Mitogenome germline mutations and colorectal cancer risk in Polish population.

INTRODUCTION: To date, several nuclear DNA variants have been shown to be associated with increased risk of developing colorectal cancer. Despite the fact that mitochondria play an important role in carcinogenesis, little is known about inherited mitochondrial DNA mutations that could be involved in this disease. Thus, potential associations between inherited mutations in the entire mitochondrial genomes and colorectal cancer were analysed in this study. MATERIAL AND METHODS: Two hundred mitogenome sequences determined for colorectal cancer patients and healthy individuals from Poland were used to investigate the association between mtDNA alleles or haplogroups and colorectal cancer. Additional mtDNA control region haplotypes determined for 1353 individuals from the general Polish population were used for comparison of haplogroup and certain allele frequencies between case and control groups. RESULTS: The non-R clades together with their diagnostic T alleles at positions 12705 and 16223 were observed with higher frequencies in healthy individuals than in colorectal cancer patients. Nevertheless, the differences of the R macrohaplogroup (as well as 12705 or 16223 alleles) frequencies between cases and controls were statistically insignificant after Bonferroni correction. Most of the non-R clades were of Asian and African origin, but none of them were prevalent in the control group. Moreover, neither mtDNA alleles nor haplogroups were associated with clinicopathological parameters of colorectal cancer patients. CONCLUSIONS: Contrary to some previous reports, the findings of this study do not support the hypothesis that mitochondrial DNA variants contribute to inherited predisposition to colorectal cancer.

TP53 somatic mutations are associated with somatic mitogenome substitutions but not indels in colorectal cancer cells.

BACKGROUND: p53 is a tumour suppressor protein that is involved in many cancer-related processes. Growing evidence suggests that p53 also plays an important role in mitochondrial (mtDNA) maintenance. Somatic mitogenome mutations are frequently observed in colorectal cancer (CC) cells. Thus, it was important to determine whether somatic mtDNA changes are associated with TP53 mutational status. METHODS: In the present study, we analysed the TP53 gene in 67 CC patients, for whom mitogenome haplotypes were previously described. In total, 134 TP53 sequences (of cancer and matched normal specimens) were determined using the dideoxy method. RESULTS: Nine hereditary polymorphisms in the TP53 gene were detected in normal colon cells. None of them (neither alleles, nor genotypes) was associated with somatic mitogenome mutations in CC cells. Moreover, 42 somatic TP53 mutations were found in approximately 36% of CC tissues. These somatic changes were significantly more frequent in CC cells with somatic mtDNA mutations (p = 0.0069). Furthermore, we show that only mitochondrial somatic substitutions (p = 0.0017), but not indels (p > 0.05), were associated with somatic TP53 mutations. CONCLUSIONS: The results of the present study suggest that changes in TP53 may modify p53 properties, which may result in the accumulation of somatic substitutions in CC mitogenomes.

Mitogenomic differences between the normal and tumor cells of colorectal cancer patients.

So far, a reliable spectrum of mitochondrial DNA mutations in colorectal cancer cells is still unknown, and neither is their significance in carcinogenesis. Indeed, it remains debatable whether mtDNA mutations are "drivers" or "passengers" of colorectal carcinogenesis. Thus, we analyzed 200 mitogenomes from normal and cancer tissues of 100 colorectal cancer patients. Minority variant mutations were detected at the 1% level. We showed that somatic mutations frequently occur in colorectal cancer cells (75%) and are randomly distributed across the mitochondrial genome. Mutational signatures of somatic mitogenome mutations suggest that they might arise through nucleotide deamination due to oxidative stress. The majority of somatic mutations localized within the coding region (in positions not known from the human phylogeny) and was potentially pathogenic to cell metabolism. Further analysis suggested that the relaxation of negative selection in the mitogenomes of colorectal cancer cells may allow accumulation of somatic mutations. Thus, a shift in glucose metabolism from oxidative phosphorylation to glycolysis may create advantageous conditions for accumulation of mtDNA mutations. Considering the fact that the presence of somatic mtDNA mutations was not associated with any clinicopathological features, we suggested that mtDNA somatic mutations are "passengers" rather than the cause of colorectal carcinogenesis.

Massively parallel targeted resequencing reveals novel genetic variants associated with aspergillosis in paediatric patients with haematological malignancies.

This study aimed to find novel genetic variants of susceptibility to aspaergillosis in paediatric patients with haematological malignancies. Complete sequences of fifteen genes of human innate immunity (CCL2, CCR2, CD209, CLEC6A, CLEC7A and ten TLR genes) were studied in 40 patients diagnosed with haematological disorders (20 unaffected and 20 affected by aspergillosis). All samples were sequenced with MiSeq (Illumina) and 454 (Roche Diagnostics) technologies. Statistical significance of the differences between studied groups was determined using the two-tailed Fisher's exact test. Sixty variants of potential importance were identified, the vast majority of which are located in non-coding parts of the targeted genes. At the threshold of p < 0.000005, one intergenic (TLR2 rs4585282) and one intronic variant (CLEC6A rs12099687) were found significant between the case and control groups for genotype and allele frequencies, respectively. Rs12099687 in CLEC6A was predicted to constitute an alternative isoform or cryptic splice site, which potentially changes activity of the Dectin-2 protein. Overall, we assume that the two strongest associations reported in this study are expected to be reproducible even in the absence of other evidence, while another twelve associations may be strong enough to justify additional research in larger cohorts.

Searching for association of the CAG repeat polymorphism in the mitochondrial DNA polymerase gamma gene (POLG) with colorectal cancer.

Mitochondrial DNA polymerase gamma (POLG) is the only DNA polymerase involved in maintaining the mitochondrial genome. Recent studies demonstrated an association of CAG repeat polymorphism in the second exon of POLG gene with the risk of cancer. We investigated the CAG repeat variability in the POLG gene in tumor and non-tumor tissues from colorectal cancer patients and in DNA samples isolated from blood obtained from age-matched healthy persons. Somatically occuring CAG-repeat alterations in cancer tissues have been observed in 10% of patients, but no association has been found between the CAG repeat variants in the POLG gene and colorectal cancer risk.

Mitochondrial DNA Polymerase γ Mutations and Their Implications in mtDNA Alterations in Colorectal Cancer.

Mitochondrial DNA was found to be highly mutated in colorectal cancer cells. One of the key molecules involved in the maintenance of the mitochondrial genome is the nuclear-encoded polymerase gamma. The aim of our study was to determine if there is a link between polymorphisms within the polymerase gamma gene (POLG) and somatic mutations within the mitochondrial genome in cancer cells. We investigated POLG sequence variability in 50 colorectal cancer patients whose complete mitochondrial genome sequences were determined. Relative mtDNA copy number was also determined. We identified 251 sequence variants in the POLG gene. Most of them were germline-specific (∼92%). Twenty-one somatic changes in POLG were found in 10 colorectal cancer patients. We have found no association between the occurrence of mtDNA somatic mutations and the somatically occurring variants in POLG. MtDNA content was reduced in patients carrying somatic variants in POLG or germline nucleotide variants located in the region encoding the POLG polymerase domain, but the difference did not reach statistical significance. Our findings suggest that somatic mtDNA mutations occurring in colorectal cancer are not a consequence of somatic mutations in POLG. Nevertheless, POLG nucleotide variants may lead to a decrease in mtDNA content, and consequently result in mitochondrial dysfunction.

The efficacy of bevacizumab in diabetic macular oedema in a 12-month follow-up.

PURPOSE: To evaluate visual acuity and anatomic response of the macula following intravitreal bevacizumab injections in diabetic macular oedema. MATERIAL AND METHODS: In the retrospective, non-randomised study 35 eyes of 28 subjects (whose mean age was 59.6 years) with focal or diffuse diabetic macular oedema were included. Patients underwent best corrected visual acuity testing with Snellen charts converted to a number of letters, intraocular pressure measurement, slit lamp examination, macular biomicroscopy, central macular thickness measurement by optical coherence tomography as well as fluorescein angiography at baseline and all follow-up visits. Patients were treated with one or two intravitreal injections of 1.25 mg of bevacizumab. RESULTS: A total of 49 intravitreal injections were performed. All patients had a 6-12-month follow-up after the first injection. The mean baseline best-corrected visual acuity was 5.0 ± 4.3 letters and the mean central macular thickness in the baseline optical coherence tomography was 482.0 ± 109.7 µm. An improvement in the mean best-corrected visual acuity (6.2 ± 6.3, p = 0.020) and central macular thickness (426.8 ± 131.7 µm, p = 0.010) was statistically significant during the follow-up after first injection. There was no statistically significant difference in the best-corrected visual acuity (6.2 ± 6.5, p = 0.055) and central macular thickness (461.2 ± 148.3 µm, p 0.200) after the second injection. There was no correlation between the best corrected visual acuity and central macular thickness. No serious adverse events were observed. CONCLUSIONS: Intravitreal bevacizumab injections significantly improve visual acuity and decrease central macular thickness in patients with diabetic macular edema. This treatment is safe for patients but the therapeutic effect is temporary.

The landscape of mitochondrial DNA variation in human colorectal cancer on the background of phylogenetic knowledge.

Recently, an increasing number of studies indicate that mutations in mitochondrial genome may contribute to cancer development or metastasis. Hence, it is important to determine whether the mitochondrial DNA might be a good, clinically applicable marker of cancer. This review describes hereditary as well as somatic mutations reported in mitochondrial DNA of colorectal cancer cells. We showed here that the entire mitochondrial genome mutational spectra are different in colorectal cancer and non-tumor cells. We also placed the described mutations on the phylogenetic context, which highlighted the recurrent problem of data quality. Therefore, the most important rules for adequately assessing the quality of mitochondrial DNA sequence analysis in cancer have been summarized. As follows from this review, neither the reliable spectrum of mtDNA somatic mutations nor the association between hereditary mutations and colorectal cancer risk have been resolved. This indicates that only high resolution studies on mtDNA variability, followed by a proper data interpretation employing phylogenetic knowledge may finally verify the utility of mtDNA sequence (if any) in clinical practice.