Resumo em Inglês:

Abstract Precise replication of genetic material is essential to maintain genome stability. DNA replication is a tightly regulated process that ensues faithful copies of DNA molecules to daughter cells during each cell cycle. Perturbation of DNA replication may compromise the transmission of genetic information, leading to DNA damage, mutations, and chromosomal rearrangements. DNA replication stress, also referred to as DNA replicative stress, is defined as the slowing or stalling of replication fork progression during DNA synthesis as a result of different insults. Oncogene activation, one hallmark of cancer, is able to disturb numerous cellular processes, including DNA replication. In fact, extensive work has indicated that oncogene-induced replication stress is an important source of genomic instability in human carcinogenesis. In this review, we focus on main oncogenes that induce DNA replication stress, such as RAS, MYC, Cyclin E, MDM2, and BCL-2 among others, and the molecular mechanisms by which these oncogenes interfere with normal DNA replication and promote genomic instability.

Resumo em Inglês:

Abstract The DNA Damage Response (DDR) is a complex network of biological processes that protect cells from accumulating aberrant DNA structures, thereby maintaining genomic stability and, as a consequence, preventing the development of cancer and other diseases. The DDR pathway is coordinated by a signaling cascade mediated by the PI3K-like kinases (PIKK) ATM and ATR and by their downstream kinases CHK2 and CHK1, respectively. Together, these kinases regulate several aspects of the cellular program in response to genomic stress. Much of our understanding of these kinases came from studies performed in the 1990s using yeast as a model organism. The purpose of this review is to present a historical perspective on the discovery of the DDR kinases in yeast and the importance of this model for the identification and functional understanding of their mammalian orthologues.

Resumo em Inglês:

Abstract The poly (adenosine diphosphate (ADP)-ribosyl) polymerase inhibitors (PARPi) selectively kill cancer cells with BRCA1 or BRCA2 (BRCA)-mutations. It has been proposed that cell death induction after PARPi depends on unrepaired double strand breaks (DSBs) that accumulate due to the homologous recombination deficiency of BRCA-mutated cells. Such accumulation of DSBs is inferred mainly from the high levels of DNA damage markers like phosphorylated histone H2AX. Herein, we developed a model of isogenic cell lines to show that depletion of BRCA causes PARPi-triggered cell death, replication stress (phosphorylated-H2AX and 53BP1 foci), and genomic instability. However, persistent DSBs accumulation was not detected under the same experimental conditions. Hence, at least in this cellular model, the trigger for cell death in PARPi-treated BRCA-depleted samples is not the accumulation of unrepaired DSBs. Instead, cell death better correlates with a rapid and aberrant resolution of DSBs by error-prone pathways that leads to severe chromosomic aberrations. Therefore, our results suggest that in PARPi-treated BRCA-deficient cells, chromosome aberrations may dually trigger both genomic instability and cell death.

Resumo em Inglês:

Abstract Post-translational modification of proteins by ADP-ribosylation, catalysed by poly (ADP-ribose) polymerases (PARPs) using NAD+ as a substrate, plays central roles in DNA damage signalling and repair, modulates a range of cellular signalling cascades and initiates programmed cell death by parthanatos. Here, we present mechanistic aspects of ADP-ribose modification, PARP activation and the cellular functions of ADP-ribose signalling, and discuss how this knowledge is uncovering therapeutic avenues for the treatment of increasingly prevalent human diseases such as cancer, ischaemic damage and neurodegeneration.

Resumo em Inglês:

Abstract Xeroderma pigmentosum (XP) is a rare, genetic, autosomal nucleotide excision repair-deficient disease characterized by sun-sensitivity and early appearance of skin and ocular tumors. Thirty-two black-skinned XP from Comoros, located in the Indian Ocean, were counted, rendering this area the highest world prevalence of XP. These patients exhibited a new homozygous XPC mutation at the 3’-end of the intron12 (IVS 12-1G>C) leading to the absence of XPC protein. This mutation, characteristic of the consanguineous Comorian families, is associated with a founder effect with an estimated age of about 800 years. Analysis of mt-DNA and Y-chromosome identified the haplogroups of patients, who are derived from the Bantu people. Although the four Comorian islands were populated by the same individuals during the 7-10th centuries, XP was found now only in the Comorian island of Anjouan. To avoid the slavery process caused by the arrival of the Arabs around the 11-13th centuries, inhabitants of Anjouan, including XP-heterozygotes, hid inland of the island protected by volcanoes. This population lived with an endogamic style, without connection with the other islands. XP patients still live in the same isolated villages as their ancestries. Local history and geography may, thus, explain the high incidence of XP located exclusively in one island.

Resumo em Inglês:

Abstract Glioblastoma (GBM) is the most common and malignant type of primary brain tumor, showing rapid development and resistance to therapies. On average, patients survive 14.6 months after diagnosis and less than 5% survive five years or more. Several pieces of evidence have suggested that the DNA damage signaling and repair activities are directly correlated with GBM phenotype and exhibit opposite functions in cancer establishment and progression. The functions of these pathways appear to present a dual role in tumorigenesis and cancer progression. Activation and/or overexpression of ATRX, ATM and RAD51 genes were extensively characterized as barriers for GBM initiation, but paradoxically the exacerbated activity of these genes was further associated with cancer progression to more aggressive stages. Excessive amounts of other DNA repair proteins, namely HJURP, EXO1, NEIL3, BRCA2, and BRIP, have also been connected to proliferative competence, resistance and poor prognosis. This scenario suggests that these networks help tumor cells to manage replicative stress and treatment-induced damage, diminishing genome instability and conferring therapy resistance. Finally, in this review we address promising new drugs and therapeutic approaches with potential to improve patient survival. However, despite all technological advances, the prognosis is still dismal and further research is needed to dissect such complex mechanisms.

Resumo em Inglês:

Abstract Mitochondrial DNA (mtDNA) deletions are a common cause of human mitochondrial diseases. Mutations in the genes encoding components of the mitochondrial replisome, such as DNA polymerase gamma (Pol γ) and the mtDNA helicase Twinkle, have been associated with the accumulation of such deletions and the development of pathological conditions in humans. Recently, we demonstrated that changes in the level of wild-type Twinkle promote mtDNA deletions, which implies that not only mutations in, but also dysregulation of the stoichiometry between the replisome components is potentially pathogenic. The mechanism(s) by which alterations to the replisome function generate mtDNA deletions is(are) currently under debate. It is commonly accepted that stalling of the replication fork at sites likely to form secondary structures precedes the deletion formation. The secondary structural elements can be bypassed by the replication-slippage mechanism. Otherwise, stalling of the replication fork can generate single- and double-strand breaks, which can be repaired through recombination leading to the elimination of segments between the recombination sites. Here, we discuss aberrances of the replisome in the context of the two debated outcomes, and suggest new mechanistic explanations based on replication restart and template switching that could account for all the deletion types reported for patients.

Resumo em Inglês:

Abstract Given the major role of the mitochondrion in cellular homeostasis, dysfunctions of this organelle may lead to several common diseases in humans. Among these, maternal diseases linked to mitochondrial DNA (mtDNA) mutations are of special interest due to the unclear pattern of mitochondrial inheritance. Multiple copies of mtDNA are present in a cell, each encoding for 37 genes essential for mitochondrial function. In cases of mtDNA mutations, mitochondrial malfunctioning relies on mutation load, as mutant and wild-type molecules may co-exist within the cell. Since the mutation load associated with disease manifestation varies for different mutations and tissues, it is hard to predict the progeny phenotype based on mutation load in the progenitor. In addition, poorly understood mechanisms act in the female germline to prevent the accumulation of deleterious mtDNA in the following generations. In this review, we outline basic aspects of mitochondrial inheritance in mammals and how they may lead to maternally-inherited diseases. Furthermore, we discuss potential therapeutic strategies for these diseases, which may be used in the future to prevent their transmission.

Resumo em Inglês:

Abstract Base and nucleotide excision repair (BER and NER) pathways are normally associated with removal of specific types of DNA damage: small base modifications (such as those induced by DNA oxidation) and bulky DNA lesions (such as those induced by ultraviolet or chemical carcinogens), respectively. However, growing evidence indicates that this scenario is much more complex and these pathways exchange proteins and cooperate with each other in the repair of specific lesions. In this review, we highlight studies discussing the involvement of NER in the repair of DNA damage induced by oxidative stress, and BER participating in the removal of bulky adducts on DNA. Adding to this complexity, UVA light experiments revealed that oxidative stress also causes protein oxidation, directly affecting proteins involved in both NER and BER. This reduces the cell’s ability to repair DNA damage with deleterious implications to the cells, such as mutagenesis and cell death, and to the organisms, such as cancer and aging. Finally, an interactome of NER and BER proteins is presented, showing the strong connection between these pathways, indicating that further investigation may reveal new functions shared by them, and their cooperation in maintaining genome stability.

Resumo em Inglês:

Abstract Splicing, the process that catalyzes intron removal and flanking exon ligation, can occur in different ways (alternative splicing) in immature RNAs transcribed from a single gene. In order to adapt to a particular context, cells modulate not only the quantity but also the quality (alternative isoforms) of their transcriptome. Since 95% of the human coding genome is subjected to alternative splicing regulation, it is expected that many cellular pathways are modulated by alternative splicing, as is the case for the DNA damage response. Moreover, recent evidence demonstrates that upon a genotoxic insult, classical DNA damage response kinases such as ATM, ATR and DNA-PK orchestrate the gene expression response therefore modulating alternative splicing which, in a reciprocal way, shapes the response to a damaging agent.

Resumo em Inglês:

Abstract Pathological processes such as bacterial, viral and parasitic infections can generate a plethora of responses such as, but not restricted to, oxidative stress that can be harmful to the host and the pathogen. This stress occurs when there is an imbalance between reactive oxygen species produced and antioxidant factors produced in response to the infection. This imbalance can lead to DNA lesions in both infected cells as well as in the pathogen. The effects of the host response on the parasite lead to several kinds of DNA damage, causing alterations in the parasite’s metabolism; the reaction and sensitivity of the parasite to these responses are related to the DNA metabolism and life cycle of each parasite. The present review will discuss the survival strategies developed by host cells and Trypanosoma cruzi, focusing on the DNA repair mechanisms of these organisms throughout infection including the relationship between DNA damage, stress response features, and the unique characteristics of these diseases.

Resumo em Inglês:

Abstract The striking and complex phenotype of Cockayne syndrome (CS) patients combines progeria-like features with developmental deficits. Since the establishment of the in vitro culture of skin fibroblasts derived from patients with CS in the 1970s, significant progress has been made in the understanding of the genetic alterations associated with the disease and their impact on molecular, cellular, and organismal functions. In this review, we provide a historic perspective on the research into CS by revisiting seminal papers in this field. We highlighted the great contributions of several researchers in the last decades, ranging from the cloning and characterization of CS genes to the molecular dissection of their roles in DNA repair, transcription, redox processes and metabolism control. We also provide a detailed description of all pathological mutations in genes ERCC6 and ERCC8 reported to date and their impact on CS-related proteins. Finally, we review the contributions (and limitations) of many genetic animal models to the study of CS and how cutting-edge technologies, such as cell reprogramming and state-of-the-art genome editing, are helping us to address unanswered questions.

Resumo em Inglês:

Abstract NOX/DUOX enzymes are transmembrane proteins that carry electrons through biological membranes generating reactive oxygen species. The NOX family is composed of seven members, which are NOX1 to NOX5 and DUOX1 and 2. DUOX enzymes were initially called thyroid oxidases, based on their high expression level in the thyroid tissue. However, DUOX expression has been documented in several extrathyroid tissues, mostly at the apical membrane of the salivary glands, the airways, and the intestinal tract, revealing additional cellular functions associated with DUOX-related H2O2 generation. In this review, we will briefly summarize the current knowledge regarding DUOX structure and physiological functions, as well as their possible role in cancer biology.

Resumo em Inglês:

Abstract The XPC protein, which is mutated in xeroderma pigmentosum (XP) complementation group C (XP-C), is a lesion recognition factor in NER, but it has also been shown to interact with and stimulate DNA glycosylases, to act as transcriptional co-activator and on energy metabolism adaptation. We have previously demonstrated that XP-C cells show increased mitochondrial H2O2 production with a shift between respiratory complexes I and II, leading to sensitivity to mitochondrial stress. Here we report a marked decrease in expression of the transcriptional co-activator PGC-1α, a master regulator of mitochondrial biogenesis, in XP-C cells. A transcriptional role for XPC in PGC-1α expression was discarded, as XPC knockdown did not downregulate PGC-1α expression and XPC-corrected cells still showed lower PGC-1α expression. DNA methylation alone did not explain PGC-1α silencing. In four different XP-C cell lines tested, reduction of PGC-1α expression was detected in three, all of them carrying the c.1643_1644delTG mutation (ΔTG) in XPC. Indeed, all cell lines carrying XPC ΔTG mutation, whether homozygous or heterozygous, presented decreased PGC-1α expression. However, this alteration in gene expression was not exclusive to XPC ΔTG cell lines, for other non-related cell lines also showed altered PGC-1α expression. Moreover, PGC1-α expression did not correlate with expression levels of TFAM and SDHA, known PGC-1α target-genes. In turn, PPRC1, another member of the PGC family of transcription co-activators controlling mitochondrial biogenesis, displayed a good correlation between its expression in 10 cell lines and TFAM and SDHA. Nonetheless, PGC-1α knockdown led to a slight decrease of its target-gene protein level, TFAM, and subsequently of a mtDNA-encoded gene, MT-CO2. These results indicate that PGC-1α and PPRC1 cooperate as regulators of mitochondrial biogenesis and maintenance in fibroblasts.