Functional validation of miRNAs targeting genes of DNA double-strand break repair to radiosensitize non-small lung cancer cells

Analysis of Radiation Toxicity in Mammalian Cells Stably Transduced with Mitochondrial Stat3

A coordinated action between nuclear and mitochondrial activities is essential for a proper cellular response to genotoxic stress. Several nuclear transcription factors, including STAT3, translocate to mitochondria to exert mitochondrial function regulation; however, the role of mitochondrial STAT3 (mitoSTAT3) under stressed conditions is still poorly understood. In this study, we examined whether the stable expression of mitoSTAT3 wild-type or mutated at the conserved serine residue (Ser727), which is involved in the mitochondrial function of STAT3, can affect the DNA damage response to UVC radiation. To address this issue, we generated mammalian cells (NIH-3T3 and HCT-116 cells) stably transduced to express the mitochondrial-targeted Stat3 gene in its wild-type or Ser727 mutated forms. Our results show that cell proliferation is enhanced in mitoStat3-transduced cells under both non-stressed and stressed conditions. Once irradiated with UVC, cells expressing wild-type mitoSTAT3 showed the highest cell survival, which was associated with a significant decrease in cell death. Low levels of oxidative stress were detected in UVC-irradiated NIH-3T3 cells expressing mitoSTAT3 wild-type or serine-related dominant active form (Ser727D), confirming a role of mitochondrial STAT3 in minimizing oxidant cellular stress that provides an advantage for cell survival.

Biological Mechanisms to Reduce Radioresistance and Increase the Efficacy of Radiotherapy: State of the Art

Cancer treatment with ionizing radiation (IR) is a well-established and effective clinical method to fight different types of tumors and is a palliative treatment to cure metastatic stages. Approximately half of all cancer patients undergo radiotherapy (RT) according to clinical protocols that employ two types of ionizing radiation: sparsely IR (i.e., X-rays) and densely IR (i.e., protons). Most cancer cells irradiated with therapeutic doses exhibit radio-induced cytotoxicity in terms of cell proliferation arrest and cell death by apoptosis. Nevertheless, despite the more tailored advances in RT protocols in the last few years, several tumors show a relatively high percentage of RT failure and tumor relapse due to their radioresistance. To counteract this extremely complex phenomenon and improve clinical protocols, several factors associated with radioresistance, of both a molecular and cellular nature, must be considered. Tumor genetics/epigenetics, tumor microenvironment, tumor metabolism, and the presence of non-malignant cells (i.e., fibroblast-associated cancer cells, macrophage-associated cancer cells, tumor-infiltrating lymphocytes, endothelial cells, cancer stem cells) are the main factors important in determining the tumor response to IR. Here, we attempt to provide an overview of how such factors can be taken advantage of in clinical strategies targeting radioresistant tumors.

The Role of MicroRNA in DNA Damage Response

DNA is essential for the development and function of organisms. A number of factors affect DNA integrity and cause DNA damages, such as ultraviolet light, ionizing radiation and hydrogen peroxide. DNA damages activate a series of intracellular reactions, called DNA damage response, which play a crucial role in the pathogenesis of cancers and other diseases. MiRNA is a type of evolutionarily conserved non-coding RNA and affects the expression of target genes by post-transcriptional regulation. Increasing evidences suggested that the expression of some miRNAs was changed in tumor cases. MiRNAs may participate in DNA damage response and affect genomic stability via influencing the processes of cell cycle, DNA damage repair and apoptosis, thus ultimately impact on tumorigenesis. Therefore, the role of miRNA in DNA damage response is reviewed, to provide a theoretical basis for the mechanism of miRNAs’ effects on DNA damage response and for the research of new therapies for diseases.

Interactions between miRNAs and Double-Strand Breaks DNA Repair Genes, Pursuing a Fine-Tuning of Repair

The repair of DNA damage is a crucial process for the correct maintenance of genetic information, thus, allowing the proper functioning of cells. Among the different types of lesions occurring in DNA, double-strand breaks (DSBs) are considered the most harmful type of lesion, which can result in significant loss of genetic information, leading to diseases, such as cancer. DSB repair occurs through two main mechanisms, called non-homologous end joining (NHEJ) and homologous recombination repair (HRR). There is evidence showing that miRNAs play an important role in the regulation of genes acting in NHEJ and HRR mechanisms, either through direct complementary binding to mRNA targets, thus, repressing translation, or by targeting other genes involved in the transcription and activity of DSB repair genes. Therefore, alteration of miRNA expression has an impact on the ability of cells to repair DSBs, which, in turn, affects cancer therapy sensitivity. This latter gives account of the importance of miRNAs as regulators of NHEJ and HRR and places them as a promising target to improve cancer therapy. Here, we review recent reports demonstrating an association between miRNAs and genes involved in NHEJ and HRR. We employed the Web of Science search query TS (“gene official symbol/gene aliases*” AND “miRNA/microRNA/miR-”) and focused on articles published in the last decade, between 2010 and 2021. We also performed a data analysis to represent miRNA–mRNA validated interactions from TarBase v.8, in order to offer an updated overview about the role of miRNAs as regulators of DSB repair.

Factors and molecular mechanisms of radiation resistance in cancer cells

PURPOSE

The aim of this work is to review the published studies on radiation resistance mechanisms and molecular markers involved in different tumors. The revision has been focused in the last 5 years (2016-2021).

CONCLUSIONS

Radioresistance is a cause of concern as it causes failure of radiation therapy and subsequent tumor relapse. Combination chemotherapy and radiation therapy are clinically successful in treating many types of tumors. Despite continued improvements in cancer treatment, locoregional recurrence or metastatic spread continues to occur in a high proportion of patients after being treated with radiation therapy or combination treatments. There is strong evidence that cancer stem cells contribute to radiation resistance, contributing to treatment failure. The mechanisms of radiation resistance in different tumors are not fully understood. A better understanding of cancer stem cells and the associated signaling pathways that regulate radiation resistance will open up new strategies for treating cancer by radiation therapy. Radiation can damage malignant cells mainly by the induction of DNA double strand breaks. However, in some tumors appear resistant cells that repopulate the tumor following therapy leading over time to the failure of the treatment. Native mechanisms and induced pathways, are the cause of radiation resistance. It has been described that numerous molecular markers acting through numerous mechanisms of action involved in radiation resistance, such as apoptosis resistance, alterations of cell growth, proliferation and DNA repair, hypoxia, increase in invasiveness and migration capacity, cell cycle alterations and expression of heat shock proteins, among others. Therefore, resistance to radiation is a multifactorial phenomenon that, in different cell types, it occurs through different regulatory mechanisms in which different molecules intervene. Resistance can be acquired by altering different regulatory pathways in different tumors. The knowledge of radiation resistance markers could help in the classification and treatment of patients with more aggressive tumors.

Targeting DNA repair pathway in cancer: Mechanisms and clinical application

Over the last decades, the growing understanding on DNA damage response (DDR) pathways has broadened the therapeutic landscape in oncology. It is becoming increasingly clear that the genomic instability of cells resulted from deficient DNA damage response contributes to the occurrence of cancer. One the other hand, these defects could also be exploited as a therapeutic opportunity, which is preferentially more deleterious in tumor cells than in normal cells. An expanding repertoire of DDR-targeting agents has rapidly expanded to inhibitors of multiple members involved in DDR pathways, including PARP, ATM, ATR, CHK1, WEE1, and DNA-PK. In this review, we sought to summarize the complex network of DNA repair machinery in cancer cells and discuss the underlying mechanism for the application of DDR inhibitors in cancer. With the past preclinical evidence and ongoing clinical trials, we also provide an overview of the history and current landscape of DDR inhibitors in cancer treatment, with special focus on the combination of DDR-targeted therapies with other cancer treatment strategies.

MicroRNAs and the DNA damage response: How is cell fate determined?

It is becoming clear that the DNA damage response orchestrates an appropriate response to a given level of DNA damage, whether that is cell cycle arrest and repair, senescence or apoptosis. It is plausible that the alternative regulation of the DNA damage response (DDR) plays a role in deciding cell fate following damage. MicroRNAs (miRNAs) are associated with the transcriptional regulation of many cellular processes. They have diverse functions, affecting, presumably, all aspects of cell biology. Many have been shown to be DNA damage inducible and it is conceivable that miRNA species play a role in deciding cell fate following DNA damage by regulating the expression and activation of key DDR proteins. From a clinical perspective, miRNAs are attractive targets to improve cancer patient outcomes to DNA-damaging chemotherapy. However, cancer tissue is known to be, or to become, well adapted to DNA damage as a means of inducing chemoresistance. This frequently results from an altered DDR, possibly owing to miRNA dysregulation. Though many studies provide an overview of miRNAs that are dysregulated within cancerous tissues, a tangible, functional association is often lacking. While miRNAs are well-documented in 'ectopic biology', the physiological significance of endogenous miRNAs in the context of the DDR requires clarification. This review discusses miRNAs of biological relevance and their role in DNA damage response by potentially 'fine-tuning' the DDR towards a particular cell fate in response to DNA damage. MiRNAs are thus potential therapeutic targets/strategies to limit chemoresistance, or improve chemotherapeutic efficacy.

Home and Away: The Role of Non-Coding RNA in Intracellular and Intercellular DNA Damage Response

Non-coding RNA (ncRNA) has recently emerged as a vital component of the DNA damage response (DDR), which was previously believed to be solely regulated by proteins. Many species of ncRNA can directly or indirectly influence DDR and enhance DNA repair, particularly in response to double-strand DNA breaks, which may hold therapeutic potential in the context of cancer. These include long non-coding RNA (lncRNA), microRNA, damage-induced lncRNA, DNA damage response small RNA, and DNA:RNA hybrid structures, which can be categorised as cis or trans based on the location of their synthesis relative to DNA damage sites. Mechanisms of RNA-dependent DDR include the recruitment or scaffolding of repair factors at DNA break sites, the regulation of repair factor expression, and the stabilisation of repair intermediates. DDR can also be communicated intercellularly via exosomes, leading to bystander responses in healthy neighbour cells to generate a population-wide response to damage. Many microRNA species have been directly implicated in the propagation of bystander DNA damage, autophagy, and radioresistance, which may prove significant for enhancing cancer treatment via radiotherapy. Here, we review recent developments centred around ncRNA and their contributions to intracellular and intercellular DDR mechanisms.

miR-27b-3p a Negative Regulator of DSB-DNA Repair

Understanding the regulation of DNA repair mechanisms is of utmost importance to identify altered cellular processes that lead to diseases such as cancer through genomic instability. In this sense, miRNAs have shown a crucial role. Specifically, miR-27b-3 biogenesis has been shown to be induced in response to DNA damage, suggesting that this microRNA has a role in DNA repair. In this work, we show that the overexpression of miR-27b-3p reduces the ability of cells to repair DNA lesions, mainly double-stranded breaks (DSB), and causes the deregulation of genes involved in homologous recombination repair (HRR), base excision repair (BER), and the cell cycle. DNA damage was induced in BALB/c-3T3 cells, which overexpress miR-27b-3p, using xenobiotic agents with specific mechanisms of action that challenge different repair mechanisms to determine their reparative capacity. In addition, we evaluated the expression of 84 DNA damage signaling and repair genes and performed pathway enrichment analysis to identify altered cellular processes. Taken together, our results indicate that miR-27b-3p acts as a negative regulator of DNA repair when overexpressed.

The Role of RNA in DNA Breaks, Repair and Chromosomal Rearrangements

Incorrect reparation of DNA double-strand breaks (DSB) leading to chromosomal rearrangements is one of oncogenesis's primary causes. Recently published data elucidate the key role of various types of RNA in DSB formation, recognition and repair. With growing interest in RNA biology, increasing RNAs are classified as crucial at the different stages of the main pathways of DSB repair in eukaryotic cells: nonhomologous end joining (NHEJ) and homology-directed repair (HDR). Gene mutations or variation in expression levels of such RNAs can lead to local DNA repair defects, increasing the chromosome aberration frequency. Moreover, it was demonstrated that some RNAs could stimulate long-range chromosomal rearrangements. In this review, we discuss recent evidence demonstrating the role of various RNAs in DSB formation and repair. We also consider how RNA may mediate certain chromosomal rearrangements in a sequence-specific manner.

MicroRNA: a novel implication for damage and protection against ionizing radiation

Ionizing radiation (IR) is a form of high energy. It poses a serious threat to organisms, but radiotherapy is a key therapeutic strategy for various cancers. It is significant to reduce radiation injury but maximize the effect of radiotherapy. MicroRNAs (miRNAs) are posttranscriptionally regulatory factors involved in cellular radioresponse. In this review, we show how miRNAs regulate important genes on cellular response to IR-induced damage and how miRNAs participate in IR-induced carcinogenesis. Additionally, we summarize the experimental and clinical evidence for miRNA involvement in radiotherapy and discuss their potential for improvement of radiotherapy. Finally, we highlight the role that miRNAs play in accident exposure to IR or radiotherapy as predictive biomarker. miRNA therapeutics have shown great perspective in radiobiology; miRNA may become a novel strategy for damage and protection against IR.

AIMP3 inhibits cell growth and metastasis of lung adenocarcinoma through activating a miR-96-5p-AIMP3-p53 axis

Aminoacyl‐tRNA synthetase‐interacting multifunctional protein‐3 (AIMP3) is a tumour suppressor, however, the roles of AIMP3 in non‐small cell lung cancer (NSCLC) are not explored yet. Here, we reported that AIMP3 significantly inhibited the cell growth and metastasis of NSCLC (lung adenocarcinoma) in vitro and in vivo. We have firstly identified that AIMP3 was down‐regulated in human NSCLC tissues compared with adjacent normal lung tissues using immunohistochemistry and western blot assays. Overexpression of AIMP3 markedly suppressed the proliferation and migration of cancer cells in a p53‐dependent manner. Furthermore, we observed that AIMP3 significantly suppressed tumour growth and metastasis of A549 cells in xenograft nude mice. Mechanically, we identified that AIMP3 was a direct target of miR‐96‐5p, and we also observed that there was a negative correlation between AIMP3 and miR‐96‐5p expression in paired NSCLC clinic samples. Ectopic miR‐96‐5p expression promoted the proliferation and migration of cancer cells in vitro and tumour growth and metastasis in vivo which partially depended on AIMP3. Taken together, our results demonstrated that the axis of miR‐96‐5p‐AIMP3‐p53 played an important role in lung adenocarcinoma, which may provide a new strategy for the diagnosis and treatment of NSCLC.

Role of microRNAs in Lung Carcinogenesis Induced by Asbestos

MicroRNAs are a class of small noncoding endogenous RNAs 19–25 nucleotides long, which play an important role in the post-transcriptional regulation of gene expression by targeting mRNA targets with subsequent repression of translation. MicroRNAs are involved in the pathogenesis of numerous diseases, including cancer. Lung cancer is the leading cause of cancer death in the world. Lung cancer is usually associated with tobacco smoking. However, about 25% of lung cancer cases occur in people who have never smoked. According to the International Agency for Research on Cancer, asbestos has been classified as one of the cancerogenic factors for lung cancer. The mechanism of malignant transformation under the influence of asbestos is associated with the genotoxic effect of reactive oxygen species, which initiate the processes of DNA damage in the cell. However, epigenetic mechanisms such as changes in the microRNA expression profile may also be implicated in the pathogenesis of asbestos-induced lung cancer. Numerous studies have shown that microRNAs can serve as a biomarker of the effects of various adverse environmental factors on the human body. This review examines the role of microRNAs, the expression profile of which changes upon exposure to asbestos, in key processes of carcinogenesis, such as proliferation, cell survival, metastasis, neo-angiogenesis, and immune response avoidance.

Jack of all trades? The versatility of RNA in DNA double-strand break repair

The mechanisms by which RNA acts in the DNA damage response (DDR), specifically in the repair of DNA double-strand breaks (DSBs), are emerging as multifaceted and complex. Different RNA species, including but not limited to; microRNA (miRNA), long non-coding RNA (lncRNA), RNA:DNA hybrid structures, the recently identified damage-induced lncRNA (dilncRNA), damage-responsive transcripts (DARTs), and DNA damage-dependent small RNAs (DDRNAs), have been shown to play integral roles in the DSB response. The diverse properties of these RNAs, such as sequence, structure, and binding partners, enable them to fulfil a variety of functions in different cellular contexts. Additionally, RNA can be modified post-transcriptionally, a process which is regulated in response to cellular stressors such as DNA damage. Many of these mechanisms are not yet understood and the literature contradictory, reflecting the complexity and expansive nature of the roles of RNA in the DDR. However, it is clear that RNA is pivotal in ensuring the maintenance of genome integrity. In this review, we will discuss and summarise recent evidence which highlights the roles of these various RNAs in preserving genomic integrity, with a particular focus on the emerging role of RNA in the DSB repair response.

Targeting DNA Double-Strand Break (DSB) Repair to Counteract Tumor Radio-resistance

During the last decade, advances of radiotherapy (RT) have been made in the clinical practice of cancer treatment. RT exerts its anticancer effect mainly via leading to the DNA Double-Strand Break (DSB), which is one of the most toxic DNA damages. Non-Homologous End Joining (NHEJ) and Homologous Recombination (HR) are two major DSB repair pathways in human cells. It is known that dysregulations of DSB repair elicit a predisposition to cancer and probably result in resistance to cancer therapies including RT. Therefore, targeting the DSB repair presents an attractive strategy to counteract radio-resistance. In this review, we describe the latest knowledge of the two DSB repair pathways, focusing on several key proteins contributing to the repair, such as DNA-PKcs, RAD51, MRN and PARP1. Most importantly, we discuss the possibility of overcoming radiation resistance by targeting these proteins for therapeutic inhibition. Recent tests of DSB repair inhibitors in the laboratory and their translations into clinical studies are also addressed.

Regulation of DNA Damage Response and Homologous Recombination Repair by microRNA in Human Cells Exposed to Ionizing Radiation

Ionizing radiation may be of both artificial and natural origin and causes cellular damage in living organisms. Radioactive isotopes have been used significantly in cancer therapy for many years. The formation of DNA double-strand breaks (DSBs) is the most dangerous effect of ionizing radiation on the cellular level. After irradiation, cells activate a DNA damage response, the molecular path that determines the fate of the cell. As an important element of this, homologous recombination repair is a crucial pathway for the error-free repair of DNA lesions. All components of DNA damage response are regulated by specific microRNAs. MicroRNAs are single-stranded short noncoding RNAs of 20–25 nt in length. They are directly involved in the regulation of gene expression by repressing translation or by cleaving target mRNA. In the present review, we analyze the biological mechanisms by which miRNAs regulate cell response to ionizing radiation-induced double-stranded breaks with an emphasis on DNA repair by homologous recombination, and its main component, the RAD51 recombinase. On the other hand, we discuss the ability of DNA damage response proteins to launch particular miRNA expression and modulate the course of this process. A full understanding of cell response processes to radiation-induced DNA damage will allow us to develop new and more effective methods of ionizing radiation therapy for cancers, and may help to develop methods for preventing the harmful effects of ionizing radiation on healthy organisms.

DNA-PK in human malignant disorders: Mechanisms and implications for pharmacological interventions

The DNA-PK holoenzyme is a fundamental element of the DNA damage response machinery (DDR), which is responsible for cellular genomic stability. Consequently, and predictably, over the last decades since its identification and characterization, numerous pre-clinical and clinical studies reported observations correlating aberrant DNA-PK status and activity with cancer onset, progression and responses to therapeutic modalities. Notably, various studies have established in recent years the role of DNA-PK outside the DDR network, corroborating its role as a pleiotropic complex involved in transcriptional programs that operate biologic processes as epithelial to mesenchymal transition (EMT), hypoxia, metabolism, nuclear receptors signaling and inflammatory responses. In particular tumor entities as prostate cancer, immense research efforts assisted mapping and describing the overall signaling networks regulated by DNA-PK that control metastasis and tumor progression. Correspondingly, DNA-PK emerges as an obvious therapeutic target in cancer and data pertaining to various pharmacological approaches have been published, largely in context of combination with DNA-damaging agents (DDAs) that act by inflicting DNA double strand breaks (DSBs). Currently, new generation inhibitors are tested in clinical trials. Several excellent reviews have been published in recent years covering the biology of DNA-PK and its role in cancer. In the current article we are aiming to systematically describe the main findings on DNA-PK signaling in major cancer types, focusing on both preclinical and clinical reports and present a detailed current status of the DNA-PK inhibitors repertoire.

Role of Rad51 and DNA repair in cancer: A molecular perspective

The maintenance of genome integrity is essential for any organism survival and for the inheritance of traits to offspring. To the purpose, cells have developed a complex DNA repair system to defend the genetic information against both endogenous and exogenous sources of damage. Accordingly, multiple repair pathways can be aroused from the diverse forms of DNA lesions, which can be effective per se or via crosstalk with others to complete the whole DNA repair process. Deficiencies in DNA healing resulting in faulty repair and/or prolonged DNA damage can lead to genes mutations, chromosome rearrangements, genomic instability, and finally carcinogenesis and/or cancer progression. Although it might seem paradoxical, at the same time such defects in DNA repair pathways may have therapeutic implications for potential clinical practice. Here we provide an overview of the main DNA repair pathways, with special focus on the role played by homologous repair and the RAD51 recombinase protein in the cellular DNA damage response. We next discuss the recombinase structure and function per se and in combination with all its principal mediators and regulators. Finally, we conclude with an analysis of the manifold roles that RAD51 plays in carcinogenesis, cancer progression and anticancer drug resistance, and conclude this work with a survey of the most promising therapeutic strategies aimed at targeting RAD51 in experimental oncology.

DNA-PK as an Emerging Therapeutic Target in Cancer

The DNA-dependent protein kinase (DNA-PK) plays an instrumental role in the overall survival and proliferation of cells. As a member of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, DNA-PK is best known as a mediator of the cellular response to DNA damage. In this context, DNA-PK has emerged as an intriguing therapeutic target in the treatment of a variety of cancers, especially when used in conjunction with genotoxic chemotherapy or ionizing radiation. Beyond the DNA damage response, DNA-PK activity is necessary for multiple cellular functions, including the regulation of transcription, progression of the cell cycle, and in the maintenance of telomeres. Here, we review what is currently known about DNA-PK regarding its structure and established roles in DNA repair. We also discuss its lesser-known functions, the pharmacotherapies inhibiting its function in DNA repair, and its potential as a therapeutic target in a broader context.