Microsatellite instability and mutation of mitochondrial and nuclear DNA in gastric carcinoma

Gastric tumorigenesis induced by combining Helicobacter pylori infection and chronic alcohol through IL-10 inhibition

Helicobacter pylori (H. pylori) infection and alcohol intake are independent risk factors in gastric carcinogenesis; however, until now, the combined effect of H. pylori infection and alcohol consumption and the specific mechanism is still problematic. Here, we developed a series of mouse models that progress from chronic gastritis to gastric cancer, induced by infecting H. pylori combined with chronic alcohol consumption and then determining the molecular mechanism of the progression by flow cytometry, Western blotting, qPCR, Mito Traker assay in the gastric cancer and T-cell lines. Interleukin-10 (IL-10) knockout mice was used to determine whether IL-10 deficiency directly contribute to H. pylori and alcohol induced gastric tumorigenesis. Alcohol consumption, together with H. pylori infection, causes gastric cancer; IL-10 downregulation and mitochondrial metabolic dysfunction in CD8 + cells are also involved. IL-10 knockout accelerates tumor development in mice with either H. pylori infection or alcohol induced gastric cancer or both. IL-10 inhibits glucose uptake and glycolysis and promotes oxidative phosphorylation with lactate inhibition. Consequently, in the absence of IL-10 signaling, CD8 + cells accumulate damaged mitochondria in a mouse model of gastric cancer induced with the combination of alcohol plus H. pylori infection, and this results in mitochondrial dysfunction and production of IL-1β. IL-1β promotes H. pylori infection and reduces NKX6.3 gene expression, resulting in increased cancer cell survival and proliferation. Gastric cancer can be induced by combination of Helicobacter pylori infection and chronic alcohol consumption through IL-10 inhibition induced CD8 + cells dysfunction and NKX6.3 suppression.

The Uprising of Mitochondrial DNA Biomarker in Cancer

Cancer is a heterogeneous group of diseases, the progression of which demands an accumulation of genetic mutations and epigenetic alterations of the human nuclear genome or possibly in the mitochondrial genome as well. Despite modern diagnostic and therapeutic approaches to battle cancer, there are still serious concerns about the increase in death from cancer globally. Recently, a growing number of researchers have extensively focused on the burgeoning area of biomarkers development research, especially in noninvasive early cancer detection. Intergenomic cross talk has triggered researchers to expand their studies from nuclear genome-based cancer researches, shifting into the mitochondria-mediated associations with carcinogenesis. Thus, it leads to the discoveries of established and potential mitochondrial biomarkers with high specificity and sensitivity. The research field of mitochondrial DNA (mtDNA) biomarkers has the great potential to confer vast benefits for cancer therapeutics and patients in the future. This review seeks to summarize the comprehensive insights of nuclear genome cancer biomarkers and their usage in clinical practices, the intergenomic cross talk researches that linked mitochondrial dysfunction to carcinogenesis, and the current progress of mitochondrial cancer biomarker studies and development.

Novel Strategies for Disrupting Cancer-Cell Functions with Mitochondria-Targeted Antitumor Drug-Loaded Nanoformulations

Any variation in normal cellular function results in mitochondrial dysregulation that occurs in several diseases, including cancer. Such processes as oxidative stress, metabolism, signaling, and biogenesis play significant roles in cancer initiation and progression. Due to their central role in cellular metabolism, mitochondria are favorable therapeutic targets for the prevention and treatment of conditions like neurodegenerative diseases, diabetes, and cancer. Subcellular mitochondria-specific theranostic nanoformulations for simultaneous targeting, drug delivery, and imaging of these organelles are of immense interest in cancer therapy. It is a challenging task to cross multiple barriers to target mitochondria in diseased cells. To overcome these multiple barriers, several mitochondriotropic nanoformulations have been engineered for the transportation of mitochondria-specific drugs. These nanoformulations include liposomes, dendrimers, carbon nanotubes, polymeric nanoparticles (NPs), and inorganic NPs. These nanoformulations are made mitochondriotropic by conjugating them with moieties like dequalinium, Mito-Porter, triphenylphosphonium, and Mitochondria-penetrating peptides. Most of these nanoformulations are meticulously tailored to control their size, charge, shape, mitochondriotropic drug loading, and specific cell-membrane interactions. Recently, some novel mitochondria-selective antitumor compounds known as mitocans have shown high toxicity against cancer cells. These selective compounds form vicious oxidative stress and reactive oxygen species cycles within cancer cells and ultimately push them to cell death. Nanoformulations approved by the FDA and EMA for clinical applications in cancer patients include Doxil, NK105, and Abraxane. The novel use of these NPs still faces tremendous challenges and an immense amount of research is needed to understand the proper mechanisms of cancer progression and control by these NPs. Here in this review, we summarize current advancements and novel strategies of delivering different anticancer therapeutic agents to mitochondria with the help of various nanoformulations.

Clinical Significance of the D-Loop Gene Mutation in Mitochondrial DNA in Laryngeal Cancer

Objective

The aim of the present study was to investigate the D-loop gene mutation and microsatellite instability in the mitochondrial DNA (mtDNA) and the correlation with the clinical and pathological parameters in laryngeal cancer.

Methods

The tumor tissues and paratumor tissues in 60 cases of laryngeal cancer were selected, and DNA was extracted from these tissues. The D-loop region in mtDNA was amplified by PCR with the gene sequence of the amplified product being detected. The gene sequence of the detected region was compared with the revised Cambridge Reference Sequence (rCRS) and the related database by using the Mitomaster software. The correlation between the D-loop gene mutation and the clinical and pathological parameters was investigated.

Results

A total of 174 mutations across 38 sites were detected in 51 (85%) of samples. Most of the mutations were concentrated in the high various (HV) I region, and the main types of mutations were the substitution of a single base or insertion and deletion of a single base. There was also microsatellite instability in the D310 region. The statistical results showed that there was no correlation between the age, gender, tumor diameter, and TNM stage, and the number of the D-loop mutations in mtDNA (P > 0.05).

Conclusion

There existed high-frequency mutation of the D-loop gene in mtDNA in laryngeal cancer, which might play an important role in the pathogenesis of laryngeal cancer.

Gastric cancer is associated with a high rate of microsatellite instability versus chronic gastritis: A retrospective study

Objective: Microsatellite instability (MSI) in gastric cancer contributes to genetic complexities of gastric cancer. In the current study, we employed a panel of mononucleotide and dinucleotide markers to detect MSI in 99 gastric cancer patients and 91 chronic gastritis patients and further analyzed the association of MSI with clinicopathologic variables of the study patients.

Methods: We retrospectively analyzed the clinicopathologic data of primary gastric cancer patients and chronic gastritis patients. MSI was analyzed using five microsatellite markers, including D2S12, D5S346, D17S799, BAT26, and D18S34. MSI was defined as either a band shift or the appearance of a novel band in DNA. Multivariate logistic regression analysis was used to predict risk of MSI.

Results: Seventeen (17.2%) gastric cancer patients and 7 (7.7%) chronic gastritis patients were positive for MSI (P=0.012). Multivariate analysis further showed that gastric cancer was associated with a significantly higher likelihood for MSI versus gastritis (OR 3.73; 95% CI 1.19, 11.72; P=0.024) while age, drinking or smoking was not associated with increased MSI.

Conclusion: Gastric cancer is associated with a high rate of MSI. MSI should be further explored in future studies with a larger sample size for its role in gastric cancer development and as a predictive biomarker.

Mitochondrial dysfunction and chronic lung disease

The functions of body gradually decrease as the age increases, leading to a higher frequency of incidence of age-related diseases. Diseases associated with aging in the respiratory system include chronic obstructive pulmonary disease (COPD), IPF (idiopathic pulmonary fibrosis), asthma, lung cancer, and so on. The mitochondrial dysfunction is not only a sign of aging, but also is a disease trigger. This article aims to explain mitochondrial dysfunction as an aging marker, and its role in aging diseases of lung. We also discuss whether the mitochondria can be used as a target for the treatment of aging lung disease.

Reduced Levels of ATP Synthase Subunit ATP5F1A Correlate with Earlier-Onset Prostate Cancer

Switching of cellular energy production from oxidative phosphorylation (OXPHOS) to aerobic glycolysis occurs in many types of tumors. However, the significance of energy metabolism for the development of prostate carcinoma is poorly understood. We investigated the expression of OXPHOS complexes in 94 human prostate carcinomas and paired benign tissue using immunohistochemistry. Overall mitochondrial mass was upregulated in carcinomas compared to benign prostate tissue in all Gleason grades. A significant direct correlation between the expression of OXPHOS complexes I, II, and V and the Gleason score was observed. However, 17% of prostate carcinomas and 18% of benign prostate tissues showed isolated or combined deficiency of OXPHOS complexes (one deficiency in 12% of the tumors, combined deficiencies in 5%). Complex I was absent in 9% of the samples, with only parts of the tumor affected. ATP5F1A, a complex V protein, was the most frequently affected subunit, in 10% of tumors and 11% of benign prostate tissues (but not both tissues in any single patient). A possible role of complex V in prostate cancer development is suggested by the significant positive correlation of ATP5F1A levels with earlier-onset prostate cancer (age at diagnosis and at prostatectomy) and free PSA percentage. The relatively high percentage (17%) of prostate carcinomas with regional foci of partial OXPHOS complex deficiencies could have important therapeutic implications.

In colonic ρ0 (rho0) cells reduced mitochondrial function mediates transcriptomic alterations associated with cancer

Background

Mitochondrial reprogramming has emerged as a hallmark of cancer pathobiology. Although it is believed this reprogramming is essential for cancer cells to thrive, how it supports cancer pathobiology is unclear. We previously generated colonic ρ0 (rho0) cells with reduced mitochondrial energy function and acquired their transcriptional signature. Here, we utilized a bioinformatics approach to identify their changes linked to cancer pathobiology.

Methods

Human colon cancer HCT116 cells, control and ρ0, were used for qPCR. Bioinformatics analysis: GeneCards, Kaplan-Meier Survival, GENT, cBioPortal.

Results

The colonic ρ0 transcriptome was linked with proliferation, DNA replication, survival, tumor morphology, and cancer. Among differentially expressed transcripts, 281 were regulators or biomarkers of human colon cancer especially those with inflammatory microsatellite instability (MSI). We identified and validated novel transcripts in ρ0 cells with altered expression in human colon cancer. Among them DGK1, HTR7, FLRT3, and ZBTB18 co-occurred with established regulators of human colon cancer pathobiology. Also, increased levels of DGKI, FLRT3, ZBTB18, and YPEL1 as well as decreased levels of HTR7, and CALML6 were linked to substantially poorer patient survival.

Conclusion

We identified established and novel regulators in colon cancer pathobiology that are dependent on mitochondrial energy reprogramming and linked to poorer patient survival.

Oxidative Phosphorylation System in Gastric Carcinomas and Gastritis

Switching of cellular energy production from oxidative phosphorylation (OXPHOS) by mitochondria to aerobic glycolysis occurs in many types of tumors. However, the significance of this switching for the development of gastric carcinoma and what connection it may have to Helicobacter pylori infection of the gut, a primary cause of gastric cancer, are poorly understood. Therefore, we investigated the expression of OXPHOS complexes in two types of human gastric carcinomas ("intestinal" and "diffuse"), bacterial gastritis with and without metaplasia, and chemically induced gastritis by using immunohistochemistry. Furthermore, we analyzed the effect of HP infection on several key mitochondrial proteins. Complex I expression was significantly reduced in intestinal type (but not diffuse) gastric carcinomas compared to adjacent control tissue, and the reduction was independent of HP infection. Significantly, higher complex I and complex II expression was present in large tumors. Furthermore, higher complex II and complex III protein levels were also obvious in grade 3 versus grade 2. No differences of OXPHOS complexes and markers of mitochondrial biogenesis were found between bacterially caused and chemically induced gastritis. Thus, intestinal gastric carcinomas, but not precancerous stages, are frequently characterized by loss of complex I, and this pathophysiology occurs independently of HP infection.

MtDNA As a Cancer Marker: A Finally Closed Chapter?

Sequence alterations of the mitochondrial DNA (mtDNA) have been identified in many tu-mor types. Their nature is not entirely clear. Somatic mutation or shifts of heteroplasmic mtDNA vari-ants may play a role. These sequence alterations exhibit a sufficient frequency in all tumor types investi-gated thus far to justify their use as a tumor marker. This statement is supported by the high copy num-ber of mtDNA, which facilitates the detection of aberrant tumor-derived DNA in bodily fluids. This will be of special interest in tumors, which release a relatively high number of cells into bodily fluids, which are easily accessible, most strikingly in urinary bladder carcinoma. Due to the wide distribution of the observed base substitutions, deletions or insertions within the mitochondrial genome, high efforts for whole mtDNA sequencing (16.5 kb) from bodily fluids would be required, if the method would be in-tended for initial tumor screening. However, the usage of mtDNA for sensitive surveillance of known tumor diseases is a meaningful option, which may allow an improved non-invasive follow-up for the urinary bladder carcinoma, as compared to the currently existing cytological or molecular methods. Fol-lowing a short general introduction into mtDNA, this review demonstrates that the scenario of a sensi-tive cancer follow-up by mtDNA-analysis deserves more attention. It would be most important to inves-tigate precisely in the most relevant tumor types, if sequencing approaches in combination with simple PCR-assays for deletions/insertions in homopolymeric tracts has sufficient sensitivity to find most tu-mor-derived mtDNAs in bodily fluids.

Genetic alterations and epigenetic alterations of cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs) are one major type of component identified in the tumor microenvironment. Studies have focused on the genetic and epigenetic status of CAFs, since they are critical in tumor progression and differ phenotypically and functionally from normal fibroblasts. The present review summarizes the recent achievements in understanding the gene profiles of CAFs and pays special attention to their possible epigenetic alterations. A total of 7 possible genetic alterations and epigenetic changes in CAFs are discussed, including gene differential expression, karyotype analysis, gene copy number variation, loss of heterozygosis, allelic imbalance, microsatellite instability, post-transcriptional control and DNA methylation. These genetic and epigenetic characteristics are hypothesized to provide a deep understanding of CAFs and a perspective on their clinical significance.

H. pylori infection is related to mitochondrial microsatellite instability in gastric carcinogenesis

BACHGROUND

To assess the correlation of H. pylori infection with mitochondrial microsatellite instability (mtMSI) and IL-8 in gastric carcinogenesis.

METHODS

H. pylori infection was evaluated through histology and a urease breath test; mtMSI was measured using PCR-single strand conformation polymorphism (PCR-SSCP); IL-8 was analyzed with ELISA methods.

RESULTS

The detection rate of mtMSI was significantly higher in specimens with H. pylori infection than in those without H. pylori infection (P < 0.05). The levels of IL-8 were significantly higher in specimens with mtMSI than in those without mtMSI (P < 0.01).An association of mtMSI with the intestinal histological type was found (P < 0.05). Increased IL-8 levels induced by H. pylori were related to the invasion, lymphnode spreading and clinical stage of gastric cancer (P < 0.05).

CONCLUSIONS

H. pylori infection is related to mitochondrial microsatellite instability in the early steps of gastric cancer development. IL-8 may play a role in the development of mtMSI induced by H. pylori. Our results support a role for mtMSI in different mechanisms of gastric carcinogenesis.

RAD51 G135C genetic polymorphism and their potential role in gastric cancer induced by Helicobacter pylori infection in Bhutan

In order to evaluate the role of the RAD51 G135C genetic polymorphism on the risk of gastric cancer induced by Helicobacter pylori infection, we determined allele frequency and genotype distribution of this polymorphism in Bhutan--a population documented with high prevalence of gastric cancer and extremely high prevalence of H. pylori infection. The status of RAD51 G135C was examined by restriction fragment length polymorphism analysis of PCR amplified fragments and sequencing. Histological scores were evaluated according to the updated Sydney system. G135C carriers showed significantly higher scores for intestinal metaplasia in the antrum than G135G carriers [mean (median) 0·33 (0) vs. 0·08 (0), P = 0·008]. Higher scores for intestinal metaplasia of G135C carriers compared to those of G135G carriers were also observed in H. pylori-positive patients [0·3 (0) vs. 0·1 (0), P = 0·002] and H. pylori-positive patients with gastritis [0·4 (0) vs. 0·1 (0), P = 0·002] but were not found in H. pylori-negative patients. Our findings revealed that a combination of H. pylori infection and RAD51 G135C genotype of the host showed an increasing score for intestinal metaplasia. Therefore, RAD51 G135C might be the important predictor for gastric cancer of H. pylori-infected patients.

Mitochondrial microsatellite instability in patients with metastatic colorectal cancer

Mitochondrial microsatellite instability (mtMSI), a change in length in mtDNA microsatellite sequences between normal and tumor tissue, has been described as a frequent occurrence in colorectal cancer (CRC). We evaluated the prevalence and prognostic value of mtMSI and its relation to nuclear microsatellite instability (MSI) in patients with metastatic CRC (mCRC). At six loci (D310, D514, D16184, ND1, ND5, and COX1), the mitochondrial DNA sequence was analyzed in normal and tumor tissue, and the mtMSI status was determined. We evaluated the prevalence and outcome in terms of overall survival (OS) in 83 CRC patients with a MSI tumor (including 39 patients with Lynch syndrome) and in 99 mCRC patients with a microsatellite stable (MSS) tumor. A meta-analysis was performed to compare our findings with existing data. mtMSI at the D-loop region was found in 54.4 % (99 out of 182) of all patients. Prevalence of mtMSI was most pronounced at the D310 locus (50.5 %). Prevalence of mtMSI at the D-loop region was not different among patients with MSI compared to MSS tumors. There was no effect of mtMSI on prognosis in patients with MSI or MSS tumors. Prevalence of mtMSI was high in mCRC patients with both MSI and MSS tumors, but there was no correlation with prognosis. mtMSI was particularly present at the D310 locus.

Identification of novel genes involved in gastric carcinogenesis by suppression subtractive hybridization

Gastric cancer (GC) is one of the most common and life-threatening types of malignancies. Identification of the differentially expressed genes in GC is one of the best approaches for establishing new diagnostic and therapeutic targets. Furthermore, these investigations could advance our knowledge about molecular biology and the carcinogenesis of this cancer. To screen for the overexpressed genes in gastric adenocarcinoma, we performed suppression subtractive hybridization (SSH) on gastric adenocarcinoma tissue and the corresponding normal gastric tissue, and eight genes were found to be overexpressed in the tumor compared with those of the normal tissue. The genes were ribosomal protein L18A, RNase H2 subunit B, SEC13, eukaryotic translation initiation factor 4A1, tetraspanin 8, cytochrome c oxidase subunit 2, NADH dehydrogenase subunit 4, and mitochondrially encoded ATP synthase 6. The common functions among the identified genes include involvement in protein synthesis, involvement in genomic stability maintenance, metastasis, metabolic improvement, cell signaling pathways, and chemoresistance. Our results provide new insights into the molecular biology of GC and drug discovery: each of the identified genes could be further investigated as targets for prognosis evaluation, diagnosis, treatment, evaluation of the response to new anticancer drugs, and determination of the molecular pathogenesis of GC.

Nested PCR for mtDNA-4977-bp deletion and comet assay for DNA damage - a combined method for radiosensitivity evaluation of tumor cells

To identify an effective method of evaluating the radiosensitivity of human tumor cell lines in vitro, the present study adopted mtDNA-4977-bp deletion coupled with comet assay. The three human tumor cell lines applied were HepG₂, EC-9706 and MCF-7. The surviving fraction (SF), ratio of the mtDNA-4977-bp deletion and DNA damage were detected by MTT assay, nested polymerase chain reaction (PCR) technique and comet assay, respectively. Clearly, lower SFs were found for the HepG₂ and EC-9706 cells as compared with the MCF-7 cells following irradiation at doses of 2, 4 and 8 Gy, indicating a higher radiosensitivity for the HepG₂ and EC-9706 cells. Additionally, no significant differences were identified in the mtDNA-4977-bp deletions found among HepG₂, EC-9706 and MCF-7 cells by PCR following 1- or 4-Gy γ-ray irradiation, while increased deletion ratios of mtDNA-4977 bp were observed in HepG₂ and EC-9706 cells following 8-Gy irradiation, in contrast to decreases in MCF-7 cells. The most notable differences among these three tumor cell lines were observed by comet assay following 8-Gy γ-ray irradiation. A combined method of nested PCR and comet assay, therefore, is the most effective and accurate method in evaluating the radiosensitivity of tumor cells.

The role of mitochondria in the development and progression of lung cancer

The influence of mitochondria in human health and disease is a rapidly expanding topic in the scientific literature due to their integral roles in cellular death and survival. Mitochondrial biology and alterations in function were first linked to cancer in the 1920s with the discovery of the Warburg effect. The utilization of aerobic glycolysis in ATP synthesis was the first of many observations of metabolic reprogramming in cancer.

Mitochondrial dysfunction in cancer has expanded to include defects in mitochondrial genomics and biogenesis, apoptotic signaling and mitochondrial dynamics. This review will focus on the role of mitochondria and their influence on cancer initiation, progression and treatment in the lung.

Improving the therapeutic efficiency of ginger extract for treatment of colon cancer using a suitably designed multiparticulate system

Ginger extract (GE), a potential natural anticancer agent, has compromised therapeutic utilization due to poor bioavailability and physicochemical properties. Present study aimed at assigning GE with a pharmaceutical couture so as to improve its biopharmaceutical performance by monitoring its localized (though prolonged) delivery in the distal parts of gastrointestinal tract for the treatment of colon cancer. Alginate beads entrapping 85.9 ± 1.78% GE were subjected to Eudragit S100 coating. Latter is insoluble at acidic and near neutral (6.8) pH of stomach and upper part of small intestine and it led to 50% retardation (upto 12 h) in release of GE. However, it was solubilised at pH > 7.0 resulting in colon targeted system. Developed beads were free flowing, showed a particle size of 0.9 ± 0.006 mm and super class-II release controlled by swelling and polymer relaxation. Preclinical evaluation using 1,2-dimethylhydrazine-induced colon cancer, in male Wistar rats, in terms of histopathology, oxidative stress, mitochondrial complex activity, β-glucuronidase and ammonia concentration determinations indicated GE loaded beads (50 mg/kg) to be significantly better (p < 0.05) than free GE. Highlight of the study was that GE loaded coated alginate beads were administered after the induction of colon cancer and significant recession of the cancers was observed after 4 weeks of treatment.

Detected microsatellite polymorphisms in genetically altered inbred mouse strains

Microsatellites are 50-200 repetitive DNA sequences composed of 1- to 6-base-pair-long reiterative motifs within the genome. They are vulnerable to DNA modifications, such as recombination and/or integration, and are recognized as "sentinel" DNA. Our previous report indicated that the genotypes of the microsatellite loci could change from mono- to poly-morphisms (CMP) in gene knockout (KO) mice, implying that genetic modification induces microsatellite mutation. However, it is still unclear whether the random insertion of DNA fragments into mice genomes produced via transgene (Tg) or N-ethyl-N-nitrosourea (ENU) would also result in microsatellite mutations or microsatellite loci genotypes changes. This study was designed to find possible clues to answer this question. In brief, 198 microsatellite loci that were distributed among almost all of the chromosomes (except for the Y) were examined through polymerase chain reaction to screen possible CMPs in six Tg strains. First, for each strain, the microsatellite sequences of all loci were compared between Tg and the corresponding background strain to exclude genetic interference. Simultaneously, to exclude spontaneous mutation-related CMPs that might exist in the examined six strains, mice from five spontaneously mutated inbred strains were used as the negative controls. Additionally, the sequences of all loci in these spontaneous mutated mice were compared to corresponding genetic background controls. The results showed that 40 of the 198 (20.2%) loci were identified as having CMPs in the examined Tg mice strains. The CMP genotypes were either homozygous or heterozygous compared to the background controls. Next, we applied the 40 CMP positive loci in ENU-mutated mice and their corresponding background controls. After that, a general comparison of CMPs that exist among Tg, ENU-treated and KO mouse strains was performed. The results indicated that four (D11mit258, D13mit3, D14mit102 and DXmit172) of the 40 (10%) CMP loci were shared by Tg and KO mice, two (D15mit5 and D14mit102) (5%) by Tg and ENU-treated mice, and one (D14mit102) (2.5%) by all three genetic modifications. Collectively, our study implies that genetic modifications by KO, Tg or chemical mutant can trigger microsatellite CMPs in inbred mouse strains. These shared microsatellite loci could be regarded as "hot spots" of microsatellite mutation for genetic monitoring in genetic modified mice.

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.

Mitochondrial DNA microsatellite instability in colorectal cancer

AIM: To investigate microsatellite instability in the non-coding region and coding regions of mitochondrial DNA in colorectal cancer.

METHODS: Mitochondrial DNA was extracted from 50 cases of fresh CRC samples and matched tumor-adjacent noncancerous tissue. Fluorescence polymerase chain reaction and short tandem repeat locus scanning were conducted to analyze microsatellite instability.

RESULTS: Mitochondrial DNA microsatellite instability was detected in 19 of 50 (38%) patients with CRC. The microsatellite instability in the non-coding region and coding region of mitochondrial DNA had a significant correlation (χ² = 4.929, P = 0.026).

CONCLUSION: There is a high frequency of microsatellite instability in mitochondrial DNA of CRC patients, and mitochondrial DNA microsatellite instability may play a role in the occurrence of colorectal cancer.

Mitochondrial and nuclear genes of mitochondrial components in cancer

Although the observation of aerobic glycolysis of tumor cells by Otto v. Warburg had demonstrated abnormalities of mitochondrial energy metabolism in cancer decades ago, there was no clear evidence for a functional role of mutant mitochondrial proteins in cancer development until the early years of the 21(st) century. In the year 2000, a major breakthrough was achieved by the observation, that several genes coding for subunits of the respiratory chain (ETC) complex II, succinate dehydrogenase (SDH) are tumor suppressor genes in heritable paragangliomas, fulfilling Knudson's classical two-hit hypothesis. A functional inactivation of both alleles by germline mutations and chromosomal losses in the tumor tissue was found in the patients. Later, SDH mutations were also identified in sporadic paragangliomas and pheochromocytomas. Genes of the mitochondrial ATP-synthase and of mitochondrial iron homeostasis have been implicated in cancer development at the level of cell culture and mouse experiments. In contrast to the well established role of some nuclear SDH genes, a functional impact of the mitochondrial genome itself (mtDNA) in cancer development remains unclear. Nevertheless, the extremely high frequency of mtDNA mutations in solid tumors raises the question, whether this small circular genome might be applicable to early cancer detection. This is a meaningful approach, especially in cancers, which tend to spread tumor cells early into bodily fluids or faeces, which can be screened by non-invasive methods.

Stable differences in intrinsic mitochondrial membrane potential of tumor cell subpopulations reflect phenotypic heterogeneity

Heterogeneity among cells that constitute a solid tumor is important in determining disease progression. Our previous work established that, within a population of metastatic colonic tumor cells, there are minor subpopulations of cells with stable differences in their intrinsic mitochondrial membrane potential (ΔΨm), and that these differences in ΔΨm are linked to tumorigenic phenotype. Here we expanded this work to investigate primary mammary, as well as colonic, tumor cell lines. We show that within a primary mammary tumor cell population, and in both primary and metastatic colonic tumor cell populations, there are subpopulations of cells with significant stable variations in intrinsic ΔΨm. In each of these 3 tumor cell populations, cells with relatively higher intrinsic ΔΨm exhibit phenotypic properties consistent with promotion of tumor cell survival and expansion. However, additional properties associated with invasive potential appear in cells with higher intrinsic ΔΨm only from the metastatic colonic tumor cell line. Thus, it is likely that differences in the intrinsic ΔΨm among cells that constitute primary mammary tumor populations, as well as primary and metastatic colonic tumor populations, are markers of an acquired tumor phenotype which, within the context of the tumor, influence the probability that particular cells will contribute to disease progression.

Association of mtDNA D-loop polymorphisms with risk of gastric cancer in Chinese population

The aim of present study was to evaluate the association of common polymorphisms detected in mitochondrial DNA (mtDNA) D-loop region (mononucleotide repetitive D310, single nucleotide polymorphism (SNP) D16521) with susceptibility to gastric cancer (GC) in northwestern Chinese population. A total of 180 GC patients and 218 healthy controls were investigated by using PCR- denaturing high performance liquid chromatography (DHPLC) assay. Genotype and allele distributions and haplotype construction were analyzed in case-control study. We found D310 and D16521 heteroplasmy were significantly different between GC cases and controls (p < 0.05), and D16521 homoplasmy showed association with histological grade of GC (p < 0.05). Haplotype 7C/T, 8C/C and 9C/C had significant association with GC risk implied from analysis of D310 and D16521. Taken together, these findings suggested that mtDNA D-Loop polymorphisms and haplotypes may contribute to genetic susceptibility to GC in Chinese population.

Mitochondrial microsatellite instability in gastric cancer and gastric epithelial dysplasia as a precancerous lesion

BACKGROUND

Genetic instability in gastric cancer represents a key molecular step that occurs early in the carcinogenesis process. To clarify the role of genetic instability in the progression from gastric dysplasia to gastric cancer, mitochondrial microsatellite instability (mtMSI) was studied in gastric cancer and gastric dysplasia.

METHODS

DNA was isolated from paired normal and tumoral tissues in 24 patients with gastric dysplasia (low grade) and 49 patients with gastric cancer. mtMSI was analyzed using eight microsatellite markers. mtMSI in gastric dysplasia was studied prospectively to elucidate the relation between mtMSI and gastric carcinogenesis.

RESULTS

mtMSI was found in 5 (10.2%) of 49 gastric cancer patients. The mtMSI phenotype was not associated with age, gender, and Helicobacter pylori infection. However, all of the mtMSI was found in intestinal-type gastric cancer (20.8%, p=0.02). In gastric dysplasia, mtMSI was detected in 3 (12.5%) of 24 patients with gastric dysplasia. mtMSI-positive gastric dysplasia showed a poor prognosis statistically compared to mtMSI negative through progression to high-grade dysplasia or gastric cancer.

CONCLUSIONS

These data suggest that mtMSI may be an early and important event in the progression of gastric carcinogenesis, especially in intestinal-type gastric cancer.

Helicobacter pylori infection generates genetic instability in gastric cells

The discovery that Helicobacter pylori is associated with gastric cancer has led to numerous studies that investigate the mechanisms by which H. pylori induces carcinogenesis. Gastric cancer shows genetic instability both in nuclear and mitochondrial DNA, besides impairment of important DNA repair pathways. As such, this review highlights the consequences of H. pylori infection on the integrity of DNA in the host cells. By down-regulating major DNA repair pathways, H. pylori infection has the potential to generate mutations. In addition, H. pylori infection can induce direct changes on the DNA of the host, such as oxidative damage, methylation, chromosomal instability, microsatellite instability, and mutations. Interestingly, H. pylori infection generates genetic instability in nuclear and mitochondrial DNA. Based on the reviewed literature we conclude that H. pylori infection promotes gastric carcinogenesis by at least three different mechanisms: (1) a combination of increased endogenous DNA damage and decreased repair activities, (2) induction of mutations in the mitochondrial DNA, and (3) generation of a transient mutator phenotype that induces mutations in the nuclear genome.

Implications of mitochondrial DNA mutations and mitochondrial dysfunction in tumorigenesis

Alterations in oxidative phosphorylation resulting from mitochondrial dysfunction have long been hypothesized to be involved in tumorigenesis. Mitochondria have recently been shown to play an important role in regulating both programmed cell death and cell proliferation. Furthermore, mitochondrial DNA (mtDNA) mutations have been found in various cancer cells. However, the role of these mtDNA mutations in tumorigenesis remains largely unknown. This review focuses on basic mitochondrial genetics, mtDNA mutations and consequential mitochondrial dysfunction associated with cancer. The potential molecular mechanisms, mediating the pathogenesis from mtDNA mutations and mitochondrial dysfunction to tumorigenesis are also discussed.

Somatic mutations in mitochondrial genome and their potential roles in the progression of human gastric cancer

BACKGROUND

Somatic mutation in mitochondrial DNA (mtDNA) has been proposed to contribute to initiation and progression of human cancer. In our previous study, high frequency of somatic mutations was found in the D-loop region of mtDNA of gastric cancers. However, it is unclear whether somatic mutations occur in the coding region of mtDNA of gastric cancers.

METHODS

Using DNA sequencing, we studied 31 gastric cancer specimens and corresponding non-cancerous stomach tissues. Moreover, a human gastric cancer SC-M1 cell line was treated with oligomycin to induce mitochondrial dysfunction. Cisplatin sensitivity and cell migration were analyzed.

RESULTS

We identified eight somatic mutations in the coding region of mtDNAs of seven gastric cancer samples (7/31, 22.6%). Patients with somatic mutations in the entire mtDNA of gastric cancers did not show significant association with their clinicopathologic features. Among the eight somatic mutations, five point mutations (G3697A, G4996A, G9986A, C12405T and T13015C) are homoplasmic and three mutations (5895delC, 7472insC and 12418insA) are heteroplasmic. Four (4/8, 50%) of these somatic mutations result in amino acid substitutions in the highly conserved regions of mtDNA, which potentially lead to mitochondrial dysfunction. In addition, in vitro experiments in SC-M1 cells revealed that oligomycin-induced mitochondrial dysfunction promoted resistance to cisplatin and enhanced cell migration. N-acetyl cysteine was effective in the prevention of the oligomycin-enhanced migration, which suggests that reactive oxygen species generated by defective mitochondria may be involved in the enhanced migration of SC-M1 cells.

GENERAL SIGNIFICANCE

Our results suggest that somatic mtDNA mutations and mitochondrial dysfunction may play an important role in the malignant progression of gastric cancer.

Analysis association between mitochondrial genome instability and xenobiotic metabolizing genes in human breast cancer

The aim of this study was to determine the existence of association between the genetic polymorphisms of metabolizing genes GSTM-1, GSTT-1, and NAT-2, and the presence of mitochondrial genome instability (mtGI) in breast cancer cases. Ninety-four pairs of tumoral/nontumoral breast cancer samples were analyzed. Our samples showed 40.42% of mtGI by analysis of two D-loop region markers, a (CA)n mtMS starting at the 514-bp position, and four informative MnlI sites between the 16,108-16,420-bp. GSTM-1 null genotype has shown a significant association with mtGI presence (chi(2) = 7.62; P = 0.006) in breast cancer cases; moreover, these genotypes also are related to an increased risk for mtDNA damage (odds ratio [OR] = 3.71 [1.41-9.88]; 95% Cornfield confidence interval [CI]). These results suggest that the absence of GSTM-1 enzymatic activity favors chemical actions in damaging the mtDNA. Analysis of GSTT-1 and NAT-2 polymorphisms showed no association with mtGI (chi(2) = 0.03; P = 0.87 and chi(2) = 2.76; P = 0.09, respectively). The analysis of invasive breast cancer cases showed mtGI in 74.36% of ILC cases (29 of 39 samples), and in only 18.75% (9 out of 48) IDC cases; this result suggests a possible relation between mtDNA mutations and variations in molecular pathways of tumor development.

Mitochondria and cancer

The authors review the role played by mutations in mitochondrial DNA and in nuclear genes encoding mitochondrial proteins in cancer development, with an emphasis on the alterations of the oxidative phosphorylation system and glycolysis.

Novel DNA mismatch-repair activity involving YB-1 in human mitochondria

Maintenance of the mitochondrial genome (mtDNA) is essential for proper cellular function. The accumulation of damage and mutations in the mtDNA leads to diseases, cancer, and aging. Mammalian mitochondria have proficient base excision repair, but the existence of other DNA repair pathways is still unclear. Deficiencies in DNA mismatch repair (MMR), which corrects base mismatches and small loops, are associated with DNA microsatellite instability, accumulation of mutations, and cancer. MMR proteins have been identified in yeast and coral mitochondria; however, MMR proteins and function have not yet been detected in human mitochondria. Here we show that human mitochondria have a robust mismatch-repair activity, which is distinct from nuclear MMR. Key nuclear MMR factors were not detected in mitochondria, and similar mismatch-binding activity was observed in mitochondrial extracts from cells lacking MSH2, suggesting distinctive pathways for nuclear and mitochondrial MMR. We identified the repair factor YB-1 as a key candidate for a mitochondrial mismatch-binding protein. This protein localizes to mitochondria in human cells, and contributes significantly to the mismatch-binding and mismatch-repair activity detected in HeLa mitochondrial extracts, which are significantly decreased when the intracellular levels of YB-1 are diminished. Moreover, YB-1 depletion in cells increases mitochondrial DNA mutagenesis. Our results show that human mitochondria contain a functional MMR repair pathway in which YB-1 participates, likely in the mismatch-binding and recognition steps.

High rate of mutation in mitochondrial DNA displacement loop region in human colorectal cancer

PURPOSE

Mitochondrial DNA mutations are found in many kinds of human cancer and the 1.1 kb displacement loop region has been identified as a "hot spot" for mutation in mitochondrial DNA of tumors. This study evaluated the mutation frequencies in hypervariable regions of mitochondrial displacement loop in patients with colorectal cancer.

METHODS

We examined the frequency of mutations in the mitochondrial DNA displacement loop region of 40 colorectal cancer samples in comparison to 150 samples from people without any type of familial cancer history, by automated DNA sequencing. Alignment was made with the revised Cambridge Reference Sequence and any differences recorded as single base substitution, insertions, and deletions.

RESULTS

Our results showed that the rate of displacement loop variations was higher in colorectal cancer patients than controls. Nineteen single nucleotide polymorphisms were found; among them eighteen occurred in the displacement loop region.

CONCLUSIONS

Mutations in mtDNA D-loop region probably do not cause colorectal cancer but are more likely to be epiphenomena; patients with the high mtDNA variants are at a higher risk of colorectal cancer.

Nuclear and mitochondrial microsatellite instability in colorectal cancer

AIM: To explore the roles of nuclear microsatellite instability (nMSI) and mitochondrial microsatellite instability (mtMSI) in the pathogenesis of colorectal cancer and their relationship.

METHODS: mtMSI was detected by using direct sequencing analysis, and nMSI by microsatellite scan method. Relationship between the positive incidence of mtMSI and nMSI was analyzed.

RESULTS: Forty cases with colorectal cancers were studied for mtMSI and nMSI. The mtMSI in at least one locus was detected in 11 out of 40 (27.5%) cases. Out of the 11 cases with mtMSI, 9 showed mtMSI at one locus (17.5%) and 2 at 11 loci (5%), but none at more than three loci. The nMSI at BAT25, BAT26 were detected in 9 out of 40 (22.5%) cases. mtMSI was found not to be associated with sex, age, subsite or TNM stage (P > 0.05). mtMSI was significantly correlated with nMSI (P < 0.05).

CONCLUSION: mtMSI may be involved in the carcinogenesis of some colorectal cancer, and mtMSI is associated with nMSI.

Different effects of novel mtDNA G3242A and G3244A base changes adjacent to a common A3243G mutation in patients with mitochondrial disorders

Two novel mitochondrial DNA base changes were identified at both sides of the 3243A>G mutation, the most common mutation associated with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). One was a 3244G>A transition in a girl with MELAS. The other was a 3242G>A transition in a girl with a mitochondrial disorder without a MELAS phenotype. Although the two base changes were adjacent to the 3243A>G mutation, they had different effects on the clinical phenotype, muscle pathology, and respiratory chain enzyme activity. Investigations of the different effects of the 3244G>A and 3242G>A base changes may provide a better understanding of tRNA dysfunction in mitochondrial disorders.

Mitochondria As A Target For Early Detection and Diagnosis of Cancer

Mitochondrial dysfunction and mutations in mitochondrial DNA (mtDNA) have been frequently reported in cancer, neurodegenerative diseases, diabetes, and aging syndromes. The mitochondrion genome (16.5 Kb) codes only for a small fraction (estimated to be 1%) of the proteins housed within this organelle. The other proteins are encoded by the nuclear DNA (nDNA) and transported into the mitochondria. The identification of mitochondrial proteins that are aberrantly expressed in cancer cells and other diseases is now possible through recent developments in proteomic and bioinformatic technologies. These developments set the stage for a comprehensive organelle-based proteomic approach for the identification of new markers for the early detection, risk assessment, and diagnosis of cancer, and other diseases and for the identification of new targets for therapeutic prevention and intervention.

Limited clinical relevance of mitochondrial DNA mutation and gene expression analyses in ovarian cancer

Background

In recent years, numerous studies have investigated somatic mutations in mitochondrial DNA in various tumours. The observed high mutation rates might reflect mitochondrial deregulation; consequently, mutation analyses could be clinically relevant. The purpose of this study was to determine if mutations in the mitochondrial D-loop region and/or the level of mitochondrial gene expression could influence the clinical course of human ovarian carcinomas.

Methods

We sequenced a 1320-base-pair DNA fragment of the mitochondrial genome (position 16,000-750) in 54 cancer samples and in 44 corresponding germline control samples. In addition, six transcripts (MT-ATP6, MT-CO1, MT-CYB, MT-ND1, MT-ND6, and MT-RNR1) were quantified in 62 cancer tissues by real-time RT-PCR.

Results

Somatic mutations in the D-loop sequence were found in 57% of ovarian cancers. Univariate analysis showed no association between mitochondrial DNA mutation status or mitochondrial gene expression and any of the examined clinicopathologic parameters. A multivariate logistic regression model revealed that the expression of the mitochondrial gene RNR1 might be used as a predictor of tumour sensitivity to chemotherapy.

Conclusion

In contrast to many previously published papers, our study indicates rather limited clinical relevance of mitochondrial molecular analyses in ovarian carcinomas. These discrepancies in the clinical utility of mitochondrial molecular tests in ovarian cancer require additional large, well-designed validation studies.

Molecular genetics of papillary thyroid carcinoma: great expectations

Papillary thyroid carcinoma (PTC) is the most prevalent type of endocrine cancer and, in recent epidemiological surveys, one of the types of human cancer whose incidence is growing. Despite the favourable outcome and long survival rates of most patients, some tumours display an aggressive behaviour and may progress to the highly aggressive and lethal, anaplastic thyroid carcinoma. In recent years, several progresses have been made on the molecular characterization of PTC, in general, and in the genetic alterations underlying the histotype diversity of this type of cancer, in particular. This holds true regarding alterations on nuclear DNA as well as mitochondrial DNA. In this review we have summarized the most recent findings in the genetic characterization of PTC, giving a particular emphasis to the genotype-phenotype associations, the prognosis implications, and the diagnostic and therapeutic value of the newly identified genetic markers.

Histological heterogeneity and somatic mtDNA mutations in gastric intraepithelial neoplasia

Somatic mutations of mitochondrial DNA (mtDNA) are associated with various types of human cancer. To elucidate their role in gastric carcinogenesis, we analyzed mutations in the displacement loop region of mtDNA in 24 paraffin-embedded gastric intraepithelial neoplasias (formerly dysplasia) from a high gastric cancer risk area in northern Italy. Helicobacter pylori infection was assessed by histological examination (Giemsa staining). Gastritis was classified according to the guidelines of the Updated Sydney System. The mtDNA displacement loop region was amplified and sequenced from gastric intraepithelial neoplasia samples and adjacent non-neoplastic gastric mucosa. The gastric intraepithelial neoplasias were divided into two groups by their association with H. pylori gastritis. Group A with lesions arising on a background of H. pylori-positive gastritis contained 7 patients, and group B with lesions associated with H. pylori-negative gastritis contained 17 patients. Group A had a larger proportion of high-grade lesions than group B and showed a foveolar phenotype (type II dysplasia). Group B had a larger proportion of cases with mtDNA displacement loop region mutations than group A (P=0.004, Fisher's exact test) and exhibited an intestinal phenotype. No evidence of heteroplasmic variants in the mtDNA displacement loop, suggestive of mutations, was detected in gastric biopsies from 25 H. pylori-negative subjects and 60 cancer-unaffected H. pylori-positive patients. These results provide further evidence for the morphologic and mtDNA biomolecular differences of gastric intraepithelial neoplasias, and suggest the existence of two distinct pathways to gastric cancer--corpus-dominant H. pylori gastritis and the atrophy-metaplasia pathway.

Novel approach for detecting global epigenetic alterations associated with tumor cell aneuploidy

Although aneuploidy is commonly observed in human cancers, the molecular mechanism underlying aneuploidization remains unclear. We used multiploid cancer model that had diploid and aneuploid cancer cells within the same cancerous tissue and attempted to detect specific epigenetic alterations associated with tumor cell aneuploidy. Thirty-four multiploid colorectal cancers were subjected to crypt isolation and cell sorting, and paired diploid and aneuploid cancer cells were separated from each cancerous tissue. A methylated CpG island amplification provided a considerable number of CpG sequences that showed different methylation status between the above 2 cell populations. BLAST homology search revealed 24 different candidates (11 hypermethylated and 13 hypomethylated) from these sequences. The putative promoter sequence of the SALL4 (sal-like 4, a human homolog to Drosophila spalt) gene was particularly more frequently hypermethylated in aneuploid cells (62%) than diploid ones (35%) in the 34 multiploid cancers. Moreover, such hypermethylation occurred more often in aneuploid cancers (8 of 16, 50%) than diploid cancers (3 of 18, 17%). In combination with demethylation study on cultured cells, these results implied a possible association between epigenetic silencing of SALL4 and tumor cell aneuploidy. SALL4 may be one of important key players that act as "caretakers" for chromosomal stability. Our new approach is a powerful tool for the global identification of such key players.

Aberrant methylation within RUNX3 CpG island associated with the nuclear and mitochondrial microsatellite instability in sporadic gastric cancers. Results of a GOIM (Gruppo Oncologico dell'Italia Meridionale) prospective study

BACKGROUND

Gastric cancer (GC) development is a multistep process, during which numerous alterations accumulate in nuclear and mitochondrial DNA. A deficiency of repair machinery brings about an accumulation of errors introduced within simple repetitive microsatellite sequences during replication of DNA. Aberrant methylation is related to microsatellite instability (MSI) by the silencing of the hMLH1 gene. The aim of this study is to investigate a possible relationship between the RUNX3 promoter methylation, nuclear microsatellite instability (nMSI) and mitochondrial microsatellite instability (mtMSI), in order to clarify its biological role in GC.

PATIENTS AND METHODS

nMSI and mtMSI were evaluated in a consecutive series of 100 GC patients. For the analysis of the nMSI, we followed the National Cancer Institute guidelines. mtMSI was assessed by analyzing a portion of the displacement-loop region. The aberrant methylation of RUNX3 was analyzed in 40 GC patients by methylation-specific PCR.

RESULTS

Overall, 55% of GC demonstrated methylation of the RUNX3 promoter; 82% of GC was classified as stable microsatellite instability, 5% as low-level microsatellite instability and 13% as high-level microsatellite instability (MSI-H); mtMSI was detected in 11% of GC. A significant association was found between mtMSI and tumor-node-metastasis staging, furthermore an interesting association between MSI-H status, mtMSI and RUNX3 methylation.

CONCLUSION

These data suggest that RUNX3 is an important target of methylation in the evolution of mtMSI and nMSI-H GC.

Mitochondrial DNA mutations in oxyphilic and chief cell parathyroid adenomas

BACKGROUND

The potential pathogenetic significance of mitochondrial DNA (mtDNA) mutations in tumorigenesis is controversial. We hypothesized that benign tumorigenesis of a slowly replicating tissue like the human parathyroid might constitute an especially fertile ground on which a selective advantage conferred by mtDNA mutation could be manifested and might contribute to the oxyphilic phenotype observed in a subset of parathyroid tumors.

METHODS

We sought acquired mitochondrial DNA mutations by sequencing the entire 16.6 kb mitochondrial genome of each of thirty sporadic parathyroid adenomas (18 chief cell and 12 oxyphil cell), eight independent, polyclonal, parathyroid primary chief cell hyperplasias plus corresponding normal control samples, five normal parathyroid glands, and one normal thyroid gland.

RESULTS

Twenty-seven somatic mutations were identified in 15 of 30 (9 of 12 oxyphil adenomas, 6 of 18 chief cell) parathyroid adenomas studied. No somatic mutations were observed in the hyperplastic parathyroid glands.

CONCLUSION

Features of the somatic mutations suggest that they may confer a selective advantage and contribute to the molecular pathogenesis of parathyroid adenomas. Importantly, the statistically significant differences in mutation prevalence in oxyphil vs. chief cell adenomas also suggest that mtDNA mutations may contribute to the oxyphil phenotype.

Relationship between mitochondrial DNA mutations and clinical characteristics in human lung cancer

Mitochondrial DNA (mtDNA) is known for its high frequencies of polymorphisms and mutations, some of which are related to various diseases, including cancers. However, roles of mutations and polymorphisms in some diseases are among heated debate, especially for cancer. To investigate the possible role of mtDNA mutations in lung cancer, we sequenced complete mtDNA of lung cancer tissues, corresponding normal (i.e., non-cancerous) lung tissues, and peripheral blood samples from 55 lung cancer patients and examined the relationship between mtDNA mutations or polymorphisms and clinical parameters. We identified 56 mutations in 33 (60%) of the 55 patients, including 48 point mutations, four single-nucleotide insertions, and four single-nucleotide deletions. Nineteen of these mutations resulted in amino acid substitution. These missense mtDNA mutations were distributed in 9 of 13 mitochondrial DNA coding genes. Three hundred eighty eight polymorphisms were identified among the 55 patients. Seventy-three polymorphisms resulted in amino acid substitution. There was no association of incidence of specific mtDNA mutation or polymorphism with patients' gender, age at diagnosis, smoking history, tumor type or tumor stage (P>0.05). This study revealed a variety of mtDNA mutations and mtDNA polymorphisms in human lung cancer, some of which might be involved in human lung carcinogenesis.

Mitochondrial DNA mutations in differentiated thyroid cancer with respect to the age factor

INTRODUCTION

Increased numbers of mitochondria in differentiated thyroid cancer and, most strikingly, mutations in human mitochondrial DNA (mtDNA) in older people have led to speculation that mtDNA mutations might contribute to aging or accumulate in postmitotic tissues with age. Mutation analyses of mtDNA in papillary (PTCs) and follicular (FTCs) thyroid carcinomas have been limited to date. The significance and frequency of mtDNA mutations in PTC and FTC are therefore controversial, as is age dependence.

METHODS

We analyzed eight sample pairs of PTC and six of FTC tissue with the corresponding normal thyroid tissue. DNA was extracted from frozen and formaldehyde-fixed tissue using the QIAmp Tissue Kit. Sequence differences in the mtDNA between tumor and normal tissue were detected using appropriate polymerase chain reaction (PCR) products for heteroduplex analysis in a denaturing high performance liquid chromatography (HPLC) Wave System (Transgenomic). Mutations were confirmed and identified by sequencing the PCR products of conspicuous chromatograms. The samples were obtained from 346 patients with PTC and 105 patients with FTC. We analyzed the whole mitochondrial genome from seven PTC and three FTC tumors along with the corresponding normal thyroid tissue. 3/7 PTC samples showed two heteroplasmic mutations and one polymorphism; all 3 FTCs showed homoplasmic and/or heteroplasmic mutations.

RESULTS

All but one of these tumors are well documented in the mitochondrial database MITOMAP. MtDNA mutations were found in all three patients aged 45 years and older. There was no correlation, however, in this small group to clinical prognostic factors for recurrence and especially for survival in differentiated thyroid carcinomas, such as histology, tumor size, lymph node metastases, distant metastases, and gender, most likely because of the short follow-up. While univariate analysis of the findings in the whole cohort of 346 patients with PTC suggested that age is a significant prognostic factor for survival (P = 0.0237) but not for recurrence (P = 0.65), this was not the case in the 105 patients with FTC.

CONCLUSIONS

Although we found accumulation of mutations in two older patients with PTC and one patient with FTC (all three patients older than 45 years had mtDNA mutations), the low frequency of these mutations in the small group of 10 analyzed patients did not correlate with statistically validated clinical prognosticators for recurrence or survival, especially not with age. The low power of our data are therefore not able to support or refute the hypothesis that these mtDNA mutations are related to age-dependent tumor progression in the thyroid or that they "may be involved in thyroid tumorigenesis."

Mitochondrial microsatellite instability of colorectal cancer stroma

Mitochondrial microsatellite instability (mtMSI) and mutations of mitochondrial DNA has been reported in cancer epithelia of carcinomas. However, mtMSI in cancer stroma has not yet been identified in human cancers. In this study, we attempted to determine if mtMSI occurs in the cancer stroma of sporadic colorectal cancers, and if the stromal mtMSI has any correlations with stromal nuclear MSI (nMSI) and cancer epithelial mtMSI. Nine microsatellite sequences within the D-loop and 5 coding genes for mtMSI, and 9 microsatellites for nMSI were analyzed in the microdissected cancer epithelia and adjacent stromas of 48 sporadic colorectal cancers. Overall, 23 somatic mitochondrial DNA alterations were detected in 15 cancer epithelia (31.2%) and 5 stromas (10.4%). The mutations consisted of 19 D-loop mtMSI alterations, and 1 missense and 3 framshift mutations of repeat sequences within the coding genes. All of the 5 stromal genetic alterations showed D-loop mtMSI. In regards to other MSI status, the stromal mtMSI had no association with stromal nMSI or epithelial mtMSI, either. These findings indicate that in addition to the cancer epithelia the cancer stroma harbor mtMSI, and suggest a possible role of stromal mtMSI in the pathogenesis of colorectal cancers. Furthermore, the data suggest that stromal mtMSI may occur independently of stromal nMSI and epithelial mtMSI in sporadic colorectal cancers.

Nuclear and mitochondrial DNA microsatellite instability in gastrointestinal stromal tumors

OBJECTIVE

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the digestive tract. Nuclear (nMSI) and mitochondrial microsatellite instability (mtMSI) play important roles in tumorigenesis in various organs. The aim of this study was to evaluate the role of nMSI and mtMSI in GISTs.

METHODS

Samples from 74 mesenchymal tumors were collected. nMSI and mtMSI were examined by microsatellite assay at BAT26 and D310 mononucleotide repeats in mtDNA, respectively. We compared nMSI, mtMSI and clinicopathologic features, including patient age and sex, tumor location, tumor size, presence of tumor ulceration and presence of distant metastasis, for 51 GISTs for which these data were available.

RESULTS

nMSI and mtMSI were detected in 3 (5%) and 10 (16%) of the 62 GISTs, respectively. There was no significant relationship between nMSI, mtMSI and clinicopathologic features.

CONCLUSION

These results suggest that mtMSI may play a role, but that nMSI may play little role in the development of GISTs.

Mutational dynamics in human tumors confirm the neutral intrinsic instability of the mitochondrial D-loop poly-cytidine repeat

Somatic mutations at a mitochondrial noncoding polycytidine (C)(n) repeat (polyC) have been associated with tumor progression. We analyzed whether these alterations are due to the inherent mutability of repeated sequences. Insertion and deletion mutations were found in colon (n = 114), stomach (n = 105), endometrium (n = 53), breast (n = 45), lung (n = 35), and prostate (n = 20) tumors. The mutation frequency in colon, gastric, and endometrial tumors was 23, 17, and 11%, respectively, which paralleled the relative extent of microsatellite instability in long mononucleotide repeats observed in tumors with mismatch repair deficiency (colon > stomach > endometrium, relative ratio 10:8:4). Colon tumors with mutations of more than one nucleotide were more advanced in tumor progression. Further, two tumors showing a T > C mutation that restored the homopolymeric repeat, harbored sequential deletion mutations of up to 4 and 6 nucleotides. These results illustrate that the increased mutability of repeated mitochondrial sequences is dependent on the repetitive structure of the DNA molecule and suggest that mutations in the (C)(n) repeat, whether homoplasmic or not, and by extrapolation, mitochondrial mutations in general, are not the result of selective pressure during tumorigenesis. We also suggest that the (C)(n) repeat may be used as an universal molecular clock to estimate the relative mitotic history of tumors.

Differences in genomic instability between intestinal- and diffuse-type gastric cancer

BACKGROUND

Microsatellite instability (MSI) and loss of heterozygosity (LOH) are lesions in the genome found with different frequencies in gastric carcinomas (GCAs). Despite a great body of studies, no systematic approach to the detailed classification of MSI and LOH in the two major types of GCA has been published.

METHODS

Thirty-seven advanced GCAs, 25 intestinal-type (IGCAs) and 12 diffuse-type (DGCAs), were assayed with 15 autosomal tetranucleotide markers on 14 chromosomal arms. The observed frequencies and types of microsatellite alterations allowed stratification into subgroups, i.e., high- and low-grade MSI (MSI-H, MSI-L) or microsatellite-stable (MSS), and high- or low-grade, or non-detectable LOH (LOH-H, LOH-L, LOH-N).

RESULTS

Collectively, the markers detected MSI-H tumors with sensitivity equal to that of BAT-26 (a single marker highly specific for MSI-H). Likewise, the markers detected LOH at chromosomal arms 5q, 18q, and 21q with a sensitivity equal to markers used previously. Seven (19%) MSI-H and six (16%) LOH-H tumors were found, with a significant association (P = 0.027) with IGCA: 92% of MSI-H and LOH-H occurred in IGCA patients only. Conversely, in DGCA, a significantly higher prevalence of a stable (LOH-N/MSS) phenotype was found as compared with IGCA (75.1% vs 28.0%; P = 0.035). The MSI-L phenotype was found in 57.9% of non-MSI-H IGCA tumors and was associated significantly (P = 0.015) with LOH-H.

CONCLUSION

A clear difference in genomic instability between IGCA and DGCA was found. In IGCA, the MSI and LOH pathways were more commonly involved, whereas in DGCA, a stable phenotype was predominant. As a novel finding, MSI-L as a true phenomenon and its association with LOH was observed in IGCA.