A DNA damage response screen identifies RHINO, a 9-1-1 and TopBP1 interacting protein required for ATR signaling

The diverse roles of the circadian clock in cancer

A growing part of the human population is affected by circadian misalignment caused by deregulated sleep, increased nighttime light exposure and erratic eating patterns. Thus, circadian rhythms are a key research area, with compelling links to cancer. Here, we review the circadian regulation of critical cellular processes, including immunity, metabolism, cell cycle control and DNA repair, under physiological homeostasis and in cancer. We discuss the divergent evidence indicating tissue-specific roles of the circadian clock in different cancer types and the potential link between circadian misalignment and early-onset cancers. Finally, we outline how understanding the circadian clock can improve cancer prevention and chronomedicine-based therapies.

FOXM1 expression reverts aging chromatin profiles through repression of the senescence-associated pioneer factor AP-1

Aging is characterized by changes in gene expression, some of which can drive deleterious cellular phenotypes and senescence. The transcriptional activation of senescence genes has been mainly attributed to epigenetic shifts, but the changes in chromatin accessibility and its underlying mechanisms remain largely elusive in natural aging. Here, we profiled chromatin accessibility in human dermal fibroblasts (HDFs) from individuals with ages ranging from neonatal to octogenarian. We found that AP-1 binding motifs are prevalent in elderly-specific accessible chromatin regions while neonatal-specific regions are highly enriched for TEAD binding motifs. We further show that TEAD4 and FOXM1 share a conserved transcriptional regulatory landscape controlled by a not previously described and age-dependent enhancer that loses accessibility with aging and whose deletion drives senescence. Finally, we demonstrate that FOXM1 ectopic expression in elderly cells partially resets chromatin accessibility to a youthful state due to FOXM1's repressive function on several members of the AP-1 complex, which is known to trigger the senescence transcriptional program. These results place FOXM1 at a top hierarchical level in chromatin remodeling required to prevent senescence.

Lipoylation inhibition enhances radiation control of lung cancer by suppressing homologous recombination DNA damage repair

Lung cancer exhibits altered metabolism, influencing its response to radiation. To investigate the metabolic regulation of radiation response, we conducted a comprehensive, metabolic-wide CRISPR-Cas9 loss-of-function screen using radiation as selection pressure in human non-small cell lung cancer. Lipoylation emerged as a key metabolic target for radiosensitization, with lipoyltransferase 1 (LIPT1) identified as a top hit. LIPT1 covalently conjugates mitochondrial 2-ketoacid dehydrogenases with lipoic acid, facilitating enzymatic functions involved in the tricarboxylic acid cycle. Inhibiting lipoylation, either through genetic LIPT1 knockout or a lipoylation inhibitor (CPI-613), enhanced tumor control by radiation. Mechanistically, lipoylation inhibition increased 2-hydroxyglutarate, leading to H3K9 trimethylation, disrupting TIP60 recruitment and ataxia telangiectasia mutated (ATM)-mediated DNA damage repair signaling, impairing homologous recombination repair. In summary, our findings reveal a critical role of LIPT1 in regulating DNA damage and chromosome stability and may suggest a means to enhance therapeutic outcomes with DNA-damaging agents.

Mono-ubiquitination of TopBP1 by PHRF1 enhances ATR activation and genomic stability

The TopBP1-ATR axis is critical for maintaining genomic stability during DNA replication stress, yet the precise regulation of TopBP1 in replication stress responses remains poorly understood. In this study, we identified PHD and Ring Finger Domains 1 (PHRF1) as an important ATR activator through its interaction with TopBP1. Our analysis revealed a correlation between PHRF1 and genomic stability in cancer patients. Mechanistically, PHRF1 is recruited to DNA lesions in a manner dependent on its PHD domain and histone methylation. Subsequently, PHRF1 mono-ubiquitinates TopBP1 at lysine 73, which enhances the TopBP1-ATR interaction and activates ATR. Depletion of PHRF1 disrupts ATR activation and sensitizes cells to replication stress-inducing agents. Furthermore, conditional knockout of Phrf1 in mice leads to early lethality and impaired ATR-Chk1 axis signaling. Collectively, our findings establish PHRF1 as a novel E3 ligase for TopBP1, coordinating the replication stress response by enhancing TopBP1-ATR signaling.

The pro-tumor activity of INTS7 on lung adenocarcinoma via inhibiting immune infiltration and activating p38MAPK pathway

Lung adenocarcinoma (LUAD) is the most common lung cancer, accounting for 19.4% of all cancer deaths. Our previous study discovered that INTS7 expression was upregulated in LUAD, while the precise mechanism by which INTS7 exerts pro-cancer effects remains unknown. In our study, shRNA was used to knockdown the expression of INTS7 in A549 cells. Cancer behaviors in vitro were determined by CCK8 and transwell assays. Xenograft mice models were constructed to detect the tumorigenesis in vivo. Immunofluorescence and toluidine blue staining were used to test the immune infiltration. Bioinformatics analysis was adopted to predict the potential signaling pathways and construct INTS7-derived genomic prognostic model. Western blot was utilized to confirm the molecular pathways. In total, downregulation of INTS7 suppressed proliferation, invasion and migration of A549 cells, as well as tumor growth. Bioinformatics and western blot analysis indicated that p38MAPK pathway participated in the regulatory mechanism of INTS7. Moreover, INTS7 expression was negatively correlated with infiltration of memory B cells and mast cells, while positively correlated with infiltration of macrophages M2. A nomogram, including INTS7-derived risk score, was used to estimate individual's survival probability. Generally, our findings provided comprehensive understanding of the molecular mechanisms about INTS7, and targeting INTS7 may represent a potential therapy for LUAD.

The Integrator complex: an emerging complex structure involved in the regulation of gene expression by targeting RNA polymerase II

The Integrator complex is a multisubunit complex that participates in the processing of small nuclear RNA molecules in eukaryotic cells by cleaving the 3' end. In protein-coding genes, Integrator is a key regulator of promoter-proximal pausing, release, and recruitment of RNA polymerase II. Research on Integrator has revealed its critical role in the regulation of gene expression and RNA processing. Dysregulation of the Integrator complex has been implicated in a variety of human diseases including cancer and developmental disorders. Therefore, understanding the structure and function of the Integrator complex is critical to uncovering the mechanisms of gene expression and developing potential therapeutic strategies for related diseases.

Recent insights into the causes and consequences of chromosome mis-segregation

Mitotic cells face the challenging task of ensuring accurate and equal segregation of their duplicated, condensed chromosomes between the nascent daughter cells. Errors in the process result in chromosome missegregation, a significant consequence of which is the emergence of aneuploidy-characterized by an imbalance in chromosome number-and the associated phenomenon of chromosome instability (CIN). Aneuploidy and CIN are common features of cancer, which leverages them to promote genome heterogeneity and plasticity, thereby facilitating rapid tumor evolution. Recent research has provided insights into how mitotic errors shape cancer genomes by inducing both numerical and structural chromosomal changes that drive tumor initiation and progression. In this review, we survey recent findings regarding the mitotic causes and consequences of aneuploidy. We discuss new findings into the types of chromosome segregation errors that lead to aneuploidy and novel pathways that protect genome integrity during mitosis. Finally, we describe new developments in our understanding of the immediate consequences of chromosome mis-segregation on the genome stability of daughter cells.

Bacterial pore-forming toxin pneumolysin drives pathogenicity through host extracellular vesicles released during infection

Streptococcus pneumoniae is a global priority respiratory pathogen that kills over a million people annually. The pore-forming cytotoxin, pneumolysin (PLY) is a major virulence factor. Here, we found that recombinant PLY as well as wild-type pneumococcal strains, but not the isogenic PLY mutant, upregulated the shedding of extracellular vesicles (EVs) harboring membrane-bound toxin from human THP-1 monocytes. PLY-EVs induced cytotoxicity and hemolysis dose-dependently upon internalization by recipient monocyte-derived dendritic cells. Proteomics analysis revealed that PLY-EVs are selectively enriched in key inflammatory host proteins such as IFI16, NLRC4, PTX3, and MMP9. EVs shed from PLY-challenged or infected cells induced dendritic cell maturation and primed them to infection. In vivo, zebrafish administered with PLY-EVs showed pericardial edema and mortality. Adoptive transfer of bronchoalveolar-lavage-derived EVs from infected mice to healthy recipients induced lung damage and inflammation in a PLY-dependent manner. Our findings identify that host EVs released during infection mediate pneumococcal pathogenesis.

RHNO1: at the crossroads of DNA replication stress, DNA repair, and cancer

The DNA replication stress (DRS) response is a crucial homeostatic mechanism for maintaining genome integrity in the face of intrinsic and extrinsic barriers to DNA replication. Importantly, DRS is often significantly increased in tumor cells, making tumors dependent on the cellular DRS response for growth and survival. Rad9-Hus1-Rad1 Interacting Nuclear Orphan 1 (RHNO1), a protein involved in the DRS response, has recently emerged as a potential therapeutic target in cancer. RHNO1 interacts with the 9-1-1 checkpoint clamp and TopBP1 to activate the ATR/Chk1 signaling pathway, the crucial mediator of the DRS response. Moreover, RHNO1 was also recently identified as a key facilitator of theta-mediated end joining (TMEJ), a DNA repair mechanism implicated in cancer progression and chemoresistance. In this literature review, we provide an overview of our current understanding of RHNO1, including its structure, function in the DRS response, and role in DNA repair, and discuss its potential as a cancer therapeutic target. Therapeutic targeting of RHNO1 holds promise for tumors with elevated DRS as well as tumors with DNA repair deficiencies, including homologous recombination DNA repair deficient (HRD) tumors. Further investigation into RHNO1 function in cancer, and development of approaches to target RHNO1, are expected to yield novel strategies for cancer treatment.

Key molecular DNA damage responses of human cells to radiation

Our understanding of the DNA damage responses of human cells to radiation has increased remarkably over the recent years although some notable signaling events remain to be discovered. Here we provide a brief account of the key molecular events of the responses to reflect the current understanding of the key underlying mechanisms involved.

Comprehensive bioinformatics analysis of integrator complex subunits: expression patterns, immune infiltration, and prognostic signature, validated through experimental approaches in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a common gastrointestinal malignancy with a high incidence and poor prognosis. The subunits of the integrator complex (INTS1-14) play a crucial role in regulating genes dependent on RNA Polymerase II, which may be associated with cancer. However, the role of INTSs in HCC remains unclear. This study aims to comprehensively analyze the clinical value and potential role of INTS family genes in HCC through systematic bioinformatics analysis.

METHODS

We employed various public databases, including UALCAN, HPA, Kaplan-Meier Plotter, GEPIA2, TNMplot, STRING, TIMER, and TISIDB, to investigate the expression levels, clinicopathological correlations, diagnostic and prognostic value, genetic alterations, co-expression network, molecular targets, and immune infiltration of INTSs in HCC. Additionally, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were utilized to investigate the biological functions of genes associated with INTSs. Furthermore, Western blot, real-time fluorescence quantitative reverse transcription polymerase chain reaction (RT-qPCR), and immunohistochemistry techniques were employed to assess the expression of relevant proteins and genes. The proliferation of HCC cells was evaluated using the CCK8 assay.

RESULTS

We found that in HCC, there was a significant upregulation of INTSs at the transcriptional level, particularly INTS1, INTS4, INTS7, and INTS8. Additionally, the protein levels of INTS1 and INTS8 were notably elevated. The overexpression of these INTSs was strongly correlated with tumor stages in HCC patients. INTS1, INTS4, INTS7, and INTS8 exhibited significant diagnostic and prognostic value in HCC. Moreover, their expression was associated with immune infiltrations and activated status, including B cells, CD8 + T cells, CD4 + T cells, NK cells, macrophages, and dendritic cells. Functional predictions indicated that INTS1, INTS4, INTS7, and INTS8 were involved in various cancer-related signaling pathways, such as TRAIL, IFN-gamma, mTOR, CDC42, Apoptosis, and the p53 pathway. Furthermore, we observed a significant upregulation of INTS1, INTS4, INTS7, and INTS8 expression in HCC cell lines compared to normal liver cell lines. The level of INTS1 protein was higher in cancerous tissues compared to adjacent non-cancerous tissues (n = 16), and the suppression of INTS1 resulted in a significant decrease in the proliferation of Huh7 cells.

CONCLUSION

These findings indicate the potential of INTS family genes as diagnostic biomarkers and therapeutic targets in HCC. Further research is needed to understand the underlying mechanisms and explore clinical applications.

SIRT2 promotes base excision repair by transcriptionally activating OGG1 in an ATM/ATR-dependent manner

Sirtuin 2 (SIRT2) regulates the maintenance of genome integrity by targeting pathways of DNA damage response and homologous recombination repair. However, whether and how SIRT2 promotes base excision repair (BER) remain to be determined. Here, we found that independent of its catalytic activity SIRT2 interacted with the critical glycosylase OGG1 to promote OGG1 recruitment to its own promoter upon oxidative stress, thereby enhancing OGG1 promoter activity and increasing BER efficiency. Further studies revealed that SIRT2 was phosphorylated on S46 and S53 by ATM/ATR upon oxidative stress, and SIRT2 phosphorylation enhanced the SIRT2-OGG1 interaction and mediated the stimulatory effect of SIRT2 on OGG1 promoter activity. We also characterized 37 cancer-derived SIRT2 mutants and found that 5 exhibited the loss of the stimulatory effects on OGG1 transcription. Together, our data reveal that SIRT2 acts as a tumor suppressor by promoting OGG1 transcription and increasing BER efficiency in an ATM/ATR-dependent manner.

Broken chromosomes heading into mitosis: More than one way to patch a flat tire

A cell dealing with a broken chromosome in mitosis is like a driver dealing with a flat tire on the highway: damage repair must occur under non-ideal circumstances. Mitotic chromosome breaks encounter problems related to structures called micronuclei. These aberrant nuclei are linked to cell death, mutagenesis, and cancer. In the last few years, a flurry of studies illuminated two mechanisms that prevent mitotic problems related to micronuclei. One mechanism prevents micronuclei from forming during mitosis and involves DNA Polymerase Theta, a DNA repair regulator that patches up broken mitotic chromosomes. A second mechanism is activated after micronuclei form and then rupture, and involves CIP2A and TOPBP1 proteins, which patch micronuclear fragments to promote their subsequent mitotic segregation. Here, we review recent progress in this field of mitotic DNA damage and discuss why multiple mechanisms exist. Future studies in this exciting area will reveal new DNA break responses and inform therapeutic strategies.

Defective Homologous Recombination Repair By Up-Regulating Lnc-HZ10/Ahr Loop in Human Trophoblast Cells Induced Miscarriage

Human trophoblast cells are crucial for healthy pregnancy. However, whether the defective homologous recombination (HR) repair of dsDNA break (DSB) in trophoblast cells may induce miscarriage is completely unknown. Moreover, the abundance of BRCA1 (a crucial protein for HR repair), its recruitment to DSB foci, and its epigenetic regulatory mechanisms, are also fully unexplored. In this work, it is identified that a novel lnc-HZ10, which is highly experssed in villous tissues of recurrent miscarriage (RM) vs their healthy control group, suppresses HR repair of DSB in trophoblast cell. Lnc-HZ10 and AhR (aryl hydrocarbon receptor) form a positive feedback loop. AhR acts as a transcription factor to promote lnc-HZ10 transcription. Meanwhile, lnc-HZ10 also increases AhR levels by suppressing its CUL4B-mediated ubiquitination degradation. Subsequently, AhR suppresses BRCA1 transcription; and lnc-HZ10 (mainly 1-447 nt) interacts with γ-H2AX; and thus, impairs its interactions with BRCA1. BPDE exposure may trigger this loop to suppress HR repair in trophoblast cells, possibly inducing miscarriage. Knockdown of murine Ahr efficiently recovers HR repair in placental tissues and alleviates miscarriage in a mouse miscarriage model. Therefore, it is suggested that AhR/lnc-HZ10/BRCA1 axis may be a promising target for alleviation of unexplained miscarriage.

A Practical Site-specific Method for the Detection of Bulky DNA Damages

Helix-distorting DNA damages block RNA and DNA polymerase, compromising cell function and fate. In human cells, these damages are removed primarily by nucleotide excision repair (NER). Here, we describe damage-sensing PCR (dsPCR), a PCR-based method for the detection of these DNA damages. Exposure to DNA damaging agents results in lower PCR signal in comparison to non-damaged DNA, and repair is measured as the restoration of PCR signal over time. We show that the method successfully detects damages induced by ultraviolet (UV) radiation, by the carcinogenic component of cigarette smoke benzo[a]pyrene diol epoxide (BPDE) and by the chemotherapeutic drug cisplatin. Damage removal measured by dsPCR in a heterochromatic region is less efficient than in a transcribed and accessible region. Furthermore, lower repair is measured in repair-deficient knock-out cells. This straight-forward method could be applied by non-DNA repair experts to study the involvement of their gene-of-interest in repair. Furthermore, this method is fully amenable for high-throughput screening of DNA repair activity.

Structural basis for intra- and intermolecular interactions on RAD9 subunit of 9-1-1 checkpoint clamp implies functional 9-1-1 regulation by RHINO

Eukaryotic DNA clamp is a trimeric protein featuring a toroidal ring structure that binds DNA on the inside of the ring and multiple proteins involved in DNA transactions on the outside. Eukaryotes have two types of DNA clamps: the replication clamp PCNA and the checkpoint clamp RAD9-RAD1-HUS1 (9-1-1). 9-1-1 activates the ATR-CHK1 pathway in DNA damage checkpoint, regulating cell cycle progression. Structure of 9-1-1 consists of two moieties: a hetero-trimeric ring formed by PCNA-like domains of three subunits and an intrinsically disordered C-terminal region of the RAD9 subunit, called RAD9 C-tail. The RAD9 C-tail interacts with the 9-1-1 ring and disrupts the interaction between 9-1-1 and DNA, suggesting a negative regulatory role for this intramolecular interaction. In contrast, RHINO, a 9-1-1 binding protein, interacts with both RAD1 and RAD9 subunits, positively regulating checkpoint activation by 9-1-1. This study presents a biochemical and structural analysis of intra- and inter-molecular interactions on the 9-1-1 ring. Biochemical analysis indicates that RAD9 C-tail binds to the hydrophobic pocket on the PCNA-like domain of RAD9, implying that the pocket is involved in multiple protein-protein interactions. The crystal structure of the 9-1-1 ring in complex with a RHINO peptide reveals that RHINO binds to the hydrophobic pocket of RAD9, shedding light on the RAD9-binding motif. Additionally, the study proposes a structural model of the 9-1-1-RHINO quaternary complex. Together, these findings provide functional insights into the intra- and inter-molecular interactions on the front side of RAD9, elucidating the roles of RAD9 C-tail and RHINO in checkpoint activation.

The C-terminal tail of Rad17, iVERGE, binds the 9‒1‒1 complex independently of AAA+ ATPase domains to provide another clamp-loader interface

The ATR pathway plays a crucial role in maintaining genome integrity as the major DNA damage checkpoint. It also attracts attention as a therapeutic target in cancer treatment. The Rad17-RFC2-5 complex loads the Rad9-Hus1-Rad1 (9-1-1) DNA clamp complex onto damaged chromatin to activate the ATR pathway. We previously reported that phosphorylation of a polyanionic C-terminal tail of human Rad17, iVERGE, is essential for the interaction between Rad17 and the 9-1-1 complex. However, the molecular mechanism has remained unclear. Here, we show that iVERGE directly interacts with the Hus1 subunit of the 9-1-1 complex through Rad17-S667 phosphorylation independently of the AAA+ ATPase domains. An exogenous iVERGE peptide interacted with the 9-1-1 complex in vivo. The binding conformation of the iVERGE peptide was analyzed by de novo modeling with docking simulation, simulated annealing-molecular dynamics simulation, and the fragment molecular orbital method. The in silico analyses predicted the association of the iVERGE peptide with the hydrophobic and basic patches on the Hus1 protein, and the corresponding Hus1 mutants were deficient in the interaction with the iVERGE peptide in vivo. The iVERGE peptide occupied the same position as the C-terminus of Saccharomyces cerevisiae RAD24 on MEC3. The interaction energy calculation suggested that the Rad17 KYxxL motif and the iVERGE peptide are the primary and secondary interaction surfaces between the Rad17-RFC2-5 and 9-1-1 complexes. Our data reveal a novel molecular interface, iVERGE, between the Rad17-RFC2-5 and 9-1-1 complexes in vertebrates and implicate that Rad17 utilizes two distinct molecular interfaces to regulate the 9-1-1 complex.

RHNO1 disruption inhibits cell proliferation and induces mitochondrial apoptosis via PI3K/Akt pathway in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) represents one of the primary liver malignancies with poor prognosis. RHNO1, which implicated in the ATR-CHK1 signaling pathway thus functions in the DNA replication stress response. However, the role and molecular mechanisms of RHNO1 in HCC remain largely elusive. Here, we imply that RHNO1 is elevated in HCC tumor tissues and that high expression of RHNO1 predicts poor prognosis of HCC patients. Moreover, RHNO1 mRNA, especially protein levels were significantly increased in most HCC cells. Knockdown of RHNO1 through small interfering RNAs (siRNAs) inhibited the proliferation and triggered cell apoptosis of HCC cells both in vitro and in vivo. Specifically, we find that RHNO1 deficiency confers apoptosis via mitochondrial-mediated pathway. Mechanistically, silencing of RHNO1 impeded HCC proliferation and induced apoptosis by inactivating the PI3K/Akt pathway. Overall, these findings unravel that RHNO1 functions as an oncogene in HCC, and involved in regulating mitochondrial apoptosis to promote HCC thus may serve as a therapeutic and diagnostic target for HCC.

The fine-tuned crosstalk between lysine acetylation and the circadian rhythm

Circadian rhythm is a roughly 24-h wake and sleep cycle that almost all of the organisms on the earth follow when they execute their biological functions and physiological activities. The circadian clock is mainly regulated by the transcription-translation feedback loop (TTFL), consisting of the core clock proteins, including BMAL1, CLOCK, PERs, CRYs, and a series of accessory factors. The circadian clock and the downstream gene expression are not only controlled at the transcriptional and translational levels but also precisely regulated at the post-translational modification level. Recently, it has been discovered that CLOCK exhibits lysine acetyltransferase activities and could acetylate protein substrates. Core clock proteins are also acetylated, thereby altering their biological functions in the regulation of the expression of downstream genes. Studies have revealed that many protein acetylation events exhibit oscillation behavior. However, the biological function of acetylation on circadian rhythm has only begun to explore. This review will briefly introduce the acetylation and deacetylation of the core clock proteins and summarize the proteins whose acetylation is regulated by CLOCK and circadian rhythm. Then, we will also discuss the crosstalk between lysine acetylation and the circadian clock or other post-translational modifications. Finally, we will briefly describe the possible future perspectives in the field.

RHINO directs MMEJ to repair DNA breaks in mitosis

Nonhomologous end-joining (NHEJ) and homologous recombination (HR) are the primary pathways for repairing DNA double-strand breaks (DSBs) during interphase, whereas microhomology-mediated end-joining (MMEJ) has been regarded as a backup mechanism. Through CRISPR-Cas9-based synthetic lethal screens in cancer cells, we identified subunits of the 9-1-1 complex (RAD9A-RAD1-HUS1) and its interacting partner, RHINO, as crucial MMEJ factors. We uncovered an unexpected function for RHINO in restricting MMEJ to mitosis. RHINO accumulates in M phase, undergoes Polo-like kinase 1 (PLK1) phosphorylation, and interacts with polymerase θ (Polθ), enabling its recruitment to DSBs for subsequent repair. Additionally, we provide evidence that MMEJ activity in mitosis repairs persistent DSBs that originate in S phase. Our findings offer insights into the synthetic lethal relationship between the genes POLQ and BRCA1 and BRAC2 and the synergistic effect of Polθ and poly(ADP-ribose) polymerase (PARP) inhibitors.

Circadian clocks in health and disease: Dissecting the roles of the biological pacemaker in cancer

In modern society, there is a growing population affected by circadian clock disruption through night shift work, artificial light-at-night exposure, and erratic eating patterns. Concurrently, the rate of cancer incidence in individuals under the age of 50 is increasing at an alarming rate, and though the precise risk factors remain undefined, the potential links between circadian clock deregulation and young-onset cancers is compelling. To explore the complex biological functions of the clock, this review will first provide a framework for the mammalian circadian clock in regulating critical cellular processes including cell cycle control, DNA damage response, DNA repair, and immunity under conditions of physiological homeostasis. Additionally, this review will deconvolute the role of the circadian clock in cancer, citing divergent evidence suggesting tissue-specific roles of the biological pacemaker in cancer types such as breast, lung, colorectal, and hepatocellular carcinoma. Recent evidence has emerged regarding the role of the clock in the intestinal epithelium, as well as new insights into how genetic and environmental disruption of the clock is linked with colorectal cancer, and the molecular underpinnings of these findings will be discussed. To place these findings within a context and framework that can be applied towards human health, a focus on how the circadian clock can be leveraged for cancer prevention and chronomedicine-based therapies will be outlined.

p130RB2 positively contributes to ATR activation in response to replication stress via the RPA32-ETAA1 axis

Ataxia-telangiectasia mutated and Rad3-related (ATR) kinase is a crucial regulator of the cell cycle checkpoint and activated in response to DNA replication stress by two independent pathways via RPA32-ETAA1 and TopBP1. However, the precise activation mechanism of ATR by the RPA32-ETAA1 pathway remains unclear. Here, we show that p130RB2, a member of the retinoblastoma protein family, participates in the pathway under hydroxyurea-induced DNA replication stress. p130RB2 binds to ETAA1, but not TopBP1, and depletion of p130RB2 inhibits the RPA32-ETAA1 interaction under replication stress. Moreover, p130RB2 depletion reduces ATR activation accompanied by phosphorylation of its targets RPA32, Chk1, and ATR itself. It also causes improper re-progression of S phase with retaining single-stranded DNA after cancelation of the stress, which leads to an increase in the anaphase bridge phenotype and a decrease in cell survival. Importantly, restoration of p130RB2 rescued the disrupted phenotypes of p130RB2 knockdown cells. These results suggest positive involvement of p130RB2 in the RPA32-ETAA1-ATR axis and proper re-progression of the cell cycle to maintain genome integrity.

RHINO restricts MMEJ activity to mitosis

DNA double-strand breaks (DSBs) are toxic lesions that can lead to genome instability if not properly repaired. Breaks incurred in G1 phase of the cell cycle are predominantly fixed by non-homologous end-joining (NHEJ), while homologous recombination (HR) is the primary repair pathway in S and G2. Microhomology-mediated end-joining (MMEJ) is intrinsically error-prone and considered a backup DSB repair pathway that becomes essential when HR and NHEJ are compromised. In this study, we uncover MMEJ as the major DSB repair pathway in M phase. Using CRISPR/Cas9-based synthetic lethal screens, we identify subunits of the 9-1-1 complex (RAD9A-HUS1-RAD1) and its interacting partner, RHINO, as critical MMEJ factors. Mechanistically, we show that the function of 9-1-1 and RHINO in MMEJ is inconsistent with their well-established role in ATR signaling. Instead, RHINO plays an unexpected and essential role in directing mutagenic repair to M phase by directly binding to Polymerase theta (Polθ) and promoting its recruitment to DSBs in mitosis. In addition, we provide evidence that mitotic MMEJ repairs persistent DNA damage that originates in S phase but is not repaired by HR. The latter findings could explain the synthetic lethal relationship between POLQ and BRCA1/2 and the synergistic effect of Polθ and PARP inhibitors. In summary, our study identifies MMEJ as the primary pathway for repairing DSBs during mitosis and highlights an unanticipated role for RHINO in directing mutagenic repair to M phase.

BMAL1 collaborates with CLOCK to directly promote DNA double-strand break repair and tumor chemoresistance

Accumulating evidence indicates a correlation between circadian dysfunction and genomic instability. However, whether the circadian machinery directly regulates DNA damage repair, especially in double-strand breaks (DSBs), remains poorly understood. Here, we report that in response to DSBs, BMAL1 is activated by ATM-mediated phosphorylation at S183. Phosphorylated BMAL1 is then localized to DNA damage sites, where it facilitates acetylase CLOCK to load in the chromatin, regulating the acetylation of histone H4 (H4Ac) at DSB sites. In this way, the BMAL1-CLOCK-H4Ac axis promotes the DNA end-resection to generate single-stranded DNA (ssDNA) and the subsequent homologous recombination (HR). BMAL1 deficient cells display defective HR, accumulation of unrepaired DSBs and genome instability. Accordingly, depletion of BMAL1 significantly enhances the sensitivity of adrenocortical carcinoma (ACC) to DNA damage-based therapy in vitro and in vivo. These findings uncover non-canonical function of BMAL1 and CLOCK in HR-mediated DSB repair, which may have an implication in cancer therapeutics.

The 9-1-1 DNA clamp subunit RAD1 forms specific interactions with clamp loader RAD17, revealing functional implications for binding-protein RHINO

The RAD9-RAD1-HUS1 complex (9-1-1) is a eukaryotic DNA clamp with a crucial role at checkpoints for DNA damage. The ring-like structure of 9-1-1 is opened for loading onto 5' recessed DNA by the clamp loader RAD17 RFC-like complex (RAD17-RLC), in which the RAD17 subunit is responsible for specificity to 9-1-1. Loading of 9-1-1 is required for activation of the ATR-CHK1 checkpoint pathway and the activation is stimulated by a 9-1-1 interacting protein, RHINO, which interacts with 9-1-1 via a recently identified RAD1-binding motif. This discovery led to the hypothesis that other interacting proteins may contain a RAD1-binding motif as well. Here, we show that vertebrate RAD17 proteins also have a putative RAD1-binding motif in their N-terminal regions, and we report the crystal structure of human 9-1-1 bound to a human RAD17 peptide incorporating the motif at 2.1 Å resolution. Our structure confirms that the N-terminal region of RAD17 binds to the RAD1 subunit of 9-1-1 via specific interactions. Furthermore, we show that the RAD1-binding motif of RHINO disturbs the interaction of the N-terminal region of RAD17 with 9-1-1. Our results provide deeper understanding of how RAD17-RLC specifically recognizes 9-1-1 and imply that RHINO has a functional role in 9-1-1 loading/unloading and checkpoint activation.

Molecular crosstalk between circadian clock and cancer and therapeutic implications

The circadian clock governs activity of many physiological processes, thereby playing a pivotal role in human health. Circadian disruption is closely associated with cancer development; in particular, recent discoveries have provided strong evidence supporting specific functions of different molecular clock components in either promoting or inhibiting tumorigenesis. This narrative review aims to summarize the existing data on molecular connections between the clock and cancer. These results along with future efforts pave the road to targeting the circadian clock as a novel pathway for therapeutic intervention. Given the implications of chrono-nutrition interventions such as time-restricted feeding in extending lifespan, chrono-nutrition may have preventive and therapeutic applications for individuals with and at-risk of age-related diseases including cancer.

Functional assessment of missense variants of uncertain significance in the cancer susceptibility gene PALB2

Germline PALB2 pathogenic variants are associated with an increased lifetime risk for breast, pancreatic, and ovarian cancer. However, the interpretation of the pathogenicity of numerous PALB2 missense variants of uncertain significance (VUSs) identified in germline genetic testing remains a challenge. Here we selected ten potentially pathogenic PALB2 VUSs identified in 2279 Chinese patients with breast cancer and evaluated their impacts on PALB2 function by systematic functional assays. We showed that three PALB2 VUSs p.K16M [c.47 A > T], p.L24F [c.72 G > C], and p.L35F [c.103 C > T] in the coiled-coil domain impaired PALB2-mediated homologous recombination. The p.L24F and p.L35F variants partially disrupted BRCA1-PALB2 interactions, reduced RAD51 foci formation in response to DNA damage, abrogated ionizing radiation-induced G2/M checkpoint maintenance, and conferred increased sensitivity to olaparib and cisplatin. The p.K16M variant presented mild effects on BRCA1-PALB2 interactions and RAD51 foci formation. Altogether, we identify two novel PALB2 VUSs, p.L24F and p.L35F, that compromise PALB2 function and may increase cancer risk. These two variants display marked olaparib and cisplatin sensitivity and may help predict response to targeted therapy in the clinical treatment of patients with these variants.

Structural basis for molecular interactions on the eukaryotic DNA sliding clamps PCNA and RAD9-RAD1-HUS1

DNA sliding clamps are widely conserved in all living organisms and play crucial roles in DNA replication and repair. Each DNA sliding clamp is a doughnut-shaped protein with a quaternary structure that encircles the DNA strand and recruits various factors involved in DNA replication and repair, thereby stimulating their biological functions. Eukaryotes have two types of DNA sliding clamp, proliferating cell nuclear antigen (PCNA) and RAD9-RAD1-HUS1 (9-1-1). The homo-trimer PCNA physically interacts with multiple proteins containing a PIP-box and/or APIM. The two motifs bind to PCNA by a similar mechanism; in addition, the bound PCNA structure is similar, implying a universality of PCNA interactions. In contrast to PCNA, 9-1-1 is a hetero-trimer composed of RAD9, RAD1, and HUS1 subunits. Although 9-1-1 forms a trimeric ring structure similar to PCNA, the C-terminal extension of the RAD9 is intrinsically unstructured. Based on the structural similarity between PCNA and 9-1-1, the mechanism underlying the interaction of 9-1-1 with its partners was thought to be analogous to that of PCNA. Unexpectedly, however, the recent structure of the 9-1-1 ring bound to a partner has revealed a novel interaction distinct from that of PCNA, potentially providing a new principle for molecular interactions on DNA sliding clamps.

A PARylation-phosphorylation cascade promotes TOPBP1 loading and RPA-RAD51 exchange in homologous recombination

The efficiency of homologous recombination (HR) in the repair of DNA double-strand breaks (DSBs) is closely associated with genome stability and tumor response to chemotherapy. While many factors have been functionally characterized in HR, such as TOPBP1, their precise regulation remains unclear. Here, we report that TOPBP1 interacts with the RNA-binding protein HTATSF1 in a cell-cycle- and phosphorylation-dependent manner. Mechanistically, CK2 phosphorylates HTATSF1 to facilitate binding to TOPBP1, which promotes S-phase-specific TOPBP1 recruitment to damaged chromatin and subsequent RPA/RAD51-dependent HR, genome integrity, and cancer-cell viability. The localization of HTATSF1-TOPBP1 to DSBs is potentially independent of the transcription-coupled RNA-binding and processing capacity of HTATSF1 but rather relies on the recognition of poly(ADP-ribosyl)ated RPA by HTATSF1, which can be blunted with PARP inhibitors. Together, our study provides a mechanistic insight into TOPBP1 loading at HR-prone DSB sites via HTATSF1 and reveals how RPA-RAD51 exchange is tuned by a PARylation-phosphorylation cascade.

The Mechanism of Long Non-coding RNA in Cancer Radioresistance/Radiosensitivity: A Systematic Review

Background and purpose: Radioresistance remains a significant challenge in tumor therapy. This systematic review aims to demonstrate the role of long non-coding RNA (lncRNA) in cancer radioresistance/radiosensitivity. Material and methods: The electronic databases Pubmed, Embase, and Google Scholar were searched from January 2000 to December 2021 to identify studies addressing the mechanisms of lncRNAs in tumor radioresistance/sensitivity, each of which required both in vivo and in vitro experiments. Results: Among the 87 studies identified, lncRNAs were implicated in tumor radioresistance/sensitivity mainly in three paradigms. 1) lncRNAs act on microRNA (miRNA) by means of a sponge, and their downstream signals include some specific molecular biological processes (DNA repair and chromosome stabilization, mRNA or protein stabilization, cell cycle and proliferation, apoptosis-related pathways, autophagy-related pathways, epithelial-mesenchymal transition (EMT), cellular energy metabolism) and some signaling mediators (transcription factors, kinases, some important signal transduction pathways) that regulate various biological processes. 2) lncRNAs directly interact with proteins, affecting the cell cycle and autophagy to contribute to tumor radioresistance. 3) lncRNAs act like transcription factors to initiate downstream signaling pathways and participate in tumor radioresistance. Conclusion: lncRNAs are important regulators involved in tumor radioresistance\sensitivity. Different lncRNAs may participate in the radioresistance with the same regulatory paradigm, and the same lncRNAs may also participate in the radioresistance in different ways. Future research should focus more on comprehensively characterizing the mechanisms of lncRNAs in tumor radioresistance to help us identify corresponding novel biomarkers and develop new lncRNA-based methods to improve radioresistance.

Disrupting PHF8-TOPBP1 connection elicits a breast tumor-specific vulnerability to chemotherapeutics

The DNA damage response (DDR) pathway generally protects against genome instability, and defects in DDR have been exploited therapeutically in cancer treatment. We have reported that histone demethylase PHF8 demethylates TOPBP1 K118 mono-methylation (K118me1) to drive the activation of ATR kinase, one of the master regulators of replication stress. However, whether dysregulation of this physiological signalling is involved in tumorigenesis remains unknown. Here, we showed PHF8-promoted TOPBP1 demethylation is clinically associated with breast tumorigenesis and patient survival. Mammary gland tumors from Phf8 knockout mice grow slowly and exhibit higher level of K118me1, lower ATR activity, and increased chromosomal instability. Importantly, we found that disruption of PHF8-TOPBP1 axis suppresses breast tumorigenesis and creates a breast tumor-specific vulnerability to PARP inhibitor (PARPi) and platinum drug. CRISPR/Cas9 mutation modelling of the deleted or truncated mutation of PHF8 in clinical tumor samples demonstrated breast tumor cells expressing the mimetic variants are more vulnerable to PARPi. Together, our study supports the pursuit of PHF8-TOPBP1 signalling pathway as promising avenues for targeted therapies of PHF8-TOPBP1 proficient tumors, and provides proof-of-concept evidence for loss-of-function of PHF8 as a therapeutic indicator of PARPis.

Multiple 9-1-1 complexes promote homolog synapsis, DSB repair, and ATR signaling during mammalian meiosis

DNA damage response mechanisms have meiotic roles that ensure successful gamete formation. While completion of meiotic double-strand break (DSB) repair requires the canonical RAD9A-RAD1-HUS1 (9A-1-1) complex, mammalian meiocytes also express RAD9A and HUS1 paralogs, RAD9B and HUS1B, predicted to form alternative 9-1-1 complexes. The RAD1 subunit is shared by all predicted 9-1-1 complexes and localizes to meiotic chromosomes even in the absence of HUS1 and RAD9A. Here, we report that testis-specific disruption of RAD1 in mice resulted in impaired DSB repair, germ cell depletion, and infertility. Unlike Hus1 or Rad9a disruption, Rad1 loss in meiocytes also caused severe defects in homolog synapsis, impaired phosphorylation of ATR targets such as H2AX, CHK1, and HORMAD2, and compromised meiotic sex chromosome inactivation. Together, these results establish critical roles for both canonical and alternative 9-1-1 complexes in meiotic ATR activation and successful prophase I completion.

INTS7-ABCD3 Interaction Stimulates the Proliferation and Osteoblastic Differentiation of Mouse Bone Marrow Mesenchymal Stem Cells by Suppressing Oxidative Stress

Increased adipocyte and decreased osteoblast differentiation, combined with the ectopic proliferation of bone marrow mesenchymal stem cells (BM-MSCs), represent the primary causes of osteoporosis. The dysregulation of numerous intracellular bioactive factors is responsible for the aberrant differentiation and growth of BM-MSCs. In this study, we focused on a new stimulative factor, integrator complex subunit 7 (INTS7), and its cooperative protein ATP-binding cassette subfamily D member 3 (ABCD3)/high-density lipoprotein-binding protein (HDLBP) in mouse BM-MSCs. We aimed to uncover the effects of the INTS7–ABCD3/HDLBP interaction on BM-MSC biological behaviors and the potential mechanism underlying these effects. Functional in vitro experiments showed that the suppression of the INTS7–ABCD3 interaction rather than HDLBP could impair BM-MSC proliferation and induce cell apoptosis. Moreover, Alizarin Red S and Oil Red O staining, respectively, revealed that INTS7 and ABCD3 knockdown but not HDLBP knockdown could decrease osteoblastic differentiation and accelerate the adipogenic differentiation of BM-MSCs. Mechanistically, reactive oxygen species (ROS) and histone γ-H2AX quantities significantly increased, whereas the levels of antioxidants declined due to INTS7 and ABCD3 inhibition in BM-MSCs. These findings indicated that the suppression of oxidative stress could be involved in the INTS7/ABCD3 co-regulatory mechanisms for BM-MSC proliferation and differentiation, identifying new potential candidates for osteoporosis therapy.

Phosphorylation-dependent assembly of DNA damage response systems and the central roles of TOPBP1

The cellular response to DNA damage (DDR) that causes replication collapse and/or DNA double strand breaks, is characterised by a massive change in the post-translational modifications (PTM) of hundreds of proteins involved in the detection and repair of DNA damage, and the communication of the state of damage to the cellular systems that regulate replication and cell division. A substantial proportion of these PTMs involve targeted phosphorylation, which among other effects, promotes the formation of multiprotein complexes through the specific binding of phosphorylated motifs on one protein, by specialised domains on other proteins. Understanding the nature of these phosphorylation mediated interactions allows definition of the pathways and networks that coordinate the DDR, and helps identify new targets for therapeutic intervention that may be of benefit in the treatment of cancer, where DDR plays a key role. In this review we summarise the present understanding of how phosphorylated motifs are recognised by BRCT domains, which occur in many DDR proteins. We particularly focus on TOPBP1 - a multi-BRCT domain scaffold protein with essential roles in replication and the repair and signalling of DNA damage.

An Eye in the Replication Stress Response: Lessons From Tissue-Specific Studies in vivo

Several inherited human syndromes that severely affect organogenesis and other developmental processes are caused by mutations in replication stress response (RSR) genes. Although the molecular machinery of RSR is conserved, disease-causing mutations in RSR-genes may have distinct tissue-specific outcomes, indicating that progenitor cells may differ in their responses to RSR inactivation. Therefore, understanding how different cell types respond to replication stress is crucial to uncover the mechanisms of RSR-related human syndromes. Here, we review the ocular manifestations in RSR-related human syndromes and summarize recent findings investigating the mechanisms of RSR during eye development in vivo. We highlight a remarkable heterogeneity of progenitor cells responses to RSR inactivation and discuss its implications for RSR-related human syndromes.

hMOB2 deficiency impairs homologous recombination-mediated DNA repair and sensitises cancer cells to PARP inhibitors

Monopolar spindle-one binder (MOBs) proteins are evolutionarily conserved and contribute to various cellular signalling pathways. Recently, we reported that hMOB2 functions in preventing the accumulation of endogenous DNA damage and a subsequent p53/p21-dependent G1/S cell cycle arrest in untransformed cells. However, the question of how hMOB2 protects cells from endogenous DNA damage accumulation remained enigmatic. Here, we uncover hMOB2 as a regulator of double-strand break (DSB) repair by homologous recombination (HR). hMOB2 supports the phosphorylation and accumulation of the RAD51 recombinase on resected single-strand DNA (ssDNA) overhangs. Physiologically, hMOB2 expression supports cancer cell survival in response to DSB-inducing anti-cancer compounds. Specifically, loss of hMOB2 renders ovarian and other cancer cells more vulnerable to FDA-approved PARP inhibitors. Reduced MOB2 expression correlates with increased overall survival in patients suffering from ovarian carcinoma. Taken together, our findings suggest that hMOB2 expression may serve as a candidate stratification biomarker of patients for HR-deficiency targeted cancer therapies, such as PARP inhibitor treatments.

A basal-level activity of ATR links replication fork surveillance and stress response

Mammalian cells use diverse pathways to prevent deleterious consequences during DNA replication, yet the mechanism by which cells survey individual replisomes to detect spontaneous replication impediments at the basal level, and their accumulation during replication stress, remain undefined. Here, we used single-molecule localization microscopy coupled with high-order-correlation image-mining algorithms to quantify the composition of individual replisomes in single cells during unperturbed replication and under replicative stress. We identified a basal-level activity of ATR that monitors and regulates the amounts of RPA at forks during normal replication. Replication-stress amplifies the basal activity through the increased volume of ATR-RPA interaction and diffusion-driven enrichment of ATR at forks. This localized crowding of ATR enhances its collision probability, stimulating the activation of its replication-stress response. Finally, we provide a computational model describing how the basal activity of ATR is amplified to produce its canonical replication stress response.

Crystal structure of the INTS3/INTS6 complex reveals the functional importance of INTS3 dimerization in DSB repair

SOSS1 is a single-stranded DNA (ssDNA)-binding protein complex that plays a critical role in double-strand DNA break (DSB) repair. SOSS1 consists of three subunits: INTS3, SOSSC, and hSSB1, with INTS3 serving as a scaffold to stabilize this complex. Moreover, the integrator complex subunit 6 (INTS6) participates in the DNA damage response through direct binding to INTS3, but how INTS3 interacts with INTS6, thereby impacting DSB repair, is not clear. Here, we determined the crystal structure of the C-terminus of INTS3 (INTS3c) in complex with the C-terminus of INTS6 (INTS6c) at a resolution of 2.4 Å. Structural analysis revealed that two INTS3c subunits dimerize and interact with INTS6c via conserved residues. Subsequent biochemical analyses confirmed that INTS3c forms a stable dimer and INTS3 dimerization is important for recognizing the longer ssDNA. Perturbation of INTS3c dimerization and disruption of the INTS3c/INTS6c interaction impair the DSB repair process. Altogether, these results unravel the underappreciated role of INTS3 dimerization and the molecular basis of INTS3/INTS6 interaction in DSB repair.

CIP2A Interacts with TopBP1 and Drives Basal-Like Breast Cancer Tumorigenesis

Basal-like breast cancers (BLBC) are characterized by defects in homologous recombination (HR), deficient mitotic checkpoint, and high-proliferation activity. Here, we discover CIP2A as a candidate driver of BLBC. CIP2A was essential for DNA damage-induced initiation of mouse BLBC-like mammary tumors and for survival of HR-defective BLBC cells. CIP2A was dispensable for normal mammary gland development and for unperturbed mitosis, but selectively essential for mitotic progression of DNA damaged cells. A direct interaction between CIP2A and a DNA repair scaffold protein TopBP1 was identified, and CIP2A inhibition resulted in enhanced DNA damage-induced TopBP1 and RAD51 recruitment to chromatin in mammary epithelial cells. In addition to its role in tumor initiation, and survival of BRCA-deficient cells, CIP2A also drove proliferative MYC and E2F1 signaling in basal-like triple-negative breast cancer (BL-TNBC) cells. Clinically, high CIP2A expression was associated with poor patient prognosis in BL-TNBCs but not in other breast cancer subtypes. Small-molecule reactivators of PP2A (SMAP) inhibited CIP2A transcription, phenocopied the CIP2A-deficient DNA damage response (DDR), and inhibited growth of patient-derived BLBC xenograft. In summary, these results demonstrate that CIP2A directly interacts with TopBP1 and coordinates DNA damage-induced mitotic checkpoint and proliferation, thereby driving BLBC initiation and progression. SMAPs could serve as a surrogate therapeutic strategy to inhibit the oncogenic activity of CIP2A in BLBCs. SIGNIFICANCE: These results identify CIP2A as a nongenetic driver and therapeutic target in basal-like breast cancer that regulates DNA damage-induced G₂-M checkpoint and proliferative signaling.

PHF8-promoted TOPBP1 demethylation drives ATR activation and preserves genome stability

The checkpoint kinase ATR [ATM (ataxia-telangiectasia mutated) and rad3-related] is a master regulator of DNA damage response. Yet, how ATR activity is regulated remains to be investigated. We report here that histone demethylase PHF8 (plant homeodomain finger protein 8) plays a key role in ATR activation and replication stress response. Mechanistically, PHF8 interacts with and demethylates TOPBP1 (DNA topoisomerase 2-binding protein 1), an essential allosteric activator of ATR, under unperturbed conditions, but replication stress results in PHF8 phosphorylation and dissociation from TOPBP1. Consequently, hypomethylated TOPBP1 facilitates RAD9 (RADiation sensitive 9) binding and chromatin loading of the TOPBP1-RAD9 complex to fully activate ATR and thus safeguard the genome and protect cells against replication stress. Our study uncovers a demethylation and phosphorylation code that controls the assembly of TOPBP1-scaffolded protein complex, and provides molecular insight into non-histone methylation switch in ATR activation.

Co-regulation and function of FOXM1/RHNO1 bidirectional genes in cancer

The FOXM1 transcription factor is an oncoprotein and a top biomarker of poor prognosis in human cancer. Overexpression and activation of FOXM1 is frequent in high-grade serous carcinoma (HGSC), the most common and lethal form of human ovarian cancer, and is linked to copy number gains at chromosome 12p13.33. We show that FOXM1 is co-amplified and co-expressed with RHNO1, a gene involved in the ATR-Chk1 signaling pathway that functions in the DNA replication stress response. We demonstrate that FOXM1 and RHNO1 are head-to-head (i.e., bidirectional) genes (BDG) regulated by a bidirectional promoter (BDP) (named F/R-BDP). FOXM1 and RHNO1 each promote oncogenic phenotypes in HGSC cells, including clonogenic growth, DNA homologous recombination repair, and poly-ADP ribosylase inhibitor resistance. FOXM1 and RHNO1 are one of the first examples of oncogenic BDG, and therapeutic targeting of FOXM1/RHNO1 BDG is a potential therapeutic approach for ovarian and other cancers.

STING enhances cell death through regulation of reactive oxygen species and DNA damage

Resistance to DNA-damaging agents is a significant cause of treatment failure and poor outcomes in oncology. To identify unrecognized regulators of cell survival we performed a whole-genome CRISPR-Cas9 screen using treatment with ionizing radiation as a selective pressure, and identified STING (stimulator of interferon genes) as an intrinsic regulator of tumor cell survival. We show that STING regulates a transcriptional program that controls the generation of reactive oxygen species (ROS), and that STING loss alters ROS homeostasis to reduce DNA damage and to cause therapeutic resistance. In agreement with these data, analysis of tumors from head and neck squamous cell carcinoma patient specimens show that low STING expression is associated with worse outcomes. We also demonstrate that pharmacologic activation of STING enhances the effects of ionizing radiation in vivo, providing a rationale for therapeutic combinations of STING agonists and DNA-damaging agents. These results highlight a role for STING that is beyond its canonical function in cyclic dinucleotide and DNA damage sensing, and identify STING as a regulator of cellular ROS homeostasis and tumor cell susceptibility to reactive oxygen dependent, DNA damaging agents.

A Link between Replicative Stress, Lamin Proteins, and Inflammation

Double-stranded breaks (DSB), the most toxic DNA lesions, are either a consequence of cellular metabolism, programmed as in during V(D)J recombination, or induced by anti-tumoral therapies or accidental genotoxic exposure. One origin of DSB sources is replicative stress, a major source of genome instability, especially when the integrity of the replication forks is not properly guaranteed. To complete stalled replication, restarting the fork requires complex molecular mechanisms, such as protection, remodeling, and processing. Recently, a link has been made between DNA damage accumulation and inflammation. Indeed, defects in DNA repair or in replication can lead to the release of DNA fragments in the cytosol. The recognition of this self-DNA by DNA sensors leads to the production of inflammatory factors. This beneficial response activating an innate immune response and destruction of cells bearing DNA damage may be considered as a novel part of DNA damage response. However, upon accumulation of DNA damage, a chronic inflammatory cellular microenvironment may lead to inflammatory pathologies, aging, and progression of tumor cells. Progress in understanding the molecular mechanisms of DNA damage repair, replication stress, and cytosolic DNA production would allow to propose new therapeutical strategies against cancer or inflammatory diseases associated with aging. In this review, we describe the mechanisms involved in DSB repair, the replicative stress management, and its consequences. We also focus on new emerging links between key components of the nuclear envelope, the lamins, and DNA repair, management of replicative stress, and inflammation.

Phosphoproteomics reveals novel modes of function and inter-relationships among PIKKs in response to genotoxic stress

The DNA damage response (DDR) is a complex signaling network that relies on cascades of protein phosphorylation, which are initiated by three protein kinases of the family of PI3-kinase-related protein kinases (PIKKs): ATM, ATR, and DNA-PK. ATM is missing or inactivated in the genome instability syndrome, ataxia-telangiectasia (A-T). The relative shares of these PIKKs in the response to genotoxic stress and the functional relationships among them are central questions in the genome stability field. We conducted a comprehensive phosphoproteomic analysis in human wild-type and A-T cells treated with the double-strand break-inducing chemical, neocarzinostatin, and validated the results with the targeted proteomic technique, selected reaction monitoring. We also matched our results with 34 published screens for DDR factors, creating a valuable resource for identifying strong candidates for novel DDR players. We uncovered fine-tuned dynamics between the PIKKs following genotoxic stress, such as DNA-PK-dependent attenuation of ATM. In A-T cells, partial compensation for ATM absence was provided by ATR and DNA-PK, with distinct roles and kinetics. The results highlight intricate relationships between these PIKKs in the DDR.

Signaling pathways involved in cell cycle arrest during the DNA breaks

Our genome bears tens of thousands of harms and devastations per day; In this regard, numerous sophisticated and complicated mechanisms are embedded by our cells in furtherance of remitting an unchanged and stable genome to their next generation. These mechanisms, that are collectively called DDR, have the duty of detecting the lesions and repairing them. it's necessary for the viability of any living cell that sustain the integrity and stability of its genetic content and this highlights the role of mediators that transduce the signals of DNA damage to the cell cycle in order to prevent the replication of a defective DNA. In this paper, we review the signaling pathways that lie between these processes and define how different ingredients of DDR are also able to affect the checkpoint signaling.

Regulation of DNA break repair by RNA

Genomic stability is critical for cell survival and its effective repair when damaged is a vital process for preserving genetic information. Failure to correctly repair the genome can lead to the accumulation of mutations that ultimately drives carcinogenesis. Life has evolved sophisticated surveillance, repair pathways, and mechanisms to recognize and mend genomic lesions to preserve its integrity. Many of these pathways involve a cascade of protein effectors that act to identify the type of damage, such as double-strand (ds) DNA breaks, propagate the damage signal, and recruit an array of other protein factors to resolve the damage without loss of genetic information. It is now becoming increasingly clear that there are a number of RNA processing factors, such as the transcriptional machinery, and microRNA biogenesis components, as well as RNA itself, that facilitate the repair of DNA damage. Here, some of the recent work unravelling the role of RNA in the DNA Damage Response (DDR), in particular the dsDNA break repair pathway, will be reviewed.

The circadian clock and inflammation: A new insight

The circadian clock is a complex cellular mechanism that controls a series of physiological processes, including inflammation. It can directly interact physically with the components of the key inflammatory pathway. Similarly, inflammation can also lead to circadian rhythm disorders, which may further amplify the inflammatory response and aggravate tissue damage. This review offers a structured overview that focusses on the core proteins of the circadian clock and their interactions with inflammatory players, and provides a potential mechanism for the pathological rhythms observed under inflammatory conditions.

PALB2 Variants: Protein Domains and Cancer Susceptibility

Since its discovery, partner and localizer of breast cancer 2 (BRCA2) (PALB2) has emerged as a major tumor suppressor gene linked to breast cancer (BC), pancreatic cancer (PC), and ovarian cancer (OC) susceptibility. Its protein product plays a pivotal role in the maintenance of genome integrity. Here we discuss the first functional evaluation of a large set of PALB2 missense variants of uncertain significance (VUSs). Assessment of 136 VUSs interrogating a range of PALB2 biological functions resulted in the identification of 15 variants with consistent loss of function across different assays. All loss-of-function variants are located at the PALB2 coiled coil (CC) or at the WD40 domain, highlighting the importance of modular domains mechanistically involved in the DNA damage response (DDR) and pinpointing their roles in tumor suppression.

Biochemical analysis of TOPBP1 oligomerization

TOPBP1 is an important scaffold protein that helps orchestrate the cellular response to DNA damage. Although it has been previously appreciated that TOPBP1 can form oligomers, how this occurs and the functional consequences for oligomerization were not yet known. Here, we use protein binding assays and other biochemical techniques to study how TOPBP1 self associates. TOPBP1 contains 9 copies of the BRCT domain, and we report that a subset of these BRCT domains interact with one another to drive oligomerization. An intact BRCT 2 domain is required for TOPBP1 oligomerization and we find that the BRCT1&2 region of TOPBP1 interacts with itself and with the BRCT4&5 pair. RAD9 and RHINO are two heterologous binding partners for TOPBP1's BRCT 1&2 domains, and we show that binding of these partners does not come at the expense of TOPBP1 oligomerization. Furthermore, we show that a TOPBP1 oligomer can simultaneously interact with both RAD9 and RHINO. Lastly, we find that the oligomeric state necessary for TOPBP1 to activate the ATR protein kinase is likely to be a tetramer.

Functional Characterization of PALB2 Variants of Uncertain Significance: Toward Cancer Risk and Therapy Response Prediction

In recent years it has become clear that pathogenic variants in PALB2 are associated with a high risk for breast, ovarian and pancreatic cancer. However, the clinical relevance of variants of uncertain significance (VUS) in PALB2, which are increasingly identified through clinical genetic testing, is unclear. Here we review recent advances in the functional characterization of VUS in PALB2. A combination of assays has been used to assess the impact of PALB2 VUS on its function in DNA repair by homologous recombination, cell cycle regulation and the control of cellular levels of reactive oxygen species (ROS). We discuss the outcome of this comprehensive analysis of PALB2 VUS, which showed that VUS in PALB2’s Coiled-Coil (CC) domain can impair the interaction with BRCA1, whereas VUS in its WD40 domain affect PALB2 protein stability. Accordingly, the CC and WD40 domains of PALB2 represent hotspots for variants that impair PALB2 protein function. We also provide a future perspective on the high-throughput analysis of VUS in PALB2, as well as the functional characterization of variants that affect PALB2 RNA splicing. Finally, we discuss how results from these functional assays can be valuable for predicting cancer risk and responsiveness to cancer therapy, such as treatment with PARP inhibitor- or platinum-based chemotherapy.