Pair DNA Research Articles

In vivo assembly of complete eukaryotic nucleosomes and (H3-H4)-only non-canonical nucleosomal particles in the model bacterium Escherichia coli.

As a fundamental unit for packaging genomic DNA into chromatin, the eukaryotic nucleosome core comprises a canonical octamer with two copies for each histone, H2A, H2B, H3, and H4, wrapped around with 147 base pairs of DNA. While H3 and H4 share structure-fold with archaeal histone-like proteins, the eukaryotic nucleosome core and the complete nucleosome (the core plus H1 histone) are unique to eukaryotes. To explore whether the eukaryotic nucleosome can assemble in prokaryotes and to reconstruct the possible route for its emergence in eukaryogenesis, we developed an in vivo system for assembly of nucleosomes in the model bacterium, Escherichia coli, and successfully reconstituted the core nucleosome, the complete nucleosome, and unexpectedly the non-canonical (H3-H4)4 octasome. The core and complete nucleosomes assembled in E. coli exhibited footprints typical of eukaryotic hosts after in situ micrococcal nuclease digestion. Additionally, they caused condensation of E. coli nucleoid. We also demonstrated the stable formation of non-canonical (H3-H4)2 tetrasome and (H3-H4)4 octasomes in vivo, which are suggested to be 'fossil complex' that marks the intermediate in the progressive development of eukaryotic nucleosome. The study presents a unique platform in a bacterium for in vivo assembly and studying the properties of non-canonical variants of nucleosome.

Abstract IA005: Tumor cell-based liquid biopsy to characterize prostate cancer

Abstract Circulating Tumor Cells (CTCs) hold the promise of comprehensive yet noninvasive molecular characterization of cancer cells during the course of tumor evolution and progression. To dissect the epigenetic profile of prostate CTCs, we undertook paired DNA methylation and RNA sequencing of single CTCs isolated from blood specimens of patients with prostate cancer. Across the genome, our study identified 40 core Partial Methylation Domains (PMDs) that arise early in tumorigenesis and are shared by all individual CTCs across multiple patients. Key among these is a single genomic locus harboring multiple interferon-inducible genes along with all the CD1 gene family members, implicated in innate immunity. Based on mouse models, we propose that early biallelic silencing of multiple genes residing within a single PMD may contribute to the escape from immune surveillance in prostate and potentially other cancers. Studies of CTC heterogeneity within individual patients are limited by the very small number of cells that can be isolated from standard 10ml blood volumes. To enable such analyses, we applied a new high throughput microfluidic platform, capable of processing an entire leukapheresis product, interrogating 2-3 L of blood volume equivalent. Applying this technology to patients with metastatic prostate cancer, we successfully enriched thousands of CTCs from individual cases, enabling the characterization of intra-patient heterogeneity at the level of cell morphology and marker expression, chromosome copy number variation and exome-wide genotyping, and transcriptionally-defined tumor cell subpopulations. Such high-volume microfluidic enrichment of CTCs constitutes a new dimension in liquid biopsies. Citation Format: Daniel A Haber, Shyamala Maheswaran, Hongshan Guo, Joanna Vuille, Shih-Bo Huang, Ben S Wittner, Lecia V Sequist, Richard J Lee, Patricia AR Brunker, David T Miyamoto, Avanish Mishra, Mehmet Toner. Tumor cell-based liquid biopsy to characterize prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Liquid Biopsy: From Discovery to Clinical Implementation; 2024 Nov 13-16; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(21_Suppl):Abstract nr IA005.

On the Hunt for the Histone Code

Our genome is not made of naked DNA, but a fiber (chromatin) composed of DNA and proteins packaged into our chromosomes. The basic building block of chromatin is the nucleosome, which has two copies of each of the proteins called histones (H2A, H2B, H3, and H4) wrapped by 146 base pairs of DNA. Regions of our genetic material are found between the more open (euchromatin) and more compact (heterochromatin) regions of the genome that can be variably accessible to the underlying genes. Furthermore, post-translational modifications (PTMs) on histones, such as on H3, are critical for regulating chromatin accessibility and gene expression. While site specific antibodies were the tool of choice for histone PTM analysis in the early days (pre-2000s), enter Don Hunt changing the histone PTM field forever. Don’s clever thinking brought new innovative mass spectrometry-based approaches to the epigenetics field. His lab’s effort led to the discovery of many new histone modifications and methods to facilitate the detection and quantification of histone PTMs, which are still considered state of the art in the proteomics field today. Due to Don’s pioneering work in this area, many labs have been able to jump into the epigenetics field and “Hunt” down their own histone targets. A walkthrough of those early histone years in the Hunt Lab are described by three of us who were fortunate enough to be at the right place, at the right time.

Localization and discrimination of GG mismatch in duplex DNA by synthetic ligand-enhanced protein nanopore analysis.

Mismatched base pairs in DNA are the basis of single-nucleotide polymorphism, one of the major issues in genetic diseases. However, the changes of physical and chemical properties of DNA caused by single-site mismatches are often influenced by the sequence and the structural flexibility of the whole duplex, resulting in a challenge of direct detection of the types and location of mismatches sensitively. In this work, we proposed a synthetic ligand-enhanced protein nanopore analysis of GG mismatch on DNA fragment, inspired by in silico investigation of the specific binding of naphthyridine dimer (ND) on GG mismatch. We demonstrated that both the importing and unzipping processes of the ligand-bound DNA duplex can be efficiently slowed down in α-hemolysin nanopore. This ligand-binding induced slow-down effect of DNA in nanopore is also sensitive to the relative location of the mismatch on DNA duplex. Especially, the GG mismatch close to the end of a DNA fragment, which is hard to be detected by either routine nanopore analysis or tedious nanopore sequencing, can be well differentiated by our ND-enhanced nanopore experiment. These findings provide a promising strategy to localize and discriminate base mismatches in duplex form directly at the single-molecule level.

Cancer-associated SF3B1-K700E mutation controls immune responses by regulating Treg function via aberrant Anapc13 splicing.

Recurrent somatic mutations in spliceosome factor 3b subunit 1 (SF3B1) are identified in hematopoietic malignancies, with SF3B1-K700E being the most common one. Here, we show that regulatory T cell (Treg)-specific expression of SF3B1-K700E (Sf3b1K700Efl/+/Foxp3YFP-Cre) results in spontaneous autoimmune phenotypes. CD4+ T cells from Sf3b1K700Efl/+/Foxp3YFP-Cre mice display defective Treg differentiation and inhibitory function, which is demonstrated by failed prevention of adoptive transfer colitis by Sf3b1K700Efl/+/Foxp3YFP-Cre Tregs. Mechanically, SF3B1-K700E induces an aberrant splicing event that results in reduced expression of a cell proliferation regulator Anapc13 due to the insertion of a 231-base pair DNA fragment to the 5' untranslated region. Forced expression of the Anapc13 gene restores the differentiation and ability of Sf3b1K700Efl/+/Foxp3YFP-Cre Tregs to prevent adoptive transfer colitis. In addition, acute myeloid leukemia grows faster in aged, but not young, Sf3b1K700Efl/+/Foxp3YFP-Cre mice compared to Foxp3YFP-Cre mice. Our results highlight the impact of cancer-associated SF3B1 mutation on immune responses, which affect cancer development.

On the Cancer

This article theoretically speculates that after replication of a pair of DNA they must be allocated to two daughter cells in a transverse division or erect division manner. Transverse division represents differentiation, while erect division represents transformation. The molecular structure determines that DNA has greater hydrophobicity than RNA. The hydrophobic modification of chromatin regulates gene activity and centromere similarity between new and old DNA. A difference in division between cancer cells and embryonic stem cells is discussed

Assessing actionability and incidental findings of germline variants in two precision oncology trials

IntroductionHigh-throughput sequencing techniques have revolutionized oncology. Paired germline-tumor DNA analysis has emerged as a comprehensive strategy to uncover actionable alterations in advanced cancer patients (ACP) enrolled in precision oncology trials. However, challenges persist in variant interpretation and managing incidental germline findings. MethodsWe conducted a study involving 288 ACP from MOSCATO (NCT01566019) and MATCHR (NCT02517892) trials to assess germline variants impacting cancer-related genes. Germline DNA sequencing was performed using a panel of 250 cancer-related genes, and the results were discussed during tumor molecular board sessions. ResultsGermline pathogenic variants (PV) were classified according to the ESCAT classification. Lung cancer (36.8 %), followed by prostate (18.4 %) and breast cancer (17.7 %), comprised the most prevalent tumor types. PVs were found in 12.5 % of patients. Most PVs were classified as ESCAT X (63.9 %), highlighting limited therapeutic actionability. Notably,2 % of patients had actionable variants (ESCAT I-A/II-A). Incidental findings included 7.3 % of patients with PVs in cancer-predisposition genes, with 2.4 % having very high-risk potential, necessitating mandatory oncogenetic counseling. Nearly one in five patients (21.9 %) had at least one VUS. DiscussionOur study underscores the significance of germline sequencing in identifying actionable alterations and the need for improved variant interpretation as well as pretest counseling plans in precision oncology trials.

Multiplexed in situ protein imaging using DNA-barcoded antibodies with extended hybridization chain reactions.

Antibodies have long served as vital tools in biological and clinical laboratories for the specific detection of proteins. Conventional methods employ fluorophore or horseradish peroxidase-conjugated antibodies to detect signals. More recently, DNA-conjugated antibodies have emerged as a promising technology, capitalizing on the programmability and amplification capabilities of DNA to enable highly multiplexed and ultrasensitive protein detection. However, the nonspecific binding of DNA-conjugated antibodies has impeded the widespread adoption of this approach. Here, we present a novel DNA-conjugated antibody staining protocol that addresses these challenges and demonstrates superior performance in suppressing nonspecific signals compared to previously published protocols. We further extend the utility of DNA-conjugated antibodies for signal-amplified in situ protein imaging through the hybridization chain reaction (HCR) and design a novel HCR DNA pair to expand the HCR hairpin pool from the previously published 5 pairs to 13, allowing for flexible hairpin selection and higher multiplexing. Finally, we demonstrate highly multiplexed in situ protein imaging using these techniques in both cultured cells and tissue sections.

Computational identification of ultra-conserved elements in the human genome: a hypothesis on homologous DNA pairing.

Thousands of prolonged sequences of human ultra-conserved non-coding elements (UCNEs) share only one common feature: peculiarities in the unique composition of their dinucleotides. Here we investigate whether the numerous weak signals emanating from these dinucleotide arrangements can be used for computational identification of UCNEs within the human genome. For this purpose, we analyzed 4272 UCNE sequences, encompassing 1 393 448 nucleotides, alongside equally sized control samples of randomly selected human genomic sequences. Our research identified nine different features of dinucleotide arrangements that enable differentiation of UCNEs from the rest of the genome. We employed these nine features, implementing three Machine Learning techniques - Support Vector Machine, Random Forest, and Artificial Neural Networks - to classify UCNEs, achieving an accuracy rate of 82-84%, with specific conditions allowing for over 90% accuracy. Notably, the strongest feature for UCNE identification was the frequency ratio between GpC dinucleotides and the sum of GpG and CpC dinucleotides. Additionally, we investigated the entire pool of 31 046 SNPs located within UCNEs for their representation in the ClinVar database, which catalogs human SNPs with known phenotypic effects. The presence of UCNE-associated SNPs in ClinVar aligns with the expectation of a random distribution, emphasizing the enigmatic nature of UCNE phenotypic manifestation.

Implementation of a comprehensive genomic profiling (CGP) panel for precision oncology at a cancer center in Brazil.

e23520 Background: Assessing molecular alterations in solid tumors is essential for providing the best care in precision oncology. CGP tests utilize next-generation sequencing (NGS) to detect clinically relevant alterations and molecular signatures that are increasingly utilized in cancer careand can be performed in-house, which decreases test turnaround time (TAT) and costs. A paucity of studies have documented the experience of in-house testing at academic centers in Brazil. Methods: The TruSight Oncology (TSO) 500 assay/TSO 500 HRD are research use only (RUO) CGP assays that were validated for the detection of small variants (SVs), copy number variants (CNVs), microsatellite instability (MSI), tumor mutation burden (TMB) and genomic instability score (GIS) in DNA and gene fusions/splice variants in RNA in the NextSeq 500 system. Secondary analysis was performed with Illumina Connected Analytics. Tertiary analysis was performed with Illumina Connected Insights (ICI) and Sophia DDM. TMB ≥ 10mut/Mb was defined as TMB-High and GIS ≥ 42 was homologous recombination deficient (HRD). Results: We performed CGP on 40 FFPE samples (16 with HRD) with variable quality and block age most of which had known alterations detected by other genomics/molecular tests: 17 TNBC (16 paired DNA and RNA, 1 DNA only), 18 lung cancer (13 paired DNA and RNA, 5 DNA only), 1 endometrium cancer (DNA only, POLE mutated, 4 replicates), 1 colorectal cancer (DNA only, MSI unstable) and 11 sarcomas (RNA only). 84%, 84%, 90% and 89% of samples with DNA integrity number (DIN) > 2.5 were qualified for analysis of SVs/TMB, MSI, CNVs, and GIS, respectively, while for samples with DIN < 2.5 these values felt to 47%, 74%, 68% and 43%, respectively. RNA isolated from blocks dated up to 5 y.o. were qualified in 90% of cases while from older blocks only 6%. The 4 replicate (single sample) analysis showed 82% and 83% overall variant concordance in the ICI and Sophia DDM software, respectively. All previously known oncogenic alterations (SVs ≥5% VAF, fusions/splice, MSI, TMB) were detected (qualified samples) and with similar performance in ICI and Sophia, respectively: concordance 0.91/p < 0.0001 vs 0.94/p < 0.0001; sensitivity 100% vs 100%; specificity 98% vs 100%. TMB had 100% concordance with previous TMB results. Of note, 73% (8/11) TNBC samples analyzed for GIS were HRD and 75% (6/8) explained by BRCA1 germline mutation (25%) and BRCA1or RAD51C somatic promoter methylation (75%). Conclusions: This study demonstrates the utility of CGP and HRD testing in identifying multiple molecular alterations in FFPE tissue samples with high sensitivity and specificity. Pre-analytical variables directly impact data generation. BRCA1/RAD51C promoter methylation showed to be a potential biomarker for selecting metastatic TNBC patients for PARP inhibitor therapies. Offering CGP can potentially bring precision oncology to more patients with cancer in Brazil.

Can TTMV clearance predict recurrence in HPV HNSCC?

6066 Background: Patients with locally advanced (LA) HPV HNSCC are treated with various types of induction chemotherapy (IC) followed by standard (sd) or reduced (rd) chemoradiation (CRT). Tumor tissue-modified viral HPV DNA (TTMV) pairs with PET-CT in predicting an early detection of treatment failure in HPV-related HNSCC. Mid-treatment TTMV assessment in HPV-related HNSCC can help identify patients who are eligible to receive a lower dose of IC and/or CRT or those who may require close follow-up. Methods: Patients with LA HPV+ HNSCC with high-risk features (radiographic ECE, T4 primary, >N2c) and <20 pack-year (py) smoking history were treated with IC followed by rdCRT (56 Gy); sdCRT (70 Gy) was used in non-responders. 16/23 received IC with TPF, 1/23 TP, and 6/23 TP-PD1, and all patients received carboplatin weekly with their CRT. Regeneron trial patients who received TP-Cemiplimab (PD1) IC followed by sdCRT are also continuing adjuvant Cemiplimab alone for 6 months (NCT05376553). PET-CT-confirmed residual, recurrent, or metastatic diseases were defined as treatment failures; TTMV + patients only if PET-CT confirmed. Results: 23 subjects treated with IC followed by CRT between 2/4/21-1/26/24, who had pre- and post-treatment TTMV were included in our analysis. The median pre-IC TTMV was 8082 (27 – 90770). The median follow-up time from treatment start was 21 months. 9/23 patients had full clearance TTMV after 1 cycle of IC defined as rapid responders (RR). 11/23 patients still had positive TTMV after 1st cycle of IC were defined as slow responders (SR). 1 patient had no TTMV done after 1 cycle of IC but was elevated after 2nd IC; he was defined as SR. 2 patients had a positive pre-IC TTMV, but no TTMV was drawn during IC to see if RR. 1 of 2 patients was TTMV negative prior to CRT, and 2/2 had a 1st post IC negative TTMV done 1 week after CRT started. They were both included in the analysis but defined as unknown response status. TTMV testing was done for all 23 subjects after CRT; all were negative. All subjects have TTMV testing done during their surveillance visits. Among 9/23 RR, none developed a failure. Among 12/23 SR, 3 patients developed a failure: 1/3 was TTMV+ but PET-, being followed with TTMV and PET-CT; and 2/3 were confirmed failures, TTMV+ and PET+; 1 locoregional, 1 metastatic. 2 patients were not known to be a SR or RR and had no recurrence. Among 23 patients, NPV of TTMV to detect failure was 100%, but PPV was 96% (1/23). Conclusions: IC followed in rapid clearance of TTMV in 39% of patients, and all remained disease-free. 3/11 (27%) with persistently elevated TTMV after cycle 1 relapsed as of this time point. This small study was not large enough to be practice-changing. However, this is significantly hypothesis-generating and should be tested in a larger trial to help identify patients for de-escalation (RR) or closer surveillance (SR).

Evaluation of the interaction between new holmium(III) complex and DNA: A comprehensive study

In this research, we conducted a comprehensive investigation into the interactions between the holmium(III)-curcumin complex ([Ho(Cur)2]+) and DNA. To elucidate these interactions, we employed various analytical techniques including cyclic voltammetry (CV), UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), fluorescence spectrophotometry, thermal gravimetric analysis (TGA), and molecular docking calculations. Our findings revealed compelling evidence of strong binding between [Ho(Cur)2]+ and DNA, as indicated by hypochromic effects in absorbance and fluorescence quenching. The binding affinity of [Ho(Cur)2]+ to DNA was substantiated by the evaluation of maximum absorption of the [Ho(Cur)2]+ spectra at different DNA concentrations. Furthermore, fluorescence resonance energy transfer experiments demonstrated that the distance between the donor (DNA) and acceptor ([Ho(Cur)2]+) was favorable for energy transfer. The combination of experimental data and molecular docking results suggested that non-covalent binding likely played a significant role in the binding of [Ho(Cur)2]+ to DNA. FT-IR spectra and molecular docking analyses provided further insights, indicating specific binding primarily between [Ho(Cur)2]+ and the base pairs of DNA. Electrochemical measurements indicated a groove binding mode between [Ho(Cur)2]+ and DNA, with a binding ratio of 1:1. Notably, our results indicated that increasing the amount of DNA resulted in a significant reduction in the current intensity of [Ho(Cur)2]+ under optimal conditions.

Reflective optical fiber SPR sensor with DNA modification for high-sensitive Hg2+ concentration measurement

A reflective optical fiber surface plasmon resonance (SPR) sensor was proposed to measure the concentration of mercury ions (Hg2+). The specific single-stranded DNA was modified on the optical fiber sensing surface coated with Au film by the combination of covalent bond and charge adsorption. The Hg2+ can mismatch with T-T (thymine-thymine) base pairs in single-stranded DNA to form T-Hg2+-T structure, which led to the change of refractive index in sensing area and the wavelength shift of SPR spectrum. The measurement results showed that when the concentration of Hg2+ increased from 0 μM to 13 μM, the resonance spectrum shifted by 14.26 nm. In the linear range between 1–8 μM, the measurement sensitivity of the sensor could reach 1.51 nm/μM. The limit of detection (LOD) was found to be 0.28 μM. Besides, the sensor showed good stability, selectivity and reusability.

Specific binding of Ag+ to central C[sbnd]C mismatched base pair but not terminal C[sbnd]C pair in duplex DNA

Metal ion-nucleic acid interactions are important for their contribution in structure formation and their potential applications in nanotechnology. Hg2+ and Ag+ bind to T–T and CC mismatched base pairs, respectively, at the center of duplex DNA to form T–Hg–T and C–Ag–C. Although primer-extension by DNA polymerases with Hg2+ incorporated thymidine 5′-triphosphate to form T–Hg–T, the same reaction with Ag+ did not incorporate deoxycytidine 5′-triphosphate to form C–Ag–C. Here, isothermal titration calorimetric analyses to examine the effect of CC position in duplex DNA on Ag+ binding demonstrated that Ag+ did not bind to the terminal CC base pair in duplex, but it bound to the central CC base pair in duplex at 1:1 molar ratio with 9 × 105 M–1 binding constant. Ag+ did not bind to the terminal and central C–A, C–G, and C–T base pairs in duplex. These findings are useful for developing efficient metal-mediated base pair formation in nanotechnology.

Heteromultivalent DNA Enhances the Assembly Yield of Hybrid Nanoparticles and Facilitates Dynamic Disassembly for Bioanalysis Using ICP-MS.

To obtain enhanced physical and biological properties, various nanoparticles are typically assembled into hybrid nanoparticles through the binding of multiple homologous DNA strands to their complementary counterparts, commonly referred to as homomultivalent assembly. However, the poor binding affinity and limited controllability of homomultivalent disassembly restrict the assembly yield and dynamic functionality of the hybrid nanoparticles. To achieve a higher binding affinity and flexible assembly choice, we utilized the paired heteromultivalency DNA to construct hybrid nanoparticles and demonstrate their excellent assembly characteristics and dynamic applications. Specifically, through heteromultivalency, DNA-functionalized magnetic beads (MBs) and gold nanoparticles (AuNPs) were efficiently assembled. By utilizing ICP-MS, the assembly efficiency of AuNPs on MBs was directly monitored, enabling quantitative analysis and optimization of heteromultivalent binding events. As a result, the enhanced assembly yield is primarily attributed to the fact that heteromultivalency allows for the maximization of effective DNA probes on the surface of nanoparticles, eliminating steric hindrance interference. Subsequently, with external oligonucleotides as triggers, it was revealed that the disassembly mechanism of hybrid nanoparticles was initiated, which was based on an increased local concentration rather than toehold-mediated displacement of paired heteromultivalency DNA probes. Capitalizing on these features, an output platform was then established based on ICP-MS signals that several Boolean operations and analytical applications can be achieved by simply modifying the design sequences. The findings provide new insights into DNA biointerface interaction, with potential applications to complex logic operations and the construction of large DNA nanostructures.

XMECP: Reaching State-of-the-Art MECP Optimization in Multiscale Complex Systems.

The Python-based program, XMECP, is developed for realizing robust, efficient, and state-of-the-art minimum energy crossing point (MECP) optimization in multiscale complex systems. This article introduces the basic capabilities of the XMECP program by theoretically investigating the MECP mechanism of several example systems including (1) the photosensitization mechanism of benzophenone, (2) photoinduced proton-coupled electron transfer in the cytosine-guanine base pair in DNA, (3) the spin-flip process in oxygen activation catalyzed by an iron-containing 2-oxoglutarate-dependent oxygenase (Fe/2OGX), and (4) the photochemical pathway of flavoprotein adjusted by the intensity of an external electric field. MECPs related to multistate reaction and multistate reactivity in large-scale complex biochemical systems can be well-treated by workflows suggested by the XMECP program. The branching plane updating the MECP optimization algorithm is strongly recommended as it provides derivative coupling vector (DCV) with explicit calculation and can equivalently evaluate contributions from non-QM residues to DCV, which can be nonadiabatic coupling or spin-orbit coupling in different cases. In the discussed QM/MM examples, we also found that the influence on the QM region by DCV can occur through noncovalent interactions and decay with distance. In the example of DNA base pairs, the nonadiabatic coupling occurs across the π-π stacking structure formed in the double-helix system. In contrast to general intuition, in the example of Fe/2OGX, the central ferrous and oxygen part contribute little to the spin-orbit coupling; however, a nearby arginine residue, which is treated by molecular mechanics in the QM/MM method, contributes significantly via two hydrogen bonds formed with α-ketoglutarate (α-KG). This indicates that the arginine residue plays a significant role in oxygen activation, driving the initial triplet state toward the productive quintet state, which is more than the previous knowledge that the arginine residue can bind α-KG at the reaction site by hydrogen bonds.

Photocontrolled Binding of Styrylnaphthyridine Ligands to Abasic Site-Containing DNA by Reversible [2+2] Cycloaddition and Cycloreversion.

Five novel styrylnaphthyridine derivatives were synthesized and shown to operate as photoswitchable, selective ligands for abasic site-containing DNA (AP-DNA), which is an important therapeutic and diagnostic target. These compounds associate with AP-DNA with binding constants of 0.5-8.4×104 M-1 as shown by photometric and fluorimetric titrations. Specifically, these ligands bind preferentially to AP-DNA relative to regularly paired duplex DNA. As a special feature, the association of these ligands with DNA can be controlled by means of a reversible [2+2] photocycloaddition. Upon irradiation at 420 nm the photodimer is formed, which does not bind to AP-DNA. In turn, the naphthyridine is regained with excitation at 315 nm. Most notably, this photoinduced deactivation and release of the DNA ligand can be performed in situ in the presence of AP-DNA, thus providing a tool for on-demand delivery of a DNA binder. Overall, these results provide a promising starting point for the development of functional AP-DNA ligands whose bioactivity can be modulated by light with local and temporal control.

Ag+-Mediated Folding of Long Polyguanine Strands to Double and Quadruple Helixes.

Metal-mediated base pairing of DNA has been a topic of extensive research spanning over more than four decades. Precise positioning of a single metal ion by predetermining the DNA sequence, as well as improved conductivity offered by the ions, make these structures interesting candidates in the context of using DNA in nanotechnology. Here, we report the formation and characterization of conjugates of long (kilo bases) homoguanine DNA strands with silver ions. We demonstrate using atomic force microscopy (AFM) and scanning tunneling microscope (STM) that binding of silver ions leads to folding of homoguanine DNA strands in a "hairpin" fashion to yield double-helical, left-handed molecules composed of G-G base pairs each stabilized by a silver ion. Further folding of the DNA-silver conjugate yields linear molecules in which the two halves of the double helix are twisted one against the other in a right-handed fashion. Quantum mechanical calculations on smaller molecular models support the helical twist directions obtained by the high resolution STM analysis. These long guanine-based nanostructures bearing a chain of silver ions have not been synthesized and studied before and are likely to possess conductive properties that will make them attractive candidates for nanoelectronics.

TP53-specific mutations serve as a potential biomarker for homologous recombination deficiency in breast cancer: a clinical next-generation sequencing study.

TP53 mutations and homologous recombination deficiency (HRD) occur frequently in breast cancer. However, the characteristics of TP53 pathogenic mutations in breast cancer patients with/without HRD are not clear. Clinical next-generation sequencing (NGS) of both tumor and paired blood DNA from 119 breast cancer patients (BRCA-119 cohort) was performed with a 520-gene panel. Mutations, tumor mutation burden (TMB), and genomic HRD scores were assessed from NGS data. NGS data from 47 breast cancer patients in the HRD test cohort were analyzed for further verification. All TP53 pathogenic mutations in patients had somatic origin, which was associated with the protein expression of estrogen receptor and progestogen receptor. Compared to patients without TP53 pathologic mutations, patients with TP53 pathologic mutations had higher levels of HRD scores and different genomic alterations. The frequency of TP53 pathologic mutation was higher in the HRD-high group (HRD score≥42) relative to that in the HRD-low group (HRD score<42). TP53 has different mutational characteristics between the HRD-low and HRD-high groups. TP53-specific mutation subgroups had diverse genomic features and TMB. Notably, TP53 pathogenic mutations predicted the HRD status of breast cancer patients with an area under the curve (AUC) of 0.61. TP53-specific mutations, namely HRD-low mutation, HRD-high mutation, and HRD common mutation, predicted the HRD status of breast cancer patients with AUC values of 0.32, 0.72, and 0.58, respectively. Interestingly, TP53 HRD-high mutation and HRD common mutation combinations showed the highest AUC values (0.80) in predicting HRD status. TP53-specific mutation combinations predict the HRD status of patients, indicating that TP53 pathogenic mutations could serve as a potential biomarker for poly-ADP-ribose polymerase (PARP) inhibitors in breast cancer patients .

Conserved methylation signatures associate with the tumor immune microenvironment and immunotherapy response

BackgroundAberrant DNA methylation is a major characteristic of cancer genomes. It remains unclear which biological processes determine epigenetic reprogramming and how these processes influence the variants in the cancer methylome, which can further impact cancer phenotypes.MethodsWe performed pairwise permutations of 381,900 loci in 569 paired DNA methylation profiles of cancer tissue and matched normal tissue from The Cancer Genome Atlas (TCGA) and defined conserved differentially methylated positions (DMPs) based on the resulting null distribution. Then, we derived independent methylation signatures from 2,465 cancer-only methylation profiles from the TCGA and 241 cell line-based methylation profiles from the Genomics of Drug Sensitivity in Cancer (GDSC) cohort using nonnegative matrix factorization (NMF). We correlated DNA methylation signatures with various clinical and biological features, including age, survival, cancer stage, tumor immune microenvironment factors, and immunotherapy response. We inferred the determinant genes of these methylation signatures by integrating genomic and transcriptomic data and evaluated the impact of these signatures on cancer phenotypes in independent bulk and single-cell RNA/methylome cohorts.ResultsWe identified 7,364 differentially methylated positions (2,969 Hyper-DMPs and 4,395 Hypo-DMPs) in nine cancer types from the TCGA. We subsequently retrieved three highly conserved, independent methylation signatures (Hyper-MS1, Hypo-MS1, and Hypo-MS4) from cancer tissues and cell lines based on these Hyper and Hypo-DMPs. Our data suggested that Hypo-MS4 activity predicts poor survival and is associated with immunotherapy response and distant tumor metastasis, and Hypo-MS4 activity is related to TP53 mutation and FOXA1 binding specificity. In addition, we demonstrated a correlation between the activities of Hypo-MS4 in cancer cells and the fractions of regulatory CD4 + T cells with the expression levels of immunological genes in the tumor immune microenvironment.ConclusionsOur findings demonstrated that the methylation signatures of distinct biological processes are associated with immune activity in the cancer microenvironment and predict immunotherapy response.