CSB protein is (a direct target of HIF-1 and) a critical mediator of the hypoxic response

A subset of human dermal fibroblasts overexpressing Cockayne syndrome group B protein resist UVB radiation-mediated premature senescence

Ultraviolet B (UVB) radiation is a major contributor to skin photoaging. Although mainly absorbed by the epidermis, UVB photons managing to penetrate the upper dermis affect human dermal fibroblasts (HDFs), leading, among others, to the accumulation of senescent cells. In vitro studies have shown that repeated exposures to subcytotoxic UVB radiation doses provoke HDFs' premature senescence shortly after the end of the treatment period. Here, we found that repetitive exposures to non-cytotoxic UVB radiation doses after several days lead to mixed cultures, containing both senescent cells and fibroblasts resisting senescence. "Resistant" fibroblasts were more resilient to a novel intense UVB radiation stimulus. RNA-seq analysis revealed that ERCC6, encoding Cockayne syndrome group B (CSB) protein, is up-regulated in resistant HDFs compared to young and senescent cells. CSB was found to be a key molecule conferring protection toward UVB-induced cytotoxicity and senescence, as siRNA-mediated CSB loss-of-expression rendered HDFs significantly more susceptible to a high UVB radiation dose, while cells from a CSB-deficient patient were found to be more sensitive to UVB-mediated toxicity, as well as senescence. UVB-resistant HDFs remained normal (able to undergo replicative senescence) and non-tumorigenic. Even though they formed a distinct population in-between young and senescent cells, resistant HDFs retained numerous tissue-impairing characteristics of the senescence-associated secretory phenotype, including increased matrix metalloprotease activity and promotion of epidermoid tumor xenografts in immunodeficient mice. Collectively, here we describe a novel subpopulation of HDFs showing increased resistance to UVB-mediated premature senescence while retaining undesirable traits that may negatively affect skin homeostasis.

ATP-Dependent Chromatin Remodeler CSB Couples DNA Repair Pathways to Transcription with Implications for Cockayne Syndrome and Cancer Therapy

Efficient DNA lesion repair is crucial for cell survival, especially within actively transcribed DNA regions that contain essential genetic information. Additionally, DNA breaks in regions of active transcription are prone to generating insertions and deletions, which are hallmark features of cancer genomes. Cockayne syndrome protein B (CSB) is the sole ATP-dependent chromatin remodeler that is essential for coupling DNA repair pathways with transcription, leading to more efficient DNA repair in regions of active transcription. CSB is best known for its essential function in transcription-coupled nucleotide excision repair (TC-NER), a process that rapidly removes helix-distorting DNA lesions that stall RNA polymerase II, such as those created by chemotherapeutic platinum compounds and UV irradiation. In addition to NER, CSB has also been reported to couple homologous recombination to transcription. Most recently, CSB has also been shown to couple single-strand DNA break repair to transcription. In this review, we will discuss the overlapping and distinct mechanisms by which CSB couples these different DNA repair pathways to transcription. We will also discuss how these CSB functions may account for Cockayne syndrome and the emerging roles of CSB as an innovative target for cancer therapy.

Transcription factors, nucleotide excision repair, and cancer: A review of molecular interplay

Bulky DNA adducts are mostly formed by external factors such as UV irradiation, smoking or treatment with DNA crosslinking agents. If such DNA adducts are not removed by nucleotide excision repair, they can lead to formation of driver mutations that contribute to cancer formation. Transcription factors (TFs) may critically affect both DNA adduct formation and repair efficiency at the binding site to DNA. For example, "hotspot" mutations in melanoma coincide with UV-induced accumulated cyclobutane pyrimidine dimer (CPD) adducts and/or inhibited repair at the binding sites of some TFs. Similarly, anticancer treatment with DNA cross-linkers may additionally generate DNA adducts leading to secondary mutations and the formation of malignant subclones. In addition, some TFs are overexpressed in response to UV irradiation or chemotherapeutic treatment, activating oncogenic and anti-oncogenic pathways independently of nucleotide excision repair itself. This review focuses on the interplay between TFs and nucleotide excision repair during cancer development and progression.

Cockayne Syndrome Patient iPSC-Derived Brain Organoids and Neurospheres Show Early Transcriptional Dysregulation of Biological Processes Associated with Brain Development and Metabolism

Cockayne syndrome (CS) is a rare hereditary autosomal recessive disorder primarily caused by mutations in Cockayne syndrome protein A (CSA) or B (CSB). While many of the functions of CSB have been at least partially elucidated, little is known about the actual developmental dysregulation in this devasting disorder. Of particular interest is the regulation of cerebral development as the most debilitating symptoms are of neurological nature. We generated neurospheres and cerebral organoids utilizing Cockayne syndrome B protein (CSB)-deficient induced pluripotent stem cells derived from two patients with distinct severity levels of CS and healthy controls. The transcriptome of both developmental timepoints was explored using RNA-Seq and bioinformatic analysis to identify dysregulated biological processes common to both patients with CS in comparison to the control. CSB-deficient neurospheres displayed upregulation of the VEGFA-VEGFR2 signalling pathway, vesicle-mediated transport and head development. CSB-deficient cerebral organoids exhibited downregulation of brain development, neuron projection development and synaptic signalling. We further identified the upregulation of steroid biosynthesis as common to both timepoints, in particular the upregulation of the cholesterol biosynthesis branch. Our results provide insights into the neurodevelopmental dysregulation in patients with CS and strengthen the theory that CS is not only a neurodegenerative but also a neurodevelopmental disorder.

Role of Cockayne Syndrome Group B Protein in Replication Stress: Implications for Cancer Therapy

A variety of endogenous and exogenous insults are capable of impeding replication fork progression, leading to replication stress. Several SNF2 fork remodelers have been shown to play critical roles in resolving this replication stress, utilizing different pathways dependent upon the nature of the DNA lesion, location on the DNA, and the stage of the cell cycle, to complete DNA replication in a manner preserving genetic integrity. Under certain conditions, however, the attempted repair may lead to additional genetic instability. Cockayne syndrome group B (CSB) protein, a SNF2 chromatin remodeler best known for its role in transcription-coupled nucleotide excision repair, has recently been shown to catalyze fork reversal, a pathway that can provide stability of stalled forks and allow resumption of DNA synthesis without chromosome breakage. Prolonged stalling of replication forks may collapse to give rise to DNA double-strand breaks, which are preferentially repaired by homology-directed recombination. CSB plays a role in repairing collapsed forks by promoting break-induced replication in S phase and early mitosis. In this review, we discuss roles of CSB in regulating the sources of replication stress, replication stress response, as well as the implications of CSB for cancer therapy.

Behavioral innovation and genomic novelty are associated with the exploitation of a challenging dietary opportunity by an avivorous bat

Foraging on nocturnally migrating birds is one of the most challenging foraging tasks in the animal kingdom. Only three bat species (e.g., Ia io) known to date can prey on migratory birds. However, how these bats have exploited this challenging dietary niche remains unknown. Here, we demonstrate that I. io hunts at the altitude of migrating birds during the bird migration season. The foraging I. io exhibited high flight altitudes (up to 4945 m above sea level) and high flight speeds (up to 143.7 km h⁻¹). I. io in flight can actively prey on birds in the night sky via echolocation cues. Genes associated with DNA damage repair, hypoxia adaptation, biting and mastication, and digestion and metabolism have evolved to adapt to this species’ avivorous habits. Our results suggest that the evolution of behavioral innovation and genomic novelty are associated with the exploitation of challenging dietary opportunities.

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Predation on nocturnally migrating birds is rare and challenging in nature

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Bats exhibit high flight altitude and speed associated with foraging on migrating birds

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Bats can actively prey on birds in the night sky via echolocation cues

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The adaptive evolution of genes enables bats to adapt to the avivorous habits

Functional indications for transposase domestications - Characterization of the human piggyBac transposase derived (PGBD) activities

Transposable elements are widespread in all living organisms. In addition to self-reproduction, they are a major source of genetic variation that drives genome evolution but our knowledge of the functions of human genes derived from transposases is limited. There are examples of transposon-derived, domesticated human genes that lost (SETMAR) or retained (THAP9) their transposase activity, however, several remnants in the human genome have not been thoroughly investigated yet. These include the five human piggyBac-derived sequences (PGBD1-5) which share ancestry with the Trichoplusia ni originated piggyBac (PB) transposase. Since PB is widely used in gene delivery applications, the potential activities of endogenous PGBDs are important to address. However, previous data is controversial, especially with the claimed transposition activity of PGBD5, it awaits further investigations. Here, we aimed to systematically analyze all five human PGBD proteins from several aspects, including phylogenetic conservation, potential transposase activity, expression pattern and their regulation in different stress conditions. Among PGBDs, PGBD5 is under the highest purifying selection, and exhibits the most cell type specific expression pattern. In a two-component vector system, none of the human PGBDs could mobilize either the insect PB transposon or the endogenous human PB-like MER75 and MER85 elements with intact terminal sequences. When cells were exposed to various stress conditions, including hypoxia, oxidative or UV stress, the expression profiles of all PGBDs showed different, often cell type specific responses; however, the pattern of PGBD5 in most cases had the opposite tendency than that of the other piggyBac-derived elements. Taken together, our results indicate that human PGBD elements did not retain their mobilizing activity, but their cell type specific, and cellular stress related expression profiles point toward distinct domesticated functions that require further characterization.

A matter of delicate balance: Loss and gain of Cockayne syndrome proteins in premature aging and cancer

DNA repair genes are critical for preserving genomic stability and it is well established that mutations in DNA repair genes give rise to progeroid diseases due to perturbations in different DNA metabolic activities. Cockayne Syndrome (CS) is an autosomal recessive inheritance caused by inactivating mutations in CSA and CSB genes. This review will primarily focus on the two Cockayne Syndrome proteins, CSA and CSB, primarily known to be involved in Transcription Coupled Repair (TCR). Curiously, dysregulated expression of CS proteins has been shown to exhibit differential health outcomes: lack of CS proteins due to gene mutations invariably leads to complex premature aging phenotypes, while excess of CS proteins is associated with carcinogenesis. Thus it appears that CS genes act as a double-edged sword whose loss or gain of expression leads to premature aging and cancer. Future mechanistic studies on cell and animal models of CS can lead to potential biological targets for interventions in both aging and cancer development processes. Some of these exciting possibilities will be discussed in this review in light of the current literature.

CSA Antisense Targeting Enhances Anticancer Drug Sensitivity in Breast Cancer Cells, including the Triple-Negative Subtype

Simple Summary

Breast cancer (BC), the most frequent malignancy in woman, shows a high rate of cancer recurrence and resistance to treatment, particularly in Triple-Negative Breast Cancer (TNBC) subtype. Starting from the observation that different subtypes of BC cells, including the TNBC one, display an increased expression of Cockayne Syndrome group A (CSA) protein, which is involved in multiple functions such as DNA repair, transcription and in conferring cell robustness when it is up-regulated, we demonstrated that CSA ablation by AntiSense Oligonucleotides (ASOs) drastically impairs tumorigenicity of BC cells by hampering their survival and proliferative capabilities without affecting normal breast cells. Suppression of CSA does result in lowering the IC₅₀ value of Oxaliplatin and Paclitaxel, two commonly used chemotherapeutic agents in breast cancer treatment, allowing the use of a very low dose of chemotherapeutic that is non-toxic to the normal breast cell line. Finally, CSA ablation restores drug sensitivity in oxaliplatin-resistant cells. Based on these findings, we can conclude that CSA may be a very attractive target for the development of new specific anticancer therapies.

Abstract

Breast cancer (BC) is the most common cancer with the highest frequency of death among women. BC is highly heterogenic at the genetic, biological, and clinical level. Despite the significant improvements in diagnosis and treatments of BC, the high rate of cancer recurrence and resistance to treatment remains a major challenge in clinical practice. This issue is particularly relevant in Triple-Negative Breast Cancer (TNBC) subtype, for which chemotherapy remains the main standard therapeutic approach. Here, we observed that BC cells, belonging to different subtypes, including the TNBC, display an increased expression of Cockayne Syndrome group A (CSA) protein, which is involved in multiple functions such as DNA repair, transcription, mitochondrial homeostasis, and cell division and that recently was found to confer cell robustness when it is up-regulated. We demonstrated that CSA ablation by AntiSense Oligonucleotides (ASOs) drastically impairs tumorigenicity of BC cells by hampering their survival and proliferative capabilities without damaging normal cells. Moreover, suppression of CSA dramatically sensitizes BC cells to platinum and taxane derivatives, which are commonly used for BC first-line therapy, even at very low doses not harmful to normal cells. Finally, CSA ablation restores drug sensitivity in oxaliplatin-resistant cells. Based on these results, we conclude that CSA might be a very attractive target for the development of more effective anticancer therapies.

Neuroblastoma Cells Depend on CSB for Faithful Execution of Cytokinesis and Survival

Neuroblastoma, the most common extra-cranial solid tumor of early childhood, is one of the major therapeutic challenges in child oncology: it is highly heterogenic at a genetic, biological, and clinical level. The high-risk cases have one of the least favorable outcomes amongst pediatric tumors, and the mortality rate is still high, regardless of the use of intensive multimodality therapies. Here, we observed that neuroblastoma cells display an increased expression of Cockayne Syndrome group B (CSB), a pleiotropic protein involved in multiple functions such as DNA repair, transcription, mitochondrial homeostasis, and cell division, and were recently found to confer cell robustness when they are up-regulated. In this study, we demonstrated that RNAi-mediated suppression of CSB drastically impairs tumorigenicity of neuroblastoma cells by hampering their proliferative, clonogenic, and invasive capabilities. In particular, we observed that CSB ablation induces cytokinesis failure, leading to caspases 9 and 3 activation and, subsequently, to massive apoptotic cell death. Worthy of note, a new frontier in cancer treatment, already proved to be successful, is cytokinesis-failure-induced cell death. In this context, CSB ablation seems to be a new and promising anticancer strategy for neuroblastoma therapy.

Elevated glucose increases genomic instability by inhibiting nucleotide excision repair

Exposure to chronic, elevated glucose inhibits nucleotide excision repair, which leads to accumulation of DNA glycation adducts, increased DNA strand breaks, and activation of the DNA damage response.

We investigated potential mechanisms by which elevated glucose may promote genomic instability. Gene expression studies, protein measurements, mass spectroscopic analyses, and functional assays revealed that elevated glucose inhibited the nucleotide excision repair (NER) pathway, promoted DNA strand breaks, and increased levels of the DNA glycation adduct N²-(1-carboxyethyl)-2ʹ-deoxyguanosine (CEdG). Glycation stress in NER-competent cells yielded single-strand breaks accompanied by ATR activation, γH2AX induction, and enhanced non-homologous end-joining and homology-directed repair. In NER-deficient cells, glycation stress activated ATM/ATR/H2AX, consistent with double-strand break formation. Elevated glucose inhibited DNA repair by attenuating hypoxia-inducible factor-1α–mediated transcription of NER genes via enhanced 2-ketoglutarate–dependent prolyl hydroxylase (PHD) activity. PHD inhibition enhanced transcription of NER genes and facilitated CEdG repair. These results are consistent with a role for hyperglycemia in promoting genomic instability as a potential mechanism for increasing cancer risk in metabolic disease. Because of the pleiotropic functions of many NER genes beyond DNA repair, these results may have broader implications for cellular pathophysiology.

NAD+ metabolism controls growth inhibition by HIF1 in normoxia and determines differential sensitivity of normal and cancer cells

The hypoxia-induced transcription factor HIF1 inhibits cell growth in normoxia through poorly understood mechanisms. A constitutive upregulation of hypoxia response is associated with increased malignancy, indicating a loss of antiproliferative effects of HIF1 in cancer cells. To understand these differences, we examined a control of cell cycle in primary human cells with activated hypoxia response in normoxia. Activated HIF1 caused a global slowdown of cell cycle progression through G1, S and G2 phases leading to the loss of mitotic cells. Cell cycle inhibition required a prolonged HIF1 activation and was not associated with upregulation of p53 or the CDK inhibitors p16, p21 or p27. Growth inhibition by HIF1 was independent of its Asn803 hydroxylation or the presence of HIF2. Antiproliferative effects of hypoxia response were alleviated by inhibition of lactate dehydrogenase and more effectively, by boosting cellular production of NAD⁺, which was decreased by HIF1 activation. In comparison to normal cells, various cancer lines showed several fold-higher expression of NAMPT which is a rate-limiting enzyme in the main biosynthetic pathway for NAD⁺. Inhibition of NAMPT activity in overexpressor cancer cells sensitized them to antigrowth effects of HIF1. Thus, metabolic changes in cancer cells, such as enhanced NAD⁺ production, create resistance to growth-inhibitory activity of HIF1 permitting manifestation of its tumor-promoting properties.AbbreviationsDMOG: dimethyloxalylglycine, DM-NOFD: dimethyl N-oxalyl-D-phenylalanine, NMN: β-nicotinamide mononucleotide.

Cockayne Syndrome Group B (CSB): The Regulatory Framework Governing the Multifunctional Protein and Its Plausible Role in Cancer

Cockayne syndrome (CS) is a DNA repair syndrome characterized by a broad spectrum of clinical manifestations such as neurodegeneration, premature aging, developmental impairment, photosensitivity and other symptoms. Mutations in Cockayne syndrome protein B (CSB) are present in the vast majority of CS patients and in other DNA repair-related pathologies. In the literature, the role of CSB in different DNA repair pathways has been highlighted, however, new CSB functions have been identified in DNA transcription, mitochondrial biology, telomere maintenance and p53 regulation. Herein, we present an overview of identified structural elements and processes that impact on CSB activity and its post-translational modifications, known to balance the different roles of the protein not only during normal conditions but most importantly in stress situations. Moreover, since CSB has been found to be overexpressed in a number of different tumors, its role in cancer is presented and possible therapeutic targeting is discussed.

Current and emerging roles of Cockayne syndrome group B (CSB) protein

Cockayne syndrome (CS) is a segmental premature aging syndrome caused primarily by defects in the CSA or CSB genes. In addition to premature aging, CS patients typically exhibit microcephaly, progressive mental and sensorial retardation and cutaneous photosensitivity. Defects in the CSB gene were initially thought to primarily impair transcription-coupled nucleotide excision repair (TC-NER), predicting a relatively consistent phenotype among CS patients. In contrast, the phenotypes of CS patients are pleiotropic and variable. The latter is consistent with recent work that implicates CSB in multiple cellular systems and pathways, including DNA base excision repair, interstrand cross-link repair, transcription, chromatin remodeling, RNAPII processing, nucleolin regulation, rDNA transcription, redox homeostasis, and mitochondrial function. The discovery of additional functions for CSB could potentially explain the many clinical phenotypes of CSB patients. This review focuses on the diverse roles played by CSB in cellular pathways that enhance genome stability, providing insight into the molecular features of this complex premature aging disease.

The emerging role of Cockayne group A and B proteins in ubiquitin/proteasome-directed protein degradation

When mutated, csa and csb genes are responsible of the complex phenotype of the premature aging Cockayne Syndrome (CS). Our working hypothesis is to reconcile the multiple cellular and molecular phenotypes associated to CS within the unifying molecular function of CSA and CSB proteins in the cascade of events leading to ubiquitin/proteasome-directed protein degradation, which occurs in processes as DNA repair, transcription and cell division. This achievement may reasonably explain the plethora of cellular UPS-regulated functions that result impaired when either CSA or CSB are mutated and suggestively explains part of their pleiotropic effect. This review is aimed to solicit the interest of the scientific community in further investigating this aspect, since we believe that the identification of the ubiquitin-proteasome machinery as a new potential therapeutic target, able to comprehensively face the different molecular aspects of CS, whether confirmed and corroborated by in vivo studies, would open a promising avenue to design effective therapeutic intervention.

The Interplay Between Tumor Suppressor p53 and Hypoxia Signaling Pathways in Cancer

Hypoxia is a hallmark of solid tumors and plays a critical role in different steps of tumor progression, including proliferation, survival, angiogenesis, metastasis, metabolic reprogramming, and stemness of cancer cells. Activation of the hypoxia-inducible factor (HIF) signaling plays a critical role in regulating hypoxic responses in tumors. As a key tumor suppressor and transcription factor, p53 responds to a wide variety of stress signals, including hypoxia, and selectively transcribes its target genes to regulate various cellular responses to exert its function in tumor suppression. Studies have demonstrated a close but complex interplay between hypoxia and p53 signaling pathways. The p53 levels and activities can be regulated by the hypoxia and HIF signaling differently depending on the cell/tissue type and the severity and duration of hypoxia. On the other hand, p53 regulates the hypoxia and HIF signaling at multiple levels. Many tumor-associated mutant p53 proteins display gain-of-function (GOF) oncogenic activities to promote cancer progression. Emerging evidence has also shown that GOF mutant p53 can promote cancer progression through its interplay with the hypoxia and HIF signaling pathway. In this review, we summarize our current understanding of the interplay between the hypoxia and p53 signaling pathways, its impact upon cancer progression, and its potential application in cancer therapy.

Identification of metabolic changes leading to cancer susceptibility in Fanconi anemia cells

Fanconi anemia (FA) is a chromosomal instability disorder of bone marrow associated with aplastic anemia, congenital abnormalities and a high risk of malignancies. The identification of more than two dozen FA genes has revealed a plethora of interacting proteins that are mainly involved in repair of DNA interstrand crosslinks (ICLs). Other important findings associated with FA are inflammation, oxidative stress response, mitochondrial dysfunction and mitophagy. In this work, we performed quantitative proteomic and metabolomic analyses on defective FA cells and identified a number of metabolic abnormalities associated with cancer. In particular, an increased de novo purine biosynthesis, a high concentration of fumarate, and an accumulation of purinosomal clusters were found. This was in parallel with decreased OXPHOS and altered glycolysis. On the whole, our results indicate an association between the need for nitrogenous bases upon impaired DDR in FA cells with a subsequent increase in purine metabolism and a potential role in oncogenesis.

Hypoxia-Inducible Lysine Methyltransferases: G9a and GLP Hypoxic Regulation, Non-histone Substrate Modification, and Pathological Relevance

Oxygen sensing is inherent among most animal lifeforms and is critical for organism survival. Oxygen sensing mechanisms collectively trigger cellular and physiological responses that enable adaption to a reduction in ideal oxygen levels. The major mechanism by which oxygen-responsive changes in the transcriptome occur are mediated through the hypoxia-inducible factor (HIF) pathway. Upon reduced oxygen conditions, HIF activates hypoxia-responsive gene expression programs. However, under normal oxygen conditions, the activity of HIF is regularly suppressed by cellular oxygen sensors; prolyl-4 and asparaginyl hydroxylases. Recently, these oxygen sensors have also been found to suppress the function of two lysine methyltransferases, G9a and G9a-like protein (GLP). In this manner, the methyltransferase activity of G9a and GLP are hypoxia-inducible and thus present a new avenue of low-oxygen signaling. Furthermore, G9a and GLP elicit lysine methylation on a wide variety of non-histone proteins, many of which are known to be regulated by hypoxia. In this article we aim to review the effects of oxygen on G9a and GLP function, non-histone methylation events inflicted by these methyltransferases, and the clinical relevance of these enzymes in cancer.

Inside the hypoxic tumour: reprogramming of the DDR and radioresistance

The hypoxic tumour is a chaotic landscape of struggle and adaption. Against the adversity of oxygen starvation, hypoxic cancer cells initiate a reprogramming of transcriptional activities, allowing for survival, metastasis and treatment failure. This makes hypoxia a crucial feature of aggressive tumours. Its importance, to cancer and other diseases, was recognised by the award of the 2019 Nobel Prize in Physiology or Medicine for research contributing to our understanding of the cellular response to oxygen deprivation. For cancers with limited treatment options, for example those that rely heavily on radiotherapy, the results of hypoxic adaption are particularly restrictive to treatment success. A fundamental aspect of this hypoxic reprogramming with direct relevance to radioresistance, is the alteration to the DNA damage response, a complex set of intermingling processes that guide the cell (for good or for bad) towards DNA repair or cell death. These alterations, compounded by the fact that oxygen is required to induce damage to DNA during radiotherapy, means that hypoxia represents a persistent obstacle in the treatment of many solid tumours. Considerable research has been done to reverse, correct or diminish hypoxia's power over successful treatment. Though many clinical trials have been performed or are ongoing, particularly in the context of imaging studies and biomarker discovery, this research has yet to inform clinical practice. Indeed, the only hypoxia intervention incorporated into standard of care is the use of the hypoxia-activated prodrug Nimorazole, for head and neck cancer patients in Denmark. Decades of research have allowed us to build a picture of the shift in the DNA repair capabilities of hypoxic cancer cells. A literature consensus tells us that key signal transducers of this response are upregulated, where repair proteins are downregulated. However, a complete understanding of how these alterations lead to radioresistance is yet to come.

HDAC inhibition improves autophagic and lysosomal function to prevent loss of subcutaneous fat in a mouse model of Cockayne syndrome

Cockayne syndrome (CS), a hereditary form of premature aging predominantly caused by mutations in the csb gene, affects multiple organs including skin where it manifests with hypersensitivity toward ultraviolet (UV) radiation and loss of subcutaneous fat. There is no curative treatment for CS, and its pathogenesis is only partially understood. Originally considered for its role in DNA repair, Cockayne syndrome group B (CSB) protein most likely serves additional functions. Using CSB-deficient human fibroblasts, Caenorhabditiselegans, and mice, we show that CSB promotes acetylation of α-tubulin and thereby regulates autophagy. At the organ level, chronic exposure of csb^m/m mice to UVA radiation caused a severe skin phenotype with loss of subcutaneous fat, inflammation, and fibrosis. These changes in skin tissue were associated with an accumulation of autophagic/lysosomal proteins and reduced amounts of acetylated α-tubulin. At the cellular level, we found that CSB directly interacts with the histone deacetylase 6 (HDAC6) and the α-tubulin acetyltransferase MEC-17. Upon UVA irradiation, CSB is recruited to the centrosome where it colocalizes with dynein and HDAC6. Administration of the pan-HDAC inhibitor SAHA (suberoylanilide hydroxamic acid) enhanced α-tubulin acetylation, improved autophagic function in CSB-deficient models from all three species, and rescued the skin phenotype in csb^m/m mice. HDAC inhibition may thus represent a therapeutic option for CS.

Oxidative nucleophilic substitution selectively produces cambinol derivatives with antiproliferative activity on bladder cancer cell lines

Methyltrioxorhenium mediated oxidative addition/elimination nucleophilic substitution yielded alkylamino and arylamino cambinol derivatives characterized by anti-proliferative activity against wild-type and p53 mutated MGH-U1 and RT112 bladder cancer cell lines. Some of the novel compounds showed an activity higher than that of the lead compound. The reaction was highly regioselective, affording for the first time a panel of C-2 cambinol substitution products. Aliphatic primary and secondary amines, and primary aromatic amines, were used as nitrogen centered nucleophiles. Surprisingly, the antiproliferative activity of C-2 substituted cambinol derivatives was not correlated to the induction of p53 protein, as evaluated by the analysis of the cell viability on wild-type and p53 mutated cancer cell lines, and further confirmed by western blot analyses. These data suggest that they exert their antiproliferative activity by a mechanism completely different from cambinol.

CSB: An Emerging Actionable Target for Cancer Therapy

The DNA repair protein Cockayne syndrome group B (CSB) is frequently found overexpressed in cancer cells. High CSB levels favor tumor cell proliferation whilst inhibiting apoptosis. Conversely, the suppression of CSB has significant anticancer effects. In this manuscript we describe CSB downregulation as a potential new therapeutic approach in cancer.

Design and characterization of chionodracine-derived antimicrobial peptides with enhanced activity against drug-resistant human pathogens

Design of new chionodracine-derived peptides with potent activity against drug-resistant human pathogens.

Nickel-induced HIF-1α promotes growth arrest and senescence in normal human cells but lacks toxic effects in transformed cells

Nickel is a human carcinogen that acts as a hypoxia mimic by activating the transcription factor HIF-1α and hypoxia-like transcriptomic responses. Hypoxia and elevated HIF-1α are typically associated with drug resistance in cancer cells, which is caused by increased drug efflux and other mechanisms. Here we examined the role of HIF-1α in uptake of soluble Ni(II) and Ni(II)-induced cell fate outcomes using si/shRNA knockdowns and gene deletion models. We found that HIF-1α had no effect on accumulation of Ni(II) in two transformed (H460, A549) and two normal human cell lines (IMR90, WI38). The loss of HIF-1α also produced no significant impact on p53-dependent and p53-independent apoptotic responses or clonogenic survival of Ni(II)-treated transformed cells. In normal human cells, HIF-1α enhanced the ability of Ni(II) to inhibit cell proliferation and cause a permanent growth arrest (senescence). Consistent with its growth-suppressive effects, HIF-1α was important for upregulation of the cell cycle inhibitors p21 (CDKN1A) and p27 (CDKN1B). Irrespective of HIF-1α status, Ni(II) strongly increased levels of MYC protein but did not change protein expression of the cell cycle-promoting phosphatase CDC25A or the CDK inhibitor p16. Our findings indicate that HIF-1α limits propagation of Ni(II)-damaged normal cells, suggesting that it may act in a tumor suppressor-like manner during early stages of Ni(II) carcinogenesis.

CSB ablation induced apoptosis is mediated by increased endoplasmic reticulum stress response

The DNA repair protein Cockayne syndrome group B (CSB) has been recently identified as a promising anticancer target. Suppression, by antisense technology, of this protein causes devastating effects on tumor cells viability, through a massive induction of apoptosis, while being non-toxic to non-transformed cells. To gain insights into the mechanisms underlying the pro-apoptotic effects observed after CSB ablation, global gene expression patterns were determined, to identify genes that were significantly differentially regulated as a function of CSB expression. Our findings revealed that response to endoplasmic reticulum stress and response to unfolded proteins were ranked top amongst the cellular processes affected by CSB suppression. The major components of the endoplasmic reticulum stress-mediated apoptosis pathway, including pro-apoptotic factors downstream of the ATF3-CHOP cascade, were dramatically up-regulated. Altogether our findings add new pieces to the understanding of CSB mechanisms of action and to the molecular basis of CS syndrome.

Identification of Novel Proteins Co-Purifying with Cockayne Syndrome Group B (CSB) Reveals Potential Roles for CSB in RNA Metabolism and Chromatin Dynamics

The CSB protein, a member of the SWI/SNF ATP dependent chromatin remodeling family of proteins, plays a role in a sub-pathway of nucleotide excision repair (NER) known as transcription coupled repair (TCR). CSB is frequently mutated in Cockayne syndrome group B, a segmental progeroid human autosomal recessive disease characterized by growth failure and degeneration of multiple organs. Though initially classified as a DNA repair protein, recent studies have demonstrated that the loss of CSB results in pleiotropic effects. Identification of novel proteins belonging to the CSB interactome may be useful not only for predicting the molecular basis for diverse pathological symptoms of CS-B patients but also for unraveling the functions of CSB in addition to its authentic role in DNA repair. In this study, we performed tandem affinity purification (TAP) technology coupled with mass spectrometry and co-immunoprecipitation studies to identify and characterize the proteins that potentially interact with CSB-TAP. Our approach revealed 33 proteins that were not previously known to interact with CSB. These newly identified proteins indicate potential roles for CSB in RNA metabolism involving repression and activation of transcription process and in the maintenance of chromatin dynamics and integrity.

Role of compartmentalization on HiF-1α degradation dynamics during changing oxygen conditions: a computational approach

HiF-1α is the central protein driving the cellular response to hypoxia. Its accumulation in cancer cells is linked to the appearance of chemoresistant and aggressive tumor phenotypes. As a consequence, understanding the regulation of HiF-1α dynamics is a major issue to design new anti-cancer therapies. In this paper, we propose a model of the hypoxia pathway, involving HiF-1α and its inhibitor pVHL. Based on data from the literature, we made the hypothesis that the regulation of HiF-1α involves two compartments (nucleus and cytoplasm) and a constitutive shuttle of the pVHL protein between them. We first show that this model captures correctly the main features of HiF-1α dynamics, including the bi-exponential degradation profile in normoxia, the kinetics of induction in hypoxia, and the switch-like accumulation. Second, we simulated the effects of a hypoxia/reoxygenation event, and show that it generates a strong instability of HiF-1α. The protein concentration rapidly increases 3 hours after the reoxygenation, and exhibits an oscillating pattern. This effect vanishes if we do not consider compartmentalization of HiF-1α. This result can explain various counter-intuitive observations about the specific molecular and cellular response to the reoxygenation process. Third, we simulated the HiF-1α dynamics in the tumor case. We considered different types of mutations associated with tumorigenesis, and we compared their consequences on HiF-1α dynamics. Then, we tested different therapeutics strategies. We show that a therapeutic decrease of HiF-1α nuclear level is not always correlated with an attenuation of reoxygenation-induced instabilities. Thus, it appears that the design of anti-HiF-1α therapies have to take into account these two aspects to maximize their efficiency.

ERCC6 dysfunction presenting as progressive neurological decline with brain hypomyelination

Mutations in ERCC6 are associated with growth failure, intellectual disability, neurological dysfunction and deterioration, premature aging, and photosensitivity. We describe siblings with biallelic ERCC6 mutations (NM_000124.2:c. [543+4delA];[2008C>T]) and brain hypomyelination, microcephaly, cognitive decline, and skill regression but without photosensitivity or progeria. DNA repair assays on cultured skin fibroblasts confirmed a defect of transcription-coupled nucleotide excision repair and increased ultraviolet light sensitivity. This report expands the disease spectrum associated with ERCC6 mutations.

The cockayne syndrome B protein is essential for neuronal differentiation and neuritogenesis

Cockayne syndrome (CS) is a progressive developmental and neurodegenerative disorder resulting in premature death at childhood and cells derived from CS patients display DNA repair and transcriptional defects. CS is caused by mutations in csa and csb genes, and patients with csb mutation are more prevalent. A hallmark feature of CSB patients is neurodegeneration but the precise molecular cause for this defect remains enigmatic. Further, it is not clear whether the neurodegenerative condition is due to loss of CSB-mediated functions in adult neurogenesis. In this study, we examined the role of CSB in neurogenesis by using the human neural progenitor cells that have self-renewal and differentiation capabilities. In this model system, stable CSB knockdown dramatically reduced the differentiation potential of human neural progenitor cells revealing a key role for CSB in neurogenesis. Neurite outgrowth, a characteristic feature of differentiated neurons, was also greatly abolished in CSB-suppressed cells. In corroboration with this, expression of MAP2 (microtubule-associated protein 2), a crucial player in neuritogenesis, was also impaired in CSB-suppressed cells. Consistent with reduced MAP2 expression in CSB-depleted neural cells, tandem affinity purification and chromatin immunoprecipitation studies revealed a potential role for CSB in the assembly of transcription complex on MAP2 promoter. Altogether, our data led us to conclude that CSB has a crucial role in coordinated regulation of transcription and chromatin remodeling activities that are required during neurogenesis.

Long-term disruption of maternal glucose homeostasis induced by prenatal glucocorticoid treatment correlates with miR-29 upregulation

Excess of glucocorticoids (GCs) during pregnancy is strongly associated with the programming of glucose intolerance in the offspring. However, the impact of high GC levels on maternal metabolism is not clearly documented. This study aimed to test the hypothesis that mothers exposed to elevated levels of GCs might also display long-term disturbances in glucose homeostasis. Dexamethasone (DEX) was administered noninvasively to the mothers via drinking water between the 14th and the 19th days of pregnancy. Mothers were subjected to glucose and insulin tolerance tests at 1, 2, 3, 6, and 12 mo postweaning. Pregnant rats not treated with DEX and age-matched virgin rats were used as controls. Pancreatic islets were isolated at the 20th day of pregnancy and 12 mo postweaning in order to evaluate glucose-stimulated insulin secretion. The expression of the miR-29 family was also studied due to its responsiveness to GCs and its well-documented role in the regulation of pancreatic β-cell function. Rats treated with DEX during pregnancy presented long-term glucose intolerance and impaired insulin secretion. These changes correlated with 1) increased expression of miR-29 and its regulator p53, 2) reduced expression of syntaxin-1a, a direct target of miR-29, and 3) altered expression of genes related to cellular senescence. Our data demonstrate that the use of DEX during pregnancy results in deleterious outcomes to the maternal metabolism, hallmarked by reduced insulin secretion and glucose intolerance. This maternal metabolic programming might be a consequence of time-sustained upregulation of miR-29s in maternal pancreatic islets.

A mathematical model of HiF-1α-mediated response to hypoxia on the G1/S transition

Hypoxia is known to influence the cell cycle by increasing the G1 phase duration or by inducing a quiescent state (arrest of cell proliferation). This entry into quiescence is a mean for the cell to escape from hypoxia-induced apoptosis. It is suggested that some cancer cells have gain the advantage over normal cells to easily enter into quiescence when environmental conditions, such as oxygen pressure, are unfavorable [43,1]. This ability contributes in the appearance of highly resistant and aggressive tumor phenotypes [2]. The HiF-1α factor is the key actor of the intracellular hypoxia pathway. As tumor cells undergo chronic hypoxic conditions, HiF-1α is present in higher level in cancer than in normal cells. Besides, it was shown that genetic mutations promoting overstabilization of HiF-1α are a feature of various types of cancers [7]. Finally, it is suggested that the intracellular level of HiF-1α can be related to the aggressiveness of the tumors [53,24,4,10]. However, up to now, mathematical models describing the G1/S transition under hypoxia, did not take into account the HiF-1α factor in the hypoxia pathway. Therefore, we propose a mathematical model of the G1/S transition under hypoxia, which explicitly integrates the HiF-1α pathway. The model reproduces the slowing down of G1 phase under moderate hypoxia, and the entry into quiescence of proliferating cells under severe hypoxia. We show how the inhibition of cyclin D by HiF-1α can induce quiescence; this result provides a theoretical explanation to the experimental observations of Wen et al. (2010) [50]. Thus, our model confirms that hypoxia-induced chemoresistance can be linked, for a part, to the negative regulation of cyclin D by HiF-1α.

Tumor hypoxia as a driving force in genetic instability

Sub-regions of hypoxia exist within all tumors and the presence of intratumoral hypoxia has an adverse impact on patient prognosis. Tumor hypoxia can increase metastatic capacity and lead to resistance to chemotherapy and radiotherapy. Hypoxia also leads to altered transcription and translation of a number of DNA damage response and repair genes. This can lead to inhibition of recombination-mediated repair of DNA double-strand breaks. Hypoxia can also increase the rate of mutation. Therefore, tumor cell adaptation to the hypoxic microenvironment can drive genetic instability and malignant progression. In this review, we focus on hypoxia-mediated genetic instability in the context of aberrant DNA damage signaling and DNA repair. Additionally, we discuss potential therapeutic approaches to specifically target repair-deficient hypoxic tumor cells.

Blinded by the UV light: how the focus on transcription-coupled NER has distracted from understanding the mechanisms of Cockayne syndrome neurologic disease

Cockayne syndrome (CS) is a devastating neurodevelopmental disorder, with growth abnormalities, progeriod features, and sun sensitivity. CS is typically considered to be a DNA repair disorder, since cells from CS patients have a defect in transcription-coupled nucleotide excision repair (TC-NER). However, cells from UV-sensitive syndrome patients also lack TC-NER, but these patients do not suffer from the neurologic and other abnormalities that CS patients do. Also, the neurologic abnormalities that affect CS patients (CS neurologic disease) are qualitatively different from those seen in NER-deficient XP patients. Therefore, the TC-NER defect explains the sun sensitive phenotype common to both CS and UVsS, but cannot explain CS neurologic disease. However, as CS neurologic disease is of much greater clinical significance than the sun sensitivity, there is a pressing need to understand its molecular basis. While there is evidence for defective repair of oxidative DNA damage and mitochondrial abnormalities in CS cells, here I propose that the defects in transcription by both RNA polymerases I and II that have been documented in CS cells provide a better explanation for many of the severe growth and neurodevelopmental defects in CS patients than defective DNA repair. The implications of these ideas for interpreting results from mouse models of CS, and for the development of treatments and therapies for CS patients are discussed.

Transcriptional regulation of human DNA repair genes following genotoxic stress: trigger mechanisms, inducible responses and genotoxic adaptation

DNA repair is the first barrier in the defense against genotoxic stress. In recent years, mechanisms that recognize DNA damage and activate DNA repair functions through transcriptional upregulation and post-translational modification were the focus of intensive research. Most DNA repair pathways are complex, involving many proteins working in discrete consecutive steps. Therefore, their balanced expression is important for avoiding erroneous repair that might result from excessive base removal and DNA cleavage. Amelioration of DNA repair requires both a fine-tuned system of lesion recognition and transcription factors that regulate repair genes in a balanced way. Transcriptional upregulation of DNA repair genes by genotoxic stress is counteracted by DNA damage that blocks transcription. Therefore, induction of DNA repair resulting in an adaptive response is only visible through a narrow window of dose. Here, we review transcriptional regulation of DNA repair genes in normal and cancer cells and describe mechanisms of promoter activation following genotoxic exposures through environmental carcinogens and anticancer drugs. The data available to date indicate that 25 DNA repair genes are subject to regulation following genotoxic stress in rodent and human cells, but for only a few of them, the data are solid as to the mechanism, homeostatic regulation and involvement in an adaptive response to genotoxic stress.

Oxidative DNA damage and nucleotide excision repair

SIGNIFICANCE

Oxidative DNA damage is repaired by multiple, overlapping DNA repair pathways. Accumulating evidence supports the hypothesis that nucleotide excision repair (NER), besides base excision repair (BER), is also involved in neutralizing oxidative DNA damage.

RECENT ADVANCES

NER includes two distinct sub-pathways: transcription-coupled NER (TC-NER) and global genome repair (GG-NER). The CSA and CSB proteins initiate the onset of TC-NER. Recent findings show that not only CSB, but also CSA is involved in the repair of oxidative DNA lesions, in the nucleus as well as in mitochondria. The XPG protein is also of importance for the removal of oxidative DNA lesions, as it may enhance the initial step of BER. Substantial evidence exists that support a role for XPC in NER and BER. XPC deficiency not only results in decreased repair of oxidative lesions, but has also been linked to disturbed redox homeostasis.

CRITICAL ISSUES

The role of NER proteins in the regulation of the cellular response to oxidative (mitochondrial and nuclear) DNA damage may be the underlying mechanism of the pathology of accelerated aging in Cockayne syndrome patients, a driving force for internal cancer development in XP-A and XP-C patients, and a contributor to the mixed exhibited phenotypes of XP-G patients.

FUTURE DIRECTIONS

Accumulating evidence indicates that DNA repair factors can be involved in multiple DNA repair pathways. However, the distinct detailed mechanism and consequences of these additional functions remain to be elucidated and can possibly shine a light on clinically related issues.

Multiple interaction partners for Cockayne syndrome proteins: implications for genome and transcriptome maintenance

Cockayne syndrome (CS) is characterized by progressive multisystem degeneration and is classified as a segmental premature aging syndrome. The majority of CS cases are caused by defects in the CS complementation group B (CSB) protein and the rest are mainly caused by defects in the CS complementation group A (CSA) protein. Cells from CS patients are sensitive to UV light and a number of other DNA damaging agents including various types of oxidative stress. The cells also display transcription deficiencies, abnormal apoptotic response to DNA damage, and DNA repair deficiencies. Herein we have critically reviewed the current knowledge about known protein interactions of the CS proteins. The review focuses on the participation of the CSB and CSA proteins in many different protein interactions and complexes, and how these interactions inform us about pathways that are defective in the disease.

From laboratory tests to functional characterisation of Cockayne syndrome

The significant progress made over the last few years on the pathogenesis of Cockayne syndrome (CS) greatly improved our knowledge on several aspects crucial for development and ageing, demonstrating that this disorder, even if rare, represents a valuable tool to clarify key aspects of human health. Primary cells from patients have been instrumental to elucidate the multiple roles of CS proteins and to approach the dissection of the complex interplay between repair and transcription that is central to the CS clinical phenotype. Here we discuss the results of the cellular assays applied for confirmation of the clinical diagnosis as well as the results of genetic and molecular studies in DNA repair defective patients. Furthermore, we provide a general overview of recent in vivo and in vitro studies indicating that both CSA and CSB proteins are involved in distinct aspects of the cellular responses to UV and oxidative stress, transcription and regulation of gene expression, chromatin remodelling, redox balance and cellular bioenergetics. In light of the literature data, we will finally discuss how inactivation of specific functional roles of CS proteins may differentially affect the phenotype, thus explaining the wide range in type and severity of symptoms reported in CS patients.

The role of CSA and CSB protein in the oxidative stress response

Cockayne syndrome (CS) is a rare hereditary disorder in which infants suffer severe developmental and neurological alterations and early death. Two genes encoding RNA polymerase II cofactors, CSA and CSB, are mutated in this syndrome. CSA and CSB proteins are known to be involved in the transcription-coupled DNA repair pathway but the sensitivity of mutant cells to a number of physical/chemical agents besides UV radiation, such as ionizing radiation, hydrogen peroxide and bioenergetic inhibitors indicate that these proteins play a pivotal role in additional pathways. In this review we will discuss the evidence that implicate CS proteins in the control of oxidative stress response with special emphasis on recent findings that show an altered redox balance and dysfunctional mitochondria in cells derived from patients. Working models of how these new functions might be key to developmental and neurological disease in CS will be discussed.

Cockayne syndrome group B (CSB) protein: at the crossroads of transcriptional networks

Cockayne syndrome (CS) is a rare genetic disorder characterized by a variety of growth and developmental defects, photosensitivity, cachectic dwarfism, hearing loss, skeletal abnormalities, progressive neurological degeneration, and premature aging. CS arises due to mutations in the CSA and CSB genes. Both gene products are required for the transcription-coupled (TC) branch of the nucleotide excision repair (NER) pathway, however, the severe phenotype of CS patients is hard to reconcile with a sole defect in TC-NER. Studies using cells from patients and mouse models have shown that the CSB protein is involved in a variety of cellular pathways and plays a major role in the cellular response to stress. CSB has been shown to regulate processes such as the transcriptional recovery after DNA damage, the p53 transcriptional response, the response to hypoxia, the response to insulin-like growth factor-1 (IGF-1), transactivation of nuclear receptors, transcription of housekeeping genes and the transcription of rDNA. Some of these processes are also affected in combined XP/CS patients. These new advances in the function(s) of CSB shed light onto the etiology of the clinical features observed in CS patients and could potentially open therapeutic avenues for these patients in the future. Moreover, the study of CS could further our knowledge of the aging process.

Repair of oxidatively generated DNA damage in Cockayne syndrome

Defects in the repair of endogenously (especially oxidatively) generated DNA modifications and the resulting genetic instability can potentially explain the clinical symptoms of Cockayne syndrome (CS), a hereditary disease characterized by developmental defects and neurological degeneration. In this review, we describe the evidence for the involvement of CSA and CSB proteins, which are mutated in most of the CS patients, in the repair and processing of DNA damage induced by reactive oxygen species and the implications for the induction of cell death and mutations. Taken together, the data demonstrate that CSA and CSB, in addition to their established role in transcription-coupled nucleotide excision repair, can modulate the base excision repair (BER) of oxidized DNA bases both directly (by interaction with BER proteins) and indirectly (by modulating the expression of the DNA repair genes). Both nuclear and mitochondrial DNA repair is affected by mutations in CSA and CSB genes. However, the observed retardations of repair and the resulting accumulation of unrepaired endogenously generated DNA lesions are often mild, thus pointing to the relevance of additional roles of the CS proteins, e.g. in the mitochondrial response to oxidatively generated DNA damage and in the maintenance of gene transcription.

Conceptual developments in the causes of Cockayne syndrome

Cockayne syndrome is an autosomal recessive disease that covers a wide range of symptoms, from mild photosensitivity to severe neonatal lethal disorder. The pathology of Cockayne syndrome may be caused by several mechanisms such as a DNA repair deficiency, transcription dysregulation, altered redox balance and mitochondrial dysfunction. Conceivably each of these mechanisms participates during a different stage in life of a Cockayne syndrome patient. Endogenous reactive oxygen is considered as an ultimate cause of DNA damage that contributes to Cockayne syndrome pathology. Here we demonstrate that mitochondrial reactive oxygen does not cause detectable nuclear DNA damage. This observation implies that a significant component of Cockayne syndrome pathology may be due to abnormal mitochondrial function independent of nuclear DNA damage. The source of nuclear DNA damage to central nervous system tissue most likely occurs from extrinsic neurotransmitter signaling.

The CSB repair factor is overexpressed in cancer cells, increases apoptotic resistance, and promotes tumor growth

In the present study we show that a number of cancer cell lines from different tissues display dramatically increased expression of the Cockayne Syndrome group B (CSB) protein, a DNA repair factor, that has recently been shown to be involved in cell robustness. Furthermore, we demonstrated that ablation of this protein by antisense technology causes devastating effects on tumor cells through a drastic reduction of cell proliferation and massive induction of apoptosis, while non-transformed cells remain unaffected. Finally, suppression of CSB in cancer cells makes these cells hypersensitive to a variety of commonly used cancer chemotherapeutic agents. Based on these results, we conclude that cancer cells overexpress CSB protein in order to enhance their anti-apoptotic capacity. The fact that CSB suppression specifically affects only cancerous cells, without harming healthy cells, suggests that CSB may be a very attractive target for the development of new anticancer therapies.

Sirt1 suppresses RNA synthesis after UV irradiation in combined xeroderma pigmentosum group D/Cockayne syndrome (XP-D/CS) cells

Specific mutations in the XPD subunit of transcription factor IIH result in combined xeroderma pigmentosum (XP)/Cockayne syndrome (CS), a severe DNA repair disorder characterized at the cellular level by a transcriptional arrest following UV irradiation. This transcriptional arrest has always been thought to be the result of faulty transcription-coupled repair. In the present study, we showed that, following UV irradiation, XP-D/CS cells displayed a gross transcriptional dysregulation compared with "pure" XP-D cells or WT cells. Furthermore, global RNA-sequencing analysis showed that XP-D/CS cells repressed the majority of genes after UV, whereas pure XP-D cells did not. By using housekeeping genes as a model, we demonstrated that XP-D/CS cells were unable to reassemble these gene promoters and thus to restart transcription after UV irradiation. Furthermore, we found that the repression of these promoters in XP-D/CS cells was not a simple consequence of deficient repair but rather an active heterochromatinization process mediated by the histone deacetylase Sirt1. Indeed, RNA-sequencing analysis showed that inhibition of and/or silencing of Sirt1 changed the chromatin environment at these promoters and restored the transcription of a large portion of the repressed genes in XP-D/CS cells after UV irradiation. Our work demonstrates that a significant part of the transcriptional arrest displayed by XP-D/CS cells arises as a result of an active repression process and not simply as a result of a DNA repair deficiency. This dysregulation of Sirt1 function that results in transcriptional repression may be the cause of various severe clinical features in patients with XP-D/CS that cannot be explained by a DNA repair defect.

Adaptive and maladaptive cardiorespiratory responses to continuous and intermittent hypoxia mediated by hypoxia-inducible factors 1 and 2

Hypoxia is a fundamental stimulus that impacts cells, tissues, organs, and physiological systems. The discovery of hypoxia-inducible factor-1 (HIF-1) and subsequent identification of other members of the HIF family of transcriptional activators has provided insight into the molecular underpinnings of oxygen homeostasis. This review focuses on the mechanisms of HIF activation and their roles in physiological and pathophysiological responses to hypoxia, with an emphasis on the cardiorespiratory systems. HIFs are heterodimers comprised of an O(2)-regulated HIF-1α or HIF-2α subunit and a constitutively expressed HIF-1β subunit. Induction of HIF activity under conditions of reduced O(2) availability requires stabilization of HIF-1α and HIF-2α due to reduced prolyl hydroxylation, dimerization with HIF-1β, and interaction with coactivators due to decreased asparaginyl hydroxylation. Stimuli other than hypoxia, such as nitric oxide and reactive oxygen species, can also activate HIFs. HIF-1 and HIF-2 are essential for acute O(2) sensing by the carotid body, and their coordinated transcriptional activation is critical for physiological adaptations to chronic hypoxia including erythropoiesis, vascularization, metabolic reprogramming, and ventilatory acclimatization. In contrast, intermittent hypoxia, which occurs in association with sleep-disordered breathing, results in an imbalance between HIF-1α and HIF-2α that causes oxidative stress, leading to cardiorespiratory pathology.

Interaction between the Cockayne syndrome B and p53 proteins: implications for aging

The CSB protein plays a role in the transcription coupled repair (TCR) branch of the nucleotide excision repair pathway. CSB is very often found mutated in Cockayne syndrome, a segmental progeroid genetic disease characterized by organ degeneration and growth failure. The tumor suppressor p53 plays a pivotal role in triggering senescence and apoptosis and suppressing tumorigenesis. Although p53 is very important to avoid cancer, its excessive activity can be detrimental for the lifespan of the organism. This is why a network of positive and negative feedback loops, which most likely evolved to fine-tune the activity of this tumor suppressor, modulate its induction and activation. Accordingly, an unbalanced p53 activity gives rise to premature aging or cancer. The physical interaction between CSB and p53 proteins has been known for more than a decade but, despite several hypotheses, nobody has been able to show the functional consequences of this interaction. In this review we resume recent advances towards a more comprehensive understanding of the critical role of this interaction in modulating p53’s levels and activity, therefore helping the system find a reasonable equilibrium between the beneficial and the detrimental effects of its activity. This crosstalk re-establishes the physiological balance towards cell proliferation and survival instead of towards cell death, after stressors of a broad nature. Accordingly, cells bearing mutations in the csb gene are unable to re-establish this physiological balance and to properly respond to some stress stimuli and undergo massive apoptosis.

Evidence for premature aging due to oxidative stress in iPSCs from Cockayne syndrome

Cockayne syndrome (CS) is a human premature aging disorder associated with neurological and developmental abnormalities, caused by mutations mainly in the CS group B gene (ERCC6). At the molecular level, CS is characterized by a deficiency in the transcription-couple DNA repair pathway. To understand the role of this molecular pathway in a pluripotent cell and the impact of CSB mutation during human cellular development, we generated induced pluripotent stem cells (iPSCs) from CSB skin fibroblasts (CSB-iPSC). Here, we showed that the lack of functional CSB does not represent a barrier to genetic reprogramming. However, iPSCs derived from CSB patient's fibroblasts exhibited elevated cell death rate and higher reactive oxygen species (ROS) production. Moreover, these cellular phenotypes were accompanied by an up-regulation of TXNIP and TP53 transcriptional expression. Our findings suggest that CSB modulates cell viability in pluripotent stem cells, regulating the expression of TP53 and TXNIP and ROS production.

The conserved Cockayne syndrome B-piggyBac fusion protein (CSB-PGBD3) affects DNA repair and induces both interferon-like and innate antiviral responses in CSB-null cells

Cockayne syndrome is a segmental progeria most often caused by mutations in the CSB gene encoding a SWI/SNF-like ATPase required for transcription-coupled DNA repair (TCR). Over 43Mya before marmosets diverged from humans, a piggyBac3 (PGBD3) transposable element integrated into intron 5 of the CSB gene. As a result, primate CSB genes now generate both CSB protein and a conserved CSB-PGBD3 fusion protein in which the first 5 exons of CSB are alternatively spliced to the PGBD3 transposase. Using a host cell reactivation assay, we show that the fusion protein inhibits TCR of oxidative damage but facilitates TCR of UV damage. We also show by microarray analysis that expression of the fusion protein alone in CSB-null UV-sensitive syndrome (UVSS) cells induces an interferon-like response that resembles both the innate antiviral response and the prolonged interferon response normally maintained by unphosphorylated STAT1 (U-STAT1); moreover, as might be expected based on conservation of the fusion protein, this potentially cytotoxic interferon-like response is largely reversed by coexpression of functional CSB protein. Interestingly, expression of CSB and the CSB-PGBD3 fusion protein together, but neither alone, upregulates the insulin growth factor binding protein IGFBP5 and downregulates IGFBP7, suggesting that the fusion protein may also confer a metabolic advantage, perhaps in the presence of DNA damage. Finally, we show that the fusion protein binds in vitro to members of a dispersed family of 900 internally deleted piggyBac elements known as MER85s, providing a potential mechanism by which the fusion protein could exert widespread effects on gene expression. Our data suggest that the CSB-PGBD3 fusion protein is important in both health and disease, and could play a role in Cockayne syndrome.

Photosensitivity syndrome brings to light a new transcription-coupled DNA repair cofactor

Three teams have applied whole-exome and proteome methods to identify a new cofactor of human RNA polymerase II that is required for the recovery of transcription on damaged templates. The identification of this new factor raises questions about the causal relationships between molecular mechanisms of transcription regulation and excision repair and developmental and neurological disease and nonmalignant skin photosensitivity.

Dysmyelination not demyelination causes neurological symptoms in preweaned mice in a murine model of Cockayne syndrome

Cockayne syndrome (CS) is a rare autosomal recessive neurodegenerative disease that is associated with mutations in either of two transcription-coupled DNA repair genes, CSA or CSB. Mice with a targeted mutation in the Csb gene (Cs-b(m/m)) exhibit a milder phenotype compared with human patients with mutations in the orthologous CSB gene. Mice mutated in Csb were crossed with mice lacking Xpc (Xp-c(-/-)), the global genome repair gene, to enhance the pathological symptoms. These Cs-b(m/m).Xp-c(-/-) mice were normal at birth but exhibited progressive failure to thrive, whole-body wasting, and ataxia and died at approximately postnatal day 21. Characterization of Cs-b(m/m).Xp-c(-/-) brains at postnatal stages demonstrated widespread reduction of myelin basic protein (MBP) and myelin in the sensorimotor cortex, the stratum radiatum, the corpus callosum, and the anterior commissure. Quantification of individual axons by electron microscopy showed a reduction in both the number of myelinated axons and the average diameter of myelin surrounding the axons. There were no significant differences in proliferation or oligodendrocyte differentiation between Cs-b(m/m).Xp-c(-/-) and Cs-b(m/+).Xp-c(-/-) mice. Rather, Cs-b(m/m).Xp-c(-/-) oligodendrocytes were unable to generate sufficient MBP or to maintain the proper myelination during early development. Csb is a multifunctional protein regulating both repair and the transcriptional response to reactive oxygen through its interaction with histone acetylase p300 and the hypoxia-inducible factor (HIF)1 pathway. On the basis of our results, combined with that of others, we suggest that in Csb the transcriptional response predominates during early development, whereas a neurodegenerative response associated with repair deficits predominates in later life.

CSA and CSB proteins interact with p53 and regulate its Mdm2-dependent ubiquitination

Mutations in Cockayne syndrome (CS) A and B genes (CSA and CSB) result in a rare genetic disease that affects the development and homeostasis of a wide range of tissues and organs. We previously correlated the degenerative phenotype of patients to the enhanced apoptotic response, exhibited by CS cells, which is associated with the exceptional induction of p53 protein, upon a variety of stress stimuli. Here we showed that the elevated and persistent levels of p53 displayed by CS cells are due to the insufficient ubiquitination of the p53 protein. We further demonstrated that CSA and CSB proteins associate in a unique complex with p53 and Mdm2; this interaction greatly stimulates the ubiquitination of p53 in an Mdm2-dependent manner. Tandem affinity purification and immunoprecipitations combined with mass spectrometry studies indicate that CSA and CSB associate within a Cullin Ring Ubiquitin Ligase complex responsible, under certain circumstances, for p53 ubiquitination. This study identifies CSA and CSB as the key elements of a regulatory mechanism that equilibrate beneficial and detrimental effects of p53 activity upon cellular stress. The deregulation of p53, in absence of either of the CS proteins, can potentially explain the early onset degeneration of tissues and organs observed in CS patients.