Biomedical subjects

Piotr A Mieczkowski

Publications and source records attributed to Piotr A Mieczkowski.

4 recordsLinked to original sources

PubMed2026

Widespread atypical UV-induced mutations form in single-stranded DNA.

Persistence of common ultraviolet (UV)-induced lesions, like cyclobutane pyrimidine dimers (CPDs) and pyrimidine-pyrimidone (6-4) photoproducts (6-4-PPs), typically results in C>T substitutions at dipyrimidines: a mutation pattern that composes the single-base substitution (SBS) signature 7 in cancer. Oncogenic melanoma mutations rarely involve SBS7-like substitutions. We recently identified noncanonical UV-induced mutations in yeast that appear to originate from atypical AC and TA photoproducts. While an AC photoproduct could account for formation of BRAF V600K, other melanoma drivers like BRAF V600E and NRAS Q61K involve other mutation types, suggesting possible existence of additional atypical photoproducts. Here, we couple temperature-induced telomeric end resection in yeast with serial UV irradiation and whole-genome sequencing to show UV light induces an extended array of noncanonical mutations in single-stranded DNA (ssDNA). This includes AT>AM, GT>GV, AC>AA, AT>TT, and TA>TT substitutions that are resistant to photo-reversion, indicating that they likely originate from atypical photoproducts. UV-induced mutation spectra in yeast lacking Rad30 indicated that Pol η plays substantial roles in the bypass of CPDs and 6-4-PPs regardless of telomere proximity. Unexpectedly, expression of a mutant DNA pol ε (pol2 M644G) reduced both canonical and noncanonical UV-induced mutations specifically within subtelomeric regions of the genome. This suggests a preferential role for pol ε in the resynthesis of uncapped telomeres, with the M644G mutation conferring accurate lesion bypass capabilities to the replicative polymerase. ssDNA-specific UV lesions provide additional damage-mediated mechanisms for the production of oncogenic mutations in melanoma, such as the BRAF V600E mutation that involves a GT>GA substitution.

Ultraviolet Rays↗

PubMed2021

Evaluating the analytical validity of circulating tumor DNA sequencing assays for precision oncology.

Circulating tumor DNA (ctDNA) sequencing is being rapidly adopted in precision oncology, but the accuracy, sensitivity and reproducibility of ctDNA assays is poorly understood. Here we report the findings of a multi-site, cross-platform evaluation of the analytical performance of five industry-leading ctDNA assays. We evaluated each stage of the ctDNA sequencing workflow with simulations, synthetic DNA spike-in experiments and proficiency testing on standardized, cell-line-derived reference samples. Above 0.5% variant allele frequency, ctDNA mutations were detected with high sensitivity, precision and reproducibility by all five assays, whereas, below this limit, detection became unreliable and varied widely between assays, especially when input material was limited. Missed mutations (false negatives) were more common than erroneous candidates (false positives), indicating that the reliable sampling of rare ctDNA fragments is the key challenge for ctDNA assays. This comprehensive evaluation of the analytical performance of ctDNA assays serves to inform best practice guidelines and provides a resource for precision oncology.

Circulating Tumor DNA↗

PubMed2004

The compact chromatin structure of a Ty repeated sequence suppresses recombination hotspot activity in Saccharomyces cerevisiae.

Recombination between repeated DNA sequences can have drastic consequences on the integrity of the genome. Repeated sequences are abundant in most eukaryotes, yet the mechanism that prevents recombination between them is currently unknown. Ty elements, the main family of dispersed repeats in Saccharomyces cerevisiae, exhibit low levels of exchange. Other regions in the genome have relatively high rates of meiotic recombination (hotspots). We show that a Ty element adjacent to the HIS4 recombination hotspot substantially reduces its activity, eliminating local DSB formation. We demonstrate that the Ty has a closed (nuclease-insensitive) chromatin configuration that is also imposed on the flanking DNA sequences. The compact chromatin structure is determined by sequences at the N terminus of the Ty. Increased binding of the Rap1 protein to the hotspot restores both open chromatin conformation and DSB formation. The chromatin configuration of Ty elements precludes initiation of recombination, thus preventing potentially lethal exchanges between repeated sequences.

Alcohol Oxidoreductases↗

PubMed2003

Genetic regulation of telomere-telomere fusions in the yeast Saccharomyces cerevisae.

Yeast strains with mutations in both TEL1 and MEC1 have short telomeres and elevated rates of chromosome deletions. By using a PCR assay, we demonstrate that mec1 tel1 strains also have telomere-telomere fusions (T-TFs). T-TFs require Lig4p (a ligase required for nonhomologous end-joining DNA repair). The highest rates of T-TFs are found in strains with combination of mutations that affect telomere length and DNA damage checkpoints (mec1 tel1, mec3 tel1, mre11 mec1, and ddc1 tel1 strains). Examining many mutant genotypes, we find good agreement between the level of T-TFs and the rate of chromosomal deletions. In addition, if telomeres are elongated in a mec1 tel1 strain, we eliminate T-TFs and reduce the deletion rate. The correlation between the level of T-TFs and the rate of deletions argues that many of these deletions reflect a cycle of T-TF formation (resulting in dicentric chromosomes), followed by chromosome breakage.

Base Sequence↗