Cockayne Syndrome: The many challenges and approaches to understand a multifaceted disease

A Review of Telomere Attrition in Cancer and Aging: Current Molecular Insights and Future Therapeutic Approaches

BACKGROUND/OBJECTIVES

As cells divide, telomeres shorten through a phenomenon known as telomere attrition, which leads to unavoidable senescence of cells. Unprotected DNA exponentially increases the odds of mutations, which can evolve into premature aging disorders and tumorigenesis. There has been growing academic and clinical interest in exploring this duality and developing optimal therapeutic strategies to combat telomere attrition in aging and cellular immortality in cancer. The purpose of this review is to provide an updated overview of telomere biology and therapeutic tactics to address aging and cancer.

METHODS

We used the Rayyan platform to review the PubMed database and examined the ClinicalTrial.gov registry to gain insight into clinical trials and their results.

RESULTS

Cancer cells activate telomerase or utilize alternative lengthening of telomeres to escape telomere shortening, leading to near immortality. Contrarily, normal cells experience telomeric erosion, contributing to premature aging disorders, such as Werner syndrome and Hutchinson-Gilford Progeria, and (2) aging-related diseases, such as neurodegenerative and cardiovascular diseases.

CONCLUSIONS

The literature presents several promising therapeutic approaches to potentially balance telomere maintenance in aging and shortening in cancer. This review highlights gaps in knowledge and points to the potential of these optimal interventions in preclinical and clinical studies to inform future research in cancer and aging.

Syndromic Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a progressive inherited retinal dystrophy, characterized by the degeneration of photoreceptors, presenting as a rod-cone dystrophy. Approximately 20-30% of patients with RP also exhibit extra-ocular manifestations in the context of a syndrome. This manuscript discusses the broad spectrum of syndromes associated with RP, pathogenic mechanisms, clinical manifestations, differential diagnoses, clinical management approaches, and future perspectives. Given the diverse clinical and genetic landscape of syndromic RP, the diagnosis may be challenging. However, an accurate and timely diagnosis is essential for optimal clinical management, prognostication, and potential treatment. Broadly, the syndromes associated with RP can be categorized into ciliopathies, inherited metabolic disorders, mitochondrial disorders, and miscellaneous syndromes. Among the ciliopathies associated with RP, Usher syndrome and Bardet-Biedl syndrome are the most well-known. Less common ciliopathies include Cohen syndrome, Joubert syndrome, cranioectodermal dysplasia, asphyxiating thoracic dystrophy, Mainzer-Saldino syndrome, and RHYNS syndrome. Several inherited metabolic disorders can present with RP including Zellweger spectrum disorders, adult Refsum disease, α-methylacyl-CoA racemase deficiency, certain mucopolysaccharidoses, ataxia with vitamin E deficiency, abetalipoproteinemia, several neuronal ceroid lipofuscinoses, mevalonic aciduria, PKAN/HARP syndrome, PHARC syndrome, and methylmalonic acidaemia with homocystinuria type cobalamin (cbl) C disease. Due to the mitochondria's essential role in supplying continuous energy to the retina, disruption of mitochondrial function can lead to RP, as seen in Kearns-Sayre syndrome, NARP syndrome, primary coenzyme Q10 deficiency, SSBP1-associated disease, and long chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Lastly, Cockayne syndrome and PERCHING syndrome can present with RP, but they do not fit the abovementioned hierarchy and are thus categorized as 'Miscellaneous'. Several first-in-human clinical trials are underway or in preparation for some of these syndromic forms of RP.

Radiosensitivity in individuals with tuberous sclerosis complex

Benign tumors, but rarely cancer, are common in patients with tuberous sclerosis complex (TSC). Blood samples from patients undergoing treatment for TSC at our institution were analyzed for their individual sensitivity to ionizing radiation. Blood samples were collected from 13 adult patients with TSC. The samples were irradiated ex vivo and analyzed by 3-color fluorescence in situ hybridization. In each patient, aberrations were analyzed in 200 metaphases of chromosomes 1, 2, and 4 and scored as breaks. Radiosensitivity was determined by mean breaks per metaphase (B/M) and compared to both healthy donors and oncologic patients. The radiosensitivity (B/M) of the TSC patient cohort (n = 13; female: 46.2%, B/M: 0.48 ± 0.11) was clearly increased compared to healthy individuals of similar age (n = 90; female: 54.4%; B/M: 0.40 ± 0.09; p = 0.001). There was no difference compared to age-matched oncological patients (n = 78; female: 67.9%; B/M 0.49 ± 0.14; p = 0.246). Similarly, the proportion of radiosensitive (B/M > 0.5) and distinctly radiosensitive individuals (B/M > 0.6) was increased in the TSC and oncological patient cohorts (TSC: 30.8% and 7.7%, oncological patients: 46.2% and 14.1%) compared to the healthy individuals (11.1% and 2.2%). Although patients with TSC develop mostly benign and rarely malignant tumors, they are similarly sensitive to radiation as patients with malignant tumors.

Differential processing of RNA polymerase II at DNA damage correlates with transcription-coupled repair syndrome severity

DNA damage severely impedes gene transcription by RNA polymerase II (Pol II), causing cellular dysfunction. Transcription-Coupled Nucleotide Excision Repair (TC-NER) specifically removes such transcription-blocking damage. TC-NER initiation relies on the CSB, CSA and UVSSA proteins; loss of any results in complete TC-NER deficiency. Strikingly, UVSSA deficiency results in UV-Sensitive Syndrome (UVSS), with mild cutaneous symptoms, while loss of CSA or CSB activity results in the severe Cockayne Syndrome (CS), characterized by neurodegeneration and premature aging. Thus far the underlying mechanism for these contrasting phenotypes remains unclear. Live-cell imaging approaches reveal that in TC-NER proficient cells, lesion-stalled Pol II is swiftly resolved, while in CSA and CSB knockout (KO) cells, elongating Pol II remains damage-bound, likely obstructing other DNA transacting processes and shielding the damage from alternative repair pathways. In contrast, in UVSSA KO cells, Pol II is cleared from the damage via VCP-mediated proteasomal degradation which is fully dependent on the CRL4CSA ubiquitin ligase activity. This Pol II degradation might provide access for alternative repair mechanisms, such as GG-NER, to remove the damage. Collectively, our data indicate that the inability to clear lesion-stalled Pol II from the chromatin, rather than TC-NER deficiency, causes the severe phenotypes observed in CS.

HiPSC-derived 3D neural models reveal neurodevelopmental pathomechanisms of the Cockayne Syndrome B

Cockayne Syndrome B (CSB) is a hereditary multiorgan syndrome which-through largely unknown mechanisms-can affect the brain where it clinically presents with microcephaly, intellectual disability and demyelination. Using human induced pluripotent stem cell (hiPSC)-derived neural 3D models generated from CSB patient-derived and isogenic control lines, we here provide explanations for these three major neuropathological phenotypes. In our models, CSB deficiency is associated with (i) impaired cellular migration due to defective autophagy as an explanation for clinical microcephaly; (ii) altered neuronal network functionality and neurotransmitter GABA levels, which is suggestive of a disturbed GABA switch that likely impairs brain circuit formation and ultimately causes intellectual disability; and (iii) impaired oligodendrocyte maturation as a possible cause of the demyelination observed in children with CSB. Of note, the impaired migration and oligodendrocyte maturation could both be partially rescued by pharmacological HDAC inhibition.

The ARK2N-CK2 complex initiates transcription-coupled repair through enhancing the interaction of CSB with lesion-stalled RNAPII

Transcription is extremely important for cellular processes but can be hindered by RNA polymerase II (RNAPII) pausing and stalling. Cockayne syndrome protein B (CSB) promotes the progression of paused RNAPII or initiates transcription-coupled nucleotide excision repair (TC-NER) to remove stalled RNAPII. However, the specific mechanism by which CSB initiates TC-NER upon damage remains unclear. In this study, we identified the indispensable role of the ARK2N-CK2 complex in the CSB-mediated initiation of TC-NER. The ARK2N-CK2 complex is recruited to damage sites through CSB and then phosphorylates CSB. Phosphorylation of CSB enhances its binding to stalled RNAPII, prolonging the association of CSB with chromatin and promoting CSA-mediated ubiquitination of stalled RNAPII. Consistent with this finding, Ark2n-/- mice exhibit a phenotype resembling Cockayne syndrome. These findings shed light on the pivotal role of the ARK2N-CK2 complex in governing the fate of RNAPII through CSB, bridging a critical gap necessary for initiating TC-NER.

Immunity in the Progeroid Model of Cockayne Syndrome: Biomarkers of Pathological Aging

Cockayne syndrome (CS) is a rare autosomal recessive disorder that affects the DNA repair process. It is a progeroid syndrome predisposing patients to accelerated aging and to increased susceptibility to respiratory infections. Here, we studied the immune status of CS patients to determine potential biomarkers associated with pathological aging. CS patients, as well as elderly and young, healthy donors, were enrolled in this study. Complete blood counts for patients and donors were assessed, immune cell subsets were analyzed using flow cytometry, and candidate cytokines were analyzed via multi-analyte ELISArray kits. In CS patients, we noticed a high percentage of lymphocytes, an increased rate of intermediate and non-classical monocytes, and a high level of pro-inflammatory cytokine IL-8. In addition, we identified an increased rate of particular subtypes of T Lymphocyte CD8+ CD28- CD27-, which are senescent T cells. Thus, an inflammatory state was found in CS patients that is similar to that observed in the elderly donors and is associated with an immunosenescence status in both groups. This could explain the CS patients' increased susceptibility to infections, which is partly due to an aging-associated inflammation process.

Clinically Actionable Topical Strategies for Addressing the Hallmarks of Skin Aging: A Primer for Aesthetic Medicine Practitioners

In this narrative review, we sought to provide a comprehensive overview of the mechanisms underlying cutaneous senescence, framed by the twelve traditional hallmarks of aging. These include genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, impaired macroautophagy, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, chronic inflammation, and dysbiosis. We also examined how topical interventions targeting these hallmarks can be integrated with conventional aesthetic medicine techniques to enhance skin rejuvenation. The potential of combining targeted topical therapies against the aging hallmarks with minimally invasive procedures represents a significant advancement in aesthetic medicine, offering personalized and effective strategies to combat skin aging. The reviewed evidence paves the way for future advancements and underscores the transformative potential of integrating scientifically validated interventions targeted against aging hallmarks into traditional aesthetic practices.

Mitochondria - Nucleus communication in neurodegenerative disease. Who talks first, who talks louder?

Mitochondria - nuclear coadaptation has been central to eukaryotic evolution. The dynamic dialogue between the two compartments within the context of multiorganellar interactions is critical for maintaining cellular homeostasis and directing the balance survival-death in case of cellular stress. The conceptualisation of mitochondria - nucleus communication has so far been focused on the communication from the mitochondria under stress to the nucleus and the consequent signalling responses, as well as from the nucleus to mitochondria in the context of DNA damage and repair. During ageing processes this dialogue may be better viewed as an integrated bidirectional 'talk' with feedback loops that expand beyond these two organelles depending on physiological cues. Here we explore the current views on mitochondria - nucleus dialogue and its role in maintaining cellular health with a focus on brain cells and neurodegenerative disease. Thus, we detail the transcriptional responses initiated by mitochondrial dysfunction in order to protect itself and the general cellular homeostasis. Additionally, we are reviewing the knowledge of the stress pathways initiated by DNA damage which affect mitochondria homeostasis and we add the information provided by the study of combined mitochondrial and genotoxic damage. Finally, we reflect on how each organelle may take the lead in this dialogue in an ageing context where both compartments undergo accumulation of stress and damage and where, perhaps, even the communications' mechanisms may suffer interruptions.

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.

Cockayne syndrome without UV-sensitivity in Vietnamese siblings with novel ERCC8 variants

Cockayne syndrome (CS) is a rare progeroid disorder characterized by growth failure, microcephaly, photosensitivity, and premature aging, mainly arising from biallelic ERCC8 (CS-A) or ERCC6 (CS-B) variants. In this study we describe siblings suffering from classical Cockayne syndrome but without photosensitivity, which delayed a clinical diagnosis for 16 years. By whole-exome sequencing we identified the two novel compound heterozygous ERCC8 variants c.370_371del (p.L124Efs*15) and c.484G>C (p.G162R). The causality of the ERCC8 variants, of which one results in a frameshift and the other affects the WD3 domain, was tested and confirmed by a rescue experiment investigating DNA repair in H₂O₂ treated patient fibroblasts. Structural modeling of the p.G162R variant indicates effects on protein-protein interaction. This case shows the importance to test for ERCC6 and ERCC8 variants even if patients do not present with a complete CS phenotype.

Whole-exome sequencing revealed a novel ERCC6 variant in a Vietnamese patient with Cockayne syndrome

We describe a case of Cockayne syndrome without photosensitivity in a Vietnamese family. This lack of photosensitivity prevented the establishment of a confirmed medical clinical diagnosis for 16 years. Whole-exome sequencing (WES) identified a novel missense variant combined with a known nonsense variant in the ERCC6 gene, NM_000124.4: c.[2839C>T;2936A>G], p.[R947*;K979R]. This case emphasizes the importance of WES in investigating the etiology of a disease when patients do not present the complete clinical phenotypes of Cockayne syndrome.

Heterogeneous clinical features in Cockayne syndrome patients and siblings carrying the same CSA mutations

Background

Cockayne syndrome (CS) is a rare autosomal recessive disorder caused by mutations in ERCC6/CSB or ERCC8/CSA that participate in the transcription-coupled nucleotide excision repair (TC-NER) of UV-induced DNA damage. CS patients display a large heterogeneity of clinical symptoms and severities, the reason of which is not fully understood, and that cannot be anticipated in the diagnostic phase. In addition, little data is available for affected siblings, and this disease is largely undiagnosed in North Africa.

Methods

We report here the clinical description as well as genetic and functional characterization of eight Tunisian CS patients, including siblings. These patients, who belonged to six unrelated families, underwent complete clinical examination and biochemical analyses. Sanger sequencing was performed for the recurrent mutation in five families, and targeted gene sequencing was done for one patient of the sixth family. We also performed Recovery RNA Synthesis (RRS) to confirm the functional impairment of DNA repair in patient-derived fibroblasts.

Results

Six out of eight patients carried a homozygous indel mutation (c.598_600delinsAA) in exon 7 of ERCC8, and displayed a variable clinical spectrum including between siblings sharing the same mutation. The other two patients were siblings who carried a homozygous splice-site variant in ERCC8 (c.843+1G>C). This last pair presented more severe clinical manifestations, which are rarely associated with CSA mutations, leading to gastrostomy and hepatic damage. Impaired TC-NER was confirmed by RRS in six tested patients.

Conclusions

This study provides the first deep characterization of case series of CS patients carrying CSA mutations in North Africa. These mutations have been described only in this region and in the Middle-East. We also provide the largest characterization of multiple unrelated patients, as well as siblings, carrying the same mutation, providing a framework for dissecting elusive genotype–phenotype correlations in CS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02257-1.

Mechanism of Rad26-assisted rescue of stalled RNA polymerase II in transcription-coupled repair

Transcription-coupled repair is essential for the removal of DNA lesions from the transcribed genome. The pathway is initiated by CSB protein binding to stalled RNA polymerase II. Mutations impairing CSB function cause severe genetic disease. Yet, the ATP-dependent mechanism by which CSB powers RNA polymerase to bypass certain lesions while triggering excision of others is incompletely understood. Here we build structural models of RNA polymerase II bound to the yeast CSB ortholog Rad26 in nucleotide-free and bound states. This enables simulations and graph-theoretical analyses to define partitioning of this complex into dynamic communities and delineate how its structural elements function together to remodel DNA. We identify an allosteric pathway coupling motions of the Rad26 ATPase modules to changes in RNA polymerase and DNA to unveil a structural mechanism for CSB-assisted progression past less bulky lesions. Our models allow functional interpretation of the effects of Cockayne syndrome disease mutations.

Identification and Characterization of a Novel Recurrent ERCC6 Variant in Patients with a Severe Form of Cockayne Syndrome B

Cockayne syndrome (CS) is a rare disease caused by mutations in ERCC6/CSB or ERCC8/CSA. We report here the clinical, genetic, and functional analyses of three unrelated patients mutated in ERCC6/CSB with a severe phenotype. After clinical examination, two patients were investigated via next generation sequencing, targeting seventeen Nucleotide Excision Repair (NER) genes. All three patients harbored a novel, c.3156dup, homozygous mutation located in exon 18 of ERCC6/CSB that affects the C-terminal region of the protein. Sanger sequencing confirmed the mutation and the parental segregation in the three families, and Western blots showed a lack of the full-length protein. NER functional impairment was shown by reduced recovery of RNA synthesis with proficient unscheduled DNA synthesis after UV-C radiations in patient-derived fibroblasts. Despite sharing the same mutation, the clinical spectrum was heterogeneous among the three patients, and only two patients displayed clinical photosensitivity. This novel ERCC6 variant in Tunisian patients suggests a founder effect and has implications for setting-up prenatal diagnosis/genetic counselling in North Africa, where this disease is largely undiagnosed. This study reveals one of the rare cases of CS clinical heterogeneity despite the same mutation. Moreover, the occurrence of an identical homozygous mutation, which either results in clinical photosensitivity or does not, strongly suggests that this classic CS symptom relies on multiple factors.

Whole Exome Sequencing Identifies a Novel Homozygous Missense Mutation in the CSB Protein-Encoding ERCC6 Gene in a Taiwanese Boy with Cockayne Syndrome

Background: Cockayne syndrome (CS) is a rare form of dwarfism that is characterized by progressive premature aging. CS is typically caused by mutations in the excision repair cross-complementing protein group 6 (ERCC6) gene that encodes the CS group B (CSB) protein. Using whole exome sequencing, we recently identified a novel homozygous missense mutation (Leu536Trp) in CSB in a Taiwanese boy with CS. Since the current database (Varsome) interprets this variant as likely pathogenic, we utilized a bioinformatic tool to investigate the impact of Leu536Trp as well as two other variants (Arg453Ter, Asp532Gly) in similar articles on the CSB protein structure stability. Methods: We used iterative threading assembly refinement (I-TASSER) to generate a predictive 3D structure of CSB. We calculated the change of mutation energy after residues substitution on the protein stability using I-TASSER as well as the artificial intelligence program Alphafold. Results: The Asp532Gly variant destabilized both modeled structures, while the Leu536Trp variant showed no effect on I-TASSER’s model but destabilized the Alphafold’s modeled structure. Conclusions: We propose here the first case of CS associated with a novel homozygous missense mutation (Leu536Trp) in CSB. Furthermore, we suggest that the Asp532Gly and Leu536Trp variants are both pathogenic after bioinformatic analysis of protein stability.

Neurovascular dysfunction and neuroinflammation in a Cockayne syndrome mouse model

Cockayne syndrome (CS) is a rare, autosomal genetic disorder characterized by premature aging-like features, such as cachectic dwarfism, retinal atrophy, and progressive neurodegeneration. The molecular defect in CS lies in genes associated with the transcription-coupled branch of the nucleotide excision DNA repair (NER) pathway, though it is not yet clear how DNA repair deficiency leads to the multiorgan dysfunction symptoms of CS. In this work, we used a mouse model of severe CS with complete loss of NER (Csa-/-/Xpa-/-), which recapitulates several CS-related phenotypes, resulting in premature death of these mice at approximately 20 weeks of age. Although this CS model exhibits a severe progeroid phenotype, we found no evidence of in vitro endothelial cell dysfunction, as assessed by measuring population doubling time, migration capacity, and ICAM-1 expression. Furthermore, aortas from CX mice did not exhibit early senescence nor reduced angiogenesis capacity. Despite these observations, CX mice presented blood brain barrier disruption and increased senescence of brain endothelial cells. This was accompanied by an upregulation of inflammatory markers in the brains of CX mice, such as ICAM-1, TNFα, p-p65, and glial cell activation. Inhibition of neovascularization did not exacerbate neither astro- nor microgliosis, suggesting that the pro-inflammatory phenotype is independent of the neurovascular dysfunction present in CX mice. These findings have implications for the etiology of this disease and could contribute to the study of novel therapeutic targets for treating Cockayne syndrome patients.

Structural basis of human transcription-DNA repair coupling

Transcription-coupled DNA repair removes bulky DNA lesions from the genome^1,2 and protects cells against ultraviolet (UV) irradiation³. Transcription-coupled DNA repair begins when RNA polymerase II (Pol II) stalls at a DNA lesion and recruits the Cockayne syndrome protein CSB, the E3 ubiquitin ligase, CRL4^CSA and UV-stimulated scaffold protein A (UVSSA)³. Here we provide five high-resolution structures of Pol II transcription complexes containing human transcription-coupled DNA repair factors and the elongation factors PAF1 complex (PAF) and SPT6. Together with biochemical and published^3,4 data, the structures provide a model for transcription–repair coupling. Stalling of Pol II at a DNA lesion triggers replacement of the elongation factor DSIF by CSB, which binds to PAF and moves upstream DNA to SPT6. The resulting elongation complex, EC^TCR, uses the CSA-stimulated translocase activity of CSB to pull on upstream DNA and push Pol II forward. If the lesion cannot be bypassed, CRL4^CSA spans over the Pol II clamp and ubiquitylates the RPB1 residue K1268, enabling recruitment of TFIIH to UVSSA and DNA repair. Conformational changes in CRL4^CSA lead to ubiquitylation of CSB and to release of transcription-coupled DNA repair factors before transcription may continue over repaired DNA.

The authors resolve the structure of five complexes containing RNA polymerase II and the CSA and CSB proteins, offering insight into how the repair of DNA lesions is coupled to transcription.

LEO1 is a partner for Cockayne syndrome protein B (CSB) in response to transcription-blocking DNA damage

Cockayne syndrome (CS) is an autosomal recessive genetic disorder characterized by photosensitivity, developmental defects, neurological abnormalities, and premature aging. Mutations in CSA (ERCC8), CSB (ERCC6), XPB, XPD, XPG, XPF (ERCC4) and ERCC1 can give rise to clinical phenotypes resembling classic CS. Using a yeast two-hybrid (Y2H) screening approach, we identified LEO1 (Phe381-Ser568 region) as an interacting protein partner of full-length and C-terminal (Pro1010-Cys1493) CSB in two independent screens. LEO1 is a member of the RNA polymerase associated factor 1 complex (PAF1C) with roles in transcription elongation and chromatin modification. Supportive of the Y2H results, purified, recombinant LEO1 and CSB directly interact in vitro, and the two proteins exist in a common complex within human cells. In addition, fluorescently tagged LEO1 and CSB are both recruited to localized DNA damage sites in human cells. Cell fractionation experiments revealed a transcription-dependent, coordinated association of LEO1 and CSB to chromatin following either UVC irradiation or cisplatin treatment of HEK293T cells, whereas the response to menadione was distinct, suggesting that this collaboration occurs mainly in the context of bulky transcription-blocking lesions. Consistent with a coordinated interaction in DNA repair, LEO1 knockdown or knockout resulted in reduced CSB recruitment to chromatin, increased sensitivity to UVC light and cisplatin damage, and reduced RNA synthesis recovery and slower excision of cyclobutane pyrimidine dimers following UVC irradiation; the absence of CSB resulted in diminished LEO1 recruitment. Our data indicate a reciprocal communication between CSB and LEO1 in the context of transcription-associated DNA repair and RNA transcription recovery.

Human Radiosensitivity and Radiosusceptibility: What Are the Differences?

The individual response to ionizing radiation (IR) raises a number of medical, scientific, and societal issues. While the term "radiosensitivity" was used by the pioneers at the beginning of the 20st century to describe only the radiation-induced adverse tissue reactions related to cell death, a confusion emerged in the literature from the 1930s, as "radiosensitivity" was indifferently used to describe the toxic, cancerous, or aging effect of IR. In parallel, the predisposition to radiation-induced adverse tissue reactions (radiosensitivity), notably observed after radiotherapy appears to be caused by different mechanisms than those linked to predisposition to radiation-induced cancer (radiosusceptibility). This review aims to document these differences in order to better estimate the different radiation-induced risks. It reveals that there are very few syndromes associated with the loss of biological functions involved directly in DNA damage recognition and repair as their role is absolutely necessary for cell viability. By contrast, some cytoplasmic proteins whose functions are independent of genome surveillance may also act as phosphorylation substrates of the ATM protein to regulate the molecular response to IR. The role of the ATM protein may help classify the genetic syndromes associated with radiosensitivity and/or radiosusceptibility.

Bioinformatics and expression analysis of the Xeroderma Pigmentosum complementation group C (XPC) of Trypanosoma evansi in Trypanosoma cruzi cells

Nucleotide excision repair (NER) acts repairing damages in DNA, such as lesions caused by cisplatin. Xeroderma Pigmentosum complementation group C (XPC) protein is involved in recognition of global genome DNA damages during NER (GG-NER) and it has been studied in different organisms due to its importance in other cellular processes. In this work, we studied NER proteins in Trypanosoma cruzi and Trypanosoma evansi, parasites of humans and animals respectively. We performed three-dimensional models of XPC proteins from T. cruzi and T. evansi and observed few structural differences between these proteins. In our tests, insertion of XPC gene from T. evansi (TevXPC) in T. cruzi resulted in slower cell growth under normal conditions. After cisplatin treatment, T. cruzi overexpressing its own XPC gene (TcXPC) was able to recover cell division rates faster than T. cruzi expressing TevXPC gene. Based on these tests, it is suggested that TevXPC (being an exogenous protein in T. cruzi) interferes negatively in cellular processes where TcXPC (the endogenous protein) is involved. This probably occurred due interaction of TevXPC with some endogenous molecules or proteins from T.cruzi but incapacity of interaction with others. This reinforces the importance of correctly XPC functioning within the cell.

Immunofluorescence studies to dissect the impact of Cockayne syndrome A alterations on the protein interaction and cellular localization

Background

Cockayne syndrome (CS), which was discovered by Alfred Cockayne nearly 75 years ago, is a rare autosomal recessive disorder characterized by growth failure, neurological dysfunction, premature aging, and other clinical features including microcephaly, ophthalmologic abnormalities, dental caries, and cutaneous photosensitivity. These alterations are caused by mutations in the CSA or CSB genes, both of which are involved in transcription-coupled nucleotide excision repair (TC-NER), the sub-pathway of NER that rapidly removes UV-induced DNA lesions which block the progression of the transcription machinery in the transcribed strand of active genes. Several studies assumed that CSA and CSB genes can play additional roles outside TC-NER, due to the wide variations in type and severity of the CS phenotype and the lack of a clear relationship between genotype and phenotype. To address this issue, our lab generated isogenic cell lines expressing wild type as well as different versions of mutated CSA proteins, fused at the C-terminus with the Flag and HA epitope tags (CSA^Flag-HA). In unpublished data, the identity of the CSA-interacting proteins was determined by mass spectrometry. Among which three subunits (namely, CCT3, CCT8, and TCP1) of the TRiC/CCT complex appeared as novel interactors. TRiC is a chaperonin involved in the folding of newly synthesized or unfolded proteins. The aim of this study is directed to investigate by immunofluorescence analysis the impact of the selected CSA mutations on the subcellular localization of the CSA protein itself as well as on its novel interactors CCT3, CCT8, and TCP1.

Results

We showed that specific CSA mutations impair the proper cellular localization of the protein, but have no impact on the cellular distribution of the TRiC subunits or CSA/TRiC co-localization.

Conclusion

We suggested that the activity of the TRiC complex does not rely on the functionality of CSA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-021-00190-7.

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 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.