MicroRNA-138 modulates DNA damage response by repressing histone H2AX expression

RETRACTED: MicroRNA138 regulates keratin 17 protein expression to affect HaCaT cell proliferation and apoptosis by targeting hTERT in psoriasis vulgaris

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. An Expression of Concern for this article was previously published while an investigation was conducted (see related editorial: https://doi.org/10.1016/j.biopha.2022.113812). This retraction notice supersedes the Expression of Concern published earlier. Concern was raised about the reliability of the flow cytometry data in Figure 9, with suspected image similarities reported between the ‘miR-138 mimic’ and ‘siRNA hTERT’ groups, as detailed here: https://pubpeer.com/publications/983120063E7603EBA705B85BBF77F5; and here: https://docs.google.com/spreadsheets/d/1r0MyIYpagBc58BRF9c3luWNlCX8VUvUuPyYYXzxWvgY/edit#gid=262337249. Independent analysis confirmed this finding and identified additional suspected image duplications within Figure 9. The journal requested the corresponding author comment on these concerns and provide the associated raw data. The authors did not respond to this request and therefore the Editor-in-Chief decided to retract the article.

MicroRNAs, DNA Damage Response, and Cancer Treatment

As a result of various stresses, lesions caused by DNA-damaging agents occur constantly in each cell of the human body. Generally, DNA damage is recognized and repaired by the DNA damage response (DDR) machinery, and the cells survive. When repair fails, the genomic integrity of the cell is disrupted—a hallmark of cancer. In addition, the DDR plays a dual role in cancer development and therapy. Cancer radiotherapy and chemotherapy are designed to eliminate cancer cells by inducing DNA damage, which in turn can promote tumorigenesis. Over the past two decades, an increasing number of microRNAs (miRNAs), small noncoding RNAs, have been identified as participating in the processes regulating tumorigenesis and responses to cancer treatment with radiation therapy or genotoxic chemotherapies, by modulating the DDR. The purpose of this review is to summarize the recent findings on how miRNAs regulate the DDR and discuss the therapeutic functions of miRNAs in cancer in the context of DDR regulation.

NEK8 regulates DNA damage-induced RAD51 foci formation and replication fork protection

Proteins essential for homologous recombination play a pivotal role in the repair of DNA double strand breaks, DNA inter-strand crosslinks and replication fork stability. Defects in homologous recombination also play a critical role in the development of cancer and the sensitivity of these cancers to chemotherapy. RAD51, an essential factor for homologous recombination and replication fork protection, accumulates and forms immunocytochemically detectable nuclear foci at sites of DNA damage. To identify kinases that may regulate RAD51 localization to sites of DNA damage, we performed a human kinome siRNA library screen, using DNA damage-induced RAD51 foci formation as readout. We found that NEK8, a NIMA family kinase member, is required for efficient DNA damage-induced RAD51 foci formation. Interestingly, knockout of Nek8 in murine embryonic fibroblasts led to cellular sensitivity to the replication inhibitor, hydroxyurea, and inhibition of the ATR kinase. Furthermore, NEK8 was required for proper replication fork protection following replication stall with hydroxyurea. Loading of RAD51 to chromatin was decreased in NEK8-depleted cells and Nek8-knockout cells. Single-molecule DNA fiber analyses revealed that nascent DNA tracts were degraded in the absence of NEK8 following treatment with hydroxyurea. Consistent with this, Nek8-knockout cells showed increased chromosome breaks following treatment with hydroxyurea. Thus, NEK8 plays a critical role in replication fork stability through its regulation of the DNA repair and replication fork protection protein RAD51.

miR-620 promotes tumor radioresistance by targeting 15-hydroxyprostaglandin dehydrogenase (HPGD)

MicroRNA contribute to tumor radiation resistance, which is an important clinical problem, and thus we are interested in identifying and characterizing their function. We demonstrate that miR-620 contributes to radiation resistance in cancer cells by increasing proliferation, and decreasing the G2/M block. We identify the hydroxyprostaglandin dehydrogenase 15-(nicotinamide adenine dinucleotide) (HPGD/15-PGDH) tumor suppressor gene as a direct miR-620 target, which results in increased prostaglandin E2 (PGE2) levels. Furthermore, we show that siRNA targeting of HPGD or administration of exogenous PGE2 recapitulates radioresistance. Targeting of the EP2 receptor that responds to PGE2 using pharmacological or genetic approaches, abrogates radioresistance. Tumor xenograft experiments confirm that miR-620 increases proliferation and tumor radioresistance in vivo. Regulation of PGE2 levels via targeting of HPGD by miR-620 is an innovative manner by which a microRNA can induce radiation resistance.

Up- regulation of miR-328-3p sensitizes non-small cell lung cancer to radiotherapy

MicroRNAs (miRNAs) are believed to be resistant against radiotherapy in certain types of cancers. The aim of our study was to determine the clinical application of miRNAs in non-small cell lung cancer (NSCLC). Sixty NSCLC tissue samples and adjacent histologically normal tissues were obtained for miRNAs microarray analysis and validated by RT-qPCR. Correlation between miRNA expression level and clinicopathological features was evaluated. Our study examined the influence of changed miRNA expression on the damaged DNA and its associated radio sensitivity. Luciferase assay was performed to determine potential effects on the targeted gene. Our study identified fifteen altered miRNAs in which miR-328-3p was down regulated in NSCLC tumour tissue as compared to normal tissues. Down-expression of miR-328-3p was positively associated with an enhanced lymph node metastasis, advanced clinical stage and a shortened survival rate. miR-328-3p expression was decreased in A549 cells compared to other NSCLC cell lines. Up-regulation of miR-328-3p demonstrated a survival inhibition effect in A549 and restored NSCLC cells' sensitivity to radio therapy. An increased miR-328-3p expression promoted irradiation-induced DNA damage in cells. γ-H2AX was identified as the direct target of miR-328-3p. Over-expressed miR-328-3p can improve the radiosensitvity of cells by altering the DNA damage/repair signalling pathways in NSCLC.

Species-specific mutual regulation of p53 and miR-138 between human, rat and mouse

In recent years, p53 was identified to regulate the expression of many miRNAs and was also regulated by miRNAs. In this paper, we found that miR-138 showed a pronounced increase after p53 activation in human non-small cell lung cancer (NSCLC) cells, which is mediated by p53 binding sites in the promoter region of its host gene, but this did not happen with rat and mouse cells. More interestingly, we found that p53 could be also regulated by miR-138 in mouse and rat cells, but not in the human NSCLC cells. Our results suggest the existence of species-specific differences of the regulations of miRNA against its targets and the regulations of miRNA itself by other proteins.

Chronic oxidative stress promotes H2AX protein degradation and enhances chemosensitivity in breast cancer patients

Anti‐cancer drugs often increase reactive oxygen species (ROS) and cause DNA damage. Here, we highlight a new cross talk between chronic oxidative stress and the histone variant H2AX, a key player in DNA repair. We observe that persistent accumulation of ROS, due to a deficient JunD‐/Nrf2‐antioxidant response, reduces H2AX protein levels. This effect is mediated by an enhanced interaction of H2AX with the E3 ubiquitin ligase RNF168, which is associated with H2AX poly‐ubiquitination and promotes its degradation by the proteasome. ROS‐mediated H2AX decrease plays a crucial role in chemosensitivity. Indeed, cycles of chemotherapy that sustainably increase ROS reduce H2AX protein levels in Triple‐Negative breast cancer (TNBC) patients. H2AX decrease by such treatment is associated with an impaired NRF2‐antioxidant response and is indicative of the therapeutic efficiency and survival of TNBC patients. Thus, our data describe a novel ROS‐mediated regulation of H2AX turnover, which provides new insights into genetic instability and treatment efficacy in TNBC patients.

Dme-miR-314-3p modulation in Cr(VI) exposed Drosophila affects DNA damage repair by targeting mus309

microRNAs (miRNAs) as one of the major epigenetic modulators negatively regulate mRNAs at post transcriptional level. It was therefore hypothesized that modulation of miRNAs by hexavalent Chromium [Cr(VI)], a priority environmental chemical, can affect DNA damage. In a genetically tractable model, Drosophila melanogaster, role of maximally up-regulated miRNA, dme-miR-314-3p, on DNA damage was examined by exposing the third instar larvae to 5.0-20.0 μg/ml Cr(VI) for 24 and 48 h. mus309, a Drosophila homologue of human Bloom's syndrome and predicted as one of the potential targets of this miRNA, was confirmed as its target by 5'RLM-RACE assay. A significant down-regulation of mus309 was observed in dme-miR-314-3p overexpression strain (myo-gal4>UAS-miR-314-3p) as compared with that in parental strains (myo-gal4 and UAS-miR-314-3p) and in w(1118). A significant increase in DNA damage including double strand breaks generation was observed in exposed myo-gal4>UAS-miR-314 and mus309 mutants as compared with that in parental strain and in unexposed control. A significant down-regulation of cell cycle regulation genes (CycA, CycB and cdc2) was observed in these exposed genotypes. Collectively, the study demonstrates that dme-miR-314-3p can mediate the downregulation of repair deficient gene mus309 leading to increased DNA damage and cell cycle arrest in exposed organism which may affect Cr(VI) mediated carcinogenesis.

Hsa-let-7g miRNA regulates the anti-tumor effects of gastric cancer cells under oxidative stress through the expression of DDR genes

Oxidative stress is linked to increased risk of gastric cancer (GC). Recent reports have found that hsa-let-7 g microRNA (miRNA) has properties of anti-tumor and resistance to damages induced by oxidized low-density lipoprotein (ox-LDL). Dysregulation of hsa-let-7 g was present in GC in vivo and in vitro under exogenous stress. However, we didn't know whether there are regulatory mechanisms of hsa-let-7 g in GC under oxidative stress. This study was aimed at investigating the effects of hsa-let-7 g microRNA (miRNA) on GC under oxidative stress. The results showed that H2O2 induced the increase of DNA damage response (DDR) genes (ATM, H2AX and Chk1) and downregulation of hsa-let-7 g in GC cells. Further study confirmed Hsa-let-7 g caused the apoptosis and loss of proliferation in GC cells exposed to H2O2 associated with repression of DDR system. Yet, we found let-7 g didn't target DDR genes (ATM, H2AX and Chk1) directly. In addition, data revealed hsa-let-7 g miRNA increased the sensitivity of GC to X-rays involving in ATM regulation as well according to application of X-rays (another DDR inducer). In conclusion, Hsa-let-7 g miRNA increased the sensitivity of GC to oxidative stress by repression activation of DDR indirectly. Let-7 g improved the effects of X-rays on GC cells involving in DDR regulation as well.

Regulators in the DNA damage response

Maintenance of genome integrity is essential for the proper function of all cells and organisms. In response to both endogenous and exogenous DNA damaging agents, mammalian cells have evolved a delicate system to sense DNA damage, stop cell cycle progression, modulate cell metabolism, repair damaged DNA, and induce programmed cell death if the damage is too severe. This coordinated global signaling network, namely the DNA damage response (DDR), ensures the genome stability under DNA damaging stress. A variety of regulators have been shown to modulate the activity and levels of key proteins in the DDR, including kinases, phosphatases, ubiquitin ligases, deubiquitinases, and other protein modifying enzymes. Epigenetic regulators, particularly microRNAs and long noncoding RNAs, have been emerging as an important payer of regulation in addition to canonical DNA damage signaling proteins. In this review, we will discuss the functional interaction between the regulators and their targets in the DDR.

MicroRNA expression and its association with DNA repair in preimplantation embryos

Active DNA repair pathways are crucial for preserving genomic integrity and are likely among the complex mechanisms involved in the normal development of preimplantation embryos. MicroRNAs (miRNA), short non-coding RNAs, are key regulators of gene expression through the post-transcriptional and post-translational modification of mRNA. The association of miRNA expression with infertility or polycystic ovarian syndrome has been widely investigated; however, there are limited data regarding the importance of miRNA regulation in DNA repair during preimplantation embryo development. In this article, we review normal miRNA biogenesis and consequences of aberrant miRNA expression in the regulation of DNA repair in gametes and preimplantation embryos.

Non-Coding RNA: Sequence-Specific Guide for Chromatin Modification and DNA Damage Signaling

Chromatin conformation shapes the environment in which our genome is transcribed into RNA. Transcription is a source of DNA damage, thus it often occurs concomitantly to DNA damage signaling. Growing amounts of evidence suggest that different types of RNAs can, independently from their protein-coding properties, directly affect chromatin conformation, transcription and splicing, as well as promote the activation of the DNA damage response (DDR) and DNA repair. Therefore, transcription paradoxically functions to both threaten and safeguard genome integrity. On the other hand, DNA damage signaling is known to modulate chromatin to suppress transcription of the surrounding genetic unit. It is thus intriguing to understand how transcription can modulate DDR signaling while, in turn, DDR signaling represses transcription of chromatin around the DNA lesion. An unexpected player in this field is the RNA interference (RNAi) machinery, which play roles in transcription, splicing and chromatin modulation in several organisms. Non-coding RNAs (ncRNAs) and several protein factors involved in the RNAi pathway are well known master regulators of chromatin while only recent reports show their involvement in DDR. Here, we discuss the experimental evidence supporting the idea that ncRNAs act at the genomic loci from which they are transcribed to modulate chromatin, DDR signaling and DNA repair.

Epigenetic-based combinatorial resveratrol and pterostilbene alters DNA damage response by affecting SIRT1 and DNMT enzyme expression, including SIRT1-dependent γ-H2AX and telomerase regulation in triple-negative breast cancer

Background

Nutrition is believed to be a primary contributor in regulating gene expression by affecting epigenetic pathways such as DNA methylation and histone modification. Resveratrol and pterostilbene are phytoalexins produced by plants as part of their defense system. These two bioactive compounds when used alone have been shown to alter genetic and epigenetic profiles of tumor cells, but the concentrations employed in various studies often far exceed physiologically achievable doses. Triple-negative breast cancer (TNBC) is an often fatal condition that may be prevented or treated through novel dietary-based approaches.

Methods

HCC1806 and MDA-MB-157 breast cancer cells were used as TNBC cell lines in this study. MCF10A cells were used as control breast epithelial cells to determine the safety of this dietary regimen. CompuSyn software was used to determine the combination index (CI) for drug combinations.

Results

Combinatorial resveratrol and pterostilbene administered at close to physiologically relevant doses resulted in synergistic (CI <1) growth inhibition of TNBCs. SIRT1, a type III histone deacetylase (HDAC), was down-regulated in response to this combinatorial treatment. We further explored the effects of this novel combinatorial approach on DNA damage response by monitoring γ-H2AX and telomerase expression. With combination of these two compounds there was a significant decrease in these two proteins which might further resulted in significant growth inhibition, apoptosis and cell cycle arrest in HCC1806 and MDA-MB-157 breast cancer cells, while there was no significant effect on cellular viability, colony forming potential, morphology or apoptosis in control MCF10A breast epithelial cells. SIRT1 knockdown reproduced the effects of combinatorial resveratrol and pterostilbene-induced SIRT1 down-regulation through inhibition of both telomerase activity and γ-H2AX expression in HCC1806 breast cancer cells. As a part of the repair mechanisms and role of SIRT1 in recruiting DNMTs, the effects of this combination treatment was also explored on DNA methyltransferases (DNMTs) expression. Interestingly, the compounds resulted in a significant down-regulation of DNMT enzymes with no significant effects on DNMT enzyme expression in MCF10A control cells.

Conclusion

Collectively, these results provide new insights into the epigenetic mechanisms of a novel combinatorial nutrient control strategy that exhibits synergy and may contribute to future recalcitrant TNBC prevention and/or therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1693-z) contains supplementary material, which is available to authorized users.

FANCI Regulates Recruitment of the FA Core Complex at Sites of DNA Damage Independently of FANCD2

The Fanconi anemia (FA)-BRCA pathway mediates repair of DNA interstrand crosslinks. The FA core complex, a multi-subunit ubiquitin ligase, participates in the detection of DNA lesions and monoubiquitinates two downstream FA proteins, FANCD2 and FANCI (or the ID complex). However, the regulation of the FA core complex itself is poorly understood. Here we show that the FA core complex proteins are recruited to sites of DNA damage and form nuclear foci in S and G2 phases of the cell cycle. ATR kinase activity, an intact FA core complex and FANCM-FAAP24 were crucial for this recruitment. Surprisingly, FANCI, but not its partner FANCD2, was needed for efficient FA core complex foci formation. Monoubiquitination or ATR-dependent phosphorylation of FANCI were not required for the FA core complex recruitment, but FANCI deubiquitination by USP1 was. Additionally, BRCA1 was required for efficient FA core complex foci formation. These findings indicate that FANCI functions upstream of FA core complex recruitment independently of FANCD2, and alter the current view of the FA-BRCA pathway.

Fanconi anemia is a genetic disease characterized by bone marrow failure, congenital malformations and cancer predisposition. Cells derived from Fanconi anemia patients have a dysfunctional FA-BRCA pathway and are deficient in the repair of a specific form of DNA damage, DNA interstrand-crosslinks, that are induced by certain chemotherapeutic drugs. Therefore, the study of FA-BRCA pathway regulation is essential for developing new treatments for Fanconi anemia patients and cancer patients in general. One of the first steps in the pathway is the detection of DNA lesions by the FA core complex. We have optimized a method to visualize the recruitment of the FA core complex to sites of DNA damage and, for the first time, explored how this process occurs. We have uncovered several factors that are required for this recruitment. Among them is a FA core complex substrate, FANCI. We report that non-phosphorylated FANCI, previously believed to be an inactive form, has an important role in the recruitment of the FA core complex and DNA interstrand-crosslink repair. Our findings change the current view of the FA-BRCA pathway and have implications for potential clinical strategies aimed at activating or inhibiting the FA-BRCA pathway.

Down-regulation of miR-133a and miR-539 are associated with unfavorable prognosis in patients suffering from osteosarcoma

Background

MicroRNAs (miRNAs) play key roles in cancer development and progression. The purpose of the present study was to determine the expression levels of miR-133a and miR-539 in osteosarcoma patients and to further investigate the clinicopathological, and prognostic value of these miRNAs.

Methods

The expression levels of miR-133a and miR-539 were determined by qRT-PCR. Associations between miRNAs expressions and various clinicopathological characteristics were analyzed. Survival rate was determined with Kaplan–Meier and statistically analyzed with the log-rank method between groups. Survival data were evaluated through multivariate Cox regression analysis

Results

Our findings revealed that the miR-133a expression was significantly decreased in clinical osteosarcoma tissues compared to adjacent normal bone tissues. The expression level of miR-539 was decreased in clinical osteosarcoma tissues as compared to those adjacent normal tissues. Low expressions of miR-133a and miR-539 were significantly association with advanced TNM stage (P = 0.002; P = 0.001), and metastasis or recurrence (P = 0.001; P = 0.01). Furthermore, Kaplan–Meier survival analysis and log-rank test showed that the low expressions of miR-133a and miR-539 were correlated with the reduced overall survival of osteosarcoma patients. Multivariate Cox proportional hazards model showed that decreased expressions of miR-133a and miR-539 (P = 0.007; P = 0.02), TNM stage (P = 0.001; P = 0.002), and metastasis or recurrence (P = 0.005; P = 0.026) were independent prognostic markers of overall survival of patients.

Conclusion

These results suggest that decreased miR-133a and miR-539 expressions may participate in the progression of osteosarcoma. Together, these results showed that miR-133a and miR-539 may have their role in both progression and prognosis of osteosarcoma.

miR-214-mediated downregulation of RNF8 induces chromosomal instability in ovarian cancer cells

Defective DNA damage response (DDR) is frequently associated with carcinogenesis. Abrogation of DDR leads to chromosomal instability, a most common characteristic of tumors. However, the molecular mechanisms underlying regulation of DDR are still elusive. The ubiquitin ligase RNF8 mediates the ubiquitination of γH2AX and recruits 53BP1 and BRCA1 to DNA damage sites which promotes DDR and inhibits chromosomal instability. Though RNF8 is a key player involved in DDR, regulation of its expression is still poorly understood. Here, we show that miR-214 could abrogate DDR by repressing RNF8 expression through direct binding to 3'-untranslated region (3' UTR) of RNF8 mRNA in human ovarian cancer cells. Antagonizing miR-214 by expressing its inhibitors in A2780 cells significantly increased RNF8 expression and thus promoted DNA damage repair. Consistent with the role of miR-214 in regulating RNF8 expression, the impaired DNA repair induced by miR-214 overexpression can be rescued by overexpressing RNF8 mRNA lacking the 3' UTR. Together, our results indicate that down-regulation of RNF8 mediated by miR-214 impedes DNA damage response to induce chromosomal instability in ovarian cancers, which may facilitate the understanding of mechanisms underlying chromosomal instability.

MicroRNA-138 negatively regulates non-small cell lung cancer cells through the interaction with cyclin D3

Previous studies demonstrate that microRNA-138 (miR-138) is critical in non-small cell lung cancer (NSCLC) regulation. We further explored the molecular mechanism of miR-138 in NSCLC. Lentivirus was used to upregulate miR-138 in NSCLC cell lines H460 and SPC-A1 cells. Previously known effects of miR-138 upregulation on NSCLC, proliferation, cell cycle division, and cisplatin sensitivity were examined in H460 and SPC-A1 cells. Moreover, previously unknown effect of miR-138 upregulation on NSCLC migration was also examined in H460 and SPC-A1 cells. A new miR-138 downstream target, cyclin D3 (CCND3), was assessed by dual-luciferase reporter assay and quantitative real-time PCR (qRT-PCR). CCND3 was then ectopically overexpressed in H460 and SPC-A1 cells. The effects of forced overexpression of CCND3 on miR-138-induced NSCLC regulations were further examined by proliferation, cell cycle, cisplatin sensitivity, and migration assays, respectively. Lentivirus-induced miR-138 upregulation inhibited NSCLC proliferation and cell cycle division, in line with previous findings. Moreover, we found that miR-138 upregulation had other anti-tumor effects, such as increasing cisplatin sensitivity and reducing cancer migration, in H460 and SPC-A1 cells. Luciferase assay and qRT-PCR showed that CCND3 was directly targeted by miR-138. Forced overexpression of CCND3 in H460 and SPC-A1 cells reversed the anti-tumor effects of miR-138 upregulation on cancer cell growth, cell cycle, cisplatin sensitivity, and migration. Our study revealed novel anti-cancer effects of miR-138 upregulation in NSCLC, as well as its new molecular target of CCND3.

MDM4 regulation by the let-7 miRNA family in the DNA damage response of glioma cells

Despite extensive investigation into the role of let-7 miRNAs in pathological tumor processes, their involvement in the DNA damage response remains unclear. Here we show that most let-7 family members down-regulate MDM4 expression via binding to MDM4 mRNA at a conserved DNA sequence. Expression of exogenous let-7 miRNA mimics decreased MDM4 protein but not mRNA levels. Several DNA damage reagents increased let-7 expression, thereby decreasing MDM4 protein levels in glioma cells. Inhibition of endogenous let-7 with antisense RNAs rescued MDM4 protein levels with or without MG132, a proteasome-dependent degradation inhibitor. An MDM4 mutation identified in a glioma patient was associated with loss of the putative MDM4 target site. Therefore, let-7 binding to MDM4 is implicated in the DNA damage response.

Bevacizumab radiosensitizes non-small cell lung cancer xenografts by inhibiting DNA double-strand break repair in endothelial cells

The aims of this study were to evaluate the effects of biweekly bevacizumab administration on a tumor microenvironment and to investigate the mechanisms of radiosensitization that were induced by it. Briefly, bevacizumab was administered intravenously to Balb/c nude mice bearing non-small cell lung cancer (NSCLC) H1975 xenografts; in addition, bevacizumab was added to NSCLC or endothelial cells (ECs) in vitro, followed by irradiation (IR). The anti-tumor efficacy, anti-angiogenic efficacy and repair of DNA double-strand breaks (DSBs) were evaluated. The activation of signaling pathways was determined using immunoprecipitation (IP) and WB analyses. Finally, biweekly bevacizumab administration inhibited the growth of H1975 xenografts and induced vascular normalization periodically. Bevacizumab more significantly increased cellular DSB and EC apoptosis when administered 1 h prior to 12 Gy/1f IR than when administered 5 days prior to IR, thereby inhibiting tumor angiogenesis and growth. In vitro, bevacizumab more effectively increased DSBs and apoptosis prior to IR and inhibited the clonogenic survival of ECs but not NSCLC cells. Using IP and WB analyses, we confirmed that bevacizumab can directly inhibit the phosphorylation of components of the VEGR2/PI3K/Akt/DNA-PKcs signaling pathway that are induced by IR in ECs. In conclusion, bevacizumab radiosensitizes NSCLC xenografts mainly by inhibiting DSB repair in ECs rather than by inducing vascular normalization.

MicroRNAs Used in Combination with Anti-Cancer Treatments Can Enhance Therapy Efficacy

MicroRNAs (miRNAs), a recently discovered class of small non-coding RNAs, constitute a promising approach to anti-cancer treatments when they are used in combination with other agents. MiRNAs are evolutionarily conserved non-coding RNAs that negatively regulate gene expression by binding to the complementary sequence in the 3'-untranslated region (UTR) of target genes. MiRNAs typically suppress gene expression by direct association with target transcripts, thus decreasing the expression levels of target proteins. The delivery to cells of synthetic miRNAs that mimic endogenous miRNA targeting genes involved in the DNA-Damage Response (DDR) can perturb the process, making cells more sensitive to chemotherapy or radiotherapy. This review examines how cells respond to combined therapy and it provides insights into the role of miRNAs in targeting the DDR repair pathway when they are used in combination with chemical compounds or ionizing radiation to enhance cellular sensitivity to treatments.

Light-regulated microRNAs

In addition to exposure to passive diurnal cycles of sunlight, humans are also subjected to intentional acute exposure to other types of electromagnetic radiation (EM). Understanding the molecular mechanisms involved in the physiological, pathological and therapeutic responses to exposure to radiation is an active area of research. With the advent of methods to readily catalog and identify patterns of changes in gene expression, many studies have reported changes in gene expression upon exposure of various human and mouse cells in vitro, whole experimental organisms such as mice and parts of human body. However, the molecular mechanisms underlying these broad ranging changes in gene expression are not yet fully understood. MicroRNAs, which are short, noncoding RNAs that regulate gene expression by targeting many messenger RNAs, are also emerging as important mediators of radiation-induced changes in gene expression and hence critical for the manifestation of light-induced cellular phenotypes and physiological responses. In this article, we review available knowledge on microRNAs implicated in responses to various forms of solar and other EM radiation. Based on this knowledge, we elaborate some unifying themes in the regulation and functions of some of these miRNAs.

MiR-630 inhibits proliferation by targeting CDC7 kinase, but maintains the apoptotic balance by targeting multiple modulators in human lung cancer A549 cells

MicroRNAome analyses have shown microRNA-630 (miR-630) to be involved in the regulation of apoptosis. However, its apoptotic role is still debated and its participation in DNA replication is unknown. Here, we demonstrate that miR-630 inhibits cell proliferation by targeting cell-cycle kinase 7 (CDC7) kinase, but maintains the apoptotic balance by targeting multiple activators of apoptosis under genotoxic stress. We identified a novel regulatory mechanism of CDC7 gene expression, in which miR-630 downregulated CDC7 expression by recognizing and binding to four binding sites in CDC7 3'-UTR. We found that miR-630 was highly expressed in A549 and NIH3T3 cells where CDC7 was downregulated, but lower in H1299, MCF7, MDA-MB-231, HeLa and 2BS cells where CDC7 was upregulated. Furthermore, the induction of miR-630 occurred commonly in a variety of human cancer and immortalized cells in response to genotoxic agents. Importantly, downregulation of CDC7 by miR-630 was associated with cisplatin (CIS)-induced inhibitory proliferation in A549 cells. Mechanistically, miR-630 exerted its inhibitory proliferation by blocking CDC7-mediated initiation of DNA synthesis and by inducing G1 arrest, but maintains apoptotic balance under CIS exposure. On the one hand, miR-630 promoted apoptosis by downregulation of CDC7; on the other hand, it reduced apoptosis by downregulating several apoptotic modulators such as PARP3, DDIT4, EP300 and EP300 downstream effector p53, thereby maintaining the apoptotic balance. Our data indicate that miR-630 has a bimodal role in the regulation of apoptosis in response to DNA damage. Our data also support the notion that a certain mRNA can be targeted by several miRNAs, and in particular an miRNA may target a set of mRNAs. These data afford a comprehensive view of microRNA-dependent control of gene expression in the regulation of apoptosis under genotoxic stress.

Targeting the microRNA-regulating DNA damage/repair pathways in cancer

INTRODUCTION

Maintenance of genome stability requires the integrity of the DNA repair machinery. DNA damage response (DDR) determines cell fate and regulates the expression of microRNAs (miRNAs), which in turn may also regulate important components of the DNA repair machinery.

AREAS COVERED

In this review, we describe the bidirectional connection between miRNAs and DDR and their link with important biological functions such as, DNA repair, cell cycle and apoptosis in cancer. Furthermore, we highlight the potential implications of recent findings on miRNA/DDR in determining chemotherapy response in cancer patients, and the use of these biomarkers for novel potential therapeutic approaches.

EXPERT OPINION

Defects in the DDR and deregulation of miRNAs are important hallmarks of human cancer. A full understanding of the mechanisms underlying the connection between miRNAs and DDR/DNA repair pathways will positively impact our knowledge on human tumor biology and on different responses to distinct drugs. Specific miRNAs interact with distinct DDR components and are promising targets for enhancing the effects of, and/or to overcome the resistance to, conventional chemotherapeutic agents. Finally, the development of innovative tools to deliver miRNA-targeting oligonucleotides may represents novel types of cancer interventions in clinic.

MicroRNAs, genomic instability and cancer

MicroRNAs (miRNAs) are small non-coding RNA transcripts approximately 20 nucleotides in length that regulate expression of protein-coding genes via complementary binding mechanisms. The last decade has seen an exponential increase of publications on miRNAs, ranging from every aspect of basic cancer biology to diagnostic and therapeutic explorations. In this review, we summarize findings of miRNA involvement in genomic instability, an interesting but largely neglected topic to date. We discuss the potential mechanisms by which miRNAs induce genomic instability, considered to be one of the most important driving forces of cancer initiation and progression, though its precise mechanisms remain elusive. We classify genomic instability mechanisms into defects in cell cycle regulation, DNA damage response, and mitotic separation, and review the findings demonstrating the participation of specific miRNAs in such mechanisms.

MiR-138 and MiR-135 directly target focal adhesion kinase, inhibit cell invasion, and increase sensitivity to chemotherapy in cancer cells

Focal Adhesion Kinase is a 125 kDa non-receptor kinase and overexpressed in many types of tumors. Recently, short noncoding RNAs, called microRNAs have been discovered as regulators of gene expression mainly through binding to the untranslated region (UTR) of mRNA. In this report we show that MiR-138 and MiR-135 down-regulated FAK expression in cancer cells. MiR-138 and MiR-135 inhibited FAK protein expression in different cancer cell lines. The computer analysis of 3'FAK-untranslated region (FAKUTR) identified one conserved MiR-138 binding site (CACCAGCA) at positions 3514-3521 and one conserved MiR-135 (AAGCCAU) binding site at positions 4278-4284 in the FAK-UTR. By a dual-luciferase assay we demonstrate that MiR-138 and MiR-135 directly bound the FAK untranslated region using FAK-UTR-Target (FAK-UTR) luciferase plasmid and inhibited its luciferase activity. The sitedirected mutagenesis of the MiR-138 and MiR-135 binding sites in the FAK-UTR abrogated MiR-138 and MiR-135-directed inhibition of FAK-UTR. Real-time PCR demonstrated that cells transfected with MiR-138 and MiR-135 expressed decreased FAK mRNA levels. Moreover, stable expression of MiR-138 and MiR-135 in 293 and HeLa cells decreased cell invasion and increased sensitivity to 5- fluorouracil (5-FU), FAK inhibitor, Y15, and doxorubicin. In addition, MiR-138 significantly decreased 293 xenograft tumor growth in vivo. This is the first report on regulation of FAK expression by MiR-135 and MiR138 that affected invasion, drug sensitivity, and tumor growth in cancer cells, which is important to the development of FAK-targeted therapeutics and understanding their novel regulations and functions.

miRNAs in tumor radiation response: bystanders or participants?

There is increasing interest in defining a functional association between miRNAs and tumor radiation response, with the double aim of rationally designing miRNA-based strategies to increase patient radiosensitivity and identifying novel biomarkers of treatment response. Although it has been demonstrated that several miRNAs directly regulate the expression of components of cell pathways relevant to radiosensitivity, and miRNA expression profiles change upon irradiation, understanding the causal role exerted by individual miRNAs in determining tumor radiation response is still at an early stage. Based on available experimental and clinical evidence, we discuss here the potential of miRNAs as targets and/or tools for modulating radioresponsivity at the clinical level, as well as possible predictive biomarkers, underlining present limits and future perspectives.

microRNAs in cancer cell response to ionizing radiation

SIGNIFICANCE

microRNAs (miRNA) have been characterized as master regulators of the genome. As such, miRNAs are responsible for regulating almost every cellular pathway, including the DNA damage response (DDR) after ionizing radiation (IR). IR is a therapeutic tool that is used for the treatment of several types of cancer, yet the mechanism behind radiation response is not fully understood.

RECENT ADVANCES

It has been demonstrated that IR can alter miRNA expression profiles, varying greatly from one cell type to the next. It is possible that this variation contributes to the range of tumor cell responsiveness that is observed after radiotherapy, especially considering the extensive role for miRNAs in regulating the DDR. In addition, individual miRNAs or miRNA families have been shown to play a multifaceted role in the DDR, regulating multiple members in a single pathway.

CRITICAL ISSUES

In this review, we will discuss the effects of radiation on miRNA expression as well as explore the function of miRNAs in regulating the cellular response to radiation-induced damage. We will discuss the importance of miRNA regulation at each stage of the DDR, including signal transduction, DNA damage sensing, cell cycle checkpoint activation, DNA double-strand break repair, and apoptosis. We will focus on emphasizing the importance of a single miRNA targeting several mediators within a pathway.

FUTURE DIRECTIONS

miRNAs will continue to emerge as critical regulators of the DDR. Understanding the role of miRNAs in the response to IR will provide insights for improving the current standard therapy.

Functional characterization of genetic polymorphisms in the H2AFX distal promoter

Due to the critical role of the H2AX histone variant in double-strand break repair, genetic variants in the H2AX gene, H2AFX, may influence cancer susceptibility. Genetic association studies have correlated H2AFX upstream variants with cancer risk; however it is unclear if any are causal. H2AFX has at least two alternate transcripts that encode the same reading frame; a short 0.6kb transcript that lacks an intron or poly-A tail and is predicted to be highly expressed during the replication stage of the cell cycle, and a long 1.6kb poly-A tailed transcript that is expressed in a replication-independent manner. To examine the functional impact of the rs643788, rs8551, rs7759, and rs2509049 upstream variants, we characterized their influence on gene expression, cell survival after DNA assault, and transcription factor binding. Analysis of allelic imbalance using quantitative sequencing of cDNA from lymphoblast cell lines did not reveal any difference in expression of the 1.6kb polyadenylated transcript between the common H2AFX upstream haplotypes. We did, however, identify a previously unreported 197 base pair intron in the H2AFX 3'untranslated region that appears to be present regardless of haplotype. Assessment of cell survival after irradiation treatment did not show any difference in survival between cell lines of different haplotypes. Gel shift assays revealed that the rs643788 C allele disrupts YY1 transcription factor binding and the rs2509049 C allele binds more strongly to a protein complex than does the rs2509049 T allele. Though we did not identify any differences in expression or survival between haplotypes, differential protein binding at two of the polymorphisms suggests further functional analyses may reveal a role for these variants in influencing gene expression at specific points of the cell cycle or in specific tissues.

microRNA expression and biogenesis in cellular response to ionizing radiation

Increasing evidence demonstrates that the expression levels of microRNAs (miRNAs) significantly change upon ionizing radiation (IR) and play a critical role in cellular response to IR. Although several radiation responsive miRNAs and their targets have been identified, little is known about how miRNAs expression and biogenesis is regulated by IR-caused DNA damage response (DDR). Hence, in this review, we summarize miRNA expression and biogenesis in cellular response to IR and mainly elucidate the regulatory mechanisms of miRNA expression and biogenesis from different aspects including ataxia-telangiectasia mutated (ATM) kinase, p53/p63/p73 family and other potential factors. Furthermore, we focus on ΔNp73, which might be a potential regulator of miRNA expression and biogenesis in cellular response to IR. miRNAs could effectively activate the IR-induced DDR and modulate the radiation response and cellular radiosensitivity, which have an important potential clinical application. Therefore, thoroughly understanding the regulatory mechanisms of miRNAs expression and biogenesis in radiation response will provide new insights for clinical cancer radiotherapy.

MicroRNAs: short non-coding players in cancer chemoresistance

Chemoresistance is one of the main problems in the therapy of cancer. There are a number of different molecular mechanisms through which a cancer cell acquires resistance to a specific treatment, such as alterations in drug uptake, drug metabolism and drug targets. There are several lines of evidence showing that miRNAs are involved in drug sensitivity of cancer cells in different tumor types and by different treatments. In this review, we provide an overview of the more recent and significant findings on the role of miRNAs in cancer cell drug resistance. In particular, we focus on specific miRNA mechanisms of action that in various steps lead from drug cell sensitivity to drug cell resistance. We also provide evidence on how miRNA profiling may unveil relevant predictive biomarkers for therapy outcomes.

MicroRNAs: short non-coding players in cancer chemoresistance

Chemoresistance is one of the main problems in the therapy of cancer. There are a number of different molecular mechanisms through which a cancer cell acquires resistance to a specific treatment, such as alterations in drug uptake, drug metabolism and drug targets. There are several lines of evidence showing that miRNAs are involved in drug sensitivity of cancer cells in different tumor types and by different treatments. In this review, we provide an overview of the more recent and significant findings on the role of miRNAs in cancer cell drug resistance. In particular, we focus on specific miRNA mechanisms of action that in various steps lead from drug cell sensitivity to drug cell resistance. We also provide evidence on how miRNA profiling may unveil relevant predictive biomarkers for therapy outcomes.

MicroRNAs down-regulate homologous recombination in the G1 phase of cycling cells to maintain genomic stability

Homologous recombination (HR)-mediated repair of DNA double-strand break (DSB)s is restricted to the post-replicative phases of the cell cycle. Initiation of HR in the G1 phase blocks non-homologous end joining (NHEJ) impairing DSB repair. Completion of HR in G1 cells can lead to the loss-of-heterozygosity (LOH), which is potentially carcinogenic. We conducted a gain-of-function screen to identify miRNAs that regulate HR-mediated DSB repair, and of these miRNAs, miR-1255b, miR-148b*, and miR-193b* specifically suppress the HR-pathway in the G1 phase. These miRNAs target the transcripts of HR factors, BRCA1, BRCA2, and RAD51, and inhibiting miR-1255b, miR-148b*, and miR-193b* increases expression of BRCA1/BRCA2/RAD51 specifically in the G1-phase leading to impaired DSB repair. Depletion of CtIP, a BRCA1-associated DNA end resection protein, rescues this phenotype. Furthermore, deletion of miR-1255b, miR-148b*, and miR-193b* in independent cohorts of ovarian tumors correlates with significant increase in LOH events/chromosomal aberrations and BRCA1 expression.

DOI:http://dx.doi.org/10.7554/eLife.02445.001

The DNA in a cell is damaged thousands of times every day. One of the most serious types of damage involves something breaking both of the strands in the double helix. Such a double-strand break can delete genes or even kill the cell. In fact, conventional cancer therapy kills cancer cells by causing irreparable double-strand breaks. Conversely, a normal cell that is constantly exposed to DNA damaging agents can become a tumor if double-strand breaks are incorrectly repaired. An efficient and accurate double-strand break repair system needs to be in place to prevent this transformation. Therefore, an in-depth understanding of double-strand break repair and the factors involved are important for both gaining insight into the cause of cancer and to improve cancer therapy.

Cells have evolved several different ways to detect and repair double-strand breaks. A method called homologous recombination, for example, uses an undamaged DNA molecule as a template that can be copied to make new DNA. Since it needs a readily available DNA template, this method only works in phases of the cell growth cycle where there are many copies of DNA—that is, in the post-DNA replication phases. In particular, homologous recombination does not work during the pre-replication, G1 phase. If homologous recombination is attempted during G1, it will block the other methods employed by cells to repair broken strands of DNA.

An important challenge is to understand how homologous recombination is restricted to particular parts of the cell cycle. Although certain proteins associated with the early stages of double-strand repair are thought to determine the type of DNA repair that occurs, the details of this process are not fully understood.

One group of molecules that are thought to be involved are microRNAs, which normally limit the number of proteins produced from certain genes. However, since a single microRNA molecule can be associated with several proteins, and since a single protein can be associated with several microRNA molecules, it has proved difficult to establish the exact effects of a specific microRNA molecule.

Choi et al. now show that seven microRNA molecules can control homologous recombination, and three microRNAs in particular restrict homologous recombination during the G1 phase of the cell cycle. If these microRNAs are inhibited during the G1 phase, which allows homologous recombination to start, and counter-intuitively more double-stranded breaks are seen. However, if a gene involved in starting homologous repair–called CtIP—is silenced while the microRNAs are inhibited, then the DNA breaks are repaired. Exactly, how the microRNA molecules produce different effects during different phases of the cell cycle will be need to be investigated by future studies.

DOI:http://dx.doi.org/10.7554/eLife.02445.002

p53 is positively regulated by miR-542-3p

The tumor suppressor p53 and miRNAs are linked through a complex network. Several miRNAs modulate p53 expression, while p53 regulates the transcription and/or biogenesis of several other miRNAs. Here, we report the development of a cell-based assay used with a library of human miRNA mimics in a high-throughput screen for miRNAs that modulate p53 expression. Overexpression of miRNA (miR)-542-3p in cancer cells elevated p53 expression, stimulated the expression of p53 targets, and inhibited cell proliferation. Mechanistically, miR-542-3p increased p53 protein stability by weakening interactions between p53 and its negative regulator MDM2. Furthermore, miR-542-3p suppressed ribosome biogenesis by downregulating a subset of ribosomal proteins such as RPS23, leading to upregulation of RPL11 and stabilization of p53. The 3'untranslated region in the RPS23 transcript contained a miR-542-3p-binding site, suggesting that RPS23 is a direct target of miR-542-3p. Our results define miR-542-3p as an important new positive regulator of p53 with potential applications in cancer treatment.

Role of microRNA in response to ionizing radiations: evidences and potential impact on clinical practice for radiotherapy

MicroRNAs (miRNA) are small, non-coding, RNAs with gene expression regulator roles. As an important class of regulators of many cellular pathways, miRNAs are involved in many signaling pathways and DNA damage repair processes, affecting cellular radiosensitivity. Their role has led to interest in oncological implications to improve treatment results. MiRNAs represent a great opportunity to enhance the efficacy of radiotherapy treatments-they can be used to profile the radioresistance of tumors before radiotherapy, monitor their response throughout the treatment, thus helping to select intensification strategies, and also to define the final response to therapy along with risks of recurrence or metastatization. Even though many interesting studies support such potential, nowadays most studies on patient data are limited to experiments profiling tumor aggressiveness and response to radiotherapy. Moreover many studies report different although not conflicting results on the miRNAs evaluated for each tumor type. Without doubt, the clinical potential of such molecules for radiotherapy is striking and of high interest.

Similarity in targets with REST points to neural and glioblastoma related miRNAs

There are groups of genes that need coordinated repression in multiple contexts, for example if they code for proteins that work together in a pathway or in a protein complex. Redundancy of biological regulatory networks implies that such coordinated repression might occur at both the pre- and post-transcriptional level, though not necessarily simultaneously or under the same conditions. Here, we propose that such redundancy in the global regulatory network can be detected by the overlap between the putative targets of a transcriptional repressor, as identified by a ChIP-seq experiment, and predicted targets of a microRNA (miRNA). To test this hypothesis, we used publicly available ChIP-seq data of the neural transcriptional repressor RE1 silencing transcription factor (REST) from 15 different cell samples. We found 20 miRNAs, each of which shares a significant amount of predicted targets with REST. The set of predicted associations between these 20 miRNAs and the overlapping REST targets is enriched in known miRNA targets. Many of the detected miRNAs have functions related to neural identity and glioblastoma, which could be expected from their overlap in targets with REST. We propose that the integration of experimentally determined transcription factor binding sites with miRNA-target predictions provides functional information on miRNAs.

MicroRNA expression profiles in human breast cancer cells after multifraction and single-dose radiation treatment

MicroRNAs (miRNAs) are small non-coding RNAs that contribute to modulating signaling pathways after radiation exposure and have emerged as a potential therapeutic target or biomarker in the radiation response of cancer. Exposing breast cancer cells to single-dose (SD) or multifractionated (MF) radiation may affect the cells differently. However, the roles of miRNAs in breast cancer cells after the response to SD or MF is not thoroughly understood. Therefore, the purpose of the present study was to comprehensively investigate the response of miRNAs in MDA-MB-361 by using various radiation exposing protocols. Our results revealed that only a small fraction of miRNAs exhibiting differential expressions (>1.5‑fold) was identified after MDA-MB-361 cells were exposed to SD (10 Gy) or MF radiation (2 Gy x 5 MF). In addition, we observed that several miRNAs in the MDA-MB-361 cells frequently exhibited differential responses to various types of radiation treatment. Among these miRNAs, the expression levels of an oncogenic miR-17-92 cluster increased following SD radiation treatment. Conversely, miR-19a-3p, miR-20a-5p, and miR-19b-3p expressions were inhibited by >1.5-fold in the following MF treatment. Further analysis of the miR-17-92 cluster expression levels revealed that miR-17, miR-18a, miR-19a/b and miR-20a were significantly overexpressed and miR-92a was downregulated in breast cancer. Functional annotation demonstrated that target genes of the miR-17-92 cluster were predominantly involved in the regulation of radiation-associated signal pathways such as mitogen-activated protein kinase (MAPK), ErbB, p53, Wnt, transforming growth factor-β (TGF-β), mTOR signaling pathways and cell cycles with an FDR <0.05. Overall, the results of the present study revealed distinct differences in the response of miRNAs to SD and MF radiation exposure, and these radiation-associated miRNAs may contribute to radiosensitivity and can be used as biomarkers for radiotherapy.

Multiple tumor suppressor microRNAs regulate telomerase and TCF7, an important transcriptional regulator of the Wnt pathway

The human TERT (hTERT) gene encodes the telomerase catalytic subunit which plays a role in telomerase regulation. Telomerase is activated in more than 90% of all human malignancies and understanding how telomerase is regulated is necessary for implementation of successful anti-cancer therapies. microRNAs (miRNAs) are important regulators of gene expression in eukaryotic cells but evidence of their role in telomerase regulation has not been documented. To determine whether hTERT activity is regulated by multiple miRNAs, eight miRNAs which have putative binding sites in the hTERT 3'UTR together with miR-138-5p were evaluated in luciferase assays with a reporter containing the hTERT 3'UTR. Six miRNAs (let-7g*, miR-133a, miR-138-5p, miR-342-5p, miR-491-5p, and miR-541-3p) specifically inhibited the expression of the reporter luciferase-driven constructs and let-7g*, miR-133a, miR-138-5p, and miR-491-5p also downregulated endogenous telomerase activity in cells. Moreover, all six miRNAs significantly inhibited cell proliferation. miRNAs (miR-133a, miR-138-5p, 342-5p, 491-5p, 541-3p) also have predicted binding sites within the 3'UTR of three genes involved in Wnt signaling (TCF7, MSI1, and PAX5). These miRNAs inhibited the expression of the luciferase reporter constructs containing 3'UTRs of these genes and downregulated protein expression of the TCF7 transcription factor, which mediates the canonical Wnt pathway. Together, these results suggest the existence of a miRNA regulatory network involving the hTERT and Wnt pathway.

Noncoding RNAs in DNA repair and genome integrity

SIGNIFICANCE

The well-studied sequences in the human genome are those of protein-coding genes, which account for only 1%-2% of the total genome. However, with the advent of high-throughput transcriptome sequencing technology, we now know that about 90% of our genome is extensively transcribed and that the vast majority of them are transcribed into noncoding RNAs (ncRNAs). It is of great interest and importance to decipher the functions of these ncRNAs in humans.

RECENT ADVANCES

In the last decade, it has become apparent that ncRNAs play a crucial role in regulating gene expression in normal development, in stress responses to internal and environmental stimuli, and in human diseases.

CRITICAL ISSUES

In addition to those constitutively expressed structural RNA, such as ribosomal and transfer RNAs, regulatory ncRNAs can be classified as microRNAs (miRNAs), Piwi-interacting RNAs (piRNAs), small interfering RNAs (siRNAs), small nucleolar RNAs (snoRNAs), and long noncoding RNAs (lncRNAs). However, little is known about the biological features and functional roles of these ncRNAs in DNA repair and genome instability, although a number of miRNAs and lncRNAs are regulated in the DNA damage response.

FUTURE DIRECTIONS

A major goal of modern biology is to identify and characterize the full profile of ncRNAs with regard to normal physiological functions and roles in human disorders. Clinically relevant ncRNAs will also be evaluated and targeted in therapeutic applications.

MicroRNAs in the DNA Damage/Repair Network and Cancer

Cancer is a multistep process characterized by various and different genetic lesions which cause the transformation of normal cells into tumor cells. To preserve the genomic integrity, eukaryotic cells need a complex DNA damage/repair response network of signaling pathways, involving many proteins, able to induce cell cycle arrest, apoptosis, or DNA repair. Chemotherapy and/or radiation therapy are the most commonly used therapeutic approaches to manage cancer and act mainly through the induction of DNA damage. Impairment in the DNA repair proteins, which physiologically protect cells from persistent DNA injury, can affect the efficacy of cancer therapies. Recently, increasing evidence has suggested that microRNAs take actively part in the regulation of the DNA damage/repair network. MicroRNAs are endogenous short noncoding molecules able to regulate gene expression at the post-transcriptional level. Due to their activity, microRNAs play a role in many fundamental physiological and pathological processes. In this review we report and discuss the role of microRNAs in the DNA damage/repair and cancer.

microRNA-383 impairs phosphorylation of H2AX by targeting PNUTS and inducing cell cycle arrest in testicular embryonal carcinoma cells

Male germ cells with aberrant DNA damage are the weighted factor contributing to male infertility. Mounting evidence shows that DNA damage in male germ cells impairs spermatogenesis and lowers fecundity. MicroRNAs (miRNAs) regulating expression of multiple genes play a significant role in spermatogenesis. Our previous results have shown that microRNA-383 (miR-383) is one of the notable down-regulated microRNAs in the testes of sterile males with maturation arrest (MA) and is located predominantly in spermatogonia and primary spermatocytes. However, the role that miR-383 plays in DNA damage during spermatogenesis remains unknown. In this study, we found that miR-383 inhibited the focal formation and abundance of γH2AX, which is the major marker of sites of DNA damage, with or without ultraviolet irradiation and cisplatin in testicular embryonal carcinoma (NT-2) cells. In addition, NT-2 cells were remarkably sensitized to DNA damage reagent (cisplatin) by forcing expression of miR-383 and silencing expression of protein phosphatase 1, regulatory subunit 10 (PNUTS). By constructing Renilla luciferase reporters and co-transfecting miR-383 and reporters in NT-2 cells, we identified that PNUTS was a valid target of miR-383. Further results demonstrated that the repression of the phosphorylated form of H2AX by miR-383 was due to independent depletion of PNUTS and cell cycle arrest. In conclusion, we found a novel function of miR-383 in the DNA damage pathway. miR-383 impairs the phosphorylation of H2AX by targeting PNUTS and inducing cell cycle arrest independently, as well as sensitizing NT-2 cells to cisplatin.

MicroRNAs in osteosarcomagenesis

The etiology of osteosarcoma (OS) remains enigmatic. Particular clinical and molecular patterns, observed with high frequency in OS, suggest that it results from some yet-to-be-discovered central driver. How else can biology generate such an aggressive, metastatic, genetically and chromosomally unstable malignancy with virtually no apparent precursor neoplasms that are partway along a disease path toward OS? With this conundrum as a backdrop, the discovery of every new native molecule with power to impact a cell's biology is usually quickly followed by a search to see if this type of molecule contains the key to unlock OS biology.

MicroRNA 23b regulates autophagy associated with radioresistance of pancreatic cancer cells

BACKGROUND & AIMS

Tumor resistance to radiation is a challenge in the treatment of patients with pancreatic cancer. Improving our understanding of the mechanisms of radioresistance could lead to strategies to increase patients' response to therapy. We investigated the roles of microRNAs (miRNAs) involved in radioresistance of pancreatic cancer cells.

METHODS

We established radioresistant pancreatic cancer cell lines and used array analysis to compare levels of different miRNAs between radioresistant cell lines and the parental cell lines from which they were derived. We transfected pancreatic cancer cells with miRNA mimics or inhibitors and evaluated their effects on cell radiosensitivity using a clonogenic survival assay. The effects of miRNA on autophagy were determined by transmission electron microscopy and immunoblot analysis. We used a luciferase reporter assay to identify messenger RNA targets of specific miRNAs.

RESULTS

Radioresistant pancreatic cancer cells had reduced levels of the miRNA miR-23b and increased autophagy compared with cells that were not radioresistant. Overexpression of miR-23b inhibited radiation-induced autophagy, whereas an inhibitor of miR-23b promoted autophagy in pancreatic cancer cells. Overexpression of miR-23b sensitized pancreatic cancer cells to radiation. The target of miR-23b, ATG12, was overexpressed in radioresistant cells; levels of ATG12 protein correlated with the occurrence of autophagy. Expression of miR-23b blocked radiation-induced autophagy and sensitized pancreatic cancer cells to radiation. We observed an inverse correlation between the level of miR-23b and autophagy in human pancreatic cancer tissue samples.

CONCLUSIONS

In pancreatic cancer cells, reduced levels of the miRNA miR-23b increase levels of ATG12 and autophagy to promote radioresistance. miR-23b might be used to increase the sensitivity of pancreatic cancer cells to radiation therapy.

Systematic screen identifies miRNAs that target RAD51 and RAD51D to enhance chemosensitivity

Homologous recombination mediates error-free repair of DNA double-strand breaks (DSB). RAD51 is an essential protein for catalyzing homologous recombination and its recruitment to DSBs is mediated by many factors including RAD51, its paralogs, and breast/ovarian cancer susceptibility gene products BRCA1/2. Deregulation of these factors leads to impaired DNA repair, genomic instability, and cellular sensitivity to chemotherapeutics such as cisplatin and PARP inhibitors. microRNAs (miRNA) are short, noncoding RNAs that posttranscriptionally regulate gene expression; however, the contribution of miRNAs in the regulation of homologous recombination is not well understood. To address this, a library of human miRNA mimics was systematically screened to pinpoint several miRNAs that significantly reduce RAD51 foci formation in response to ionizing radiation in human osteosarcoma cells. Subsequent study focused on two of the strongest candidates, miR-103 and miR-107, as they are frequently deregulated in cancer. Consistent with the inhibition of RAD51 foci formation, miR-103 and miR-107 reduced homology-directed repair and sensitized cells to various DNA-damaging agents, including cisplatin and a PARP inhibitor. Mechanistic analyses revealed that both miR-103 and miR-107 directly target and regulate RAD51 and RAD51D, which is critical for miR-103/107-mediated chemosensitization. Furthermore, endogenous regulation of RAD51D by miR-103/107 was observed in several tumor subtypes. Taken together, these data show that miR-103 and miR-107 overexpression promotes genomic instability and may be used therapeutically to chemosensitize tumors.

IMPLICATIONS

These findings demonstrate a role for miR-103 and -107 in regulating DNA damage repair, thereby identifying new players in the progression of cancer and response to chemotherapy.

MiR-138 downregulates miRNA processing in HeLa cells by targeting RMND5A and decreasing Exportin-5 stability

MicroRNAs (miRNAs) are a class of non-coding small RNAs that consist of ∼22 nt and are involved in several biological processes by regulating target gene expression. MiR-138 has many biological functions and is often downregulated in cancers. Our results showed that overexpression of miR-138 downregulated target RMND5A (required for meiotic nuclear division 5 homolog A) and reduced Exportin-5 stability, which results in decreased levels of pre-miRNA nuclear export in HeLa cells. We also found that miR-138 could significantly inhibit HeLa cell migration by targeting RMND5A. Our study therefore identifies miR-138–RMND5A–Exportin-5 as a previously unknown miRNA processing regulatory pathway in HeLa cells.