Proapoptotic Bid mediates the Atr-directed DNA damage response to replicative stress

Highly expressed of BID indicates poor prognosis and mediates different tumor microenvironment characteristics in clear cell renal cell carcinoma

BACKGROUND

Studies have found that BH3 interacting domain death agonist (BID) is closely related to the occurrence and development of many kinds of tumors. However, little attention has been paid to the situation of BID in clear cell renal cell carcinoma (ccRCC). So, our aim was to explore the effect of BID in ccRCC.

METHODS

Survival analysis, ROC curve, correlation analysis and Cox regression analysis were executed to analyze the prognostic value and clinical correlation of BID in ccRCC. The risk prognosis model was constructed in the training cohort and further validated in the internal testing cohort, ICGC cohort, and GEO cohort. Transcriptome sequencing and immunohistochemical staining of clinical specimens were used to validate the results of bioinformatics analysis. The GSEA, ESTIMATE algorithm, CIBERSORT algorithm, ssGSEA, TIDE score, correlation and difference analysis were used to analyze the effects of BID on immune infiltration in tumor microenvironment (TME).

RESULTS

BID was highly expressed in ccRCC tissues, which was verified by transcriptome sequencing and immunohistochemical staining of clinical specimens. Patients with high expression of BID had a worse prognosis. BID is an independent prognostic factor for ccRCC. The prognostic model based on BID can accurately predict the prognosis of patients in different cohorts. In addition, the expression levels of BID was closely related to immunomodulatory molecules such as PD-1, LAG3, and CTLA4. Enrichment analysis indicated that BID was significantly enriched in immune-related responses and cancer-related pathways. The change of BID expression mediates different characteristics of immune infiltration in TME.

CONCLUSIONS

BID is highly expressed in ccRCC, which is a reliable biomarker of ccRCC prognosis. It is closely related to TME, and may be a potential target for immunotherapy in patients with ccRCC.

Replication stress response defects are associated with response to immune checkpoint blockade in nonhypermutated cancers

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Control of replication stress and mitosis in colorectal cancer stem cells through the interplay of PARP1, MRE11 and RAD51

Cancer stem cells (CSCs) are tumor subpopulations driving disease development, progression, relapse and therapy resistance, and their targeting ensures tumor eradication. CSCs display heterogeneous replication stress (RS), but the functionality/relevance of the RS response (RSR) centered on the ATR-CHK1 axis is debated. Here, we show that the RSR is efficient in primary CSCs from colorectal cancer (CRC-SCs), and describe unique roles for PARP1 and MRE11/RAD51. First, we demonstrated that PARP1 is upregulated in CRC-SCs resistant to several replication poisons and RSR inhibitors (RSRi). In these cells, PARP1 modulates replication fork speed resulting in low constitutive RS. Second, we showed that MRE11 and RAD51 cooperate in the genoprotection and mitosis execution of PARP1-upregulated CRC-SCs. These roles represent therapeutic vulnerabilities for CSCs. Indeed, PARP1i sensitized CRC-SCs to ATRi/CHK1i, inducing replication catastrophe, and prevented the development of resistance to CHK1i. Also, MRE11i + RAD51i selectively killed PARP1-upregulated CRC-SCs via mitotic catastrophe. These results provide the rationale for biomarker-driven clinical trials in CRC using distinct RSRi combinations.

Defective Replication Stress Response Is Inherently Linked to the Cancer Stem Cell Phenotype

Extensive spontaneous DNA damage from oncogene-induced replication stress is ubiquitous in precancerous lesions. While this damage induces differentiation, senescence, or apoptosis in normal cells, defects in DNA replication stress response (RSR) allow cells to continue proliferating, ultimately leading to early tumorigenesis. Using systems-level approaches, we developed a replication stress response defect gene signature that predicted risk of cancer development from hyperplastic lesions. Intriguingly, we found that replication stress response defects rewire non-malignant cells into a cancer stem cell (CSC)-like state, and analysis of CSCs indicated that they inherently harbor replication stress response defects. High-throughput drug screening to elucidate molecules required for survival of replication stress response defective cells identified a dependence on MEK/ERK signaling. Inhibition of this signaling cascade restored oncogene-induced senescence through a p53-independent MDM2/p21 axis. Moreover, MEK/ERK inhibition also depleted CSC populations. Together, these findings provide insights into the role of replication stress response defects in CSCs and an actionable pathway for therapeutic targeting.

A Gene Signature of Survival Prediction for Kidney Renal Cell Carcinoma by Multi-Omic Data Analysis

Kidney renal cell carcinoma (KIRC), which is the most common subtype of kidney cancer, has a poor prognosis and a high mortality rate. In this study, a multi-omics analysis is performed to build a multi-gene prognosis signature for KIRC. A combination of a DNA methylation analysis and a gene expression data analysis revealed 863 methylated differentially expressed genes (MDEGs). Seven MDEGs (BID, CCNF, DLX4, FAM72D, PYCR1, RUNX1, and TRIP13) were further screened using LASSO Cox regression and integrated into a prognostic risk score model. Then, KIRC patients were divided into high- and low-risk groups. A univariate cox regression analysis revealed a significant association between the high-risk group and a poor prognosis. The time-dependent receiver operating characteristic (ROC) curve shows that the risk group performs well in predicting overall survival. Furthermore, the risk group is contained in the best multivariate model that was obtained by a multivariate stepwise analysis, which further confirms that the risk group can be used as a potential prognostic biomarker. In addition, a nomogram was established for the best multivariate model and shown to perform well in predicting the survival of KIRC patients. In summary, a seven-MDEG signature is a powerful prognosis factor for KIRC patients and may provide useful suggestions for their personalized therapy.

Bid maintains mitochondrial cristae structure and function and protects against cardiac disease in an integrative genomics study

Bcl-2 family proteins reorganize mitochondrial membranes during apoptosis, to form pores and rearrange cristae. In vitro and in vivo analysis integrated with human genetics reveals a novel homeostatic mitochondrial function for Bcl-2 family protein Bid. Loss of full-length Bid results in apoptosis-independent, irregular cristae with decreased respiration. Bid-/- mice display stress-induced myocardial dysfunction and damage. A gene-based approach applied to a biobank, validated in two independent GWAS studies, reveals that decreased genetically determined BID expression associates with myocardial infarction (MI) susceptibility. Patients in the bottom 5% of the expression distribution exhibit >4 fold increased MI risk. Carrier status with nonsynonymous variation in Bid’s membrane binding domain, Bid^M148T, associates with MI predisposition. Furthermore, Bid but not Bid^M148T associates with Mcl-1^Matrix, previously implicated in cristae stability; decreased MCL-1 expression associates with MI. Our results identify a role for Bid in homeostatic mitochondrial cristae reorganization, that we link to human cardiac disease.

Cells contain specialized structures called mitochondria, which help to convert fuel into energy. These tiny energy factories have a unique double membrane, with a smooth outer and a folded inner lining. The folds, called cristae, provide a scaffold for the molecular machinery that produces chemical energy that the cell can use. The cristae are dynamic, and can change shape, condensing to increase energy output.

Mitochondria also play a role in cell death. In certain situations, cristae can widen and release the proteins held within their folds. This can trigger a program of self-destruction in the cell. A family of proteins called Bcl-2 control such a ‘programmed cell death’ through the release of mitochondrial proteins. Some family members, including a protein called Bid, can reorganize cristae to regulate this cell-death program. When cells die, Bid proteins that had been split move to the mitochondria. But, even when cells are healthy, Bid molecules that are intact are always there, suggesting that this form of the protein may have another purpose.

To investigate this further, Salisbury-Ruf, Bertram et al. used mice with Bid, and mice that lacked the protein. Without Bid, cells – including heart cells – struggled to work properly and used less oxygen than their normal counterparts. A closer look using electron microscopy revealed abnormalities in the cristae. However, adding ‘intact’ Bid proteins back in to the deficient cells restored them to normal.

Moreover, without Bid, the mice hearts were less able to respond to an increased demand for energy. This decreased their performance and caused the formation of scars in the heart muscle called fibrosis, similar to a pattern observed in human patients following a heart attack.

DNA data from an electronic health record database revealed a link between low levels of Bid genes and heart attack in humans, which was confirmed in further studies. In addition, a specific mutation in the Bid gene was found to affect its ability to regulate the formation of proper cristae.

Combining evidence from mice with human genetics revealed new information about heart diseases. Mitochondrial health may be affected by a combination of specific variations in genes and changes in the Bid protein, which could affect heart attack risk. Understanding more about this association could help to identify and potentially reduce certain risk factors for heart attack.

Replication stress in hematopoietic stem cells in mouse and man

Life-long blood regeneration relies on a rare population of self-renewing hematopoietic stem cells (HSCs). These cells' nearly unlimited self-renewal potential and lifetime persistence in the body signifies the need for tight control of their genome integrity. Their quiescent state, tightly linked with low metabolic activity, is one of the main strategies employed by HSCs to preserve an intact genome. On the other hand, HSCs need to be able to quickly respond to increased blood demands and rapidly increase their cellular output in order to fight infection-associated inflammation or extensive blood loss. This increase in proliferation rate, however, comes at the price of exposing HSCs to DNA damage inevitably associated with the process of DNA replication. Any interference with normal replication fork progression leads to a specialized molecular response termed replication stress (RS). Importantly, increased levels of RS are a hallmark feature of aged HSCs, where an accumulating body of evidence points to causative relationships between RS and the aging-associated impairment of the blood system's functional capacity. In this review, we present an overview of RS in HSCs focusing on its causes and consequences for the blood system of mice and men.

Non-apoptotic functions of BCL-2 family proteins

The BCL-2 family proteins are major regulators of the apoptosis process, but the mechanisms by which they regulate this process are only partially understood. It is now well documented that these proteins play additional non-apoptotic roles that are likely to be related to their apoptotic roles and to provide important clues to cracking their mechanisms of action. It seems that these non-apoptotic roles are largely related to the activation of cellular survival pathways designated to maintain or regain cellular survival, but, if unsuccessful, will switch over into a pro-apoptotic mode. These non-apoptotic roles span a wide range of processes that include the regulation of mitochondrial physiology (metabolism, electron transport chain, morphology, permeability transition), endoplasmic reticulum physiology (calcium homeostasis, unfolded protein response (UPR)), nuclear processes (cell cycle, DNA damage response (DDR)), whole-cell metabolism (glucose and lipid), and autophagy. Here we review all these different non-apoptotic roles, make an attempt to link them to the apoptotic roles, and present many open questions for future research directions in this fascinating field.

Bcl-2 family proteins: master regulators of cell survival

The most prominent function of proteins of the Bcl-2 family is regulation of the initiation of intrinsic (mitochondrial) pathways of apoptosis. However, recent research has revealed that in addition to regulation of mitochondrial apoptosis, proteins of the Bcl-2 family play important roles in regulating other cellular pathways with a strong impact on cell survival like autophagy, endoplasmic reticulum (ER) stress response, intracellular calcium dynamics, cell cycle progression, mitochondrial dynamics and energy metabolism. This review summarizes the recent knowledge about functions of Bcl-2 family proteins that are related to cell survival.

BH3-Only Proteins in Health and Disease

BH3-only proteins are proapoptotic members of the broader Bcl-2 family, which promote cell death by directly or indirectly activating Bax and Bak. The expression of BH3-only proteins is regulated both transcriptionally and posttranscriptionally in a cell type-specific and a tissue-specific manner. Research over the last 20 years has provided significant insights into their roles in tissue homeostasis and various pathologies, which in turn has led to the development of novel therapeutics for numerous diseases. In this review, a snapshot of the progress over this period is given, including our current understanding of their regulation, mode of action, role in mammalian development, and pathology.

Synergy of BID with doxorubicin in the killing of cancer cells

Overexpression of the BH3-interacting domain death agonist (BID) protein sensitizes certain cancer cell lines to apoptosis induced by anticancer agents, particularly by those acting through death receptors (e.g. TRAIL). Previously, we showed that recombinant BID fused with TAT cell penetrating peptide (TAT-BID) allowed for controlled delivery of BID to different cancer cell lines and moderately sensitized some of them to TRAIL or slightly to camptothecin. In the present study, we showed that TAT-BID delivered to HeLa cells strongly sensitized them to doxorubicin, as identified by cell viability and apoptosis assays. Another cell line sensitized to doxorubicin was PC3, whereas A549 and LNCaP cells were sensitized moderately or not at all, respectively. Sensitization was more pronounced at 1 μM doxorubicin administered for 48 h than for lower doses and shorter treatments. TAT-BID and doxorubicin may thus be considered as a potential therapeutic combination for cervical carcinoma and advanced prostate cancer treatment.

BH3-only proteins: a 20-year stock-take

BH3-only proteins are the sentinels of cellular stress, and their activation commits cells to apoptosis. Since the discovery of the first BH3-only protein BAD almost 20 years ago, at least seven more BH3-only proteins have been identified in mammals. They are regulated by a variety of environmental stimuli or by developmental cues, and play a crucial role in cellular homeostasis. Some are considered to be tumor suppressors, and also play a significant role in other pathologies. Their non-apoptotic functions are controversial, but there is broad consensus emerging regarding their role in apoptosis, which may help in designing better therapeutic agents for treating a variety of human diseases.

Controlled delivery of BID protein fused with TAT peptide sensitizes cancer cells to apoptosis

BACKGROUND

Low cellular level of BID is critical for viability of numerous cancer cells. Sensitization of cells to anticancer agents by BID overexpression from adenovirus or pcDNA vectors is a proposed strategy for cancer therapy; however it does not provide any stringent control of cellular level of BID. The aim of this work was to examine whether a fusion of BID with TAT cell penetrating peptide (TAT-BID) may be used for controlled sensitization of cancer cells to anticancer agents acting through death receptors (TRAIL) or DNA damage (camptothecin). Prostate cancer PC3 and LNCaP, non-small human lung cancer A549, and cervix carcinoma HeLa cells were used in the study.

METHODS

Uptake of TAT-BID protein by cells was studied by quantitative Western blot analysis of cells extracts. Cells viability was monitored by MTT test. Apoptosis was detected by flow cytometry and cytochrome c release assay.

RESULTS

TAT-BID was delivered to all cancer cells in amounts depending on time, dose and the cell line. Recombinant BID sensitized PC3 cells to TRAIL or, to lesser extent, to camptothecin. Out of remaining cells, TAT-BID sensitized A549, and only slightly HeLa cells to TRAIL. None of the latter cell lines were sensitized to camptothecin. In all cases the mutant not phosphorylable by CK2 (TAT-BIDT59AS76A) was similarly efficient in sensitization as the wild type TAT-BID.

CONCLUSIONS

TAT-BID may be delivered to cancer cells in controlled manner and efficiently sensitizes PC3 and A549 cells to TRAIL. Therefore, it may be considered as a potential therapeutic agent that enhances the efficacy of TRAIL for the treatment of prostate and non-small human lung cancer.

Gli1 protein regulates the S-phase checkpoint in tumor cells via Bid protein, and its inhibition sensitizes to DNA topoisomerase 1 inhibitors

Aberrant expression of hedgehog molecules, particularly Gli1, is common in cancers of many tissues and is responsible for their aggressive behavior and chemoresistance. Here we demonstrate a novel and tumor-specific role for aberrant Gli1 in the regulation of the S-phase checkpoint that suppresses replication stress and resistance to chemotherapy. Inhibition of Gli1 in tumor cells induced replication stress-mediated DNA damage response, attenuated their clonogenic potential, abrogated camptothecin (CPT)-induced Chk1 phosphorylation, and potentiated its cytotoxicity. However, in normal fibroblasts, Gli1 siRNAs showed no significant changes in CPT-induced Chk1 phosphorylation. Further analysis of ataxia telangiectasia and Rad3-related protein (ATR)/Chk1 signaling cascade genes in tumor cells revealed an unexpected mechanism whereby Gli1 regulates ATR-mediated Chk1 phosphorylation by transcriptional regulation of the BH3-only protein Bid. Consistent with its role in DNA damage response, Bid down-regulation in tumor cells abolished CPT-induced Chk1 phosphorylation and sensitized them to CPT. Correspondingly, Gli1 inhibition affected the expression of Bid and the association of replication protein A (RPA) with the ATR- interacting protein (ATRIP)-ATR complex, and this compromised the S-phase checkpoint. Conversely, complementation of Bid in Gli1-deficient cells restored CPT-induced Chk1 phosphorylation. An in silico analysis of the Bid promoter identified a putative Gli1 binding site, and further studies using luciferase reporter assays confirmed Gli1-dependent promoter activity. Collectively, our studies established a novel connection between aberrant Gli1 and Bid in the survival of tumor cells and their response to chemotherapy, at least in part, by regulating the S-phase checkpoint. Importantly, our data suggest a novel drug combination of Gli1 and Top1 inhibitors as an effective therapeutic strategy in treating tumors that expresses Gli1.

N-benzyl-N-methyldecan-1-amine, a phenylamine derivative isolated from garlic cloves, induces G2/M phase arrest and apoptosis in U937 human leukemia cells

Epidemiological studies indicate that components of garlic (Allium sativum) have anti-proliferative effects against various types of cancer. In the present study, we investigated the effect of newly isolated phenylamine derivative N-benzyl-N-methyldecan-1-amine (NBNMA) from garlic cloves on the inhibition of the growth and apoptosis of human leukemia U937 cells and its potential anticancer mechanism. NBNMA exhibited an antiproliferative effect in U937 cells by inducing cell cycle arrest at the G2/M phase and apoptotic cell death. Western blot analyses revealed that NBNMA decreased the expression of the regulator genes of G2/M phase progression, cyclin dependent kinase (Cdk) 2 and Cdc2 and elevated the expression of the Cdk inhibitor p21WAF1/CIP1 in a p53-independent manner. In addition, NBNMA activated caspase-8 and caspase-9, initiator caspases of the extrinsic and intrinsic pathways of apoptosis, respectively, which led to activation of executioner caspase-3 along with degradation of poly(ADP-ribose) polymerase. NBNMA-induced apoptosis was observed in parallel with an increased ratio of pro-apoptotic Bax and Bad/anti-apoptotic Bcl-2 and Bcl-xL, and inhibition of inhibitor of apoptosis protein (IAP) family members XIAP and cIAP-1. Furthermore, NBNMA-treated cells displayed enhanced release of cytochrome c from the mitochondria into the cytosol concomitant with a loss of mitochondrial membrane potential and downregulation of Bid, suggesting that NBNMA-induced apoptosis occurred via the extrinsic and intrinsic apoptotic pathways with a possible link to Bid protein activity between the two pathways. These results indicate that NBNMA has promising potential to become a novel anticancer agent for the treatment of leukemia. We provide new insight into the mechanisms underlying the anticancer effect of NBNMA.

The loss of the BH3-only Bcl-2 family member Bid delays T-cell leukemogenesis in Atm-/- mice

Multicellular organisms maintain genomic integrity and resist tumorigenesis through a tightly regulated DNA damage response (DDR) that prevents propagation of deleterious mutations either through DNA repair or programmed cell death. An impaired DDR leads to tumorigenesis that is accelerated when programmed cell death is prevented. Loss of the ATM (ataxia telangiectasia mutated)-mediated DDR in mice results in T-cell leukemia driven by accumulation of DNA damage accrued during normal T-cell development. Pro-apoptotic BH3-only Bid is a substrate of Atm, and Bid phosphorylation is required for proper cell cycle checkpoint control and regulation of hematopoietic function. In this report, we demonstrate that, surprisingly, loss of Bid increases the latency of leukemogenesis in Atm-/- mice. Bid-/-Atm-/- mice display impaired checkpoint control and increased cell death of DN3 thymocytes. Loss of Bid thus inhibits T-cell tumorigenesis by increasing clearance of damaged cells, and preventing propagation of deleterious mutations.

Evolution of Bcl-2 homology motifs: homology versus homoplasy

Bcl-2 family proteins regulate apoptosis in animals. This protein family includes several homologous proteins and a collection of other proteins lacking sequence similarity except for a Bcl-2 homology (BH)3 motif. Thus, membership in the Bcl-2 family requires only one of the four BH motifs. On this basis, a growing number of diverse BH3-only proteins are being reported. Although compelling cell biological and biophysical evidence validates many BH3-only proteins, claims of significant BH3 sequence similarity are often unfounded. Computational and phylogenetic analyses suggest that only some BH3 motifs arose by divergent evolution from a common ancestor (homology), whereas others arose by convergent evolution or random coincidence (homoplasy), challenging current assumptions about which proteins constitute the extended Bcl-2 family.

A ROS rheostat for cell fate regulation

Cellular reactive oxygen species (ROS) are tightly regulated to prevent tissue damage. ROS also help to monitor different cell fates, suggesting that a 'ROS rheostat' exists in cells. It is well established that ROS are crucial for stem cell biology; in this review, we discuss how mitochondrial ROS influence hematopoietic cell fates. We also examine the importance in this process of BID and other BCL-2 family members, many of which have been implicated in regulating cell fates by modulating mitochondrial integrity/activity and cell cycle progression in the hematopoietic lineage. Based on this knowledge, we propose that selected BCL-2 proteins coordinate mitochondria and nuclear activities via ROS to enable 'synchronized' cell fate decisions.

Rejuvenating Bi(d)ology

The BH3-only Bid protein is a critical sentinel of cellular stress in the liver and the hematopoietic system. Bid's initial 'claim to fame' came from its ability-as a caspase-truncated product-to trigger the mitochondrial apoptotic program following death receptor activation. Today we know that Bid can response to multiple types of proteases, which are activated under different conditions such as T-cell activation, ischemical reperfusion injury and lysosomal injury. Activation of the mitochondrial apoptotic program by Bid-via its recently identified receptor mitochondrial carrier homolog 2-involves multiple mechanisms, including release of cytochrome c and second mitochondria-derived activator of caspase (Smac), alteration of mitochondrial cristae organization, generation of reactive oxygen species and engagement of the permeability transition pore. Bid is also emerging-in its full-length form-as a pivotal sentinel of DNA damage in the bone marrow regulated by the ataxia telangiectasia mutated (ATM)/ataxia telangiectasia and Rad3-related (ATR) kinases. The ATM/ATR-Bid pathway is critically involved in preserving the quiescence and survival of hematopoietic stem cells both in the absence and presence of external stress, and a large part of this review will be dedicated to recent advances in this area of research.

Bid protects the mouse hematopoietic system following hydroxyurea-induced replicative stress

Hematopoietic stem cells (HSCs) possess long-term self-renewal capacity and multipotent differentiative capacity, to maintain the hematopoietic system. Long-term hematopoietic homeostasis requires effective control of genotoxic damage to maintain HSC function and prevent propagation of deleterious mutations. Here we investigate the role of the BH3-only Bcl-2 family member Bid in the response of murine hematopoietic cells to long-term replicative stress induced by hydroxyurea (HU). The PI3-like serine/threonine kinase, ATR, initiates the DNA damage response (DDR) to replicative stress. The pro-apoptotic Bcl-2 family member, Bid, facilitates this response to replicative stress in hematopoietic cells, but the in vivo role of this DDR function of Bid has not been defined. Surprisingly, we demonstrate that long-term HU treatment expands wild-type myeloid progenitor cells (MPCs) and HSC-enriched Lin(-)Sca1(+)Kit(+) (LSK) cells to maintain bone marrow function as measured by long-term competitive repopulating ability. Bid-/- MPCs demonstrate increased sensitivity to HU and are depleted. Bid-/- LSK cells demonstrate increased mobilization manifest by increased Bromodeoxyuridine (BrdU) incorporation. Bid-/- MPCs and LSK cells are relatively depleted, however, and bone marrow from Bid-/- mice demonstrates decreased long-term competitive repopulating ability in both primary and secondary transplants. We thus describe a survival function of Bid in hematopoiesis in the setting of chronic replicative stress.

Non-apoptotic functions of apoptosis-regulatory proteins

During the past two decades, apoptotic cell death has been the subject of an intense wave of investigation, leading to the discovery of multiple gene products that govern both its induction and execution. In parallel, it has progressively become evident that most, if not all, proteins that had initially been discovered for their essential role in apoptosis also mediate a wide range of non-apoptotic functions. On the one hand, apoptotic regulators and executioners are involved in non-lethal physiological processes as diverse as cell cycle progression, differentiation, metabolism, autophagy and inflammation. On the other hand, pro-apoptotic proteins can control other modalities of programmed cell death, in particular regulated necrosis. In this review, we summarize the unconventional roles of the apoptotic core machinery from a functional perspective and discuss their pathophysiological implications.

BID binds to replication protein A and stimulates ATR function following replicative stress

Proapoptotic BH3-interacting death domain agonist (BID) regulates apoptosis and the DNA damage response. Following replicative stress, BID associates with proteins of the DNA damage sensor complex, including replication protein A (RPA), ataxia telangiectasia and Rad3 related (ATR), and ATR-interacting protein (ATRIP), and facilitates an efficient DNA damage response. We have found that BID stimulates the association of RPA with components of the DNA damage sensor complex through interaction with the basic cleft of the N-terminal domain of the RPA70 subunit. Disruption of the BID-RPA interaction impairs the association of ATR-ATRIP with chromatin as well as ATR function, as measured by CHK1 activation and recovery of DNA replication following hydroxyurea (HU). We further demonstrate that the association of BID with RPA stimulates the association of ATR-ATRIP to the DNA damage sensor complex. We propose a model in which BID associates with RPA and stimulates the recruitment and/or stabilization of ATR-ATRIP to the DNA damage sensor complex.

ATR signalling: more than meeting at the fork

Preservation of genome integrity via the DNA-damage response is critical to prevent disease. ATR (ataxia telangiectasia mutated- and Rad3-related) is essential for life and functions as a master regulator of the DNA-damage response, especially during DNA replication. ATR controls and co-ordinates DNA replication origin firing, replication fork stability, cell cycle checkpoints and DNA repair. Since its identification 15 years ago, a model of ATR activation and signalling has emerged that involves localization to sites of DNA damage and activation through protein-protein interactions. Recent research has added an increasingly detailed understanding of the canonical ATR pathway, and an appreciation that the canonical model does not fully capture the complexity of ATR regulation. In the present article, we review the ATR signalling process, focusing on mechanistic findings garnered from the identification of new ATR-interacting proteins and substrates. We discuss how to incorporate these new insights into a model of ATR regulation and point out the significant gaps in our understanding of this essential genome-maintenance pathway.