Cell Repair Processes Research Articles

Matrine alkaloids modulating DNA damage repair in chemoresistant non-small cell lung cancer cells

BackgroundNon-small cell lung cancer (NSCLC) presents a significant challenge in the medical field due to its high incidence and resistance to chemotherapy. Chemoresistance in NSCLC diminishes treatment efficacy and contributes to poor patient outcomes. Matrine alkaloids have shown promise in reversing chemotherapy resistance in NSCLC by targeting DNA repair mechanisms.MethodsUtilizing molecular dynamics simulations, we explored the interactions between Matrine alkaloids and DNA repair-related proteins to elucidate their impact on NSCLC cells. In vitro experiments involved treating A549/DDP cells with Matrine alkaloids to evaluate their sensitizing effects on lung cancer cells. Additionally, animal model experiments were conducted to validate the therapeutic potential of Matrine alkaloids in NSCLC treatment.ResultsOur findings demonstrate that Matrine alkaloids disrupt DNA damage repair processes in NSCLC cells, leading to increased sensitivity to chemotherapy. Molecular docking studies revealed the intricate mechanisms by which Matrine alkaloids interact with DNA repair proteins, impacting cell survival and proliferation. Both cell experiments and animal models confirmed the chemosensitizing effects of Matrine alkaloids in NSCLC treatment.ConclusionMatrine alkaloids offer a promising avenue for overcoming chemotherapy resistance in NSCLC by interfering with DNA repair pathways. This study lays a solid foundation for future clinical investigations into the potential of Matrine alkaloids as effective therapeutic agents for enhancing NSCLC treatment outcomes.

Transcriptomic analysis reveals the mechanism of isorhamnetin in the treatment of diabetes mellitus erectile dysfunction

PurposeExploring the therapeutic effect and mechanism of isorhamnetin in the treatment of DMED. MethodsUsing a high glucose environment to induce endothelial cells damage in the corpus cavernosum, and combining with intervention agents such as ferroptosis inhibitors to observe the process of cell damage and repair, evaluating cell status through CCK-8 and DAPI; To establish the STZ-induced diabetes rat model and detect the erectile function and tissue changes; Perform transcriptomic sequencing on rat models and samples treated with isorhamnetin to analyze differentially expressed genes and their GO functions; Identify critical pathways by combining with the ferroptosis database; Flow cytometry was used to detect ROS and mitochondrial membrane potential, and RT-PCR was used to verify gene expression, Seahorse detects mitochondrial oxygen consumption rate, revealing the mechanism of action of isorhamnetin. ResultsFerroptosis inhibitors and isorhamnetin can effectively reverse the damage of corpus cavernosum endothelial cells induced by high glucose and ferroptosis agonists. Isorhamnetin has the ability to reinstate the erectile function of diabetic rats, while enhancing the quantity of endothelial cells and refining the morphology of collagen fibers. Immunohistochemistry revealed that ferroptosis existed in the penis tissue of diabetes rats. Transcriptomic analysis showed that isorhamnetin improves gene expression in DM rats by regulating genes such as GFER, IGHM, GPX4 and HMOX1, involving multiple pathways and biological processes. Flow cytometry and RT-PCR confirmed that isorhamnetin can reduce reactive oxygen species levels, restore essential gene expression, improve mitochondrial membrane potential, and alleviate oxidative stress and ferroptosis. Seahorse detection found that isorhamnetin can restore mitochondrial oxygen consumption rate. ConclusionIsorhamnetin attenuates high glucose damage to cavernous endothelial cells by inhibiting ferroptosis and oxidative stress, restores erectile function and improves tissue morphology in diabetic rats, and its multi-pathway and multi-targeting regulatory mechanism suggests that it is promising to be an effective drug for the treatment of DMED.

Stimulating macropinocytosis of peptide-drug conjugates through DNA-dependent protein kinase inhibition for treating KRAS-mutant cancer

KRAS-mutant cancers, due to their protein targeting complexity, present significant therapeutic hurdles. The identification of the macropinocytic phenotype in these cancers has emerged as a promising alternative therapeutic target. Our study introduces MPD1, an macropinocytosis-targeting peptide-drug conjugates (PDC), which is developed to treat KRAS mutant cancers. This PDC is specifically designed to trigger a positive feedback loop through its caspase-3 cleavable characteristic. However, we observe that this loop is hindered by DNA-PK mediated DNA damage repair processes in cancer cells. To counter this impediment, we employ AZD7648, a DNA-PK inhibitor. Interestingly, the combined treatment of MPD1 and AZD7648 resulted in a 100% complete response rate in KRAS-mutant xenograft model. We focus on the synergic mechanism of it. We discover that AZD7648 specifically enhances macropinocytosis in KRAS-mutant cancer cells. Further analysis uncovers a significant correlation between the increase in macropinocytosis and PI3K signaling, driven by AMPK pathways. Also, AZD7648 reinforces the positive feedback loop, leading to escalated apoptosis and enhanced payload accumulation within tumors. AZD7648 possesses broad applications in augmenting nano-sized drug delivery and preventing DNA repair resistance. The promising efficacy and evident synergy underscore the potential of combining MPD1 with AZD7648 as a strategy for treating KRAS-mutant cancers.

A Review on Traditional uses, Bioactive Chemical Constituents, Pharmacology, and Toxicity of Tinospora cordifolia (Guduchi or Giloy)

Traditional medicine is a body of knowledge, skills, and practices based on traditional cultures' presumptions, beliefs, and experiences in order to maintain their health. Traditional herbal treatments are highly valued among many rural or indigenous people in many underdeveloped nations. According to the World Health Organization, about 80% of the world's population relies on traditional medicine, with 60% of rural Indians using herbal treatments. During the previous five years, utilization of herbal supplements grew from 2.5% to 12percent. Tinospora cordifolia is a member of the Menispermaceae family and possesses a wide range of immunotherapeutic qualities, including antipyretic, anti-inflammatory, antiallergic, antidiabetic, antihepatotoxic, and antibacterial activities, as well as relatively low toxicity. Tinospora cordifolia (Guduchi), a perennial and climbing shrub with succulent stems and papery barks, is found all over the world. It has been discovered that the leaf extract is beneficial in treating infections caused by B. subtilis, P. vulgaris, S. aureus, E. coli, and S. pyrogens. Furthermore, it supports the process of cell renewal and repair. The plant is used to make herbal medicines on a yearly basis in about 10,000 tonnes. Phenyl propanoid glycosides like Syringin, Cordifolioside A, and Cordifolioside B, as well as the immunostimulatory molecule d-glucan, are among the main active substances identified from the plant. Tannins, alkaloids, carbohydrates, terpenoids, steroids, flavonoids, and phenols are some of the chemical components found in medicinal plants that have a distinct physiological effect on the human body. Medicinal plants do not only exhibit natural therapeutic properties, but also provide natural prevention against various diseases. As a result, we are attempting to summarize, gather the number of plants, and their ethnopharmacological qualities in this complete review study research.

Temperature and immune challenges modulate the transcription of genes of the ubiquitin and apoptosis pathways in two high-latitude Notothenioid fish across the Antarctic Polar Front.

Thermal variations due to global climate change are expected to modify the distributions of marine ectotherms, with potential pathogen translocations. This is of particular concern at high latitudes where cold-adapted stenothermal fish such as the Notothenioids occur. However, little is known about the combined effects of thermal fluctuations and immune challenges on the balance between cell damage and repair processes in these fish. The aim of this study was to determine the effect of thermal variation on specific genes involved in the ubiquitination and apoptosis pathways in two congeneric Notothenioid species, subjected to simulated bacterial and viral infections. Adult fish of Harpagifer bispinis and Harpagifer antarcticus were collected from Punta Arenas (Chile) and King George Island (Antarctica), respectively, and distributed as follows: injected with PBS (control), LPS (2.5mg/kg) or Poly I:C (2mg/kg) and then submitted to 2, 5 and 8°C. After 1week, samples of gills, liver and spleen were taken to evaluate the expression by real-time PCR of specific genes involved in ubiquitination (E3-ligase enzyme) and apoptosis (BAX and SMAC/DIABLO). Gene expression was tissue-dependent and increased with increasing temperature in the gills and liver while showing an opposite pattern in the spleen. Studying a pair of sister species that occur across the Antarctic Polar Front can help us understand the particular pressures of intertidal lifestyles and the effect of temperature in combination with biological stressors on cell damage and repair capacity in a changing environment.

New approaches to second-degree burn healing: Polyvinyl alcohol membrane loaded to arnica combined to laser therapy.

Second-degree burns require greater care, as the damage is more extensive and worrisome and the use of a biomaterial can help in the cell repair process, with better planning, low cost, and better accessibility. Arnica has anti-inflammatory and analgesic properties in skin lesions treatments and laser therapy is another therapeutic alternative for burns. Evaluate the effects of arnica incorporated into PVA associated or not with low intensity laser on burns in rats. PVA and PVA with arnica (PVA+A) were obtained and characterized physicochemically. Through in vivo studies, the effects of PVA and PVA+A with or without the application of laser on the lesions allowed histological and immunohistochemical analyzes. PVA+A was biocompatible and with sustained release of the active, being a promising pharmacological tool and confirmed that laser therapy was effective in accelerating the healing process, due to its potential biomodulator, improving inflammatory aspects, promoting rapid healing in skin lesions.

The Role of Chromatin Assembly Factors in Induced Mutagenesis at Low Levels of DNA Damage.

The problem of low-dose irradiation has been discussed in the scientific literature for several decades, but it is impossible to come to a generally accepted conclusion about the presence of any specific features of low-dose irradiation in contrast to acute irradiation. We were interested in the effect of low doses of UV radiation on the physiological processes, including repair processes in cells of the yeast Saccharomyces cerevisiae, in contrast to high doses of radiation. Cells utilize excision repair and DNA damage tolerance pathways without significant delay of the cell cycle to address low levels of DNA damage (such as spontaneous base lesions). For genotoxic agents, there is a dose threshold below which checkpoint activation is minimal despite the measurable activity of the DNA repair pathways. Here we report that at ultra-low levels of DNA damage, the role of the error-free branch of post-replicative repair in protection against induced mutagenesis is key. However, with an increase in the levels of DNA damage, the role of the error-free repair branch is rapidly decreasing. We demonstrate that with an increase in the amount of DNA damage from ultra-small to high, asf1Δ-specific mutagenesis decreases catastrophically. A similar dependence is observed for mutants of gene-encoding subunits of the NuB4 complex. Elevated levels of dNTPs caused by the inactivation of the SML1 gene are responsible for high spontaneous reparative mutagenesis. The Rad53 kinase plays a key role in reparative UV mutagenesis at high doses, as well as in spontaneous repair mutagenesis at ultra-low DNA damage levels.

Triumphs and challenges in exploiting poly(ADP-ribose) polymerase inhibition to combat triple-negative breast cancer.

Poly(ADP-ribose) polymerase 1 (PARP1) regulates a myriad of DNA repair mechanisms to preserve genomic integrity following DNA damage. PARP inhibitors (PARPi) confer synthetic lethality in malignancies with a deficiency in the homologous recombination (HR) pathway. Patients with triple-negative breast cancer (TNBC) fail to respond to most targeted therapies because their tumors lack expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Certain patients with TNBC harbor mutations in HR mediators such as breast cancer susceptibility gene 1 (BRCA1) and breast cancer susceptibility gene 2 (BRCA2), enabling them to respond to PARPi. PARPi exploits the synthetic lethality of BRCA-mutant cells. However, de novo and acquired PARPi resistance frequently ensue. In this review, we discuss the roles of PARP in mediating DNA repair processes in breast epithelial cells, mechanisms of PARPi resistance in TNBC, and recent advances in the development of agents designed to overcome PARPi resistance in TNBC.

Mechanistic Modelling of DNA Damage Repair by the Radiation Adaptive Response Mechanism and Its Significance

The radiation adaptive response effect is a biophysical phenomenon responsible for the enhancement of repair processes in irradiated cells. This can be observed in dedicated radiobiological experiments, e.g., where the small priming dose of ionising radiation is given before the high challenging one (the so-called Raper–Yonezawa effect). The situation is more complicated when the whole complex system (the organism) is taken into consideration; many other mechanisms make the adaptive response weaker and—in some cases—practically insignificant. The recently published simplified Monte Carlo model of human lymphocytes irradiation by X-rays allows for the calculation of the level of repair enhancement by the adaptive response when every other cellular biological mechanism is implemented. The qualitative results show that the adaptive response phenomenon, observed with some probability on a basic level, usually blurs among other effects and becomes weaker than expected. Regardless, the radiation adaptive response is still an important biophysical effect which needs to be taken into consideration in low-dose radiobiological studies.

Unexpected Photocatalytic Degeneration of NAD + for Inducing Apoptosis of Hypoxia Cancer Cells

Unexpected Photocatalytic Degeneration of NAD ⁺ for Inducing Apoptosis of Hypoxia Cancer Cells

Preliminary Study on 53BP1-Mediated DNA Double-Strand Break Response in Spermatogonial Stem Cells.

53BP1 mediates DNA repair process in somatic cells; however, the function of 53BP1 in germline stem cells still remains unclear. In the present study, animals and cells DNA damage repair (DDR) model was established by irradiation and HU treatment; immunofluorescence staining and laser confocal microscopy were used to detect the expression of 53BP1, p-CHK2, and p-P53 in the DDR process of mSSCs. 53BP1 knockdown expression mSSCs cell line conducted by Trp53bp1-shRNA was established and EdU staining was adopted to analyze cell cycle and cell proliferation. Moreover, NHEJ reporter vector was applied to detect the repair efficacy after Trp53bp1 knocked-down (KD) expression. Results showed that 53BP1 could form foci signals in mSSCs during DDR process both in vivo and in vitro, which was independent of γH2AX. 53BP1 downstream protein, p-P53, and p-CHK2 were involved and dynamically expressed in DDR response. Knocking down of Trp53bp1 expression in mSSCs could not dramatically inhibit cell proliferation, but may increase cell sensitivity to HU. The NHEJ repair efficacy was sharply decreased in Trp53bp-KD SSCs via flow cytometry analysis. We revealed the specific mechanism of 53BP1 in SSCs DDR process, which is expected to provide a new theoretical basis and insights for the diagnosis and treatment of male infertility.

Quercetin Augments Cisplatin-Induced Apoptosis, DNA Damage Response, and MiR-22 Expression While It Prevents DNA Repair in Osteosarcoma Cells.

Osteosarcoma (OS) patients are commonly treated with chemotherapeutic agents like cisplatin (Cis). Quercetin with fewer side effects can improve the potency of chemotherapy and be used in combinational therapies. Herein, we aimed to evaluate the effects of Cis plus quercetin on DNA damage response (DDR), DNA repair, and apoptosis in Saos-2 cells. The effects of Cis and quercetin single or in combination on Saos-2 cell viability and the cytotoxicity of the drugs were measured by MTT assay. The expression of DDR and repair components including P53, ATM, ATR, RAD51, and H2AX, and also miR-22 were analyzed by real-time PCR. The rate of apoptosis was measured by flow cytometry. Quercetin potentiated the cytotoxic effects of Cis in Saos-2 cells. The IC50 of Cis reduced from 6.12 µM to 4.25 µM. The combination of quercetin and Cis was associated with the up-regulation of miR-22 and DDR components, including P53, ATM, ATR, and H2AX as well as the down-regulation of RAD51. Moreover, this combined regimen significantly induced apoptosis in Saos-2 cells compared to mono drugs. The co-treatment of quercetin and Cis can accelerate DNA damage, DNA damage response, and apoptosis while interfering with the DNA repair process in Saos-2 cells. Moreover, this combination provokes the tumor suppressor miR-22 expression in these cells.

Abstract 227: Kethoxal-assisted single-stranded DNA sequencing (KAS-seq) reveals dynamic and temporal changes in transcription in response to UVB exposure

Abstract Skin cancer is the most common form of cancer, with over 5 million cases reported in 2021. UVB exposure derived from sunlight is the major carcinogenic driver of skin cancer and poses a major public health risk. In response to UVB exposure, keratinocytes must activate DNA repair pathways to avoid mutagenesis. In addition to DNA repair pathways, cells initiate well-coordinated DNA damage response pathways to facilitate the repair process, including arresting global transcription. Here we report the use of kethoxal-assisted single-strand DNA-Sequencing (KAS-Seq) technology to profile the transcriptional dynamics that underlie the DNA damage response upon UVB exposure. Mechanistically, KAS-Seq involves the addition of an azide-tagged kethoxal group (N3-kethoxal) to DNA samples, which then reacts with guanines on single-stranded DNA (ssDNA). A “KAS signal” is therefore only obtained when DNA is unwound, allowing the N3-kethoxal reaction with accessible guanines to occur. Accordingly, in response to DNA damage, DNA can form ssDNA bubbles in order to facilitate DNA damage recognition and repair processes. KAS-Seq is therefore a suitable method to profile the transcriptional dynamics that occur in response to UVB-induced DNA damage. Here we show that UVB exposure in normal human keratinocytes (NHEK) cells induces a temporal and dynamic reprogramming in transcription using KAS-Seq. In terms of global transcription, our data show that the greatest loss of KAS signal occurs rapidly between 30mins and 3hrs post-UVB exposure, signifying transcriptional arrest. Interestingly, KAS signal is regained between 6-24hrs post-UVB, which is representative of a transition towards transcriptional recovery and induction of DNA damage processes. Furthermore, a more discrete and targeted analysis shows that the gain and loss of KAS signals primarily occur within the gene body, followed by promoter and intergenic regions. Overall, our data shows that transcriptional control in response to UVB-induced DNA damage is both dynamic and temporal. Further analysis is required to identify which transcriptional phenotype (transcriptional arrest or transcriptional recovery) is the most deleterious to the cell and DNA damage repair processes when disrupted. Additionally, we aim to further elucidate the molecular mechanisms that underlie these global changes in transcription, which will provide expanded insights into the wide-ranging oncogenic mechanisms that underlie UVB exposure. Citation Format: Emma A. Wilkinson, Tong Wu, Gayoung Park, Yan-Hong Cui, Chuan He, Yu-Ying He. Kethoxal-assisted single-stranded DNA sequencing (KAS-seq) reveals dynamic and temporal changes in transcription in response to UVB exposure [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 227.

Enhancing Membrane Repair in Neuronal Cell Types as a Potential Therapeutic for Neurodegenerative Diseases

Cell membrane repair is an essential cellular process to repair damage to the membrane and maintain the integrity of the cell membrane. Impaired membrane resealing kinetics can potentially lead to neurodegenerative diseases. Enhancing membrane repair via therapeutic intervention could minimize neurodegeneration in neuronal disease states. Recombinant human MG53 (rhMG53) and poloxamers have been an effective therapeutic to enhance membrane repair in muscle and non‐muscle cell types. Here, we aimed to assess if the membrane repair response is active and the efficacy of enhancing membrane resealing in neuronal cells. To assess if neuronal cells have an active membrane repair response, mouse neuroblastoma N2a cells were transfected with GFP or GFP‐MG53. MG53 localization was tracked following multiphoton infrared laser injury. N2a cells were transfected with GFP or GFP‐MG53, and subjected to multiphoton infrared laser injury to investigate if MG53 expression enhances membrane resealing following damage. An infrared laser was used to damage the cell membrane of N2a cells and primary mouse dorsal root ganglion neurons (DRG) in the presence of FM4‐64 dye. To test the efficacy of therapeutics, N2as and DRGs were treated with 1μM rhMG53 or 100μM Poloxamer 188 (P188) and challenged with the multiphoton laser injury. Lastly, the therapeutic potential of rhMG53 was tested in vivo with a sciatic nerve crush injury model. C57Bl/6 mice sciatic nerves were mechanically crushed for 10 seconds and then injected with 1μL rhMG53 (1mg/mL) or saline. The sciatic nerves were harvested and immunostained with an axonal regeneration marker, SCG10. SCG10 staining intensity was measured to calculate the regeneration index. Overall, we observed MG53 trafficking to the injury site which indicates there is an activate membrane repair mechanism within neuronal cells. Therapeutic levels of rhMG53 and P188 increased membrane resealing in both N2as and DRGs. Lastly, rhMG53‐treated sciatic nerves displayed a two‐fold increase in regenerative capacity following sciatic nerve crush injury compared to the saline vehicle control. These results illustrate an active membrane repair process in neuronal cells and potential for therapeutic intervention in the context of neuronal diseases, specifically neurodegenerative diseases.

213P Photobiomodulation therapy for the management of chemotherapy-induced alopecia: Preliminary results of a randomized, controlled trial

Chemotherapy-induced alopecia (CIA) is one of the most traumatizing experiences for oncological patients. Although CIA is reversible, it still requires several months for the hair to regrow, and cases of permanent CIA are reported. Photobiomodulation (PBM) therapy is based on applying (near)-infrared light on target tissue to stimulate cell repair processes. Positive results were demonstrated in clinical trials applying PBM for the treatment of androgenetic alopecia. The aim of this trial is to evaluate if PBM can accelerate hair regrowth after chemotherapy in breast cancer patients.

Probing the Mechanism of Action of Cry41Aa on HepG2 through the Establishment of a Resistant Subline.

Cry41Aa, also called parasporin-3, belongs to a group of toxins from the entomopathogenic bacterium Bacillus thuringiensis that show activity against human cancer cells. Cry41Aa exhibits preferential cytocidal activity towards HL-60 (human promyelocytic leukaemia cells) and HepG2 (human liver cancer cells) cell lines after being proteolytically activated. To better understand the mechanism of action of Cry41Aa, we evolved resistance in HepG2 cells through repeated exposure to increasing doses of the toxin. Concentrations of Cry41Aa that killed over 50% of the parental HepG2 cells had no significant effect on the viability of the resistant cells and did not induce either pore formation or p38 phosphorylation (both characteristic features of pore-forming toxins). Preliminary RNA sequencing data identified AQP9 as a potential mediator of resistance, but extensive investigations failed to show a causal link and did not support an enhanced cell repair process as the resistance mechanism.

A water-soluble near-infrared fluorescent probe for monitoring change of hydrogen sulfide during cell damage and repair process

As a signal molecule involved in autophagy, hydrogen sulfide (H2S) is considered to be essential in the development and treatment of diseases. In order to clarify the complex role of H2S in organism and the participation of H2S in disease process, it is urgently needed to visualize the dynamics of H2S. In this contribution, a water-soluble near-infrared (695 nm emission) self-immolative fluorescent probe CySO3N3 was constructed for H2S detection. The ability of self-immolative strategy to detect H2S was verified to increase the metabolic capacity and reduce the toxicity of probe. This probe can not only be used to detect H2S in living cell and mice, but also shows great potential in detecting H2S changes to monitor cell self-repair during inflammation and myocardial injury.

Karanahan: A Potential New Treatment Option for Human Breast Cancer and Its Validation in a Clinical Setting.

Introduction:Karanahan, a cancer treatment technology aimed at eradicating tumor-initiating stem cells, has already proven effective in 7 tumor models. Karanahan comprises the following procedures: (1) collecting surgical specimens, (2) determining the duration of the DNA repair process in tumor cells exposed to a cross-linking cytostatic agent, and (3) determining the time point, when cells, including tumor-initiating stem cells, are synchronized in the certain phase of the cell cycle after triple exposure to the cytostatic, becoming vulnerable for the terminal treatment, which is supposed to completely eliminate the rest of survived tumor-initiating stem cells. Determining these basic tumor properties allows to design the schedule for the administration of a cross-linking cytostatic and a complex composite DNA preparation. Being conducted in accordance with the schedule designed, Karanahan results in the large-scale apoptosis of tumor cells with elimination of tumor-initiating stem cells.Methods:Breast tumor specimens were obtained from patients, and basic tumor properties essential for conducting Karanahan therapy were determined.Results:We report the first use of Karanahan in patients diagnosed with breast cancer. Technical details of handling surgical specimens for determining the essential Karanahan parameters (tumor volume, cell number, cell proliferation status, etc) have been worked out. The terminally ill patient, who was undergoing palliative treatment and whose tumor specimen matched the required criteria, received a complete course of Karanahan.Conclusions:The results of the treatment conducted indicate that Karanahan technology has a therapeutic potency and can be used as a breast cancer treatment option.

X-ray scattering reveals disordered linkers and dynamic interfaces in complexes and mechanisms for DNA double-strand break repair impacting cell and cancer biology.

Evolutionary selection ensures specificity and efficiency in dynamic metastable macromolecular machines that repair DNA damage without releasing toxic and mutagenic intermediates. Here we examine non‐homologous end joining (NHEJ) as the primary conserved DNA double‐strand break (DSB) repair process in human cells. NHEJ has exemplary key roles in networks determining the development, outcome of cancer treatments by DSB‐inducing agents, generation of antibody and T‐cell receptor diversity, and innate immune response for RNA viruses. We determine mechanistic insights into NHEJ structural biochemistry focusing upon advanced small angle X‐ray scattering (SAXS) results combined with X‐ray crystallography (MX) and cryo‐electron microscopy (cryo‐EM). SAXS coupled to atomic structures enables integrated structural biology for objective quantitative assessment of conformational ensembles and assemblies in solution, intra‐molecular distances, structural similarity, functional disorder, conformational switching, and flexibility. Importantly, NHEJ complexes in solution undergo larger allosteric transitions than seen in their cryo‐EM or MX structures. In the long‐range synaptic complex, X‐ray repair cross‐complementing 4 (XRCC4) plus XRCC4‐like‐factor (XLF) form a flexible bridge and linchpin for DNA ends bound to KU heterodimer (Ku70/80) and DNA‐PKcs (DNA‐dependent protein kinase catalytic subunit). Upon binding two DNA ends, auto‐phosphorylation opens DNA‐PKcs dimer licensing NHEJ via concerted conformational transformations of XLF‐XRCC4, XLF–Ku80, and LigIVBRCT–Ku70 interfaces. Integrated structures reveal multifunctional roles for disordered linkers and modular dynamic interfaces promoting DSB end processing and alignment into the short‐range complex for ligation by LigIV. Integrated findings define dynamic assemblies fundamental to designing separation‐of‐function mutants and allosteric inhibitors targeting conformational transitions in multifunctional complexes.

Autophagy deficiency downregulates O6methylguanine-DNA methyltransferase and increases chemosensitivity of liver cancer cells.

It is known that autophagy-deficient cells are prone to DNA damage, but the specific role of autophagy in DNA damage repair is not fully known. Here, we show that autophagy-deficient liver cancer cells exhibit increased DNA damage caused by the chemotherapeutic agent epirubicin. Autophagy deficiency promotes downregulation of the DNA repair enzyme O6methylguanine-DNA methyltransferase (MGMT) in liver cancer cells. However, autophagy induction with epirubicin had no impact on MGMT gene or protein expression in liver cancer cells. In the absence of autophagy, the chemosensitivity of liver cancer cells was increased, but this was reversed by MGMT overexpression, indicating that autophagy mediates resistance to chemotherapy in liver cancer cells via MGMT. These findings demonstrate a direct link between autophagy, MGMT, and DNA damage repair in liver cancer cells, and show that MGMT not only regulates chemosensitivity to alkylating agents, but may also be involved in other DNA damage repair processes in autophagy-deficient cells.