Mutations of the D310 mitochondrial mononucleotide repeat in primary tumors and cytological specimens

A novel approach for rapid screening of mitochondrial D310 polymorphism

Background

Mutations in the mitochondrial DNA (mtDNA) have been reported in a wide variety of human neoplasms. A polynucleotide tract extending from 303 to 315 nucleotide positions (D310) within the non-coding region of mtDNA has been identified as a mutational hotspot of primary tumors. This region consists of two polycytosine stretches interrupted by a thymidine nucleotide. The number of cytosines at the first and second stretches are 7 and 5 respectively, according to the GeneBank sequence. The first stretch exhibits a polymorphic length variation (6-C to 9-C) among individuals and has been investigated in many cancer types. Large-scale studies are needed to clarify the relationship between cytosine number and cancer development/progression. However, time and money consuming methods such as radioactivity-based gel electrophoresis and sequencing, are not appropriate for the determination of this polymorphism for large case-control studies. In this study, we conducted a rapid RFLP analysis using a restriction enzyme, BsaXI, for the single step simple determination of 7-C carriers at the first stretch in D310 region.

Methods

25 colorectal cancer patients, 25 breast cancer patients and 41 healthy individuals were enrolled into the study. PCR amplification followed by restriction enzyme digestion of D310 region was performed for RFLP analysis. Digestion products were analysed by agarose gel electrophoresis. Sequencing was also applied to samples in order to confirm the RFLP data.

Results

Samples containing 7-C at first stretch of D310 region were successfully determined by the BsaXI RFLP method. Heteroplasmy and homoplasmy for 7-C content was also determined as evidenced by direct sequencing. Forty-one percent of the studied samples were found to be BsaXI positive. Furthermore, BsaXI status of colorectal cancer samples were significantly different from that of healthy individuals.

Conclusion

In conclusion, BsaXI RFLP analysis is a simple and rapid approach for the single step determination of D310 polymorphism of mitochondrial DNA. This method allows the evaluation of a significant proportion of samples without the need for sequencing- and/or radioactivity-based techniques.

Mutations in the mitochondrial DNA D-loop region are frequent in cervical cancer

Background

Mitochondrial DNA (mtDNA) is known for high mutation rates caused by lack of protective histones, inefficient DNA repair systems, and continuous exposure to mutagenic effects of oxygen radicals. Alterations in the non-coding displacement (D) loop of mitochondrial DNA are present in many cancers. It has been suggested that the extent of mitochondrial DNA mutations might be useful in the prognosis of cancer outcome and/or the response to certain therapies. In order to investigate whether a high incidence of mutations exist in mitochondrial DNA of cervical cancer patients, we examined the frequency of mutations in the D-loop region in 19 patients of cervical cancer.

Results

Mutations, often multiple, were detected in 18 of 19 (95%) patients. The presence of mutations correlated with Human Papilloma Virus (HPV) infection in these patients. Mutations were also detected in normal samples and lymphocytes obtained from cervical cancer patients, but their frequency of occurrence was much lower as compared to the cervical cancer tissues.

Conclusion

Our findings indicate that D-loop alterations are frequent in cervical cancers and are possibly caused by HPV infection. There was no association of mtDNA D-loop mutations with the histopathological grade and tumor staging.

Mitochondrial DNA as a cancer biomarker

As part of a national effort to identify biomarkers for the early detection of cancer, we developed a rapid and high-throughput sequencing protocol for the detection of sequence variants in mitochondrial DNA. Here, we describe the development and implementation of this protocol for clinical samples. Heteroplasmic and homoplasmic sequence variants occur in the mitochondrial genome in patient tumors. We identified these changes by sequencing mitochondrial DNA obtained from tumors and blood from the same individual. We confirmed previously identified primary lung tumor changes and extended these findings in a small patient cohort. Eight sequence variants were identified in stage I to stage IV tumor samples. Two of the sequence variants identified (22%) were found in the D-loop region, which accounts for 6.8% of the mitochondrial genome. The other sequence variants were distributed throughout the coding region. In the forensic community, the sequence variations used for identification are localized to the D-loop region because this region appears to have a higher rate of mutation. However, in lung tumors the majority of sequence variation occurred in the coding region. Hence, incomplete mitochondrial genome sequencing, designed to scan discrete portions of the genome, misses potentially important sequence variants associated with cancer or other diseases.

Mitochondrial DNA instability in malignant melanoma of the skin is mostly restricted to nodular and metastatic stages

Ultraviolet (UV) radiation is thought to be a major contributor to the development of sporadic malignant melanoma of the skin. It may induce alterations in genomic or mitochondrial DNA (mtDNA), especially C to T or CC to TT changes. Mutations or other alterations in mtDNA have been reported in a variety of human cancers and may be due to different mechanisms. In this study, we have attempted to elucidate whether aberrations in the mtDNA of melanoma are due to UV radiation or other factors by investigating two parts of the mitochondrial D-loop and two mitochondrial genes, as well as looking for the delta4977 mtDNA deletion and mtDNA duplications, in 61 primary malignant melanomas and neighbouring normal skin tissue (in 70% of primary tumours; otherwise, corresponding blood samples). Point mutations were a rare feature, occurring in only seven tumour samples and never as a C to T change, whereas mtDNA instability in the D-loop (mtMSI) was found in 13% of primary nodular tumours and 20% of metastases. A de novo delta4977 mtDNA deletion was demonstrated in 10% of melanomas; in 20% of patients, mtDNA duplications and/or the delta4977 mtDNA deletion was detectable. Our data indicate that mtDNA alterations in malignant melanoma are not induced by UV radiation. In addition, point mutations and mtMSI were mostly a feature of nodular and metastatic melanoma samples.

Relationship between mitochondrial DNA instability, mitochondrial DNA large deletions, and nuclear microsatellite instability in head and neck squamous cell carcinomas

Mitochondrial DNA (mtDNA) mutations in coding and noncoding regions have been reported in a variety of human cancers. Despite a greater number of studies, the relationship between such alterations and nuclear microsatellite instability (nMSI) of the tumor cells remains controversial. To contribute new data to this discussion, we investigated head and neck squamous cell carcinomas (HNSCC) for mutations and mitochondrial microsatellite instability (mtMSI) in 2 parts of the mitochondrial D-loop as well as mutations in 2 mitochondrial genes and for the delta4977 mtDNA deletion. These results were compared with data of an analysis for microsatellite instability at IGFIIR, hMSH3, hMSH6, and 5 dinucleotide repeats. We found mtMSI, low nMSI, and high nMSI in 42%, 36%, and 13% of HNSCC primary tumors, respectively. A de novo delta4977 mtDNA deletion could be demonstrated in 25% of HNSCCs. A correlation between mtMSI and nMSI or between a de novo occurrence of the delta4977 mtDNA deletion and nMSI could not be detected in our HNSCC samples (P values 0.527 and 0.078, respectively). Nevertheless, the high rate of mtMSI suggests an involvement of mtDNA alterations in the tumorigenesis of this head and neck cancer and supports the proposal that this aberration may be a new tumor marker.

Detection of bladder tumours: role of cytology, morphology-based assays, biochemical and molecular markers

PURPOSE OF REVIEW

Cystoscopy is currently considered the gold standard for the detection of bladder tumours. The role of urine cytology in the initial detection and follow-up of patients is under discussion. Many efforts have been made to increase the detection rates and to predict the outcome of bladder cancer. In this subject review, a series of morphology-based, biochemical and molecular markers were compared with urine cytology for the detection of bladder cancer.

RECENT FINDINGS

Among the various markers reviewed, the average published sensitivity and specificity for the Bard tumour antigen test was 60 and 77%; for the nuclear matrix protein 22 test it was 67 and 72%; for the hyaluronic acid and hyaluronidase test it was 91 and 84%; for the ImmunoCyt it was 90 and 75%; for fluorescence in-situ hybridization it was 85 and 95%; for the telomerase assay it was 77 and 85%; and for the microsatellite assay it was 89 and 100%. DNA ploidy measurements, recent molecular markers and immunoassays designed to detect keratins, proteins, cell adhesion molecules, fibrinogen degradation products, and fibrinolysis markers were also included.

SUMMARY

As is clear from the brief summary of available assays, the optimal method of application is not yet clear. The integration of an assay into clinical practice takes more than just the documentation of its sensitivity and specificity. However, several of the procedures have received considerable support from urologists as assisting them in the management of their patients.

New diagnostic strategies in the detection and staging of bladder cancer

PURPOSE OF REVIEW

Bladder cancer is a very frequent disease and represents the second most common genitourinary neoplasm. The most prevalent form of the disease, superficial bladder cancer, can recur in more than 70% of cases, despite correct management. Any way to improve our disease diagnostic and treatment policy is therefore welcome.

RECENT FINDINGS

This review covers the following topics: (1). endoscopic tools: standard cystoscopy versus fluorescence cystoscopy and virtual endoscopy; (2). bladder cancer staging: histopathological analysis developments and imaging techniques (positron emission tomography, magnetic resonance imaging, computed tomography); (3). cytology and ancillary procedures (ImmunoCyt and fluorescence in-situ hybridization test, and others); (4). first-generation (bladder tumour antigen, nuclear matrix protein 22, telomerase repeat amplification protocol) and second-generation (loss of heterozygosity, minichromosome maintenance 5, DNA methylation, microsatellite) urine and serum markers.

SUMMARY

New diagnostic and therapeutic (endoscopic) tools in superficial bladder cancer should eventually modify our disease management policy. Fluorescence cystoscopy detects carcinoma in situ with a high accuracy, and seems to have a positive impact on reducing residual tumour and recurrence rate. A more specific staining of tissue specimens facilitates histological analysis and helps achieve better staging, especially in T1 diseases. Improving the sensitivity of cytology for low-grade diseases, ancillary procedures to classic cytology such as fluorescence in-situ hybridization and ImmunoCyt tests, may reduce the number of unpleasant cystoscopies in surveillance protocols of selected groups of patients. Second-generation urine markers such as loss of heterozygosity, microsatellite, minichromosome maintenance 5, with a high level of accuracy, show great potential for influencing bladder cancer detection and screening policy.