Senescence induced by RECQL4 dysfunction contributes to Rothmund-Thomson syndrome features in mice

Autophagy Dysfunction: The Kernel of Hair Loss?

Autophagy is recognized as a crucial regulatory process, instrumental in the removal of senescent, dysfunctional, and damaged cells. Within the autophagic process, lysosomal digestion plays a critical role in the elimination of impaired organelles, thus preserving fundamental cellular metabolic functions and various biological processes. Mitophagy, a targeted autophagic process that specifically focuses on mitochondria, is essential for sustaining cellular health and energy balance. Therefore, a deep comprehension of the operational mechanisms and implications of autophagy and mitophagy is vital for disease prevention and treatment. In this context, we examine the role of autophagy and mitophagy during hair follicle cycles, closely scrutinizing their potential association with hair loss. We also conduct a thorough review of the regulatory mechanisms behind autophagy and mitophagy, highlighting their interaction with hair follicle stem cells and dermal papilla cells. In conclusion, we investigate the potential of manipulating autophagy and mitophagy pathways to develop innovative therapeutic strategies for hair loss.

Senescent cells at the crossroads of aging, disease, and tissue homeostasis

Originally identified as an outcome of continuous culture of primary cells, cellular senescence has moved beyond the culture dish and is now a bona fide driver of aging and disease in animal models, and growing links to human disease. This cellular stress response consists of a stable proliferative arrest coupled to multiple phenotypic changes. Perhaps the most important of these is the senescence-associated secretory phenotype, or senescence-associated secretory phenotype -a complex and variable collection of secreted molecules release by senescent cells with a number of potent biological activities. Senescent cells appear in multiple age-associated conditions in humans and mice, and interventions that eliminate these cells can prevent or even reverse multiple diseases in mouse models. Here, we review salient aspects of senescent cells in the context of human disease and homeostasis. Senescent cells increase in abundance during several diseases that associated with premature aging. Conversely, senescent cells have a key role in beneficial processes such as development and wound healing, and thus can help maintain tissue homeostasis. Finally, we speculate on mechanisms by which deleterious aspects of senescent cells might be targeted while retaining homeostatic aspects in order to improve age-related outcomes.

Biallelic variants in CRIPT cause a Rothmund-Thomson-like syndrome with increased cellular senescence

PURPOSE

Rothmund-Thomson syndrome (RTS) is characterized by poikiloderma, sparse hair, small stature, skeletal defects, cancer, and cataracts, resembling features of premature aging. RECQL4 and ANAPC1 are the 2 known disease genes associated with RTS in >70% of cases. We describe RTS-like features in 5 individuals with biallelic variants in CRIPT (OMIM 615789).

METHODS

Two newly identified and 4 published individuals with CRIPT variants were systematically compared with those with RTS using clinical data, computational analysis of photographs, histologic analysis of skin, and cellular studies on fibroblasts.

RESULTS

All CRIPT individuals fulfilled the diagnostic criteria for RTS and additionally had neurodevelopmental delay and seizures. Using computational gestalt analysis, CRIPT individuals showed greatest facial similarity with individuals with RTS. Skin biopsies revealed a high expression of senescence markers (p53/p16/p21) and the senescence-associated ß-galactosidase activity was elevated in CRIPT-deficient fibroblasts. RECQL4- and CRIPT-deficient fibroblasts showed an unremarkable mitotic progression and unremarkable number of mitotic errors and no or only mild sensitivity to genotoxic stress by ionizing radiation, mitomycin C, hydroxyurea, etoposide, and potassium bromate.

CONCLUSION

CRIPT causes an RTS-like syndrome associated with neurodevelopmental delay and epilepsy. At the cellular level, RECQL4- and CRIPT-deficient cells display increased senescence, suggesting shared molecular mechanisms leading to the clinical phenotypes.

RecQ dysfunction contributes to social and depressive-like behavior and affects aldolase activity in mice

RecQ helicase family proteins play vital roles in maintaining genome stability, including DNA replication, recombination, and DNA repair. In human cells, there are five RecQ helicases: RECQL1, Bloom syndrome (BLM), Werner syndrome (WRN), RECQL4, and RECQL5. Dysfunction or absence of RecQ proteins is associated with genetic disorders, tumorigenesis, premature aging, and neurodegeneration. The biochemical and biological roles of RecQ helicases are rather well established, however, there is no systematic study comparing the behavioral changes among various RecQ-deficient mice including consequences of exposure to DNA damage. Here, we investigated the effects of ionizing irradiation (IR) on three RecQ-deficient mouse models (RecQ1, WRN and RecQ4). We find abnormal cognitive behavior in RecQ-deficient mice in the absence of IR. Interestingly, RecQ dysfunction impairs social ability and induces depressive-like behavior in mice after a single exposure to IR, suggesting that RecQ proteins play roles in mood and cognition behavior. Further, transcriptomic and metabolomic analyses revealed significant alterations in RecQ-deficient mice, especially after IR exposure. In particular, pathways related to neuronal and microglial functions, DNA damage repair, cell cycle, and reactive oxygen responses were downregulated in the RecQ4 and WRN mice. In addition, increased DNA damage responses were found in RecQ-deficient mice. Notably, two genes, Aldolase Fructose-Bisphosphate B (Aldob) and NADPH Oxidase 4 (Nox4), were differentially expressed in RecQ-deficient mice. Our findings suggest that RecQ dysfunction contributes to social and depressive-like behaviors in mice, and that aldolase activity may be associated with these changes, representing a potential therapeutic target.

Understanding the Impact of Obesity on Ageing in the Radiance of DNA Metabolism

Ageing is a multi-factorial phenomenon which is considered as a major risk factor for the development of neurodegeneration, osteoporosis, cardiovascular disease, dementia, cancer, and other chronic diseases. Phenotypically, ageing is related with a combination of molecular, cellular, and physiological levels like genomic and epi-genomic alterations, loss of proteostasis, deregulation of cellular and subcellular function and mitochondrial dysfunction. Though, no single molecular mechanism accounts for the functional decline of different organ systems in older humans but accumulation of DNA damage or mutations is a dominant theory which contributes largely to the development of ageing and age-related diseases. However, mechanistic, and hierarchical order of these features of ageing has not been clarified yet. Scientific community now focus on the effect of obesity on accelerated ageing process. Obesity is a complex chronic disease that affects multiple organs and tissues. It can not only lead to various health conditions such as diabetes, cancer, and cardiovascular disease but also can decrease life expectancy which shows similar phenotype of ageing. Higher loads of DNA damage were also observed in the genome of obese people. Thus, inability of DNA damage repair may contribute to both ageing and obesity apart from cancer predisposition. The present review emphasizes on the involvement of molecular phenomenon of DNA metabolism in development of obesity and how it accelerates ageing in mammals.

The Face- and Neck-Lift Objective Photo-Numerical Assessment Scale: A Complete Scale for Face-Lift Evaluation

BACKGROUND

Success or failure of plastic surgery procedures relies on cosmetic results. Understanding the objective perception of favorable aesthetic results is critical to ensure patient satisfaction. The aim of this study was to develop and validate a new facial rating scale that could objectively assess face- and neck-lift outcomes: the Face- and Neck-Lift Objective Photo-Numerical Assessment Scale.

METHODS

One thousand White patients were included in the authors' study and assessed. To validate the authors' scale, the interrater reliability and the test-retest reliability were analyzed. The Rasch model was used as part of the scale validation process.

RESULTS

Eleven scales for face- and neck-lift outcomes assessment were developed. All scales exceeded criteria for acceptability, reliability, and validity. The interrater and intrarater reliabilities were good, with a substantial or virtually perfect interrater reliability for the total score ( P = 0.15).

CONCLUSIONS

The authors' results allowed us to validate the Face- and Neck-Lift Objective Photo-Numerical Assessment Scale as a reliable and reproducible tool to assess face- and neck-lift outcomes. This scale could be also considered as an important new metric to be used in facial rejuvenation surgery clinical research.

ML216 Prevents DNA Damage-Induced Senescence by Modulating DBC1-BLM Interaction

DNA damage is the major cause of senescence and apoptosis; however, the manner by which DNA-damaged cells become senescent remains unclear. We demonstrate that DNA damage leads to a greater level of senescence rather than apoptosis in DBC1-deficient cells. In addition, we show that BLM becomes degraded during DNA damage, which induces p21 expression and senescence. DBC1 binds to and shields BLM from degradation, thus suppressing senescence. ML216 promotes DBC1-BLM interaction, which aids in the preservation of BLM following DNA damage and suppresses senescence. ML216 enhances pulmonary function by lowering the levels of senescence and fibrosis in both aged mice and a mouse model of bleomycin-induced idiopathic pulmonary fibrosis. Our data reveal a unique mechanism preventing DNA-damaged cells from becoming senescent, which may be regulated by the use of ML216 as a potential treatment for senescence-related diseases.

Ross J, Scott Herron G. Genetic and Epigenetic Influences on Cutaneous Cellular Senescence

Skin is the largest human organ system, and its protective function is critical to survival. The epithelial, dermal, and subcutaneous compartments are heterogeneous mixtures of cell types, yet they all display age-related skin dysfunction through the accumulation of an altered phenotypic cellular state called senescence. Cellular senescence is triggered by complex and dynamic genetic and epigenetic processes. A senescence steady state is achieved in different cell types under various and overlapping conditions of chronological age, toxic injury, oxidative stress, replicative exhaustion, DNA damage, metabolic dysfunction, and chromosomal structural changes. These inputs lead to outputs of cell-cycle withdrawal and the appearance of a senescence-associated secretory phenotype, both of which accumulate as tissue pathology observed clinically in aged skin. This review details the influence of genetic and epigenetic factors that converge on normal cutaneous cellular processes to create the senescent state, thereby dictating the response of the skin to the forces of both intrinsic and extrinsic aging. From this work, it is clear that no single biomarker or process leads to senescence, but that it is a convergence of factors resulting in an overt aging phenotype.

Mammalian Resilience Revealed by a Comparison of Human Diseases and Mouse Models Associated With DNA Helicase Deficiencies

Maintaining genomic integrity is critical for sustaining individual animals and passing on the genome to subsequent generations. Several enzymes, such as DNA helicases and DNA polymerases, are involved in maintaining genomic integrity by unwinding and synthesizing the genome, respectively. Indeed, several human diseases that arise caused by deficiencies in these enzymes have long been known. In this review, the author presents the DNA helicases associated with human diseases discovered to date using recent analyses, including exome sequences. Since several mouse models that reflect these human diseases have been developed and reported, this study also summarizes the current knowledge regarding the outcomes of DNA helicase deficiencies in humans and mice and discusses possible mechanisms by which DNA helicases maintain genomic integrity in mammals. It also highlights specific diseases that demonstrate mammalian resilience, in which, despite the presence of genomic instability, patients and mouse models have lifespans comparable to those of the general population if they do not develop cancers; finally, this study discusses future directions for therapeutic applications in humans that can be explored using these mouse models.

DNA-PKcs-dependent phosphorylation of RECQL4 promotes NHEJ by stabilizing the NHEJ machinery at DNA double-strand breaks

Non-homologous end joining (NHEJ) is the major pathway that mediates the repair of DNA double-strand breaks (DSBs) generated by ionizing radiation (IR). Previously, the DNA helicase RECQL4 was implicated in promoting NHEJ, but its role in the pathway remains unresolved. In this study, we report that RECQL4 stabilizes the NHEJ machinery at DSBs to promote repair. Specifically, we find that RECQL4 interacts with the NHEJ core factor DNA-PK_cs and the interaction is increased following IR. RECQL4 promotes DNA end bridging mediated by DNA-PK_cs and Ku70/80 in vitro and the accumulation/retention of NHEJ factors at DSBs in vivo. Moreover, interaction between DNA-PK_cs and the other core NHEJ proteins following IR treatment is attenuated in the absence of RECQL4. These data indicate that RECQL4 promotes the stabilization of the NHEJ factors at DSBs to support formation of the NHEJ long-range synaptic complex. In addition, we observed that the kinase activity of DNA-PK_cs is required for accumulation of RECQL4 to DSBs and that DNA-PK_cs phosphorylates RECQL4 at six serine/threonine residues. Blocking phosphorylation at these sites reduced the recruitment of RECQL4 to DSBs, attenuated the interaction between RECQL4 and NHEJ factors, destabilized interactions between the NHEJ machinery, and resulted in decreased NHEJ. Collectively, these data illustrate reciprocal regulation between RECQL4 and DNA-PK_cs in NHEJ.

Molecular Mechanisms of the RECQ4 Pathogenic Mutations

The human RECQ4 gene encodes an ATP-dependent DNA helicase that contains a conserved superfamily II helicase domain located at the center of the polypeptide. RECQ4 is one of the five RECQ homologs in human cells, and its helicase domain is flanked by the unique amino and carboxyl termini with sequences distinct from other members of the RECQ helicases. Since the identification of the RECQ4 gene in 1998, multiple RECQ4 mutations have been linked to the pathogenesis of three clinical diseases, which are Rothmund-Thomson syndrome, Baller-Gerold syndrome, and RAPADILINO. Patients with these diseases show various developmental abnormalities. In addition, a subset of RECQ4 mutations are associated with high cancer risks, especially for osteosarcoma and/or lymphoma at early ages. The discovery of clinically relevant RECQ4 mutations leads to intriguing questions: how is the RECQ4 helicase responsible for preventing multiple clinical syndromes? What are the mechanisms by which the RECQ4 disease mutations cause tissue abnormalities and drive cancer formation? Furthermore, RECQ4 is highly overexpressed in many cancer types, raising the question whether RECQ4 acts not only as a tumor suppressor but also an oncogene that can be a potential new therapeutic target. Defining the molecular dysfunctions of different RECQ4 disease mutations is imperative to improving our understanding of the complexity of RECQ4 clinical phenotypes and the dynamic roles of RECQ4 in cancer development and prevention. We will review recent progress in examining the molecular and biochemical properties of the different domains of the RECQ4 protein. We will shed light on how the dynamic roles of RECQ4 in human cells may contribute to the complexity of RECQ4 clinical phenotypes.

RecQ-like helicase 4 (RECQL4) exacerbates resistance to oxaliplatin in colon adenocarcinoma via activation of the PI3K/AKT signaling pathway

Oxaliplatin (OXA) resistance is a great challenge for colon adenocarcinoma (COAD) chemotherapy. The promoting role of RecQ-Like Helicase 4 (RECQL4) in chemoresistance to platinum-based drugs has been identified, whereas the effect and specific mechanism of RECQL4 in regulating OXA resistance within COAD have not been explicated yet. In this work, RECQL4 mRNA expression was detected by RT-qPCR. RECQL4, phosphorylated PI3K (p-PI3K), PI3K, phosphorylated AKT (p-AKT), and AKT protein expression were measured by western blotting. CCK-8, flow cytometry, wound healing, and transwell assays were utilized to analyze OXA resistance, cell proliferation, apoptosis, cell cycle, migration and invasion. Herein, we found RECQL4 was upregulated in COAD, especially in OXA-resistant COAD tissues and cells. RECQL4 overexpression facilitated proliferation and metastasis of OXA-resistant COAD cells; on the contrary, RECQL4 knockdown attenuated proliferative and metastatic capabilities in OXA-resistant COAD cells. Moreover, RECQL4 promoted OXA resistance in OXA-resistant COAD cells via activating the P13 K/AKT signaling. To sum up, the results suggest that RECQL4 depletion may be a crucial mechanism to reverse OXA resistance in COAD via inhibition of the P13 K/AKT pathway in vitro, thereby providing a novel target for overcoming OXA resistance in COAD.

Human RecQL4 as a Novel Molecular Target for Cancer Therapy

Human RecQ helicases play diverse roles in the maintenance of genomic stability. Inactivating mutations in 3 of the 5 human RecQ helicases are responsible for the pathogenesis of Werner syndrome (WS), Bloom syndrome (BS), Rothmund-Thomson syndrome (RTS), RAPADILINO, and Baller-Gerold syndrome (BGS). WS, BS, and RTS patients are at increased risk for developing many age-associated diseases including cancer. Mutations in RecQL1 and RecQL5 have not yet been associated with any human diseases so far. In terms of disease outcome, RecQL4 deserves special attention because mutations in RecQL4 result in 3 autosomal recessive syndromes (RTS type II, RAPADILINO, and BGS). RecQL4, like other human RecQ helicases, has been demonstrated to play a crucial role in the maintenance of genomic stability through participation in diverse DNA metabolic activities. Increased incidence of osteosarcoma in RecQL4-mutated RTS patients and elevated expression of RecQL4 in sporadic cancers including osteosarcoma suggest that loss or gain of RecQL4 expression is linked with cancer susceptibility. In this review, current and future perspectives are discussed on the potential use of RecQL4 as a novel cancer therapeutic target.

Faces of cellular senescence in skin aging

The skin is comprised of different cell types with different proliferative capacities. Skin aging occurs with chronological age and upon exposure to extrinsic factors such as photodamage. During aging, senescent cells accumulate in different compartments of the human skin, leading to impaired skin physiology. Diverse skin cell types may respond differently to senescence-inducing stimuli and it is not clear how this results in aging-associated skin phenotypes and pathologies. This review aims to examine and provide an overview of current evidence of cellular senescence in the skin. We will focus on cellular characteristics and behaviour of different skin cell types undergoing senescence in the epidermis and dermis, with a particular focus on the complex interplay between mitochondrial dysfunction, autophagy and DNA damage pathways. We will also examine how the dermis and epidermis cope with the accumulation of DNA damage during aging.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund-Thomson syndrome (RTS), Baller-Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

The multifaceted roles of DNA repair and replication proteins in aging and obesity

Efficient mechanisms for genomic maintenance (i.e., DNA repair and DNA replication) are crucial for cell survival. Aging and obesity can lead to the dysregulation of genomic maintenance proteins/pathways and are significant risk factors for the development of cancer, metabolic disorders, and other genetic diseases. Mutations in genes that code for proteins involved in DNA repair and DNA replication can also exacerbate aging- and obesity-related disorders and lead to the development of progeroid diseases. In this review, we will discuss the roles of various DNA repair and replication proteins in aging and obesity as well as investigate the possible mechanisms by which aging and obesity can lead to the dysregulation of these proteins and pathways.

Skin Abnormalities in Disorders with DNA Repair Defects, Premature Aging, and Mitochondrial Dysfunction

Defects in DNA repair pathways and alterations of mitochondrial energy metabolism have been reported in multiple skin disorders. More than 10% of patients with primary mitochondrial dysfunction exhibit dermatological features including rashes and hair and pigmentation abnormalities. Accumulation of oxidative DNA damage and dysfunctional mitochondria affect cellular homeostasis leading to increased apoptosis. Emerging evidence demonstrates that genetic disorders of premature aging that alter DNA repair pathways and cause mitochondrial dysfunction, such as Rothmund-Thomson syndrome, Werner syndrome, and Cockayne syndrome, also exhibit skin disease. This article summarizes recent advances in the research pertaining to these syndromes and molecular mechanisms underlying their skin pathologies.

RECQL4 regulates DNA damage response and redox homeostasis in esophageal cancer

Objective:

RECQL4 (a member of the RECQ helicase family) upregulation has been reported to be associated with tumor progression in several malignancies. However, whether RECQL4 sustains esophageal squamous cell carcinoma (ESCC) has not been elucidated. In this study, we determined the functional role for RECQL4 in ESCC progression.

Methods:

RECQL4 expression in clinical samples of ESCC was examined by immunohistochemistry. Cell proliferation, cellular senescence, the epithelial-mesenchymal transition (EMT), DNA damage, and reactive oxygen species in ESCC cell lines with RECQL4 depletion or overexpression were analyzed. The levels of proteins involved in the DNA damage response (DDR), cell cycle progression, survival, and the EMT were determined by Western blot analyses.

Results:

RECQL4 was highly expressed in tumor tissues when compared to adjacent non-tumor tissues in ESCC (P < 0.001) and positively correlated with poor differentiation (P = 0.011), enhanced invasion (P = 0.033), and metastasis (P = 0.048). RECQL4 was positively associated with proliferation and migration in ESCC cells. Depletion of RECQL4 also inhibited growth of tumor xenografts in vivo. RECQL4 depletion induced G0/G1 phase arrest and cellular senescence. Importantly, the levels of DNA damage and reactive oxygen species were increased when RECQL4 was depleted. DDR, as measured by the activation of ATM, ATR, CHK1, and CHK2, was impaired. RECQL4 was also shown to promote the activation of AKT, ERK, and NF-kB in ESCC cells.

Conclusions:

The results indicated that RECQL4 was highly expressed in ESCC and played critical roles in the regulation of DDR, redox homeostasis, and cell survival.

Aberrantly Expressed RECQL4 Helicase Supports Proliferation and Drug Resistance of Human Glioma Cells and Glioma Stem Cells

Simple Summary

Human RecQ helicases participate in DNA replication, repair and transcription. Due to important roles in many cellular processes, deregulation of these helicases in cancer could be tumour promoting. We found upregulated RECQL4 expression in highly malignant brain tumours (glioblastomas) associated with poor survival of patients. While RECQL4 depletion in human glioma cells with genetic tools slightly impaired cell viability and DNA replication, it induced gross changes in gene expression and increased sensitivity of glioma cells and glioma stem cells to chemotherapeutics. Therefore, targeting RECQL4 in deadly brain tumours could be a new strategy to improve eradication of tumour cells by chemotherapeutics.

Abstract

Anti-tumour therapies eliminate proliferating tumour cells by induction of DNA damage, but genomic aberrations or transcriptional deregulation may limit responses to therapy. Glioblastoma (GBM) is a malignant brain tumour, which recurs inevitably due to chemo- and radio-resistance. Human RecQ helicases participate in DNA repair, responses to DNA damage and replication stress. We explored if a helicase RECQL4 contributes to gliomagenesis and responses to chemotherapy. We found upregulated RECQL4 expression in GBMs associated with poor survival of GBM patients. Increased levels of nuclear and cytosolic RECQL4 proteins were detected in GBMs on tissue arrays and in six glioma cell lines. RECQL4 was detected both in cytoplasm and mitochondria by Western blotting and immunofluorescence. RECQL4 depletion in glioma cells with siRNAs and CRISPR/Cas9 did not affect basal cell viability, slightly impaired DNA replication, but induced profound transcriptomic changes and increased chemosensitivity of glioma cells. Sphere cultures originated from RECQL4-depleted cells had reduced sphere forming capacity, stronger responded to temozolomide upregulating cell cycle inhibitors and pro-apoptotic proteins. RECQL4 deficiency affected mitochondrial network and reduced mitochondrial membrane polarization in LN18 glioblastoma cells. We demonstrate that targeting RECQL4 overexpressed in glioblastoma could be a new strategy to sensitize glioma cells to chemotherapeutics.

Interaction between RECQL4 and OGG1 promotes repair of oxidative base lesion 8-oxoG and is regulated by SIRT1 deacetylase

OGG1 initiated base excision repair (BER) is the major pathway for repair of oxidative DNA base damage 8-oxoguanine (8-oxoG). Here, we report that RECQL4 DNA helicase, deficient in the cancer-prone and premature aging Rothmund-Thomson syndrome, physically and functionally interacts with OGG1. RECQL4 promotes catalytic activity of OGG1 and RECQL4 deficiency results in defective 8-oxoG repair and increased genomic 8-oxoG. Furthermore, we show that acute oxidative stress leads to increased RECQL4 acetylation and its interaction with OGG1. The NAD⁺-dependent protein SIRT1 deacetylates RECQL4 in vitro and in cells thereby controlling the interaction between OGG1 and RECQL4 after DNA repair and maintaining RECQL4 in a low acetylated state. Collectively, we find that RECQL4 is involved in 8-oxoG repair through interaction with OGG1, and that SIRT1 indirectly modulates BER of 8-oxoG by controlling RECQL4–OGG1 interaction.

Werner Syndrome Protein Expression in Breast Cancer

INTRODUCTION

Werner protein (WRN) plays an important role in DNA repair, replication, transcription, and consequently genomic stability via its DNA-helicase and exonuclease activity. Loss of function of WRN is associated with Werner syndrome (WS), which is characterized by premature aging and cancer predisposition. Malignancies that are commonly linked to WS are thyroid carcinoma, melanoma, breast cancer, meningioma, and soft tissue and bone sarcomas. Currently, the clinicopathologic significance of WRN in breast cancer is largely unknown.

PATIENTS AND METHODS

We investigated the clinicopathologic and prognostic significance of WRN protein expression in a cohort of clinically annotated series of sporadic (n = 1650) and BRCA-mutated (n = 75) invasive breast cancers. We correlated WRN protein expression to clinicopathologic characteristics, DNA repair protein expression, and survival outcomes.

RESULTS

There is strong evidence of association between low nuclear and cytoplasmic WRN co-expression and low levels of KU70/KU80, DNA-PK, DNA Pol-B, CKD18, cytoplasmic RECQL4, and nuclear BLM protein expression (adjusted P-values < .05). Tumors with low nuclear or cytoplasmic WRN expression have worse overall breast cancer-specific survival (BCSS) (adjusted P-values < .05). In topoisomerase I overexpressed tumors, low WRN nuclear expression was associated with poor BCSS (P-value < .05). In BRCA-mutated tumors, low WRN cytoplasmic expression conferred shortest BCSS (P < .05).

CONCLUSIONS

Low WRN protein expression is associated with poor BCSS in patients with breast cancer. This can be used to optimize the risk stratification for personalized treatment.

MIB1-mediated degradation of WRN promotes cellular senescence in response to camptothecin treatment

Werner syndrome protein (WRN) plays critical roles in DNA replication, recombination, and repair, as well as transcription and cellular senescence. Ubiquitination and degradation of WRN have been reported, however, the E3 ubiquitin ligase of WRN is little known. Here, we identify mindbomb E3 ubiquitin protein ligase 1 (MIB1) as a novel E3 ubiquitin ligase for WRN protein. MIB1 physically interacts with WRN in vitro and in vivo and induces ubiquitination and degradation of WRN in the ubiquitin-proteasome pathway. Camptothecin (CPT) enhances the interaction between MIB1 and WRN, and promotes WRN degradation in a MIB1-dependent manner. In addition, CPT-induced cellular senescence is facilitated by the expression of MIB1 and attenuated by WRN expression. Our results show that MIB1-mediated degradation of WRN promotes cellular senescence and reveal a novel model executed by MIB1 and WRN to regulate cellular senescence.

Human pluripotent stem cell-based models suggest preadipocyte senescence as a possible cause of metabolic complications of Werner and Bloom Syndromes

Werner Syndrome (WS) and Bloom Syndrome (BS) are disorders of DNA damage repair caused by biallelic disruption of the WRN or BLM DNA helicases respectively. Both are commonly associated with insulin resistant diabetes, usually accompanied by dyslipidemia and fatty liver, as seen in lipodystrophies. In keeping with this, progressive reduction of subcutaneous adipose tissue is commonly observed. To interrogate the underlying cause of adipose tissue dysfunction in these syndromes, CRISPR/Cas9 genome editing was used to generate human pluripotent stem cell (hPSC) lacking either functional WRN or BLM helicase. No deleterious effects were observed in WRN^−/− or BLM^−/− embryonic stem cells, however upon their differentiation into adipocyte precursors (AP), premature senescence emerged, impairing later stages of adipogenesis. The resulting adipocytes were also found to be senescent, with increased levels of senescent markers and senescence-associated secretory phenotype (SASP) components. SASP components initiate and reinforce senescence in adjacent cells, which is likely to create a positive feedback loop of cellular senescence within the adipocyte precursor compartment, as demonstrated in normal ageing. Such a scenario could progressively attenuate adipose mass and function, giving rise to “lipodystrophy-like” insulin resistance. Further assessment of pharmacological senolytic strategies are warranted to mitigate this component of Werner and Bloom syndromes.

RECQ DNA Helicases and Osteosarcoma

The RECQ family of DNA helicases is a conserved group of enzymes that plays an important role in maintaining genomic stability. Humans possess five RECQ helicase genes, and mutations in three of them - BLM, WRN, and RECQL4 - are associated with the genetic disorders Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome (RTS), respectively. These syndromes share overlapping clinical features, and importantly they are all associated with an increased risk of cancer. Patients with RTS have the highest specific risk of developing osteosarcoma compared to all other cancer predisposition syndromes; therefore, RTS serves as a relevant model to study the pathogenesis and molecular genetics of osteosarcoma. The "tumor suppressor" function of the RECQ helicases continues to be an area of active investigation. This chapter will focus primarily on the known cellular functions of RECQL4 and how these may relate to tumorigenesis, as well as ongoing efforts to understand RECQL4's functions in vivo using animal models. Understanding the RECQ pathways will provide insight into avenues for novel cancer therapies in the future.

Human RECQL4 represses the RAD52-mediated single-strand annealing pathway after ionizing radiation or cisplatin treatment

Ionizing radiation (IR) and cisplatin are frequently used cancer treatments, although the mechanisms of error-prone DNA repair-mediated genomic instability after anticancer treatment are not fully clarified yet. RECQL4 mutations mainly in the C-terminal region of the RECQL4 gene lead to the cancer-predisposing Rothmund-Thomson syndrome, but the function of RECQL4ΔC (C-terminus deleted) in error-prone DNA repair remains unclear. We established several RECQL4ΔC cell lines and found that RECQL4ΔC cancer cells, but not RECQL4ΔC nontumorigenic cells, exhibited IR/cisplatin hypersensitivity. Notably, RECQL4ΔC cancer cells presented increased RPA2/RAD52 foci after cancer treatments. RECQL4ΔC HCT116 cells exhibited increased error-prone single-strand annealing (SSA) activity and decreased alternative end-joining activities, suggesting that RECQL4 regulates the DNA repair pathway choice at double-strand breaks. RAD52 depletion by siRNA or RAD52 inhibitors (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside [AICAR], (-)-epigallocatechin [EGC]) or a RAD52-phenylalanine 79 aptamer significantly restrained the growth of RAD52-upregulated RECQL4ΔC HCT116 cells in vitro and in mouse xenografts. Remarkably, compared to single-agent cisplatin or EGC treatment, cisplatin followed by low-concentration EGC had a significant suppressive effect on RECQL4ΔC HCT116 cell growth in vivo. Together, the regimens targeting the RAD52-mediated SSA pathway after anticancer treatment may be applicable for cancer patients with RECQL4 gene mutations.

Studying Werner syndrome to elucidate mechanisms and therapeutics of human aging and age-related diseases

Aging is a natural and unavoidable part of life. However, aging is also the primary driver of the dominant human diseases, such as cardiovascular disease, cancer, and neurodegenerative diseases, including Alzheimer's disease. Unraveling the sophisticated molecular mechanisms of the human aging process may provide novel strategies to extend 'healthy aging' and the cure of human aging-related diseases. Werner syndrome (WS), is a heritable human premature aging disease caused by mutations in the gene encoding the Werner (WRN) DNA helicase. As a classical premature aging disease, etiological exploration of WS can shed light on the mechanisms of normal human aging and facilitate the development of interventional strategies to improve healthspan. Here, we summarize the latest progress of the molecular understandings of WRN protein, highlight the advantages of using different WS model systems, including Caenorhabditis elegans, Drosophila melanogaster and induced pluripotent stem cell (iPSC) systems. Further studies on WS will propel drug development for WS patients, and possibly also for normal age-related diseases.

Cellular senescence: a view throughout organismal life

Cellular senescence is the final fate of most cells in response to specific stimuli, but is not the end. Indeed, it is the beginning of a singular life, with multiple side roads leading to diverse effects on the organism. Many studies have been done in the last few years to elucidate the intriguing role of senescent cells in the organism, demonstrating them as the cause of several age-related diseases. However, these cells are also positively implicated in other important pathways, such as embryogenesis and wound healing. It appears that the multiple effects are time-dependent: long-term senescence is mostly implicated in chronic inflammation and disease, whereas in the short term, senescent cells seem to be beneficial, being rapidly targeted by the innate immune system. The influence of senescent cells on their neighbors by paracrine factors, differential activity depending on developmental stage, and duration of the effects make the cellular senescent program a unique spatial-temporal mechanism. During pathological conditions such as progeroid syndromes, this mechanism is deregulated, leading to accelerated onset of some aging-related diseases and a shorter lifespan, among other physiological defects. Here, we review the three primary cell senescence programs described so far (replicative, stress-induced, and developmentally programmed senescence), their onset during development, and their potential roles in diseases with premature aging. Finally, we discuss the role of immune cells in keeping senescence burden below the threshold of disease.

Camptothecin targets WRN protein: mechanism and relevance in clinical breast cancer

Werner syndrome protein (WRN) is a RecQ helicase that participates in DNA repair, genome stability and cellular senescence. The five human RecQ helicases, RECQL1, Bloom, WRN, RECQL4 and RECQL5 play critical roles in DNA repair and cell survival after treatment with the anticancer drug camptothecin (CPT). CPT derivatives are widely used in cancer chemotherapy to inhibit topoisomerase I and generate DNA double-strand breaks during replication. Here we studied the effects of CPT on the stability and expression dynamics of human RecQ helicases. In the cells treated with CPT, we observed distinct effects on WRN compared to other human RecQ helicases. CPT altered the cellular localization of WRN and induced its degradation by a ubiquitin-mediated proteasome pathway. WRN knockdown cells as well as CPT treated cells became senescent and stained positive for senescence-associated β-galactosidase at a higher frequency compared to control cells. However, the senescent phenotype was attenuated by ectopic expression of WRN suggesting functional implication of WRN degradation in CPT treated cells. Approximately 5-23% of breast cancer tumors are known to respond to CPT-based chemotherapy. Interestingly, we found that the extent of CPT-induced WRN degradation correlates with increasing sensitivity of breast cancer cells to CPT. The abundance of WRN decreased in CPT-treated sensitive cells; however, WRN remained relatively stable in CPT-resistant breast cancer cells. In a large clinical cohort of breast cancer patients, we find that WRN and topoisomerase I expression correlate with an aggressive tumor phenotype and poor prognosis. Our novel observations suggest that WRN abundance along with CPT-induced degradation could be a promising strategy for personalizing CPT-based cancer chemotherapeutic regimens.

Cell cycle-dependent phosphorylation regulates RECQL4 pathway choice and ubiquitination in DNA double-strand break repair

Pathway choice within DNA double-strand break (DSB) repair is a tightly regulated process to maintain genome integrity. RECQL4, deficient in Rothmund-Thomson Syndrome, promotes the two major DSB repair pathways, non-homologous end joining (NHEJ) and homologous recombination (HR). Here we report that RECQL4 promotes and coordinates NHEJ and HR in different cell cycle phases. RECQL4 interacts with Ku70 to promote NHEJ in G1 when overall cyclin-dependent kinase (CDK) activity is low. During S/G2 phases, CDK1 and CDK2 (CDK1/2) phosphorylate RECQL4 on serines 89 and 251, enhancing MRE11/RECQL4 interaction and RECQL4 recruitment to DSBs. After phosphorylation, RECQL4 is ubiquitinated by the DDB1-CUL4A E3 ubiquitin ligase, which facilitates its accumulation at DSBs. Phosphorylation of RECQL4 stimulates its helicase activity, promotes DNA end resection, increases HR and cell survival after ionizing radiation, and prevents cellular senescence. Collectively, we propose that RECQL4 modulates the pathway choice of NHEJ and HR in a cell cycle-dependent manner.

DNA double-strand break (DSB) repair is a tightly regulated process that can occur via non-homologous end joining (NHEJ) or homologous recombination (HR). Here, the authors investigate how RECQL4 modulates DSB repair pathway choice by differentially regulating NHEJ and HR in a cell cycle-dependent manner.

Hallmarks of progeroid syndromes: lessons from mice and reprogrammed cells

Ageing is a process that inevitably affects most living organisms and involves the accumulation of macromolecular damage, genomic instability and loss of heterochromatin. Together, these alterations lead to a decline in stem cell function and to a reduced capability to regenerate tissue. In recent years, several genetic pathways and biochemical mechanisms that contribute to physiological ageing have been described, but further research is needed to better characterize this complex biological process. Because premature ageing (progeroid) syndromes, including progeria, mimic many of the characteristics of human ageing, research into these conditions has proven to be very useful not only to identify the underlying causal mechanisms and identify treatments for these pathologies, but also for the study of physiological ageing. In this Review, we summarize the main cellular and animal models used in progeria research, with an emphasis on patient-derived induced pluripotent stem cell models, and define a series of molecular and cellular hallmarks that characterize progeroid syndromes and parallel physiological ageing. Finally, we describe the therapeutic strategies being investigated for the treatment of progeroid syndromes, and their main limitations.

Summary: This Review defines the molecular and cellular hallmarks of progeroid syndromes according to the main cellular and animal models, and discusses the therapeutic strategies developed to date.

Human RecQL4 helicase plays multifaceted roles in the genomic stability of normal and cancer cells

Human RecQ helicases that share homology with E. coli RecQ helicase play critical roles in diverse biological activities such as DNA replication, transcription, recombination and repair. Mutations in three of the five human RecQ helicases (RecQ1, WRN, BLM, RecQL4 and RecQ5) result in autosomal recessive syndromes characterized by accelerated aging symptoms and cancer incidence. Mutational inactivation of Werner (WRN) and Bloom (BLM) genes results in Werner syndrome (WS) and Bloom syndrome (BS) respectively. However, mutations in RecQL4 result in three human disorders: (I) Rothmund-Thomson syndrome (RTS), (II) RAPADILINO and (III) Baller-Gerold syndrome (BGS). Cells from WS, BS and RTS are characterized by a unique chromosomal anomaly indicating that each of the RecQ helicases performs specialized function(s) in a non-redundant manner. Elucidating the biological functions of RecQ helicases will enable us to understand not only the aging process but also to determine the cause for age-associated human diseases. Recent biochemical and molecular studies have given new insights into the multifaceted roles of RecQL4 that range from genomic stability to carcinogenesis and beyond. This review summarizes some of the existing and emerging knowledge on diverse biological functions of RecQL4 and its significance as a potential molecular target for cancer therapy.

Recent Advances in Understanding Werner Syndrome

Aging, the universal phenomenon, affects human health and is the primary risk factor for major disease pathologies. Progeroid diseases, which mimic aging at an accelerated rate, have provided cues in understanding the hallmarks of aging. Mutations in DNA repair genes as well as in telomerase subunits are known to cause progeroid syndromes. Werner syndrome (WS), which is characterized by accelerated aging, is an autosomal-recessive genetic disorder. Hallmarks that define the aging process include genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulation of nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. WS recapitulates these hallmarks of aging and shows increased incidence and early onset of specific cancers. Genome integrity and stability ensure the normal functioning of the cell and are mainly guarded by the DNA repair machinery and telomeres. WRN, being a RecQ helicase, protects genome stability by regulating DNA repair pathways and telomeres. Recent advances in WS research have elucidated WRN’s role in DNA repair pathway choice regulation, telomere maintenance, resolution of complex DNA structures, epigenetic regulation, and stem cell maintenance.

The structural and functional characterization of human RecQ4 reveals insights into its helicase mechanism

RecQ4 is a member of the RecQ helicase family, an evolutionarily conserved class of enzymes, dedicated to preserving genomic integrity by operating in telomere maintenance, DNA repair and replication. While reduced RecQ4 activity is associated with cancer predisposition and premature aging, RecQ4 upregulation is related to carcinogenesis and metastasis. Within the RecQ family, RecQ4 assumes an exceptional position, lacking several characteristic RecQ domains. Here we present the crystal structure of human RecQ4, encompassing the conserved ATPase core and a novel C-terminal domain that lacks resemblance to the RQC domain observed in other RecQ helicases. The new domain features a zinc-binding site and two distinct types of winged-helix domains, which are not involved in canonical DNA binding or helicase activity. Based on our structural and functional analysis, we propose that RecQ4 exerts a helicase mechanism, which may be more closely related to bacterial RecQ helicases than to its human family members.

RecQ helicases are important for maintaining genomic integrity. Here, the authors present functional data and the crystal structure of human RecQ4, which exerts a helicase mechanism that may be more closely related to bacterial RecQ helicases than to its human family members.

Ribosomal Protein S3 Negatively Regulates Unwinding Activity of RecQ-like Helicase 4 through Their Physical Interaction

Human RecQ-like helicase 4 (RECQL4) plays crucial roles in replication initiation and DNA repair; however, the contextual regulation of its unwinding activity is not fully described. Mutations in RECQL4 have been linked to three diseases including Rothmund-Thomson syndrome, which is characterized by osteoskeletal deformities, photosensitivity, and increased osteosarcoma susceptibility. Understanding regulation of RECQL4 helicase activity by interaction partners will allow deciphering its role as an enzyme and a signaling cofactor in different cellular contexts. We became interested in studying the interaction of RECQL4 with ribosomal protein S3 (RPS3) because previous studies have shown that RPS3 activity is sometimes associated with phenotypes mimicking those of mutated RECQL4. RPS3 is a small ribosomal protein that also has extraribosomal functions, including apurnic-apyrimidinic endonuclease-like activity suggested to be important during DNA repair. Here, we report a functional and physical interaction between RPS3 and RECQL4 and show that this interaction may be enhanced during cellular stress. We show that RPS3 inhibits ATPase, DNA binding, and helicase activities of RECQL4 through their direct interaction. Further domain analysis shows that N-terminal 1-320 amino acids of RECQL4 directly interact with the C-terminal 94-244 amino acids of RPS3 (C-RPS3). Biochemical analysis of C-RPS3 revealed that it comprises a standalone apurnic-apyrimidinic endonuclease-like domain. We used U2OS cells to show that oxidative stress and UV exposure could enhance the interaction between nuclear RPS3 and RECQL4. Regulation of RECQL4 biochemical activities by RPS3 along with nuclear interaction during UV and oxidative stress may serve to modulate active DNA repair.

Aging in Rothmund-Thomson syndrome and related RECQL4 genetic disorders

Rothmund-Thomson Syndrome (RTS) is a rare autosomal recessive disease which manifests several clinical features of accelerated aging. These findings include atrophic skin and pigment changes, alopecia, osteopenia, cataracts, and an increased incidence of cancer for patients carrying RECQL4 germline mutations. Mutations in RECQL4 are responsible for the majority of cases of RTS. RECQL4 belongs to RECQ DNA helicase family which has been shown to participate in many aspects of DNA metabolism. In the past several years, accumulated evidence indicates that RECQL4 is important not only in cancer development but also in the aging process. In this review, based on recent research data, we summarize the common aging findings in RTS patients and propose possible mechanisms to explain the aging features in these patients.

RECQL4 Promotes DNA End Resection in Repair of DNA Double-Strand Breaks

The RecQ helicase RECQL4, mutated in Rothmund-Thomson syndrome, regulates genome stability, aging, and cancer. Here, we identify a crucial role for RECQL4 in DNA end resection, which is the initial and an essential step of homologous recombination (HR)-dependent DNA double-strand break repair (DSBR). Depletion of RECQL4 severely reduces HR-mediated repair and 5' end resection in vivo. RECQL4 physically interacts with MRE11-RAD50-NBS1 (MRN), which senses DSBs and initiates DNA end resection with CtIP. The MRE11 exonuclease regulates the retention of RECQL4 at laser-induced DSBs. RECQL4 also directly interacts with CtIP via its N-terminal domain and promotes CtIP recruitment to the MRN complex at DSBs. Moreover, inactivation of RECQL4's helicase activity impairs DNA end processing and HR-dependent DSBR without affecting its interaction with MRE11 and CtIP, suggesting an important role for RECQL4's unwinding activity in the process. Thus, we report that RECQL4 is an important participant in HR-dependent DSBR.