and increased mitochondrial membrane potential (Delta Psi(m)). Additional RT-PCR analyses demonstrated that gene transcripts from both the heavy (ND2, COXI, ATP6) and light (ND6) strands of mtDNA were up-regulated approximately 3-fold in HA7C cells. Together, these mitochondrial changes are consistent with many previous reports and reveal several possible mechanisms by which HMGA1 over-expression, a common feature of naturally occurring cancers, may affect tumor progression.

Expression of transforming K-Ras oncogene affects mitochondrial function and morphology in mouse fibroblasts

K-ras transformed fibroblasts have been shown to have a stronger dependence from glycolysis, reduced oxidative phosphorylation ability and a fragility towards glucose depletion compared to their immortalized, normal counterparts. In this paper, using RNA profiling assays and metabolic perturbations, we report changes in expression of genes encoding mitochondrial proteins and alterations in mitochondrial morphology that correlate with mitochondrial functionality. In fact, unlike normal cells, transformed cells show reduced ATP content and inability to modify mitochondria morphology upon glucose depletion. Being reverted by GEF-DN expression, such morphological and functional changes are directly connected to Ras activation. Taken together with reported partial mitochondrial uncoupling and more sustained apoptosis of transformed cells, our results indicate that activation of the Ras pathway strikingly impacts on energy and signaling-related aspects of mitochondria functionality, that in turn may affect the terminal phenotype of transformed cells.

Cell surface F1Fo ATP synthase: a new paradigm?

The mitochondrial F1Fo adenosine triphosphate (ATP) synthase is one of the most thoroughly studied enzyme complexes known. Yet, a number of new observations suggesting that the enzyme is also located on the cell surface necessitate further investigation. While the mitochondrial synthase utilizes the proton gradient generated by oxidative phosphorylation to power ATP synthesis, the cell surface synthase has instead been implicated in numerous activities, including the mediation of intracellular pH, cellular response to antiangiogenic agents, and cholesterol homeostasis. Intriguingly, a common thread uniting these various models of cell surface ATP synthase functions is the apparently caveolar distribution of the enzyme. Recent studies concerning the cell surface ATP synthase manifest applications in the regulation of serum cholesterol levels, cellular proliferation and antitumor strategies. This review addresses the expression, interactions, functions, and consequences of inhibition of cell surface ATP synthase, an enzyme now displaying a shift in paradigm, as well as of location.