Timely termination of repair DNA synthesis by ATAD5 is important in oxidative DNA damage-induced single-strand break repair

Protein Phosphatase 2ACα Regulates ATR-Mediated Endogenous DNA Damage Response Against Microcephaly

Protein phosphatase 2A (PP2A) is an abundant heterotrimeric holoenzyme in eukaryotic cells coordinating with specific kinases to regulate spatial-temporal protein dephosphorylation in various biological processes. However, the function of PP2A in cortical neurogenesis remains largely unknown. Here, we report that neuronal-specific deletion of Pp2acα in mice displayed microcephaly, with significantly smaller brains and defective learning and memory ability. Mechanistically, neuronal Pp2acα deficiency resulted in elevated endogenous DNA damage and activation of ATR/CHK1 signaling. It was further induced by the loss of direct interaction between PP2AC and ATR as well as the function of PP2AC to dephosphorylate ATR. Importantly, ATR/CHK1 signaling dysregulation altered both the expression and activity of several critical downstream factors including P53, P21, Bcl2, and Bax, which led to decreased proliferation of cortical progenitor cells and increased apoptosis in developing cortical neurons. Taken together, our results indicate an essential function of PP2ACα in endogenous DNA damage response-mediated ATR signaling during neurogenesis, and defective PP2ACα in neurons contributes to microcephaly.

ATAD5-BAZ1B interaction modulates PCNA ubiquitination during DNA repair

Mono-ubiquitinated PCNA (mono-Ub-PCNA) is generated when replication forks encounter obstacles, enabling the bypass of DNA lesions. After resolving stalled forks, Ub-PCNA must be de-ubiquitinated to resume high-fidelity DNA synthesis. ATAD5, in cooperation with the UAF1-USP1 complex, is responsible for this de-ubiquitination. However, the precise regulation of timely Ub-PCNA de-ubiquitination remains unclear. Our research reveals that BAZ1B, a regulatory subunit of the BAZ1B-SMARCA5 chromatin-remodeling complex (also known as the WICH complex), plays a crucial role in fine-tuning the de-ubiquitination process of Ub-PCNA. The BAZ1B binding region of ATAD5 encompasses the UAF1-binding domain of ATAD5. Disruption of the ATAD5-BAZ1B interaction results in premature de-ubiquitination of Ub-PCNA following treatment with hydrogen peroxide. Cells with impaired BAZ1B binding to ATAD5 display increased sensitivity to oxidative stress compared to wild-type cells. These findings suggest that BAZ1B prevents premature Ub-PCNA de-ubiquitination, thereby safeguarding genome integrity.

The human ATAD5 has evolved unique structural elements to function exclusively as a PCNA unloader

Humans have three different proliferating cell nuclear antigen (PCNA) clamp-loading complexes: RFC and CTF18-RFC load PCNA onto DNA, but ATAD5-RFC can only unload PCNA from DNA. The underlying structural basis of ATAD5-RFC unloading is unknown. We show here that ATAD5 has two unique locking loops that appear to tie the complex into a rigid structure, and together with a domain that plugs the DNA-binding chamber, prevent conformation changes required for DNA binding, likely explaining why ATAD5-RFC is exclusively a PCNA unloader. These features are conserved in the yeast PCNA unloader Elg1-RFC. We observe intermediates in which PCNA bound to ATAD5-RFC exists as a closed planar ring, a cracked spiral or a gapped spiral. Surprisingly, ATAD5-RFC can open a PCNA gap between PCNA protomers 2 and 3, different from the PCNA protomers 1 and 3 gap observed in all previously characterized clamp loaders.

Polyubiquitinated PCNA triggers SLX4-mediated break-induced replication in alternative lengthening of telomeres (ALT) cancer cells

Replication stresses are the major source of break-induced replication (BIR). Here, we show that in alternative lengthening of telomeres (ALT) cells, replication stress-induced polyubiquitinated proliferating cell nuclear antigen (PCNA) (polyUb-PCNA) triggers BIR at telomeres and the common fragile site (CFS). Consistently, depleting RAD18, a PCNA ubiquitinating enzyme, reduces the occurrence of ALT-associated promyelocytic leukemia (PML) bodies (APBs) and mitotic DNA synthesis at telomeres and CFS, both of which are mediated by BIR. In contrast, inhibiting ubiquitin-specific protease 1 (USP1), an Ub-PCNA deubiquitinating enzyme, results in an increase in the above phenotypes in a RAD18- and UBE2N (the PCNA polyubiquitinating enzyme)-dependent manner. Furthermore, deficiency of ATAD5, which facilitates USP1 activity and unloads PCNAs, augments recombination-associated phenotypes. Mechanistically, telomeric polyUb-PCNA accumulates SLX4, a nuclease scaffold, at telomeres through its ubiquitin-binding domain and increases telomere damage. Consistently, APB increase induced by Ub-PCNA depends on SLX4 and structure-specific endonucleases. Taken together, our results identified the polyUb-PCNA-SLX4 axis as a trigger for directing BIR.

Unveiling differential gene co-expression networks and its effects on levodopa-induced dyskinesia

Levodopa-induced dyskinesia (LID) refers to involuntary motor movements of chronic use of levodopa in Parkinson's disease (PD) that negatively impact the overall well-being of people with this disease. The molecular mechanisms involved in LID were investigated through whole-blood transcriptomic analysis for differential gene expression and identification of new co-expression and differential co-expression networks. We found six differentially expressed genes in patients with LID, and 13 in patients without LID. We also identified 12 co-expressed genes exclusive to LID, and six exclusive hub genes involved in 23 gene-gene interactions in patients with LID. Convergently, we identified novel genes associated with PD and LID that play roles in mitochondrial dysfunction, dysregulation of lipid metabolism, and neuroinflammation. We observed significant changes in disease progression, consistent with previous findings of maladaptive plastic changes in the basal ganglia leading to the development of LID, including a chronic pro-inflammatory state in the brain.

Identification of inflammatory response-related molecular mechanisms based on the ATM/ATR/p53 pathway in tumor cells

Inflammatory response is a crucial factor that affects prognosis and therapeutic effect in tumor cells. Although some studies have shown that inflammation could make DNA more vulnerable to external attacks, resulting in serious DNA damage, the underlying mechanism remains unknown. Then, using tumor necrosis factor α (TNF-α) and lipopolysaccharide (LPS), this research elevated the level of inflammation in cancer cells, and hydrogen peroxide (H2O2) and ultraviolet (UV) were utilized as common reactive oxygen species (ROS)-induced DNA damage agents. We show that either H2O2 or UV achieved a more substantial antiproliferative effect in the inflammation environment compared with H2O2 or UV treatment alone. The inflammation environment enhanced H2O2- or UV-induced cell apoptosis and ROS production. Although the phenomenon that inflammation itself could trigger ROS-dependent DNA damage was well known, the underlying mechanism for the sensitization of inflammation to trigger intense DNA damage via ROS in cancer cells remains unclear. In this study, the inflammation-related genes and the corresponding expression information were obtained from the TCGA and fetched genes associated with inflammatory factors. Screening of thirteen inflammatory-related, including ATM, and prognostic genes. In addition, KEGG analysis of prognostic genes shows that biological processes such as DNA replication. ATM and ATR, which belong to the PI3/PI4-kinase family, can activate p53. Inflammation promotes the vulnerability of DNA by activating the ATM/ATR/p53 pathway, while not affecting the DNA damage repair pathway. In brief, this research suggested that inflammation made DNA vulnerable due to the amplifying H2O2- or UV-induced ROS production and the motoring ATM/ATR/p53 pathway. In addition, our findings revealed that inflammation's motoring of the ATM/ATR/p53 pathway plays a crucial role in DNA damage. Therefore, exploring the mechanism between inflammation and ROS-dependent DNA damage would be extremely valuable and innovative. This study would somewhat establish a better understanding of inflammation, DNA damage, and cancer.

ATAD5 functions as a regulatory platform for Ub-PCNA deubiquitination

Ubiquitination status of proliferating cell nuclear antigen (PCNA) is crucial for regulating DNA lesion bypass. After the resolution of fork stalling, PCNA is subsequently deubiquitinated, but the underlying mechanism remains undefined. We found that the N-terminal domain of ATAD5 (ATAD5-N), the largest subunit of the PCNA-unloading complex, functions as a scaffold for Ub-PCNA deubiquitination. ATAD5 recognizes DNA-loaded Ub-PCNA through distinct DNA-binding and PCNA-binding motifs. Furthermore, ATAD5 forms a heterotrimeric complex with UAF1-USP1 deubiquitinase, facilitating the deubiquitination of DNA-loaded Ub-PCNA. ATAD5 also enhances the Ub-PCNA deubiquitination by USP7 and USP11 through specific interactions. ATAD5 promotes the distinct deubiquitination process of UAF1-USP1, USP7, and USP11 for poly-Ub-PCNA. Additionally, ATAD5 mutants deficient in UAF1-binding had increased sensitivity to DNA-damaging agents. Our results ultimately reveal that ATAD5 and USPs cooperate to efficiently deubiquitinate Ub-PCNA prior to its release from the DNA in order to safely deactivate the DNA repair process.

Predicting phase-I metabolism of piceatannol: an in silico study

Piceatannol is a natural compound found in plants and can be derived from resveratrol. While resveratrol has been extensively researched for its effects and how the body processes it, there are concerns about its use. These concerns include its limited absorption in the body, the need for specific dosages, potential interactions with other drugs, lack of standardization, and limited clinical evidence to support its benefits. Interestingly, Piceatannol, another compound derived from resveratrol, has received less attention from researchers but appears to offer advantages. It has better bioavailability and seems to have a more favorable therapeutic profile compared to resveratrol. Surprisingly, no previous attempts have been made to explore or predict the metabolites of piceatannol when it interacts with the enzyme cytochrome P450. This study aims to fill that gap by predicting how piceatannol is metabolized by cytochrome P450 and assessing any potential toxicity associated with its metabolites. This research is interesting because it's the first of its kind to investigate the metabolic fate of piceatannol, especially in the context of cytochrome P450. The findings have the potential to significantly contribute to the field of piceatannol research, particularly in the food industry where this compound has applications and implications.

Graphical abstract

PCNA cycling dynamics during DNA replication and repair in mammals

Proliferating cell nuclear antigen (PCNA) is a eukaryotic replicative DNA clamp. Furthermore, DNA-loaded PCNA functions as a molecular hub during DNA replication and repair. PCNA forms a closed homotrimeric ring that encircles the DNA, and association and dissociation of PCNA from DNA are mediated by clamp-loader complexes. PCNA must be actively released from DNA after completion of its function. If it is not released, abnormal accumulation of PCNA on chromatin will interfere with DNA metabolism. ATAD5 containing replication factor C-like complex (RLC) is a PCNA-unloading clamp-loader complex. ATAD5 deficiency causes various DNA replication and repair problems, leading to genome instability. Here, we review recent progress regarding the understanding of the action mechanisms of PCNA unloading complex in DNA replication/repair pathways.

Nanoscale Interaction of Endonuclease APE1 with DNA

Apurinic/apyrimidinic endonuclease 1 (APE1) is involved in DNA repair and transcriptional regulation mechanisms. This multifunctional activity of APE1 should be supported by specific structural properties of APE1 that have not yet been elucidated. Herein, we applied atomic force microscopy (AFM) to characterize the interactions of APE1 with DNA containing two well-separated G-rich segments. Complexes of APE1 with DNA containing G-rich segments were visualized, and analysis of the complexes revealed the affinity of APE1 to G-rich DNA sequences, and their yield was as high as 53%. Furthermore, APE1 is capable of binding two DNA segments leading to the formation of loops in the DNA-APE1 complexes. The analysis of looped APE1-DNA complexes revealed that APE1 can bridge G-rich segments of DNA. The yield of loops bridging two G-rich DNA segments was 41%. Analysis of protein size in various complexes was performed, and these data showed that loops are formed by APE1 monomer, suggesting that APE1 has two DNA binding sites. The data led us to a model for the interaction of APE1 with DNA and the search for the specific sites. The implication of these new APE1 properties in organizing DNA, by bringing two distant sites together, for facilitating the scanning for damage and coordinating repair and transcription is discussed.

Structure of the PCNA unloader Elg1-RFC

During DNA replication, the proliferating cell nuclear antigen (PCNA) clamps are loaded onto primed sites for each Okazaki fragment synthesis by the AAA+ heteropentamer replication factor C (RFC). PCNA encircling duplex DNA is quite stable and is removed from DNA by the dedicated clamp unloader Elg1-RFC. Here, we show the cryo-EM structure of Elg1-RFC in various states with PCNA. The structures reveal essential features of Elg1-RFC that explain how it is dedicated to PCNA unloading. Specifically, Elg1 contains two external loops that block opening of the Elg1-RFC complex for DNA binding, and an "Elg1 plug" domain that fills the central DNA binding chamber, thereby reinforcing the exclusive PCNA unloading activity of Elg1-RFC. Elg1-RFC was capable of unloading PCNA using non-hydrolyzable AMP-PNP. Both RFC and Elg1-RFC could remove PCNA from covalently closed circular DNA, indicating that PCNA unloading occurs by a mechanism that is distinct from PCNA loading. Implications for the PCNA unloading mechanism are discussed.

Short-range end resection requires ATAD5-mediated PCNA unloading for faithful homologous recombination

Homologous recombination (HR) requires bidirectional end resection initiated by a nick formed close to a DNA double-strand break (DSB), dysregulation favoring error-prone DNA end-joining pathways. Here we investigate the role of the ATAD5, a PCNA unloading protein, in short-range end resection, long-range resection not being affected by ATAD5 deficiency. Rapid PCNA loading onto DNA at DSB sites depends on the RFC PCNA loader complex and MRE11-RAD50-NBS1 nuclease complexes bound to CtIP. Based on our cytological analyses and on an in vitro system for short-range end resection, we propose that PCNA unloading by ATAD5 is required for the completion of short-range resection. Hampering PCNA unloading also leads to failure to remove the KU70/80 complex from the termini of DSBs hindering DNA repair synthesis and the completion of HR. In line with this model, ATAD5-depleted cells are defective for HR, show increased sensitivity to camptothecin, a drug forming protein-DNA adducts, and an augmented dependency on end-joining pathways. Our study highlights the importance of PCNA regulation at DSB for proper end resection and HR.

Combination therapy with HSP90 inhibitors and piperlongumine promotes ROS-mediated ER stress in colon cancer cells

Colon cancer is a major cause of cancer-related death. Despite recent improvements in the treatment of colon cancer, new strategies to improve the overall survival of patients are urgently needed. Heat shock protein 90 (HSP90) is widely recognized as a promising target for treating various cancers, including colon cancer. However, no HSP90 inhibitor has been approved for clinical use due to limited efficacy. In this study, we evaluated the antitumor activities of HSP90 inhibitors in combination with piperlongumine in colon cancer cells. We show that combination treatment with HSP90 inhibitors and piperlongumine displayed strong synergistic interaction in colon cancer cells. These agents synergize by promoting ER stress, JNK activation, and DNA damage. This process is fueled by oxidative stress, which is caused by the accumulation of reactive oxygen species. These studies nominated piperlongumine as a promising agent for HSP90 inhibitor-based combination therapy against colon cancer.

Alkylation of nucleobases by 2-chloro-N,N-diethylethanamine hydrochloride (CDEAH) sensitizes PARP1-deficient tumors

Targeting BRCA1- and BRCA2-deficient tumors through synthetic lethality using poly(ADP-ribose) polymerase inhibitors (PARPi) has emerged as a successful strategy for cancer therapy. PARPi monotherapy has shown excellent efficacy and safety profiles in clinical practice but is limited by the need for tumor genome mutations in BRCA or other homologous recombination genes as well as the rapid emergence of resistance. In this study, we identified 2-chloro-N,N-diethylethanamine hydrochloride (CDEAH) as a small molecule that selectively kills PARP1- and xeroderma pigmentosum A-deficient cells. CDEAH is a monofunctional alkylating agent that preferentially alkylates guanine nucleobases, forming DNA adducts that can be removed from DNA by either a PARP1-dependent base excision repair or nucleotide excision repair. Treatment of PARP1-deficient cells leads to the formation of strand breaks, an accumulation of cells in S phase and activation of the DNA damage response. Furthermore, CDEAH selectively inhibits PARP1-deficient xenograft tumor growth compared to isogenic PARP1-proficient tumors. Collectively, we report the discovery of an alkylating agent inducing DNA damage that requires PARP1 activity for repair and acts synergistically with PARPi.

Gut microbes involvement in gastrointestinal cancers through redox regulation

Gastrointestinal (GI) cancers are among the most common and lethal cancers worldwide. GI microbes play an important role in the occurrence and development of GI cancers. The common mechanisms by which GI microbes may lead to the occurrence and development of cancer include the instability of the microbial internal environment, secretion of cancer-related metabolites, and destabilization of the GI mucosal barrier. In recent years, many studies have found that the relationship between GI microbes and the development of cancer is closely associated with the GI redox level. Redox instability associated with GI microbes may induce oxidative stress, DNA damage, cumulative gene mutation, protein dysfunction and abnormal lipid metabolism in GI cells. Redox-related metabolites of GI microbes, such as short-chain fatty acids, hydrogen sulfide and nitric oxide, which are involved in cancer, may also influence GI redox levels. This paper reviews the redox reactions of GI cells regulated by microorganisms and their metabolites, as well as redox reactions in the cancer-related GI microbes themselves. This study provides a new perspective for the prevention and treatment of GI cancers.

PCNA Ser46-Leu47 residues are crucial in preserving genomic integrity

Proliferating cell nuclear antigen (PCNA) is a maestro of DNA replication. PCNA forms a homotrimer and interacts with various proteins, such as DNA polymerases, DNA ligase I (LIG1), and flap endonuclease 1 (FEN1) for faithful DNA replication. Here, we identify the crucial role of Ser46-Leu47 residues of PCNA in maintaining genomic integrity using in vitro, and cell-based assays and structural prediction. The predicted PCNAΔSL47 structure shows the potential distortion of the central loop and reduced hydrophobicity. PCNAΔSL47 shows a defective interaction with PCNAWT leading to defects in homo-trimerization in vitro. PCNAΔSL47 is defective in the FEN1 and LIG1 interaction. PCNA ubiquitination and DNA-RNA hybrid processing are defective in PCNAΔSL47-expressing cells. Accordingly, PCNAΔSL47-expressing cells exhibit an increased number of single-stranded DNA gaps and higher levels of γH2AX, and sensitivity to DNA-damaging agents, highlighting the importance of PCNA Ser46-Leu47 residues in maintaining genomic integrity.

Lethal and Non-Lethal Functions of Caspases in the DNA Damage Response

Members of the caspase family are well known for their roles in the initiation and execution of cell death. Due to their function in the removal of damaged cells that could otherwise become malignant, caspases are important players in the DNA damage response (DDR), a network of pathways that prevent genomic instability. However, emerging evidence of caspases positively or negatively impacting the accumulation of DNA damage in the absence of cell death demonstrates that caspases play a role in the DDR that is independent of their role in apoptosis. This review highlights the apoptotic and non-apoptotic roles of caspases in the DDR and how they can impact genomic stability and cancer treatment.

Distinct Motifs in ATAD5 C-Terminal Domain Modulate PCNA Unloading Process

Proliferating cell nuclear antigen (PCNA) is a DNA clamp that functions in key roles for DNA replication and repair. After the completion of DNA synthesis, PCNA should be unloaded from DNA in a timely way. The ATAD5-RFC-Like Complex (ATAD5-RLC) unloads PCNA from DNA. However, the mechanism of the PCNA-unloading process remains unclear. In this study, we determined the minimal PCNA-unloading domain (ULD) of ATAD5. We identified several motifs in the ATAD5 ULD that are essential in the PCNA-unloading process. The C-terminus of ULD is required for the stable association of RFC2-5 for active RLC formation. The N-terminus of ULD participates in the opening of the PCNA ring. ATAD5-RLC was more robustly bound to open-liable PCNA compared to the wild type. These results suggest that distinct motifs of the ATAD5 ULD participate in each step of the PCNA-unloading process.