Evidence for association of mitochondrial DNA sequence amplification and nuclear localization in human low-grade gliomas

Ketogenic metabolic therapy in conjunction with standard treatment for glioblastoma: A case report

Glioblastoma (GBM) is the most common primary malignant brain tumour in adults. The standard of care consists of surgical resection and concurrent chemoradiation, followed by adjuvant temozolomide chemotherapy. This protocol is associated with a median survival of 12-15 months, and <5% of patients survive >3 years. Ketogenic metabolic therapy (KMT) targets cancer cell metabolism by restricting glucose availability and evoking differential stress resistance and sensitization, which may augment the standard treatments and lead to therapeutic benefit. The present study reports the case of a 64-year-old woman with isocitrate dehydrogenase (IDH)-wildtype GBM who pursued the standard treatment protocol in conjunction with an intensive, multimodal KMT program for 3 years. The KMT program consisted of a series of prolonged (7-day, fluid-only) fasts, which were specifically timed to maximize the tolerability and efficacy of the standard treatments, combined with a time-restricted ketogenic diet on all other days. During the first and second treatment years the patient sustained a glucose ketone index (GKI) of 1.65 and 2.02, respectively, which coincided with complete clinical improvement, a healthy body-mass index and a high quality of life, with no visible progressive tumour detected on imaging at the end of the second year. In the setting of the death of an immediate family member leading to increased life stress, slightly relaxed KMT adherence, and a higher GKI of 3.20, slow cancer progression occurred during the third year. The adverse effects attributed to KMT were mild. Despite the limitations of this case report, it highlights the feasibility of implementing the standard treatment protocol for GBM in conjunction with an intensive, long-term, multimodal and specifically timed KMT program, the potential therapeutic efficacy of which may depend upon achieving as low a GKI as possible.

The known unknowns of mitochondrial carcinogenesis: de novo NUMTs and intercellular mitochondrial transfer

The translocation of mitochondrial DNA (mtDNA) sequences into the nuclear genome, resulted in the occurrence of nuclear sequences of mitochondrial origin (NUMTs) which can be detected in nearly all sequenced eukaryotes. However, de novo mtDNA insertions can contribute to the development of pathological conditions including cancer. Recent data indicate that de novo mtDNA translocation into chromosomes can occur due to genotoxic influence of DNA double-strand break-inducing environmental mutagens. This confirms the hypothesis of the involvement of genome instability in the occurrence of mtDNA fragments in chromosomes. Mounting evidence indicates that mitochondria can be transferred from normal cells to cancer cells and recover cellular respiration. These exchanged mitochondria can facilitate cancer progression and metastasis. This review article provides a comprehensive overview of the potential carcinogenicity of mtDNA insertions, and the relevance of mtDNA escape in cancer progression, metastasis, and treatment resistance in humans. Potential molecular targets involved in mtDNA escape and exchange of mitochondria that can be of possible clinical benefits are presented and discussed. Understanding these processes could lead to improved diagnostic approaches, novel therapeutic strategies, and a deeper understanding of the intricate relationship between mitochondria, nuclear DNA, and cancer biology.

Non-invasive diagnosis of endometriosis: Immunologic and genetic markers

Endometriosis, a benign gynecologic and chronic inflammatory disease, is defined by the presence of endometrial tissue outside the uterus characterized mainly by pelvic pain and infertility. Because endometriosis affects approximately 10% of females, it represents a significant socioeconomic burden worldwide having tremendous impact on daily quality of life. Accurate and prompt diagnosis is crucial for the management of this debilitating disorder. Unfortunately, diagnosis is typically delayed to lack of specific symptoms and readily accessible biomarkers. Although histopathologic examination remains the current gold standard, this approach is highly invasive and not applicable for early screening. Recent work has focused on the identification of reliable biomarkers including immunologic, ie, immune cells, antibodies and cytokines, as well as genetic and biochemical markers, ie, microRNAs, lncRNAs, circulating and mitochondrial nucleic acids, along with some hormones, glycoproteins and signaling molecules. Confirmatory research studies are, however, needed to more fully establish these markers in the diagnosis, progression and staging of these endometrial lesions.

Mitochondrial DNA insert into CD40 ligand gene-associated X-linked hyper-IgM syndrome

BACKGROUND

X-linked hyper-IgM (X-HIGM), which results from mutations in the CD40LG gene located on chromosome Xq26.3, is the most common form of HIGM. To date, more than 130 variants of the CD40L gene have been reported. We described a patient with novel de novo nuclear mitochondrial DNA sequences (NUMTs) in the CD40LG gene that have resulted in X-HIGM.

METHODS

Whole-exome sequencing (WES) analysis was used to screen for causal variants in the genome, and the candidate breakpoint was confirmed by Sanger sequencing.

RESULTS

A new mutation of CD40LG, which deletes A at position 17 followed by a 147-nucleotide from mitochondrial DNA copies insertion in exon 1, was detected in a 20-month-old boy harbouring an X-HIGM combined with immunodeficiency syndrome.

CONCLUSION

This is one of the few cases of a human genetic disease caused by nuclear mitochondrial DNA sequences (NUMTs). The presented data serve to demonstrate that de novo NUMT transfer of nucleic acid is a novel mechanism of X-HIGM.

Targeting reduced mitochondrial DNA quantity as a therapeutic approach in pediatric high-grade gliomas

Background

Despite increased understanding of the genetic events underlying pediatric high-grade gliomas (pHGGs), therapeutic progress is static, with poor understanding of nongenomic drivers. We therefore investigated the role of alterations in mitochondrial function and developed an effective combination therapy against pHGGs.

Methods

Mitochondrial DNA (mtDNA) copy number was measured in a cohort of 60 pHGGs. The implication of mtDNA alteration in pHGG tumorigenesis was studied and followed by an efficacy investigation using patient-derived cultures and orthotopic xenografts.

Results

Average mtDNA content was significantly lower in tumors versus normal brains. Decreasing mtDNA copy number in normal human astrocytes led to a markedly increased tumorigenicity in vivo. Depletion of mtDNA in pHGG cells promoted cell migration and invasion and therapeutic resistance. Shifting glucose metabolism from glycolysis to mitochondrial oxidation with the adenosine monophosphate–activated protein kinase activator AICAR (5-aminoimidazole-4-carboxamide ribonucleotide) or the pyruvate dehydrogenase kinase inhibitor dichloroacetate (DCA) significantly inhibited pHGG viability. Using DCA to shift glucose metabolism to mitochondrial oxidation and then metformin to simultaneously target mitochondrial function disrupted energy homeostasis of tumor cells, increasing DNA damage and apoptosis. The triple combination with radiation therapy, DCA and metformin led to a more potent therapeutic effect in vitro and in vivo.

Conclusions

Our results suggest metabolic alterations as an onco-requisite factor of pHGG tumorigenesis. Targeting reduced mtDNA quantity represents a promising therapeutic strategy for pHGG.

Mitochondrial DNA deletions accurately detect endometriosis in symptomatic females of child-bearing age

Aim: Accurate noninvasive diagnostic aids for endometriosis are needed. We evaluated mitochondrial DNA deletions as potential biomarkers for endometriosis. Methods: The diagnostic accuracy of deletions was evaluated by quantitative polymerase chain reaction (QPCR) using well-characterized clinical specimens from all subtypes and stages of endometriosis in a case–control format (n = 182). Results: Deletions (1.2 and 3.7 kb) detected in blood differentiated between endometriosis and controls (area under the curve [AUC] 0.71–0.90). Differences in deletion levels were statistically significant (p < 0.05) for all disease subtypes and stages. Neither deletion was correlated with patient or specimen age or hormone status. The 1.2 kb deletion was not correlated with menstrual stage; the 3.7 kb deletion was significantly correlated between two of the groups. Conclusion: Biomarkers of the mitochondrial genome, including the deletions described here, offer a promising and largely unexplored avenue in the pursuit of diagnostic markers for endometriosis that can be effectively translated to clinical application.

Identification of abnormal nuclear and mitochondrial genes in esophageal cancer cells

The present study aimed to detect the mutation characteristics of mitochondrial DNA (mtDNA) in Eca109 of Ec9706 cells, and to investigate their association with the nuclear genome (nDNA), thus providing a basis for gene targeting therapies for esophageal squamous cell carcinoma (ESCC). In vitro-cultured Ec9706 and Eca109 cells were analyzed the changes of single-nucleotide polymorphisms (SNPs), insertions/deletions (INDELs), copy number variation, and structure variation (SV) of their genome by high-throughput sequencing. The loci with SV on chromosome 1–12 of the two ESCC cell lines were ≥5% of the mtDNA, but SV on chromosome 13–22, X and Y was ≤3%; >40% of loci exhibited gain or loss; intergenic loci with INDEL changes and SNP features accounted for the majority of mutations. The affected genes encoded proteins including nDNA-encoding intra-mitochondrial-transporting proteins, ATP energy generation-associated proteins and mitochondrial electron respiratory chain proteins, and these proteins were all nucleus-encoded mitochondrial proteins. The transcription, duplication, and translation of the abnormally expressed mtDNA in Ec9706 and Eca109 cells were closely associated with disorders of nuclear DNA products.

Quantifying the Number of Independent Organelle DNA Insertions in Genome Evolution and Human Health

Fragments of organelle genomes are often found as insertions in nuclear DNA. These fragments of mitochondrial DNA (numts) and plastid DNA (nupts) are ubiquitous components of eukaryotic genomes. They are, however, often edited out during the genome assembly process, leading to systematic underestimation of their frequency. Numts and nupts, once inserted, can become further fragmented through subsequent insertion of mobile elements or other recombinational events that disrupt the continuity of the inserted sequence relative to the genuine organelle DNA copy. Because numts and nupts are typically identified through sequence comparison tools such as BLAST, disruption of insertions into smaller fragments can lead to systematic overestimation of numt and nupt frequencies. Accurate identification of numts and nupts is important, however, both for better understanding of their role during evolution, and for monitoring their increasingly evident role in human disease. Human populations are polymorphic for 141 numt loci, five numts are causal to genetic disease, and cancer genomic studies are revealing an abundance of numts associated with tumor progression. Here, we report investigation of salient parameters involved in obtaining accurate estimates of numt and nupt numbers in genome sequence data. Numts and nupts from 44 sequenced eukaryotic genomes reveal lineage-specific differences in the number, relative age and frequency of insertional events as well as lineage-specific dynamics of their postinsertional fragmentation. Our findings outline the main technical parameters influencing accurate identification and frequency estimation of numts in genomic studies pertinent to both evolution and human health.

Cancer-associated isocitrate dehydrogenase mutations induce mitochondrial DNA instability

A major advance in understanding the progression and prognostic outcome of certain cancers, such as low-grade gliomas, acute myeloid leukaemia, and chondrosarcomas, has been the identification of early-occurring mutations in the NADP⁺-dependent isocitrate dehydrogenase genes IDH1 and IDH2 These mutations result in the production of the onco-metabolite D-2-hydroxyglutarate (2HG), thought to contribute to disease progression. To better understand the mechanisms of 2HG pathophysiology, we introduced the analogous glioma-associated mutations into the NADP⁺isocitrate dehydrogenase genes (IDP1, IDP2, IDP3) in Saccharomyces cerevisiae Intriguingly, expression of the mitochondrial IDP1^R148H mutant allele results in high levels of 2HG production as well as extensive mtDNA loss and respiration defects. We find no evidence for a reactive oxygen-mediated mechanism mediating this mtDNA loss. Instead, we show that 2HG production perturbs the iron sensing mechanisms as indicated by upregulation of the Aft1-controlled iron regulon and a concomitant increase in iron levels. Accordingly, iron chelation, or overexpression of a truncated AFT1 allele that dampens transcription of the iron regulon, suppresses the loss of respirative capacity. Additional suppressing factors include overexpression of the mitochondrial aldehyde dehydrogenase gene ALD5 or disruption of the retrograde response transcription factor RTG1 Furthermore, elevated α-ketoglutarate levels also suppress 2HG-mediated respiration loss; consistent with a mechanism by which 2HG contributes to mtDNA loss by acting as a toxic α-ketoglutarate analog. Our findings provide insight into the mechanisms that may contribute to 2HG oncogenicity in glioma and acute myeloid leukaemia progression, with the promise for innovative diagnostic and prognostic strategies and novel therapeutic modalities.

Association of leukocyte mitochondrial DNA content with glioma risk: evidence from a Chinese case-control study

Background

Increasing evidence suggests that alterations in mitochondrial DNA (mtDNA) content may be implicated in the tumorigenesis of several malignancies. However, the association between mtDNA content in peripheral blood lymphocytes (PBLs) and glioma risk has not been investigated.

Methods

Real-time PCR was used to examine the mtDNA content in PBLs of 414 glioma patients and 414 matched controls in a hospital-based case–control study. The association between mtDNA content and glioma risk was evaluated using an unconditional multivariate logistic regression model.

Results

We found that glioma patients exhibited a significantly higher median mtDNA content than healthy controls (0.99 vs. 0.71, P < 0.001). Unconditional multivariate logistic regression analysis adjusting for age, gender, smoking status, and family cancer history showed that there was an S-shaped association between mtDNA content and glioma risk. Higher mtDNA content was significantly associated with an elevated risk of glioma. Compared with the first quartile, the odds ratio (95% confidence interval) for subjects in the second, third, and fourth quartiles of mtDNA content were 0.90 (0.52-1.53), 3.38 (2.15-5.31), and 5.81 (3.74-9.03), respectively (P for nonlinearity = 0.009). Stratified analysis showed that the association between mtDNA content and glioma risk was not modulated by major host characteristics.

Conclusions

Our findings demonstrate for the first time that a higher mtDNA content in PBLs is associated with an elevated risk of glioma, which warrants further investigation in larger populations.

Reversible mitochondrial DNA accumulation in nuclei of pluripotent stem cells

According to the endosymbiotic hypothesis, the precursor of mitochondria invaded the precursor of eukaryotic cells, a process that began roughly 2 billion years ago. Since then, the majority of the genetic material translocated from the mitochondria to the nucleus, where now almost all mitochondrial proteins are expressed. Only a tiny amount of DNA remained in the mitochondria, known as mitochondrial DNA (mtDNA). In this study, we report that the transfer of mtDNA fragments to the nucleus of pluripotent stem cells is still ongoing. We show by in situ hybridization and agarose DNA two-dimensional gel technique that induced pluripotent stem (iPS) cells contain high levels of mtDNA in the nucleus. We found that a large proportion of the accumulated mtDNA sequences appear to be extrachromosomal. Accumulation of mtDNA in the nucleus is present not only in the iPS cells, but also in embryonic stem (ES) cells. However upon differentiation, the level of mtDNA in the nuclei of iPS and ES cells is substantially reduced. This reversible accumulation of mtDNA in the nucleus supports the notion that the nuclear copy number of mtDNA sequences may provide a novel mechanism by which chromosomal DNA is dynamically regulated in pluripotent stem cells.

Oncocytic glioblastoma: a glioblastoma showing oncocytic changes and increased mitochondrial DNA copy number

Ten cases of glioblastomas showing oncocytic changes are described. The tumors showed mononuclear to multinuclear cells and abundant, granular, eosinophilic cytoplasm. The cytoplasm of these same cells was filled by strongly immunoreactive mitochondria. At ultrastructure, numerous mitochondria, some of which were large, were evidenced in the cytoplasm of neoplastic cells. Finally, 9 of 10 of these cases had a significantly high mitochondrial DNA content compared with control tissue (P < .01). It seems that, for these tumors, the designation of oncocytic glioblastoma is appropriate. To the best of our knowledge, oncocytic changes have not been previously reported in such neoplasms. Oncocytic glioblastomas have to be added to the long list of various tumors that can manifest "unexpected" oncocytic changes in different organs. Albeit failing to show statistical significance (log-rank test, P = .597; Wilcoxon test, P = .233), we observed a trend for longer median survival in oncocytic glioblastomas, when compared with "ordinary" glioblastomas (median survival of 16 versus 8.7 months). Thus, it seems that the definition of neoplasms showing oncocytic changes, currently based on classic morphological parameters (ie, histology, ultrastructure, and immunohistochemistry), can be expanded by including the quantitative assessment of mitochondrial DNA content.

The mitochondrial genome: a biosensor for early cancer detection?

Mutations in the mitochondrial genome have been reported as biomarkers for the detection of cancer. Hallmarks of cancer development include the accumulation of genetic alterations in the mitochondrial and nuclear genomes. Damage to mitochondria affects energy metabolism, generation of reactive oxygen species, apoptosis, cell growth and other processes that contribute to the neoplastic process. Furthermore, mitochondrial DNA mutations occur frequently in cancer. Little work has been done to link a pathway between mitochondrial mutations and cancer etiology. Volumes of work have been reported on the association of mitochondrial mutations and almost all types of cancer including the use of body fluids for early detection. This review examines the measurement of mitochondrial mutations for the application of detecting human tumor tissue.

The intra-nucleus integration of mitochondrial DNA (mtDNA)in cervical mucosa cells and its relation with c-myc expression

OBJECTIVE

To explore the relationship between the integration of mitochondrial DNA(mtDNA) in the nuclei of cervical epithelium cells and the expression of c-myc.

METHODS

The expression of c-myc protein was measured by immunohistochemical test in 40 cases of the uterine cervix cancer, 30 cases of cervical intraepithelial neoplasia (CIN) and 30 cases of normal cervical epithelium; the sequence of mtDNA in the nuclei was detected by in situ hybridization technique.

RESULTS

The detection rates of mtDNA in the nuclei of cervical epithelium cells were 27.5%, 13.3% and 0% in cervical carcinoma, CIN, and normal cervical epithelium respectively. The expression rate of c-myc in cervical mucoma cells was 67% in the mtDNA sequence positive group and was significantly higher than that in the negative group (36%).

CONCLUSION

The integration of mtDNA into the nuclei of cervical epithelium cells may be involved in the carcinogenesis of cervical epithelium cells and the expression of c-myc might be related to the integration of mtDNA sequence into nuclei of cervical epithelium cells.

Mitochondrial DNA mutations in human cancer

Somatic mitochondrial DNA (mtDNA) mutations have been increasingly observed in primary human cancers. As each cell contains many mitochondria with multiple copies of mtDNA, it is possible that wild-type and mutant mtDNA can co-exist in a state called heteroplasmy. During cell division, mitochondria are randomly distributed to daughter cells. Over time, the proportion of the mutant mtDNA within the cell can vary and may drift toward predominantly mutant or wild type to achieve homoplasmy. Thus, the biological impact of a given mutation may vary, depending on the proportion of mutant mtDNAs carried by the cell. This effect contributes to the various phenotypes observed among family members carrying the same pathogenic mtDNA mutation. Most mutations occur in the coding sequences but few result in substantial amino acid changes raising questions as to their biological consequence. Studies reveal that mtDNA play a crucial role in the development of cancer but further work is required to establish the functional significance of specific mitochondrial mutations in cancer and disease progression. The origin of somatic mtDNA mutations in human cancer and their potential diagnostic and therapeutic implications in cancer are discussed. This review article provides a detailed summary of mtDNA mutations that have been reported in various types of cancer. Furthermore, this review offers some perspective as to the origin of these of mutations, their functional consequences in cancer development, and possible therapeutic implications.

Somatic Mitochondrial DNA Mutations in Neurofibromatosis Type 1-Associated Tumors

Neurofibromatosis type 1 is an autosomal dominantly inherited disease predisposing to a multitude of tumors, most characteristically benign plexiform neurofibromas and diffuse cutaneous neurofibromas. We investigated the presence and distribution of somatic mitochondrial DNA (mtDNA) mutations in neurofibromas and in nontumor tissue of neurofibromatosis type 1 patients. MtDNA alterations in the entire mitochondrial genome were analyzed by temporal temperature gradient gel electrophoresis followed by DNA sequencing. Somatic mtDNA mutations in tumors were found in 7 of 19 individuals with cutaneous neurofibromas and in 9 of 18 patients with plexiform neurofibromas. A total of 34 somatic mtDNA mutations were found. All mutations were located in the displacement loop region of the mitochondrial genome. Several plexiform neurofibromas from individual patients had multiple homoplasmic mtDNA mutations. In cutaneous neurofibromas, the same mtDNA mutations were always present in tumors from different locations of the same individual. An increase in the proportion of the mutant mtDNA was always found in the neurofibromas when compared with nontumor tissues. The somatic mtDNA mutations were present in the Schwann cells of the analyzed multiple cutaneous neurofibromas of the same individual. The observed dominance of a single mtDNA mutation in multiple cutaneous neurofibromas of individual patients indicates a common tumor cell ancestry and suggests a replicative advantage rather than random segregation for cells carrying these mutated mitochondria.

Chromosomal localization of DNA amplifications in neuroblastoma tumors using cDNA microarray comparative genomic hybridization

Conventional comparative genomic hybridization (CGH) profiling of neuroblastomas has identified many genomic aberrations, although the limited resolution has precluded a precise localization of sequences of interest within amplicons. To map high copy number genomic gains in clinically matched stage IV neuroblastomas, CGH analysis using a 19,200-feature cDNA microarray was used. A dedicated (freely available) algorithm was developed for rapid in silico determination of chromosomal localizations of microarray cDNA targets, and for generation of an ideogram-type profile of copy number changes. Using these methodologies, novel gene amplifications undetectable by chromosome CGH were identified, and larger MYCN amplicon sizes (in one tumor up to 6 Mb) than those previously reported in neuroblastoma were identified. The genes HPCAL1, LPIN1/KIAA0188, NAG, and NSE1/LOC151354 were found to be coamplified with MYCN. To determine whether stage IV primary tumors could be further subclassified based on their genomic copy number profiles, hierarchical clustering was performed. Cluster analysis of microarray CGH data identified three groups: 1) no amplifications evident, 2) a small MYCN amplicon as the only detectable imbalance, and 3) a large MYCN amplicon with additional gene amplifications. Application of CGH to cDNA microarray targets will help to determine both the variation of amplicon size and help better define amplification-dependent and independent pathways of progression in neuroblastoma.

Mitochondrial defects in cancer

Mitochondria play important roles in cellular energy metabolism, free radical generation, and apoptosis. Defects in mitochondrial function have long been suspected to contribute to the development and progression of cancer. In this review article, we aim to provide a brief summary of our current understanding of mitochondrial genetics and biology, review the mtDNA alterations reported in various types of cancer, and offer some perspective as to the emergence of mtDNA mutations, their functional consequences in cancer development, and therapeutic implications.

Mitochondrial DNA in human malignancy

Alterations in expression of mitochondrial DNA (mtDNA)-encoded polypeptides required for oxidative phosphorylation and cellular ATP generation may be a general characteristic of cancer cells. Mitochondrial DNA has been proposed to be involved in carcinogenesis because of high susceptibility to mutations and limited repair mechanisms in comparison to nuclear DNA. Since mtDNA lacks introns, it has been suggested that most mutations will occur in coding sequences and subsequent accumulation of mutations may lead to tumor formation. The mitochondrial genome is dependent upon the nuclear genome for transcription, translation, replication and repair, but precise mechanisms for how the two genomes interact and integrate with each other are poorly understood. In solid tumors, elevated expression of mtDNA-encoded subunits of the mitochondrial electron respiratory chain may reflect mitochondrial adaptation to perturbations in cellular energy requirements. In this paper, we review mitochondrial genomic aberrations reported in solid tumors of the breast, colon, stomach, liver, kidney, bladder, head/neck and lung as well as for hematologic diseases such as leukemia, myelodysplastic syndrome and lymphoma. We include data for elevated expression of mtDNA-encoded electron respiratory chain subunits in breast, colon and liver cancers and also the mutations reported in cancers of the colon, stomach, bladder, head/neck and lung. Finally, we examine the role of reactive oxygen species (ROS) generated by mitochondria in the process of carcinogenesis.

Mitochondria are selectively eliminated from eukaryotic cells after blockade of caspases during apoptosis

Pan caspase inhibitors are potentially powerful cell-protective agents that block apoptosis in response to a wide variety of insults that cause tissue degeneration. In many conditions, however, the blockade of apoptosis by caspase inhibitors does not permit long-term cell survival, but the reasons are not entirely clear. Here we show that the blockade of apoptosis by Boc.Aspartyl(O-methyl)CH2F can result in the highly selective elimination of the entire cohort of mitochondria, including mitochondrial DNA, from both neurons and HeLa cells, irrespective of the stimulus used to trigger apoptosis. In cells that lose their mitochondria, the nuclear DNA, Golgi apparatus, endoplasmic reticulum, centrioles, and plasma membrane remain undamaged. The capacity to remove mitochondria is both specific and regulated since mitochondrial loss in neurons is completely prevented by the expression of the antiapoptotic protein Bcl-2 and partially suppressed by the autolysosomal inhibitor bafilomycin. Cells without mitochondria are more tolerant to an anaerobic environment but are essentially irreversibly committed to death. Prevention of mitochondrial loss may be crucial for the long-term regeneration of tissues emerging from an apoptotic episode in which death was prevented by caspase blockade.

Identification of a novel human mitochondrial D-loop RNA species which exhibits upregulated expression following cellular immortalization

We report the identification and characterization of a novel human mitochondrial RNA species approximately 0.47 kb long that is transcribed from the mtDNA L-strand and is derived from the D-loop. Its expression increases when human cells become immortal, a key event in tumorigenesis. The RNA is therefore designated IDL (Immortalization-associated D-Loop). Sequence and hybrid cell analyses suggest that the increased level of IDL RNA in immortal cells is due to a recessive change, possibly in the activity of a trans-acting factor that controls IDL RNA expression.

Frequent assimilation of mitochondrial DNA by grasshopper nuclear genomes

Multiple copies of mitochondrial-like DNA were found in the brown mountain grasshopper, Podisma pedestris (Orthoptera: Acrididae), paralogous to COI and ND5 regions. The same was discovered using the ND5 regions of nine other grasshopper species from four separate subfamilies (Podisminae, Calliptaminae, Cyrtacanthacridinae, and Gomphocerinae). The extra ND5-like sequences were shown to be nuclear in the desert locust, Schistocerca gregaria (Cyrtacanthacridinae), and probably so in P. pedestris and an Italopodisma sp. (Podisminae). Eighty-seven different ND5-like nuclear mitochondrial pseudogenes (Numts) were sequenced from 12 grasshopper individuals. Different nuclear mitochondrial pseudogenes, if descended from the same mitochondrial immigrant, will have diverged from each other under no selective constraints because of their loss of functionality. Evidence of selective constraints in the differences between any two Numt sequences (e.g., if most differences are at third positions of codons) implies that they have separate mitochondrial origins. Through pairwise comparisons of pseudogene sequences, it was established that there have been at least 12 separate mtDNA integrations into P. pedestris nuclear genomes. This is the highest reported rate of horizontal transfer between organellar and nuclear genomes within a single animal species. The occurrence of numerous mitochondrial pseudogenes in nuclear genomes derived from separate integration events appears to be a common phenomenon among grasshoppers. More than one type of mechanism appears to have been involved in generating the observed grasshopper Numts.

Mitochondrial DNA determines the cellular response to cancer therapeutic agents

Mutations in the mitochondrial genome leading to mitochondrial dysfunction have been reported in a variety of cancers. However, the potential implication of these findings in the cellular response to cancer therapeutic agents is unclear. To examine the importance of mitochondrial DNA (mitDNA) encoded functions in cancer therapeutic response, we determined the clonogenic survival of HSL2 (Rho+, HeLa subline), and its derivative cell line lacking mitDNA (Rho0) after exposure to different anticancer agents. We found that isogenic Rho0 cells lacking mitDNA were extremely resistant to adriamycin and photodynamic therapy (PDT) induced cell death, whereas the Rho+ cell line was sensitive. However, there was no measurable difference in the responses of these cell lines to either alkylating agent or gamma-radiation. We show that the development of resistance to adriamycin was not due to changes in apoptotic cell death, cell cycle response or to the uptake of adriamycin in isogenic Rho0 cells. We also demonstrate that exposure of HeLa cells to adriamycin leads to mutations in mitDNA. These studies provide direct evidence that mitDNA plays an important role in cellular sensitivity to cancer therapeutic agents.

Escape of mitochondrial DNA to the nucleus in yme1 yeast is mediated by vacuolar-dependent turnover of abnormal mitochondrial compartments

Inactivation of Yme1p, a mitochondrially-localized ATP-dependent metallo-protease in the yeast Saccharomyces cerevisiae, causes a high rate of DNA escape from mitochondria to the nucleus as well as pleiotropic functional and morphological mitochondrial defects. The evidence presented here suggests that the abnormal mitochondria of a yme1 strain are degraded by the vacuole. First, electron microscopy of Yme1p-deficient strains revealed mitochondria physically associated with the vacuole via electron dense structures. Second, disruption of vacuolar function affected the frequency of mitochondrial DNA escape from yme1 and wild-type strains. Both PEP4 or PRC1 gene disruptions resulted in a lower frequency of mitochondrial DNA escape. Third, an in vivo assay that monitors vacuole-dependent turnover of the mitochondrial compartment demonstrated an increased rate of mitochondrial turnover in yme1 yeast when compared to the rate found in wild-type yeast. In this assay, vacuolar alkaline phosphatase, encoded by PHO8, was targeted to mitochondria in a strain bearing disruption to the genomic PHO8 locus. Maturation of the mitochondrially localized alkaline phosphatase pro-enzyme requires proteinase A, which is localized in the vacuole. Therefore, alkaline phosphatase activity reflects vacuole-dependent turnover of mitochondria. This assay reveals that mitochondria of a yme1 strain are taken up by the vacuole more frequently than mitochondria of an isogenic wild-type strain when these yeast are cultured in medium necessitating respiratory growth. Degradation of abnormal mitochondria is one pathway by which mitochondrial DNA escapes and migrates to the nucleus.

Receptor expression, cytogenetic, and molecular analysis of six continuous human glioma cell lines

Six human glioma cell lines were established from tissues obtained from five patients diagnosed with Kernohan grade IV glioblastoma multiforme and one from a patient with a grade II astrocytoma. One line was from a recurrent patient who had received prior therapy; the other lines were derived from patients at initial diagnosis and/or before cytoreductive therapies other than surgery were given. Considerable variability in phenotypic, karyotypic, and cell surface marker expression was displayed between the six human glioma cell lines. The karyotypes ranged from apparently normal (grade II astrocytoma) to those with complex rearrangements. Trisomy of chromosome 7 was the most common abnormality. The extensive cytogenetic and molecular characterization of these lines may facilitate their utilization in cellular and molecular biologic studies.

Mutagenesis, tumorigenicity, and apoptosis: are the mitochondria involved?

Early studies have shown mitochondrially-mediated oxidative phosphorylation is diminished in cancer cells, with glycolysis being the main source of energy production. More recent provocative reports have indicated that the mitochondria may be involved in a host of different aspects of tumorigenesis, including mutagenesis, maintenance of the malignant phenotype, and control of apoptosis. These studies have broadened the possible roles mitochondria may play in malignancy. Further studies to define the importance of mitochondria should revolve around the functional assessment of these changes in vitro and in vivo, and will be interesting for determining their significance in human cancer.

Selected nuclear LINE elements with mitochondrial-DNA-like inserts are more plentiful and mobile in tumor than in normal tissue of mouse and rat

The nuclear DNA of normal and tumor mouse and rat tissue was examined for mitochondrial-DNA-like inserts by means of the Southern blot technique. The two probes were 32P-labeled cloned mitochondrial DNA. KpnI, which doesn't cut either mitochondrial DNA, was one of the restriction enzymes, while the enzymes that fragment mitochondrial DNA were for mouse and rat PstI and BamHI, respectively. When KpnI alone was used in the procedure a nuclear LINE family whose elements had mitochondrial-DNA-like insertions was selected. Such elements were much more abundant in tumor than in normal tissue. The results with PstI alone and BamHI alone and each combined with KpnI indicated that there were mobile LINE elements with mitochondrial-DNA-like inserts in the nuclear genome of tumor. The mouse tissues were normal liver and a transplantable lymphoid leukemic ascites cell line L1210 that had been carried for 40 years. The rat tissues were normal liver and a hepatoma freshly induced by diethylnitrosoamine in order to minimize the role of 40 years of transplantation. Our unitary hypothesis for carcinogenesis of 1971, which suggested these experiments, has been augmented to include mobile nuclear elements with inserts of mitochondrial-DNA-like sequences. Such elements have been related to diseases of genetic predisposition such as breast cancer and Huntington's disease.