Radiotherapy is a form of cancer treatment that utilizes the ability of ionizing radiation to induce cell inactivation and cell death, generally via inflicting DNA double-strand breaks. However, different tumors and their normal surrounding tissues are not equally sensitive to radiation, posing a major challenge in the field: to seek out factors that influence radiosensitivity. In this review, we summarize the evidence for microRNA (miRNA) involvement in the radioresponse and discuss their potential as radiosensitizers. MicroRNAs are endogenous small, noncoding RNAs that regulate gene expression post-transcriptionally, influencing many processes including, as highlighted here, cellular sensitivity to radiation. Profiling studies demonstrate that miRNA expression levels change in response to radiation, while certain miRNAs, when overexpressed or knocked down, alter radiosensitivity. Finally, we discuss specific miRNA-target pairs that affect response to radiation and DNA damage as good potential targets for modulating radioresponsitivity.
Lung cancer is the leading cause of cancer deaths worldwide, and current therapies fail to treat this disease in the vast majority of cases. The RAS and p53 pathways are two of the most frequently altered pathways in lung cancers, with such alterations resulting in loss of responsiveness to current therapies and decreased patient survival. The microRNA-34 (mir-34) gene family members are downstream transcriptional targets of p53, and miR-34 expression is reduced in p53 mutant tumors; thus, we hypothesized that treating mutant Kras;p53 tumors with miR-34 would represent a powerful new therapeutic to suppress lung tumorigenesis. To this end we examined the therapeutically resistant KrasLSL-G12D/+;Trp53LSL-R172H/+ mouse lung cancer model. We characterized tumor progression in these mice following lung-specific transgene activation and found tumors as early as 10 weeks post-activation, and severe lung inflammation by 22 weeks. Tumors harvested from these lungs have elevated levels of oncogenic miRNAs miR-21 and miR-155; are deficient for p53-regulated miRNAs; and have heightened expression of miR-34 target genes, such as Met and Bcl-2. In the presence of exogenous miR-34, epithelial cells derived from these tumors show reduced proliferation and invasion. In vivo treatment with miR-34a prevented tumor formation and progression in KrasLSL-G12D/+;Trp53LSL-R172H/+ mice. Animals infected with mir-34a-expressing lentivirus at the same time as transgene activation had little to no evidence of tumorigenesis, and lentivirus-induced miR-34a also prevented further progression of pre-formed tumors. These data support the use of miR-34 as a lung tumor-preventative and tumor-static agent.
miRNA; lung cancer; therapy; Kras; p53; in vivo
Once considered genetic “oddities”, microRNAs (miRNAs)
are now recognized as key epigenetic regulators of numerous biological
processes, including some with a causal link to the pathogenesis, maintenance,
and treatment of cancer. The crux of small RNA-based therapeutics lies in the
antagonism of potent cellular targets; the main shortcoming of the field in
general, lies in ineffective delivery. Inhibition of oncogenic miRNAs is a
relatively nascent therapeutic concept, but as with predecessor RNA-based
therapies, success hinges on delivery efficacy. This review will describe the
canonical (e.g. pharmacokinetics and clearance, cellular uptake, endosome
escape, etc.) and non-canonical (e.g. spatial localization and accessibility of
miRNA, technical limitations of miRNA inhibition, off-target impacts, etc.)
challenges to the delivery of antisense-based anti-miRNA therapeutics (i.e.
antimiRs) for the treatment of cancer. Emphasis will be placed on how the
current leading antimiR platforms—ranging from naked chemically modified
oligonucleotides to nanoscale delivery vehicles—are affected by and
overcome these barriers. The perplexity of antimiR delivery presents both
engineering and biological hurdles that must be overcome in order to capitalize
on the extensive pharmacological benefits of antagonizing tumor-associated
antimiR; cancer therapy; chemical modification; microRNA inhibition; liposome; polymer nanoparticle; oligonucleotide; oncomiR; therapeutics; tumor targeting
MicroRNAs, a class of small, non-coding RNAs, are now widely known for their importance in many aspects of biology. These small regulatory RNAs have critical functions in diverse biological events, including development and disease. Recent findings show that microRNAs are essential for lifespan determination in the model organisms, C. elegans and Drosophila, suggesting that microRNAs are also involved in the complex process of ageing. Further, short RNA fragments derived from longer parental RNAs, such as transfer RNA cleavage fragments, have now emerged as a novel class of regulatory RNAs that inhibit translation in response to stress. In addition, the RNA editing pathway is likely to act in the double-stranded RNA-mediated silencing machinery to suppress unfavorable RNA interference activity in the ageing process. These multiple, redundant layers in gene regulatory networks may make it possible to both stably and flexibly regulate genetic pathways in ensuring robustness of developmental and ageing processes.
Aging; microRNA; small non-coding RNA; RNA editing; C. elegans
MicroRNAs (miRNAs) have emerged as key genetic regulators of a wide variety of biological processes, including growth, proliferation, and survival. Recent advances have led to the recognition that miRNAs can act as potent oncogenes and tumor suppressors, playing crucial roles in the initiation, maintenance, and progression of the oncogenic state in a variety of cancers. Determining how miRNA expression and function is altered in cancer is an important goal, and a necessary prerequisite to the development and adoption of miRNA-based therapeutics in the clinic. Highly promising clinical applications of miRNAs are the use of miRNA signatures as biomarkers for cancer (for example, for early detection or diagnosis), and therapeutic supplementation or inhibition of specific miRNAs to alter the cancer phenotype. In this review, we discuss the main methods used for miRNA profiling, and examine key miRNAs that are commonly altered in a variety of tumors. Current studies underscore the functional versatility and potency of miRNAs in various aspects of the cancer phenotype, pointing to their potential clinical applications. Consequently, we discuss the application of miRNAs as biomarkers, clinical agents, and therapeutic targets, highlighting both the enormous potential and major challenges in this field.
Next generation sequencing is widely used to study complex diseases because of its ability to identify both common and rare variants without prior single nucleotide polymorphism (SNP) information. Pooled sequencing of implicated target regions can lower costs and allow more samples to be analyzed, thus improving statistical power for disease-associated variant detection. Several methods for disease association tests of pooled data and for optimal pooling designs have been developed under certain assumptions of the pooling process, e.g. equal/unequal contributions to the pool, sequencing depth variation, and error rate. However, these simplified assumptions may not portray the many factors affecting pooled sequencing data quality, such as PCR amplification during target capture and sequencing, reference allele preferential bias, and others. As a result, the properties of the observed data may differ substantially from those expected under the simplified assumptions. Here, we use real datasets from targeted sequencing of pooled samples, together with microarray SNP genotypes of the same subjects, to identify and quantify factors (biases and errors) affecting the observed sequencing data. Through simulations, we find that these factors have a significant impact on the accuracy of allele frequency estimation and the power of association tests. Furthermore, we develop a workflow protocol to incorporate these factors in data analysis to reduce the potential biases and errors in pooled sequencing data and to gain better estimation of allele frequencies. The workflow, Psafe, is available at http://bioinformatics.med.yale.edu/group/.
pooled sequencing; allele frequency estimation; next-generation sequencing; disease association tests
Comment on: Cirera-Salinas D, et al. Cell Cycle 2012; 11:922–33
Dysregulation of microRNAs (miRNAs), particularly their downregulation, has been widely shown to be associated with the development of lung cancer. Downregulation of miRNAs leads to the overactivation of their oncogene targets, while upregulation of some miRNAs leads to inhibition of important tumor suppressors. Research has implicated cigarette smoke in miRNA dysregulation, leading to carcinogenesis. Cigarette smoke may lead to genetic or epigenetic damage to miRNAs, many of which map to fragile sites and some of which contain single nucleotide polymorphisms. Cigarette smoke may also cause dysregulation by affecting regulatory mechanisms controlling miRNA expression. Researchers have shown a correlation between smoke-exposure-induced dysregulation of miRNAs and age. Furthermore, dysregulation seems to be associated with intensity and duration of smoke exposure and duration of cessation. Longer exposure at a threshold level is needed for irreversibility of changes in expression. Better understanding of miRNA dysregulation may allow for improved biomonitoring and treatment regimens for lung cancer.
It has long been established that cancers can become addicted to particular oncogenes. Despite the genetic complexity that governs tumorigenesis, certain cancers can exhibit a critical dependency on the expression of a single oncogene, which when removed leads to death of the cancer cell. Recent observations on the relationships between regulatory RNAs and cancer have revealed that this concept of oncogene addiction extends to microRNAs (miRNAs) as well. Certain cancers exhibit a dependency on the expression of a single oncogenic miRNA, or oncomiR. The field of miRNA biology and its involvement in diseases such as cancer has seen tremendous advances over the past decade. However, little is known about the phenomenon of oncomiR addiction. In this review, we introduce the concept of proto-oncomiRs, or miRNAs that gain oncogenic activity after an initiating event. Further, by highlighting the role of proto-oncomiRs in generating malignant phenotypes, we glean possible insights into the mechanisms that guide oncomiR addiction. Additionally, toward the realization of genetically-driven personalized medicine, some of the most clinically successful anticancer strategies have involved targeting addictive oncogenes such as HER2, BCR/ABL, EGFR, and VEGF. Elucidating how addictive miRNAs can perpetuate cancer may reveal additional critical molecular targets to exploit for therapeutic purposes. Therefore, in this review, we also summarize the field of anti-miRNA therapeutics, in which antisense and nanoscale delivery technologies are the driving force. Addictive oncomiRs are a double-edged sword; addicted cancers are dependent on oncomiRs that are highly potent therapeutic targets. Dissection of this phenomenon may reveal the mechanisms through which lynchpin miRNAs can perpetuate cancer and present a new paradigm for miRNA-based cancer therapy.
oncomiR addiction; oncogene; microRNA; proto-oncomiR; tumorigenesis; oncogenesis; cell circuitry; anticancer therapy; anti-miR; molecular targeting
It has long been understood that many of the same manipulations that increase longevity in Caenorhabditis elegans also increase resistance to various acute stressors, and vice-versa; moreover these findings hold in more complex organisms as well. Nevertheless, the mechanistic relationship between these phenotypes remains unclear, and in many cases the overlap between stress resistance and longevity is inexact. Here we review the known connections between stress resistance and longevity, discuss instances in which these connections are absent, and summarize the theoretical explanations that have been posited for these phenomena.
In the nematode Caenorhabditis elegans, the let-7 microRNA (miRNA) controls the timing of key developmental events and terminal differentiation in part by directly regulating lin-41. C. elegans lin-41 mutants display precocious cell cycle exit and terminal differentiation of epidermal skin cells. lin-41 orthologues are found in more complex organisms including both mice and humans, but their roles are not known. We generated Mlin41 mouse mutants to ascertain a functional role for Mlin41. Strong loss of function Mlin41 gene-trap mutants demonstrated a striking neural tube closure defect during development, and embryonic lethality. Like C. elegans lin-41, Mlin41 also appears to be regulated by the let-7 and mir-125 miRNAs. Since Mlin41 is required for neural tube closure and survival it points to human lin-41 (HLIN41/TRIM71) as a potential human development and disease gene.
microRNA; let-7; mir-125; mlin41; lin-41; mouse; knock-out; development; cell cycle
MicroRNAs (miRNAs) are noncoding RNAs that regulate numerous target genes through a posttranscriptional mechanism and thus control major developmental pathways. The phylogenetically conserved let-7 miRNA regulates cell proliferation and differentiation, thus functioning as a key regulator of developmental timing in C. elegans and a tumor suppressor gene in humans. Using a reverse genetic screen, we have identified genetic interaction partners of C. elegans let-7, including known and novel potential target genes. Initial identification of several translation initiation factors as suppressors of a let-7 mutation led us to systematically examine genetic interaction between let-7 and the translational machinery, which we found to be widespread. In the presence of wild-type let-7, depletion of the translation initiation factor eIF3 resulted in precocious cell differentiation, suggesting that developmental timing is translationally regulated, possibly by let-7. As overexpression of eIF3 in humans promotes translation of mRNAs that are also targets of let-7-mediated repression, we suggest that eIF3 may directly or indirectly oppose let-7 activity. This might provide an explanation for the opposite functions of let-7 and eIF3 in regulating tumorigenesis.
miRNA; let-7; translation factor; heterochronic; C. elegans; RNAi; eIF3; eIF6
Maintenance of normal endothelial function is critical to various aspects of blood vessel function but its regulation is poorly understood. In this study we show that disruption of baseline FGF signaling to the endothelium leads to a dramatic reduction in let-7 miRNA levels that in turns increases expression of TGFβ ligands and receptors and activation of TGFβ signaling leading to endothelial-to-mesenchymal transition (Endo-MT). We further find that Endo-MT is an important driver of neointima formation in a murine transplant arteriopathy model and in rejecting human transplants lesions. The decline in endothelial FGF signaling input is due to the appearance of an FGF resistance state that is characterized by inflammation-dependent reduction in expression and activation of key components of the FGF signaling cascade. These results establish FGF signaling as a critical factor in maintenance of endothelial homeostasis and point to an unexpected role of Endo-MT in vascular pathology.
MicroRNA (miRNA) are aiding our understanding of cancer biology, and are now coming close to therapeutic use as well. Here, we focus specifically on the interaction between miRNAs and genomic instability. .MiRNA regulation is essential to many cellular processes, and escape from this regulatory network seems to be a common characteristic of malignant transformation. Genomic instability may preferentially target miRNAs either because of selective pressure or because of inherent vulnerability related to their location near fragile sites. Furthermore, disruption of miRNA processing elements affords a more global release from miRNA regulation. Finally, we review how miRNAs function as both effectors and modulators of the DNA damage response, intricately weaved with traditional elements such as ATM, P53 and MMR. Thus, miRNAs are both an important substrate for genomic instability, as well as having a crucial role in cellular DNA sensing and repair mechanisms.
miR-155 is a prominent microRNA (miRNA) that regulates genes involved in immunity and cancer-related pathways. miR-155 is overexpressed in lung cancer, which correlates with poor patient prognosis. It is unclear how miR-155 becomes increased in lung cancers and how this increase contributes to reduced patient survival. Here, we show that hypoxic conditions induce miR-155 expression in lung cancer cells and trigger a corresponding decrease in a validated target, FOXO3A. Furthermore, we find that increased levels of miR-155 radioprotects lung cancer cells, while inhibition of miR-155 radiosensitizes these cells. Moreover, we reveal a therapeutically important link between miR-155 expression, hypoxia, and irradiation by demonstrating that anti-miR-155 molecules also sensitize hypoxic lung cancer cells to irradiation. Our study helps explain how miR-155 becomes elevated in lung cancers, which contain extensive hypoxic microenvironments, and demonstrates that inhibition of miR-155 may have important therapeutic potential as a means to radiosensitize hypoxic lung cancer cells.
microRNAs; miR-155; hypoxia; radiosensitizer; lung cancer
The in vivo mechanisms that coordinate the timing of axon growth and guidance are not well understood. In the C. elegans hermaphrodite specific neurons, the lin-4 microRNA controls the stage of axon initiation independent of the UNC-40 and SAX-3 ventral guidance receptors. lin-4 loss-of-function mutants exhibit marked delays in axon outgrowth, while lin-4 overexpression, leads to precocious growth in the L3. Here we show that loss of the POU transcription factor UNC-86 not only results in penetrant ventral axon growth defects in the HSNs, but also causes processes to extend in the L1, three stages earlier than wild-type. This temporal shift is not dependent on UNC-40 or SAX-3, and does not require the presence of lin-4. We propose that unc-86(lf) HSN axons are misguided due to the temporal decoupling of axon initiation and ventral guidance responses.
timing; axon growth; axon guidance; UNC-86; Brn3; DCC; UNC-40
Cancer is a complex and dynamic disease, involving a variety of changes in gene expression and structure. Traditionally, the study of cancer has focused on protein-coding genes, considering these as the principal effectors and regulators of tumorigenesis. Recent advances, however, have brought non-protein-coding RNA into the spotlight. MicroRNAs (miRNAs), one such class of non-coding RNAs, have been implicated in the regulation of cell growth, differentiation, and apoptosis . While their study is still at an early stage, and their mechanism of action along with their importance in cancer is not yet fully understood, they may provide an important layer of genetic regulation in tumorigenesis, and ultimately become valuable therapeutic tools.
Melanoma is an aggressive cancer that is highly resistance to therapies once metastasized. We studied microRNA (miRNA) expression in clinical melanoma subtypes and evaluated different miRNA signatures in the background of gain of function somatic and inherited mutations associated with melanoma. Total RNA from 42 patient derived primary melanoma cell lines and three independent normal primary melanocyte cell cultures was evaluated by miRNA array. MiRNA expression was then analyzed comparing subtypes and additional clinicopathologic criteria including somatic mutations. The prevalence and association of an inherited variant in a miRNA binding site in the 3′UTR of the KRAS oncogene, referred to as the KRAS-variant, was also evaluated. We show that seven miRNAs, miR-142-3p, miR-486, miR-214, miR-218, miR-362, miR-650 and miR-31, were significantly correlated with acral as compared to non-acral melanomas (p < 0.04). In addition, we discovered that the KRAS-variant was enriched in non-acral melanoma (25%), and that miR-137 under expression was significantly associated with melanomas with the KRAS-variant. Our findings indicate that miRNAs are differentially expressed in melanoma subtypes and that their misregulation can be impacted by inherited gene variants, supporting the hypothesis that miRNA misregulation reflects biological differences in melanoma.
melanoma; microRNA profiling; biomarker; acral; KRAS-variant; SNP
Genetic markers identifying women at an increased risk of developing breast cancer exist, yet the majority of inherited risk remains elusive. While numerous BRCA1 coding sequence mutations are associated with breast cancer risk, BRCA1 mutations account for less then 5% of breast cancer risk. Since 3′ untranslated region (3′UTR) polymorphisms disrupting microRNA (miRNA) binding can be functional and can act as genetic markers of cancer risk, we tested the hypothesis that such polymorphisms in the 3′UTR of BRCA1 and haplotypes containing these functional polymorphisms may be associated with breast cancer risk. We sequenced the BRCA1 3′UTR from breast cancer patients to identify miRNA disrupting polymorphisms. We further evaluated haplotypes of this region including the identified 3′UTR variants in a large population of controls and breast cancer patients (n = 221) with known breast cancer subtypes and ethnicities. We identified three 3′UTR variants in BRCA1 that are polymorphic in breast cancer populations, and haplotype analysis including these variants revealed that breast cancer patients harbor five rare haplotypes not generally found among controls (9.50% for breast cancer chromosomes, 0.11% for control chromosomes, p = 0.0001). Three of these rare haplotypes contain the rs8176318 BRCA1 3′UTR functional variant. These haplotypes are not biomarkers for BRCA1 coding mutations, as they are found rarely in BRCA1 mutant breast cancer patients (1/129 patients = 0.78%). These rare BRCA1 haplotypes and 3′UTR SNPs may represent new genetic markers of breast cancer risk.
BRCA1; haplotype; microRNA; SNP; 3′UTR; breast cancer; triple negative breast cancer
Aging is under genetic control in C. elegans but the mechanisms of lifespan regulation are not completely known. MicroRNAs (miRNAs) regulate various aspects of development and metabolism and one miRNA has been previously implicated in lifespan.
Here we show that multiple miRNAs change expression in C. elegans aging, including novel miRNAs, and that mutations in several of the most up-regulated miRNAs lead to lifespan defects. Some act to promote normal lifespan and stress resistance while others inhibit these phenomena. We find that these miRNAs genetically interact with genes in the DNA damage checkpoint response pathway and in the insulin signaling pathway.
Our findings reveal that miRNAs both positively and negatively influence lifespan. Since several miRNAs up-regulated during aging regulate genes in conserved pathways of aging and thereby influence lifespan in C. elegans, we propose that miRNAs may play important roles in stress response and aging of more complex organisms.
microRNAs; longevity; lifespan; aging; stress; C. elegans
Casein Kinase I (CKI) is a conserved component of the Wnt signaling pathway that regulates cell fate determination in metazoans. We show that post-embryonic asymmetric division and fate specification of C. elegans epidermal stem cells are controlled by a non-canonical Wnt/β-catenin signaling pathway, involving the β-catenins WRM-1 and SYS-1, and that C. elegans kin-19/CKIα functions in this pathway. Furthermore, we find that kin-19 is the only member of the Wnt asymmetry pathway that functions with, or in parallel to, the heterochronic temporal patterning pathway to control withdrawal from self-renewal and subsequent terminal differentiation of epidermal stem cells. We show that, except in the case of kin-19, the Wnt asymmetry pathway and the heterochronic pathway function separately and in parallel to control different aspects of epidermal stem cell fate specification. However, given the function of kin-19/CKIα in both pathways, and that CKI, Wnt signaling pathway and heterochronic pathway genes are widely conserved in animals, our findings suggest that CKIα may function as a regulatory hub through which asymmetric division and terminal differentiation are coordinated in adult stem cells of vertebrates.
C. elegans; kin-19; casein kinase Ialpha (CKIα); Wnt; stem cell; asymmetric cell division; heterochronic; temporal identity; terminal differentiation; self-renewal
Neither genetic nor environmental factors fully account for variability in individual longevity: genetically identical invertebrates in homogenous environments often experience no less variability in lifespan than outbred human populations. Such variability is often assumed to result from stochasticity in damage accumulation over time; however, the identification of early-life gene expression states that predict future longevity would suggest that lifespan is least in part epigenetically determined. Such “biomarkers of aging,” genetic or otherwise, nevertheless remain rare. In this work, we sought early-life differences in organismal robustness in unperturbed individuals and examined the utility of microRNAs, known regulators of lifespan, development, and robustness, as aging biomarkers. We quantitatively examined Caenorhabditis elegans reared individually in a novel apparatus and observed throughout their lives. Early-to-mid–adulthood measures of homeostatic ability jointly predict 62% of longevity variability. Though correlated, markers of growth/muscle maintenance and of metabolic by-products (“age pigments”) report independently on lifespan, suggesting that graceful aging is not a single process. We further identified three microRNAs in which early-adulthood expression patterns individually predict up to 47% of lifespan differences. Though expression of each increases throughout this time, mir-71 and mir-246 correlate with lifespan, while mir-239 anti-correlates. Two of these three microRNA “biomarkers of aging” act upstream in insulin/IGF-1–like signaling (IIS) and other known longevity pathways, thus we infer that these microRNAs not only report on but also likely determine longevity. Thus, fluctuations in early-life IIS, due to variation in these microRNAs and from other causes, may determine individual lifespan.
Why do some individuals live longer than others? Unexpectedly, genetic differences contribute surprisingly little to lifespan variation in humans. The situation is thrown into relief in studies of C. elegans, in which genetically identical siblings reared in identical environments usually experience different lifespans. In this work, we show that physiological differences between identical animals begin to appear relatively early in life and that markers of ill health in young adulthood presage shorter lifespans. Using fluorescent markers to examine the level of activation of several genes, we found three regulatory microRNA genes that vary in activity between individuals in a manner that predicts future lifespan. Moreover, two of these regulate insulin signaling, which is well known to alter lifespan in diverse species when experimentally manipulated. This indicates that different levels of insulin signaling in otherwise identical individuals may determine differences in lifespan.
Developmental timing in the nematode Caenorhabditis elegans is controlled by heterochronic genes, mutations in which cause changes in the relative timing of developmental events. One of the heterochronic genes, let-7, encodes a microRNA that is highly evolutionarily conserved, suggesting that similar genetic pathways control developmental timing across phyla. Here we report that the nuclear receptor nhr-25, which belongs to the evolutionarily conserved fushi tarazu-factor 1/nuclear receptor NR5A subfamily, interacts with heterochronic genes that regulate the larva-to-adult transition in C. elegans. We identified nhr-25 as a regulator of apl-1, a homolog of the Alzheimer’s amyloid precursor protein-like gene that is downstream of let-7 family microRNAs. NHR-25 controls not only apl-1 expression but also regulates developmental progression in the larva-to-adult transition. NHR-25 negatively regulates the expression of the adult-specific collagen gene col-19 in lateral epidermal seam cells. In contrast, NHR-25 positively regulates the larva-to-adult transition for other timed events in seam cells, such as cell fusion, cell division and alae formation. The genetic relationships between nhr-25 and other heterochronic genes are strikingly varied among several adult developmental events. We propose that nhr-25 has multiple roles in both promoting and inhibiting the C. elegans heterochronic gene pathway controlling adult differentiation programs.
apl-1; Caenorhabditis elegans; heterochronic gene; developmental timing; let-7; nuclear receptor; nhr-25