Common mitochondrial polymorphisms as risk factor for endometrial cancer

Our current understanding of the biological impact of endometrial cancer mtDNA genome mutations and their potential use as a biomarker

Endometrial cancer (EC) is a devastating and common disease affecting women's health. The NCI Surveillance, Epidemiology, and End Results Program predicted that there would be >66,000 new cases in the United States and >13,000 deaths from EC in 2023, and EC is the sixth most common cancer among women worldwide. Regulation of mitochondrial metabolism plays a role in tumorigenesis. In proliferating cancer cells, mitochondria provide the necessary building blocks for biosynthesis of amino acids, lipids, nucleotides, and glucose. One mechanism causing altered mitochondrial activity is mitochondrial DNA (mtDNA) mutation. The polyploid human mtDNA genome is a circular double-stranded molecule essential to vertebrate life that harbors genes critical for oxidative phosphorylation plus mitochondrial-derived peptide genes. Cancer cells display aerobic glycolysis, known as the Warburg effect, which arises from the needs of fast-dividing cells and is characterized by increased glucose uptake and conversion of glucose to lactate. Solid tumors often contain at least one mtDNA substitution. Furthermore, it is common for cancer cells to harbor mixtures of wild-type and mutant mtDNA genotypes, known as heteroplasmy. Considering the increase in cancer cell energy demand, the presence of functionally relevant carcinogenesis-inducing or environment-adapting mtDNA mutations in cancer seems plausible. We review 279 EC tumor-specific mtDNA single nucleotide variants from 111 individuals from different studies. Many transition mutations indicative of error-prone DNA polymerase γ replication and C to U deamination events were present. We examine the spectrum of mutations and their heteroplasmy and discuss the potential biological impact of recurrent, non-synonymous, insertion, and deletion mutations. Lastly, we explore current EC treatments, exploiting cancer cell mitochondria for therapy and the prospect of using mtDNA variants as an EC biomarker.

The Role of Genetic Mutations in Mitochondrial-Driven Cancer Growth in Selected Tumors: Breast and Gynecological Malignancies

There is an increasing understanding of the molecular and cytogenetic background of various tumors that helps us better conceptualize the pathogenesis of specific diseases. Additionally, in many cases, these molecular and cytogenetic alterations have diagnostic, prognostic, and/or therapeutic applications that are heavily used in clinical practice. Given that there is always room for improvement in cancer treatments and in cancer patient management, it is important to discover new therapeutic targets for affected individuals. In this review, we discuss mitochondrial changes in breast and gynecological (endometrial and ovarian) cancers. In addition, we review how the frequently altered genes in these diseases (BRCA1/2, HER2, PTEN, PIK3CA, CTNNB1, RAS, CTNNB1, FGFR, TP53, ARID1A, and TERT) affect the mitochondria, highlighting the possible associated individual therapeutic targets. With this approach, drugs targeting mitochondrial glucose or fatty acid metabolism, reactive oxygen species production, mitochondrial biogenesis, mtDNA transcription, mitophagy, or cell death pathways could provide further tailored treatment.

Mitochondrial DNA sequence variation and risk of glioma

BACKGROUND

Malignant gliomas are the most common primary adult brain tumors, with a poor prognosis and ill-defined etiology. Mitochondrial DNA (mtDNA) sequence variation has been linked with certain cancers; however, research on glioma is lacking.

METHODS

We examined the association of common (minor allele frequency ≥ 5%) germline mtDNA variants and haplogroups with glioma risk in 1,566 glioma cases and 1,017 controls from a US case-control study, and 425 glioma cases and 1,534 matched controls from the UK Biobank cohort (UKB). DNA samples were genotyped using the UK Biobank array that included a set of common and rare mtDNA variants. Risk associations were examined separately for glioblastoma (GBM) and lower grade tumors (non-GBM).

RESULTS

In the US study, haplogroup W was inversely associated with glioma when compared with haplogroup H (OR = 0.43, 95%CI: 0.23-0.79); this association was not demonstrated in the UKB (OR = 1.07, 95%CI: 0.47-2.43). In the UKB, the variant m.3010G > A was significantly associated with GBM (OR = 1.32; 95%CI: 1.01-1.73; p = 0.04), but not non-GBM (1.23; 95%CI: 0.78-1.95; p = 0.38); no similar association was observed in the US study. In the US study, the variant m.14798 T > C, was significantly associated with non-GBM (OR = 0.72; 95%CI: 0.53-0.99), but not GBM (OR = 0.86; 95%CI: 0.66-1.11), whereas in the UKB, a positive association was observed between this variant and GBM (OR = 1.46; 95%CI: 1.06-2.02) but not non-GBM (OR = 0.92; 95%CI: 0.52-1.63). None of these associations were significant after adjustment for multiple testing.

CONCLUSION

The association of inherited mtDNA variation, including rare and singleton variants, with glioma risk merits further study.

Effects of Low Luteinizing Hormone During Ovarian Stimulation on Endometrial Gene Expression and Function - Transcriptome Analysis During the Implantation Window

This study explored the impact of low luteinizing hormone (LH) levels during ovarian stimulation on endometrial function. Based on previous studies by us and others, we divided the patients into low (< 4 IU/L), medium (4-10 IU/L), and high (> 10 IU/L) LH groups. The study utilized a comparison control group design with three groups of 10 patients. Gene set enrichment analysis (GSEA) was applied for functional annotation. By analyzing the exon differentially expressed genes in the endometrium of these three patient groups during the embryo implantation window, we found that when compared to the medium LH group, low LH downregulated endometrial cell metabolism, including mitochondrial-nicotinamide adenine dinucleotide (Normalized Enrichment Scores, NES =  - 1.53) and glycolytic metabolism (NES =  - 1.22), immune regulation, and autophagy (NES =  - 1.58). Transcription factors were the main regulators of cell function. We found that MCM2 was probably involved in regulating the endometrial function induced by low LH. MCM2 target genes were enriched in low LH group, NES =  - 1.54. Low LH, but not high LH, altered the endometrial receptivity assay gene expression in comparison to the medium LH. Our results indicated that low LH impacted the endometrial cell function, with a greater effect than high LH. This research provides timely and necessary data on the involvement of LH in important endometrial cellular processes and these data support further clinical development of endometrial receptivity.

Mitochondrial sirtuins genetic variations and gastric cancer risk: Evidence from retrospective observational study

AIMS

The purpose of the present study was to analyze the role of selected polymorphisms of SIRT3 and SIRT5 in gastric carcinogenesis.

METHODS

For this study, 500 blood samples of GC patients and 500 blood samples of healthy individuals were collected. Six selected polymorphisms of mitochondrial sirtuins were analyzed for analysis using Tetra-Arms PCR followed by DNA sequencing.

RESULTS

Mutant allele frequencies of selected polymorphisms [rs3782116 (p < 0.0001), rs6598072 (p < 0.0001) and rs11246020 (p < 0.0001), rs938222 (p = 0.0136), rs3757261 (p = 0.0005) and rs2841511 (p = 0.0015)] were observed significant higher in GC patients vs controls. Haplotype analysis was performed, and 51 haplotypes were generated using haploview software. Among these haplotypes, eleven haplotypes were found associated with a significantly increased risk of GC. Furthermore, SNP-SNP interaction showed a significant correlation between studied SNPs and GC risk. Kaplan Meier analysis showed that mutant allele frequencies of selected polymorphisms are linked with a significant decrease in survival of GC patients CONCLUSIONS: It can be concluded that selected SNPs may be associated with enhanced risk of GC and hence can be potential prognostic markers for prognosis and predisposition of GC.

The Role of Mitochondria in Carcinogenesis

The mitochondria are essential for normal cell functioning. Changes in mitochondrial DNA (mtDNA) may affect the occurrence of some chronic diseases and cancer. This process is complex and not entirely understood. The assignment to a particular mitochondrial haplogroup may be a factor that either contributes to cancer development or reduces its likelihood. Mutations in mtDNA occurring via an increase in reactive oxygen species may favour the occurrence of further changes both in mitochondrial and nuclear DNA. Mitochondrial DNA mutations in postmitotic cells are not inherited, but may play a role both in initiation and progression of cancer. One of the first discovered polymorphisms associated with cancer was in the gene NADH-ubiquinone oxidoreductase chain 3 (mt-ND3) and it was typical of haplogroup N. In prostate cancer, these mutations and polymorphisms involve a gene encoding subunit I of respiratory complex IV cytochrome c oxidase subunit 1 gene (COI). At present, a growing number of studies also address the impact of mtDNA polymorphisms on prognosis in cancer patients. Some of the mitochondrial DNA polymorphisms occur in both chronic disease and cancer, for instance polymorphism G5913A characteristic of prostate cancer and hypertension.

Mitochondrial DNA haplogroups J and T increase the risk of glioma

The presence of different sets of mitochondrial polymorphisms generated by the accumulation of mutations in different maternal lineages has allowed differentiating mitochondrial haplogroups in human populations. These polymorphisms, in turn, may have effects at the phenotypic level, considering a possible contribution of these germinal mutations to the development of certain diseases such as cancer. The main goal of the present study is to establish a possible association between mitochondrial haplogroups and the risk of suffering glioma. Blood samples were obtained from 32 patients from Catalonia (Spain) diagnosed with different grades of glioma (II, III and IV), according to the World Health Organization. The mitochondrial genome was amplified and sequenced using MiSeq 2000 (Illumina). The HaploGrep tool implemented in mtDNA-Server v.1.0.5 was used for the identification of mitochondrial haplogroups. Data obtained in the present study was further pooled with data from previous European studies including glioma patients from Galicia (Spain) and Italy. Results for the Catalonian samples showed an association between individuals with haplogroup J and the increased risk of suffering glioma, with a significant increase of the frequency of individuals with this haplogroup (25%) regarding the general population (7%). Combining different sets of patients with European origin, it appears that individuals with haplogroups J and T have a significantly higher risk of suffering glioma (p < 0.001; OR: 2.407 and p = 0.007; OR: 1.82, respectively). This is the first study that establishes an association between different mitochondrial haplogroups and the risk of suffering glioma, highlighting the role of mitochondrial variants in this disease.

Role of Mitochondrial DNA (mtDNA) Variations in Cancer Development: A Systematic Review

mtDNA is the closed circular, ds-DNA present in mitochondria of eukaryotic cells and are inherited maternally. Besides being the power house of the cell, mitochondria are also responsible for the regulation of redox homeostasis, signaling, metabolism, immunity, survival and apoptosis. Lack of a 'Systematic Review' on mtDNA variations and cancers encouraged us to perform the present study. Pubmed', 'Embase' and 'Cochrane Library' databases were searched using keywords 'Mitochondrial DNA' OR 'mtDNA' OR 'mDNA' AND 'polymorphism' AND 'cancer' AND 'risk' to retrieve literature. Polymorphisms occupy first rank among mtDNA variations followed by CNV, MSI, mutations and hold a great potential to emerge as key predictors for human cancers.

ImtRDB: a database and software for mitochondrial imperfect interspersed repeats annotation

BACKGROUND

Mitochondria is a powerhouse of all eukaryotic cells that have its own circular DNA (mtDNA) encoding various RNAs and proteins. Somatic perturbations of mtDNA are accumulating with age thus it is of great importance to uncover the main sources of mtDNA instability. Recent analyses demonstrated that somatic mtDNA deletions depend on imperfect repeats of various nature between distant mtDNA segments. However, till now there are no comprehensive databases annotating all types of imperfect repeats in numerous species with sequenced complete mitochondrial genome as well as there are no algorithms capable to call all types of imperfect repeats in circular mtDNA.

RESULTS

We implemented naïve algorithm of pattern recognition by analogy to standard dot-plot construction procedures allowing us to find both perfect and imperfect repeats of four main types: direct, inverted, mirror and complementary. Our algorithm is adapted to specific characteristics of mtDNA such as circularity and an excess of short repeats - it calls imperfect repeats starting from the length of 10 b.p. We constructed interactive web available database ImtRDB depositing perfect and imperfect repeats positions in mtDNAs of more than 3500 Vertebrate species. Additional tools, such as visualization of repeats within a genome, comparison of repeat densities among different genomes and a possibility to download all results make this database useful for many biologists. Our first analyses of the database demonstrated that mtDNA imperfect repeats (i) are usually short; (ii) associated with unfolded DNA structures; (iii) four types of repeats positively correlate with each other forming two equivalent pairs: direct and mirror versus inverted and complementary, with identical nucleotide content and similar distribution between species; (iv) abundance of repeats is negatively associated with GC content; (v) dinucleotides GC versus CG are overrepresented on light chain of mtDNA covered by repeats.

CONCLUSIONS

ImtRDB is available at http://bioinfodbs.kantiana.ru/ImtRDB/ . It is accompanied by the software calling all types of interspersed repeats with different level of degeneracy in circular DNA. This database and software can become a very useful tool in various areas of mitochondrial and chloroplast DNA research.

Mitochondrial Dysfunctions in Type I Endometrial Carcinoma: Exploring Their Role in Oncogenesis and Tumor Progression

Type I endometrial cancer (EC) is the most common form of EC, displaying less aggressive behavior than type II. The development of type I endometrial cancer is considered a multistep process, with slow progression from normal endometrium to hyperplasia, the premalignant form, and endometrial cancer as a result of an unopposed estrogenic stimulation. The role of mitochondria in type I EC tumor progression and prognosis is currently emerging. This review aims to explore mitochondrial alterations in this cancer and in endometrial hyperplasia focusing on mitochondrial DNA mutations, respiratory complex I deficiency, and the activation of mitochondrial quality control systems. A deeper understanding of altered mitochondrial pathways in type I EC could provide novel opportunities to discover new diagnostic and prognostic markers as well as potential therapeutic targets.

Detection of somatic mutations in the mitochondrial DNA control region D-loop in brain tumors: The first report in Malaysian patients

Although the role of nuclear-encoded gene alterations has been well documented in brain tumor development, the involvement of the mitochondrial genome in brain tumorigenesis has not yet been fully elucidated and remains controversial. The present study aimed to identify mutations in the mitochondrial DNA (mtDNA) control region D-loop in patients with brain tumors in Malaysia. A mutation analysis was performed in which DNA was extracted from paired tumor tissue and blood samples obtained from 49 patients with brain tumors. The D-loop region DNA was amplified using the PCR technique, and genetic data from DNA sequencing analyses were compared with the published revised Cambridge sequence to identify somatic mutations. Among the 49 brain tumor tissue samples evaluated, 25 cases (51%) had somatic mutations of the mtDNA D-loop, with a total of 48 mutations. Novel mutations that had not previously been identified in the D-loop region (176 A-deletion, 476 C>A, 566 C>A and 16405 A-deletion) were also classified. No significant associations between the D-loop mutation status and the clinicopathological parameters were observed. To the best of our knowledge, the current study presents the first evidence of alterations in the mtDNA D-loop regions in the brain tumors of Malaysian patients. These results may provide an overview and data regarding the incidence of mitochondrial genome alterations in Malaysian patients with brain tumors. In addition to nuclear genome aberrations, these specific mitochondrial genome alterations may also be considered as potential cancer biomarkers for the diagnosis and staging of brain cancers.

Mitochondrial changes in endometrial carcinoma: possible role in tumor diagnosis and prognosis (review)

Endometrial carcinoma (EC) is a solid neoplasia for which a role for mitochondria in cancer progression is currently emerging and yet represents a diagnostic and prognostic challenge. EC is one of the most frequently occurring gynecological malignancies in the Western world whose incidence has increased significantly during the last decades. Here, we review the literature data on mitochondrial changes reported in EC, namely, mitochondrial DNA (mtDNA) mutations, increase in mitochondrial biogenesis and discuss whether they may be used as new cancer biomarkers for early detection and prognosis of this cancer.

The saga of the many studies wrongly associating mitochondrial DNA with breast cancer

Background

A large body of genetic research has focused on the potential role that mitochondrial DNA (mtDNA) variants might play on the predisposition to common and complex (multi-factorial) diseases. It has been argued however that many of these studies could be inconclusive due to artifacts related to genotyping errors or inadequate design.

Methods

Analyses of the data published in case–control breast cancer association studies have been performed using a phylogenetic-based approach. Variation observed in these studies has been interpreted in the light of data available on public resources, which now include over >27,000 complete mitochondrial sequences and the worldwide phylogeny determined by these mitogenomes. Complementary analyses were carried out using public datasets of partial mtDNA sequences, mainly corresponding to control-region segments.

Results

By way of example, we show here another kind of fallacy in these medical studies, namely, the phenomenon of SNP-SNP interaction wrongly applied to haploid data in a breast cancer study. We also reassessed the mutually conflicting studies suggesting some functional role of the non-synonymous polymorphism m.10398A > G (ND3 subunit of mitochondrial complex I) in breast cancer. In some studies, control groups were employed that showed an extremely odd haplogroup frequency spectrum compared to comparable information from much larger databases. Moreover, the use of inappropriate statistics signaled spurious “significance” in several instances.

Conclusions

Every case–control study should come under scrutiny in regard to the plausibility of the control-group data presented and appropriateness of the statistical methods employed; and this is best done before potential publication.

Mitochondrial dysfunction in cancer

Mitochondria are semi-autonomous organelles of eukaryotic cells. They perform crucial functions such as generating most of the cellular energy through the oxidative phosphorylation (OXPHOS) system and some other metabolic processes. In addition, mitochondria are involved in regulation of cell death and reactive oxygen species (ROS) generation. Also, mitochondria play important roles in carcinogenesis via altering energy metabolism, resistance to apoptosis, increase of production of ROS and mtDNA (mitochondrial genome) changes. Studies have suggested that aerobic glycolysis is high in malignant tumors. Probably, it correlates with high glucose intake of cancerous tissues. This observation is contrary to Warburg's theory that the main way of energy generation in cancer cells is non-oxidative glycolysis. Further studies have suggested that in tumor cells both oxidative phosphorylation and glycolysis were active at various rates.

An increase of intracellular oxidative stress induces damage of cellular structure and somatic mutations. Further studies confirmed that permanent activity of oxidative stress and the influence of chronic inflammation damage the healthy neighboring epithelium and may lead to carcinogenesis. For instance, chronic inflammatory bowel disease could be related to high risk of colon adenocarcinoma.

The data have shown a role of ROS generation, mtDNA or nDNA alterations and abnormal apoptotic machinery in endometrial cancer progress. Recent studies suggest that mtDNA mutations might play a potential role in endometrial cancer progress and indicate an increase of mitochondrial biogenesis in this cancer. The investigators suggested that MtCOI and MtND6 alteration has an influence on assembly of respiratory complexes in endometrial cancer.

In many human cancers, there is a deregulation of the balance between cell growth and death. The tumor cells can avoid apoptosis through a loss of balance between anti- and pro-apoptotic proteins, reduced caspase function and impaired death receptor signaling. Over-expression of the anti-apoptotic BCL-2 gene has also been identified in numerous cancers including colon, thyroid, breast and endometrial cancer. Most studies have found low BCL-2 family gene expression, which could be a sign of blocking apoptosis in breast and endometrial cancer. Moreover, BCL-2 gene expression is correlated with the degree of aggressiveness and differentiation in endometrial cancer. As a result, it could be a valuable predictor of disease progression.

The mitochondrial C16069T polymorphism, not mitochondrial D310 (D-loop) mononucleotide sequence variations, is associated with bladder cancer

Background

Bladder cancer is a relatively common and potentially life-threatening neoplasm that ranks ninth in terms of worldwide cancer incidence. The aim of this study was to determine deletions and sequence variations in the mitochondrial displacement loop (D-loop) region from the blood specimens and tumoral tissues of patients with bladder cancer, compared to adjacent non-tumoral tissues.

Methods

The DNA from blood, tumoral tissues and adjacent non-tumoral tissues of twenty-six patients with bladder cancer and DNA from blood of 504 healthy controls from different ethnicities were investigated to determine sequence variation in the mitochondrial D-loop region using multiplex polymerase chain reaction (PCR), DNA sequencing and southern blotting analysis.

Results

From a total of 110 variations, 48 were reported as new mutations. No deletions were detected in tumoral tissues, adjacent non-tumoral tissues and blood samples from patients. Although the polymorphisms at loci 16189, 16261 and 16311 were not significantly correlated with bladder cancer, the C16069T variation was significantly present in patient samples compared to control samples (p < 0.05). Interestingly, there was no significant difference (p > 0.05) of C variations, including C7TC6, C8TC6, C9TC6 and C10TC6, in D310 mitochondrial DNA between patients and control samples.

Conclusion

Our study suggests that 16069 mitochondrial DNA D-Loop mutations may play a significant role in the etiology of bladder cancer and facilitate the definition of carcinogenesis-related mutations in human cancer.

Mitochondrial D-Loop polymorphism and microsatellite instability in prostate cancer and benign hyperplasia patients

In this study mitochondrial D-Loop variations in Iranian prostate cancer and benign prostatic hyperplasia (BPH) patients were investigated. Tumour samples and corresponding non-cancerous prostate tissue from 40 prostate cancer patients and 40 age-matched BPH patients were collected. The entire mtD-loop region (16024-576) was amplified using the PCR method and products were gel-purified and subjected to direct nucleotide sequencing. A total of 129 variations were found, the most frequent being 263A-G and 310T-C among both BPH and prostate cancer patients. Variation of 309 C-T was significantly more frequent in prostate cancer patients (P value<0.05). Four novel variations were observed on comparison with the MITOMAP database. Novel variations were np16154delT, np366G-A, np389G-A and 56insT. There was no correspondence between the different variations and the age of subjects. Considering that D-loop variations were frequent in both BPH and prostate cancer patients in our study, the fact that both groups had high average age can be a possible contributing factor. D-loop polymorphisms and microsatellite instability can influence cell physiology and result in a benign or malignant phenotype. Significantly higher frequency of 309 C-T variation in cancer patients is a notable finding and must be a focus of attention in future studies.

The awakening of an advanced malignant cancer: an insult to the mitochondrial genome

BACKGROUND

In only months-to-years a primary cancer can progress to an advanced phenotype that is metastatic and resistant to clinical treatments. As early as the 1900s, it was discovered that the progression of a cancer to the advanced phenotype is often associated with a shift in the metabolic profile of the disease from a state of respiration to anaerobic fermentation - a phenomenon denoted as the Warburg Effect.

SCOPE OF REVIEW

Reports in the literature strongly suggest that the Warburg Effect is generated as a response to a loss in the integrity of the sequence and/or copy number of the mitochondrial genome content within a cancer.

MAJOR CONCLUSIONS

Multiple studies regarding the progression of cancer indicate that mutation, and/or, a flux in the copy number, of the mitochondrial genome content can support the early development of a cancer, until; the mutational load and/or the reduction-to-depletion of the copy number of the mitochondrial genome content induces the progression of the disease to an advanced phenotype.

GENERAL SIGNIFICANCE

Collectively, evidence has revealed that the human cell has incorporated the mitochondrial genome content into a cellular mechanism that, when pathologically actuated, can de(un)differentiate a cancer from the parental tissue of origin into an autonomous disease that disrupts the hierarchical structure-and-function of the human body. This article is part of a Special Issue entitled: Biochemistry of Mitochondria.

Oxidative stress and therapeutic opportunities: focus on the Ewing's sarcoma family of tumors

Reactive oxygen species (ROS) are highly reactive by-products of energy production that can have detrimental as well as beneficial effects. Unchecked, high levels of ROS result in an imbalance of cellular redox state and oxidative stress. High levels of ROS have been detected in most cancers, where they promote tumor development and progression. Many anticancer agents work by further increasing cellular levels of ROS, to overcome the antioxidant detoxification capacity of the cancer cell and induce cell death. However, adaptation of the level of cellular antioxidants can lead to drug resistance. The challenge for the design of effective cancer therapeutics exploiting oxidative stress is to tip the cellular redox balance to induce ROS-dependent cell death but without increasing the antioxidant activity of the cancer cell or inducing toxicity in normal cells.

The role of the mitochondrial genome in ageing and carcinogenesis

Mitochondrial DNA mutations and polymorphisms have been the focus of intensive investigations for well over a decade in an attempt to understand how they affect fundamental processes such as cancer and aging. Initial interest in mutations occurring in mitochondrial DNA of cancer cells diminished when most were found to be the same mutations which occurred during the evolution of human mitochondrial haplogroups. However, increasingly correlations are being found between various mitochondrial haplogroups and susceptibility to cancer or diseases in some cases and successful aging in others.

Mitochondrial genotype in vulvar carcinoma - cuckoo in the nest

Vulvar squamous cell carcinoma (VSCC) is a rare female genital neoplasm. Although numerous molecular changes have been reported in VSCC, biomarkers of clinical relevance are still lacking. On the other hand, there is emerging evidence on the use of mtDNA as a diagnostic tool in oncology. In order to investigate mtDNA status in VSCC patients, haplogroup distribution analysis and D-loop sequencing were performed. The results were compared with available data for the general Polish population, cancer free-centenarians as well as patients with endometrial and head and neck cancer. The obtained data were also compared with the current status of mitochondrial databases. Significant differences in haplogroup distribution between VSCC cohort, general Polish population and cancer-free centenarians cohort were found. Moreover, a correlation between the VSCC patients haplogroup and HPV status was observed. Finally, a specific pattern of mtDNA polymorphisms was found in VSCC. Our results suggest that the mitochondrial genetic background may influence the risk of VSCC occurrence as well as susceptibility to HPV infection.

Length heteroplasmies in human mitochondrial DNA control regions and breast cancer risk

It has been proposed that the presence of heteroplasmy in the hypervariable (HV) regions of the mitochondrial DNA (mtDNA) may be an indicator of mitochondrial genome instability, mtDNA dysfunction, and, thus, may be associated with increased cancer risk. However, whether heteroplasmy in the HV regions of mtDNA could be a risk predictor of oxidative stress-related human cancers, such as breast cancer, remains to be determined. To explore the role of heteroplasmy in the HV regions of mtDNA in breast cancer etiology, we analyzed heteroplasmy in the HV regions of mtDNA in whole blood from 103 patients with breast cancer and 103 matched control subjects. Both cases and controls displayed heteroplasmies in both of the HV1 and HV2 regions. Closer examination of the prevalence of length heteroplasmy indicated that the prevalence of heteroplasmies in both of the HV1 and HV2 regions was much higher in the cases than in the controls (HV1: 68% vs 49%, P=0.007; HV2: 46% vs 25%, P=0.002). The presence of length heteroplasmies in both of the HV1 and HV2 regions was associated with 2.18- and 2.49-folds increased risk of breast cancer, respectively, (HV1: OR=2.18, 95% CI: 1.19 - 4.00; HV2: OR=2.49, 95% CI: 1.32 - 4.69). Interestingly, we observed that the controls with length heteroplasmies in both HV1 and HV2 had statistically significantly lower copy number of mtDNA than the ones without heteroplasmies. These results suggest that the length heteroplasmy in the HV regions of mtDNA could be associated with a risk of breast cancer, perhaps through affecting the copy number of mtDNA.