Mitochondrial D-loop mutations and polymorphisms are connected with canine malignant cancers

Evaluation of the tRNA-Leu (UUR) gene haplotype profile observed in canine mammary gland tumours based on comparative analysis with the MT-TL1 human gene

The aetiology and pathogenesis of many canine tumours are likely to be similar to cancers found in humans. This study aimed to evaluate a plausible link between changes in the tRNA-Leu (UUR) gene and the carcinogenesis process in dogs with mammary gland tumours. The whole mitochondrial DNA (mtDNA) isolated from blood and tumour tissues of 13 dogs with malignant mammary gland tumours was sequenced. The present work is the first report showing that some polymorphisms might occur at the corresponding positions in the human and canine mtDNA genome, which in turn may provoke similar deleterious effects. The homology between the human MT-TL1 and canine tRNA-Leu (UUR) genes was 84%. After resequencing of the whole mitochondrial DNA genome with the use of the NGS technology, two polymorphisms in two haplotypes were identified: m.2683G>A (observed in 18 out of 27 samples) and m.2678_2679insG (27 out of 27 samples). The m.2683G>A polymorphism corresponded to a deleterious change at m.3243A>G, which is linked with MELAS (Mitochondrial Encephalomyopathy, Lactic Acidosis, Stroke-like episodes) syndrome and with different types of cancers in humans as well. The comparative analysis of MT-TL1 and tRNA-Leu (UUR) led us to hypothesise that the m.2678_2679insG and m.2683G>A polymorphisms might influence the dog’s condition and might be linked with tumourigenesis, as observed in humans.

Molecular differences in mitochondrial DNA genomes of dogs with malignant mammary tumours

The aim of this study was to determine molecular defects in mitochondrial DNA (mtDNA) with the use of large-scale genome analysis in malignant canine mammary gland tumours and indicate whether these changes were linked with the carcinogenesis process. With the use of the NGS technology, we sequenced 27 samples of mtDNA isolated from blood and tumours obtained from 13 dogs with mammary gland tumours. The total number of mutations and polymorphisms in the analysed mitochondrial genomes was 557. We identified 383 single nucleotide polymorphisms (SNP), 32 indels (or length polymorphisms), 4 mutations, 137 heteroplasmic positions and 1 indel mutation. The highest variability (132 changes) was observed in the variable number of tandem repeats (VNTR) region. The heteroplasmy rate in VNTR varied among individuals and even between two tumours in one organism. Our previous study resulted in determination of a probable CpG island in this region, thus it is not excluded that these changes might alter mtDNA methylation. Only the ATP8 gene was not affected by any polymorphisms or mutations, whereas the COX1 gene had the highest number of polymorphisms from all protein-coding genes. One change m.13594G>A was detected in a region spanning two genes: ND5 and ND6, from which a deleterious effect was observed for the ND5 protein. Molecular changes were frequently observed in the TΨC loop, which is thought to interact with ribosomal RNA.

Defect in Mitochondrial NADH-Dehydrogenase Genes in Canine Mast Cell Tumours

Recent studies have demonstrated a significant role of mitochondrial DNA (mtDNA) defects in the pathogenesis of many human and some canine tumours. The aim of this study was to identify mutations in the ND2 and ND4 mitochondrial genes in canine mast cell tumours and determine their association with the process of neoplastic transformation and the phenotypic traits of dogs. In total, 136 gene sequences from 68 biological samples, including blood and neoplastic tissue samples from 34 dogs with diagnosed MCTs, were analysed. The study consisted in DNA sequencing of the ND2 and ND4 genes as well as bioinformatics and statistical analyses. For the first time, mutations in NADH-dehydrogenase genes were detected in dogs with MCTs. In total, 22 polymorphic loci and 19 mutations in the ND2 and ND4 genes were identified. The majority of the identified mutations were homoplasmic, and tumour heteroplasmy was detected in eight nucleotide positions in three dogs. Seven of the ND2 mutations and two of the ND4 mutations caused an amino acid change. The changes in non-synonymous protein-coding SNPs did not exert an adverse effect on proteins. A statistically significant correlation of the presence of mutations/polymorphisms with the sex, age, and size of the dogs and the tumour location was demonstrated. Polymorphisms and mutations in NADH-dehydrogenase genes, including mastocyte-specific changes, in canine mast cell tumours that had not been reported earlier in the literature were identified. Some of these changes may imply that these are the hotspot mutations in canine mast cell tumours. It cannot be excluded that the molecular changes are directly associated with the development of mast cell tumours, and further investigations are needed to verify whether they can become molecular markers of MCTs in the future.

Analysis of Mitochondrial Genome from Labrador (Canis lupus familiaris) with Mammary Gland Tumour Reveals Novel Mutations and Polymorphisms

The aim of the study was to find associations between the process of neoplastic transformation and mtDNA mutations/polymorphisms, i.e. factors with potential prognostic significance, and to determine their impact on the biochemical properties, as well as structural, and functional properties of proteins. Blood and neoplastic tissue samples were collected from a 9-year-old Labrador dog with a diagnosed malignant mammary tumour. Next-generation genome sequencing (NGS) of the entire mitochondrial genome was performed using Illumina technology, and bioinformatics analyses were carried out. This is the first report demonstrating the application of NGS in the analysis of the canine mtDNA genome in neoplastic disease. The proposed strategy is innovative and promising. For the first time in the literature, the sequence of 29 genes was analysed to determine their association with the prevalence of tumour. In total, 32 polymorphic loci and 15 mutations were identified. For the first time, as many as 24 polymorphisms and all the mutations have been described to be associated with the neoplastic process in dogs. Most polymorphisms/mutations were found in the D-loop (31% of the polymorphisms and 93% of the mutations) and the COX1 gene sequence (16% of the polymorphisms). Blood or cancer heteroplasmy was noted in 93% of the mutations. Four of the 18 polymorphisms detected in the protein-coding genes were non-synonymous polymorphisms that have not been described in the literature so far (m.T7593C in COX2, m.G8807A in COX3, m.A9911G in ND4L, and m.T13299A in ND5) but resulted in changes in amino acids in proteins. These mutations and polymorphisms can affect mitochondrial functions and may be a result of cell adaptation to the changes in the environment occurring during carcinogenesis. The replacement of “wild type” mtDNA by a mutated molecule may be an important phenomenon accompanying carcinogenesis.

Heteroplasmic Mutations and Polymorphisms in the Cyb Gene of Mitochondrial DNA in Canine Mast Cell Tumours

AIM

Identification of mutations and polymorphisms in the cytochrome b gene (Cyb) of mitochondrial DNA (mtDNA) in canine mast cell tumours and determinatiion of their association with the process of neoplastic transformation.

MATERIALS AND METHODS

The samples comprised tumour tissues and blood obtained from 34 dogs of various breeds. Mutations and polymorphisms in the Cyb gene were detected using amplification and sequencing methods.

RESULTS

Heteroplasmic mutations were detected at seven positions of mtDNA in 86% of the individuals. Blood and tumour heteroplasmy were recorded at five nucleotide positions of the Cyb gene, whereas tumour heteroplasmy was detected at two positions. Polymorphisms were detected at 14 Cyb gene positions in in the blood of 91% of dogs with mast cell tumours.

CONCLUSION

The presence of numerous mutations and polymorphisms of Cyb in the blood and tumour tissues and the high frequency of heteroplasmy indicate their involvement in the process of neoplastic transformation in dogs.

Relevance of Molecular Changes in the ND4 Gene in German Shepherd Dog Tumours

The aim of the study was to identify polymorphisms and mutations in the mitochondrial ND4 gene and to analyse the associations between the occurrence of molecular changes in mtDNA and phenotypic traits in tumours in German Shepherd dogs. Fifty samples obtained from blood and tumour tissues of German Shepherd dogs with diagnosed tumours were analysed. DNA extraction, amplification, and sequencing of the mtDNA ND4 gene, and bioinformatics, statistical, and in silico protein coding SNP analyses were performed. ND4 mutations and/or polymorphisms were noted in eleven nucleotide positions in nearly half of the examined dogs. All the changes were substitution mutations. A majority of the changes identified were homoplasmic. In one dog with osteosarcoma, blood heteroplasmy was detected. In two positions of the ND4 gene, presence of non-synonymous mutations leading to amino acid changes in the ND4 protein was reported. Analyses carried out to determine the deleterious effect of mutations indicated an almost 97 and 62% probability that a single amino acid substitution (p.G239V and p.I401T, respectively) in the protein has a negative impact on its function. The results of statistical analyses indicate a significant association between the occurrence of mutations in three loci of the ND4 gene and the location of tumours. The mutations identified may be a result of cell adaptation to the changes in the environment occurring during carcinogenesis. The high frequency of mutations in the tumours may indicate genetic instability of mtDNA, which may also play a role in carcinogenesis.

Defect in ND2, COX2, ATP6 and COX3 mitochondrial genes as a risk factor for canine mammary tumour

The aim of this study was to identify mutations in ND2, COX2, ATP6 and COX3 mitochondrial genes in canine mammary tumour, determine their association with the process of neoplastic transformation, and phenotypic traits of dogs. In total, 93 biological samples, including blood, normal and neoplastic tissue samples from 31 dogs with diagnosed malignant canine mammary tumours were analysed. DNA sequencing of genes as well as bioinformatics and statistical analyses were performed. A total of 28 polymorphic loci and 11 mutations were identified. One of the mutations was blood heteroplasmy and two of the mutations caused an amino acid change in p.N117S and p.A184T. For the first time, mutations in mitochondrial genes were detected in dogs with mammary tumours. A statistically significant association between the presence of mutations and the size and age of dogs was demonstrated. Some of these changes may imply that these are the hotspot mutations of canine mammary tumour.

Defect of the mitochondrial DNA hypervariable region as a risk factor for canine mammary tumour

The aim of this study was to identify mutations in the hypervariable region of mitochondrial DNA in canine mammary tumours and to determine their association with the process of neoplastic transformation. A total of 93 biological samples, including blood as well as normal and neoplastic tissue samples from 31 dogs with diagnosed malignant canine mammary tumours were analysed. DNA extraction, amplification and sequencing of the D-loop as well as bioinformatic and statistical analyses were performed. In the mitochondrial D-loop sequence, 26 polymorphic loci and 5 mutations were identified. For the first time, D-loop length heteroplasmy was detected in dogs with mammary tumours. The malignancy grade exerted no effect on the presence of nucleotide changes. A statistically significant association between the presence of mutations and polymorphisms and the size of dogs was demonstrated. The 100% frequency of length heteroplasmy may imply that this is a hotspot mutation of canine mammary tumour.

Identification of mitochondrial DNA transfer in canine transmissible venereal tumours obtained from dogs in Mexico

Canine transmissible venereal tumour (CTVT) has been transmitted by cell transplantation from dog to dog, for over 10 000 years. Although initial studies report a single genetic origin for CTVT, recent samples from around the world reveal high genetic diversity. An elevated number of polymorphisms have been determined in mitochondrial DNA (mtDNA) of CTVT. The recent discovery of mtDNA transference from the host into tumoural cells could be a novel source of genetic diversity in CTVT. The aim of this study was to determine the presence of host mtDNA in samples of CTVT in Mexican dogs. Genotyping of 49 samples of CTVT and 49 samples of blood cells pertaining to affected dogs was performed by direct sequencing from the mtDNA D-loop region. Exogenous mtDNA was observed in 6% of the analysed tumours. This is the first investigation reporting the prevalence of exogenous mtDNA in CTVT in the Mexican dog population.

Identification of additional mitochondrial DNA mutations in canine mast cell tumours

BACKGROUND

Research has revealed the presence of somatic mutations in mitochondrial DNA (mtDNA) of certain types of tumours. As this has not been studied for canine mast cell tumours, the aim of this study was to identify mutations in the hypervariable region of mtDNA in mast cell tumours in dogs and determine their association with the process of neoplastic transformation.

RESULTS

Samples from 17 dogs with histopathologically confirmed mast cell tumours were analysed. The samples consisted of tumour tissues (n = 17), normal tissues (n = 17), and blood (n = 17). Amplicons of the displacement loop (D-loop) were sequenced and the obtained nucleotide sequences were subjected to bioinformatics analyses. Somatic mutations were detected in seven positions of the D-loop nucleotide sequences in 47 % of the dogs, while polymorphisms were identified in 94 % of the dogs. Most of these changes were homoplasmic, while heteroplasmy was detected in two individuals. Six new haplotypes were established as being characteristic for canine mast cell tumours. There was no association between the presence of the mutations and sex, haplotype, or malignancy grade assessed in 3 and 2-grade scales.

CONCLUSIONS

Differences in the frequency of somatic mutations imply their direct association with the neoplastic transformation. However, their functional consequences and clinical significance are not clear. The mutations may be used for diagnosis and prognosis of canine mast cell tumours in the future.

Novel mitochondrial mutations in the ATP6 and ATP8 genes in patients with breast cancer

The role of the mitochondria in the process of carcinogenesis, mainly oxidative phosphorylation, mostly concerns their participation in the production of free radicals and ATP and in the process of apoptosis. The purpose of this study was to detect potential changes in the genes encoding the subunits 6 and 8 of the ATP synthase and their impact on the enzyme's biochemical properties, structure and function in patients with breast tumors. The tested material was mitochondrial DNA (mtDNA) isolated from specimens of ductal carcinoma (carcinoma ductale) Tp1-2Np0-1Mp0, blood and non-cancerous tissue of mammary gland (control), sampled from 50 patients who had been operated for breast cancer. In the case of missense-type changes in the mtDNA, protein prediction software was used to assess their effect on the biochemical properties of the protein, its structure and function. We identified 8 changes in the ATP6 gene in 36/50 examined breast cancer cell samples and 5 changes in the ATP8 gene (10/50). Most of them were homoplasmic changes of missense type. Four of the changes (A8439C, G8858C, C9130G and T9119G) had not been described in the literature before. The identified mutations and polymorphisms, especially those of missense type, can affect mitochondrial functions, especially if the conservative domain of the protein is concerned. Replacement of 'wild-type' mtDNA by mutated mtDNA can be an important event in carcinogenesis.

Mitochondrial NADH dehydrogenase polymorphisms are associated with breast cancer in Poland

Complex I NADH-oxidoreductase-ubiquinone transports reducing equivalents from the reduced form of NADH to ubiquinone (coenzyme Q-CoQ). The purpose of this study was to analyze mutations in MT-ND1, MT-ND2, MT-ND3 and MT-ND6 genes and their effect on the biochemical properties, structure and functioning of proteins in patients with breast tumours. In research materials, in 50 patients, 28 total polymorphisms and five mutations were detected. Most detected polymorphisms (50 %, 14/28) were observed in MT-ND2 gene. Most of them were silent mutations. Five polymorphisms (m.G3916A, m.C4888T, m.A4918G, m.C5363T, m.C10283T) do not exist in the database. A total of five mutations in 13 patients (13/50) were detected, including two not described in the literature: m.C4987G and m.T10173C. It cannot be excluded that, through the mutations and polymorphism impact on the protein structure, they may cause mitochondrial dysfunction and contribute to the appearance of other changes in mtDNA. The results of our study indicate the presence of homological changes in the sequence of mtDNA in both breast cancer and in some mitochondrial diseases. Mutations in the examined genes in breast cancer may affect the cell and cause its dysfunction, as is the case in mitochondrial diseases.