Loss-of-function screening to identify miRNAs involved in senescence: tumor suppressor activity of miRNA-335 and its new target CARF

Fragile X Messenger Ribonucleoprotein Protein and Its Multifunctionality: From Cytosol to Nucleolus and Back

Silencing of the fragile X messenger ribonucleoprotein 1 (FMR1) gene and a consequent lack of FMR protein (FMRP) synthesis are associated with fragile X syndrome, one of the most common inherited intellectual disabilities. FMRP is a multifunctional protein that is involved in many cellular functions in almost all subcellular compartments under both normal and cellular stress conditions in neuronal and non-neuronal cell types. This is achieved through its trafficking signals, nuclear localization signal (NLS), nuclear export signal (NES), and nucleolar localization signal (NoLS), as well as its RNA and protein binding domains, and it is modulated by various post-translational modifications such as phosphorylation, ubiquitination, sumoylation, and methylation. This review summarizes the recent advances in understanding the interaction networks of FMRP with a special focus on FMRP stress-related functions, including stress granule formation, mitochondrion and endoplasmic reticulum plasticity, ribosome biogenesis, cell cycle control, and DNA damage response.

Regulatory miRNAs in cancer cell recovery from therapy exposure and its implications as a novel therapeutic strategy for preventing disease recurrence

The desired outcome of cancer therapies is the eradication of disease. This can be achieved when therapy exposure leads to therapy-induced cancer cell death as the dominant outcome. Theoretically, a permanent therapy-induced growth arrest could also contribute to a complete response, which has the potential to lead to remission. However, preclinical models have shown that therapy-induced growth arrest is not always durable, as recovering cancer cell populations can contribute to the recurrence of cancer. Significant research efforts have been expended to develop strategies focusing on the prevention of recurrence. Recovery of cells from therapy exposure can occur as a result of several cell stress adaptations. These include cytoprotective autophagy, cellular quiescence, a reversable form of senescence, and the suppression of apoptosis and necroptosis. It is well documented that microRNAs regulate the response of cancer cells to anti-cancer therapies, making targeting microRNAs therapeutically a viable strategy to sensitization and the prevention of recovery. We propose that the use of microRNA-targeting therapies in prolonged sequence, that is, a significant period after initial therapy exposure, could reduce toxicity from the standard combination strategy, and could exploit new epigenetic states essential for cancer cells to recover from therapy exposure. In a step toward supporting this strategy, we survey the available scientific literature to identify microRNAs which could be targeted in sequence to eliminate residual cancer cell populations that were arrested as a result of therapy exposure. It is our hope that by successfully identifying microRNAs which could be targeted in sequence we can prevent disease recurrence.

Circular RNA circFOXP1 promotes angiogenesis by regulating microRNA -127-5p/CDKN2AIP signaling pathway in osteosarcoma

Osteosarcoma is known to have a high metastatic potential, which is closely related to angiogenesis. circRNAs are closely associated with osteosarcoma metastasis. This study aims to investigate the role of Circular RNA circFOXP1 in angiogenesis in osteosarcoma. We detected circFOXP1 expression in osteosarcoma, as well as its prognostic value. Tube formation assay and immunohistochemistry staining were conducted to determine the condition of tube formation. RT-qPCR was performed to explore targeted genes. Luciferase reporter assays were carried out to explore the interaction between miR-127-5p, ircFOXP1, and CDKN2AIP, respectively. In vivo studies further confirmed the relationship between circFOXP1 and tumor angiogenesis in osteosarcoma. We found that circFOXP1 expression was increased in osteosarcoma, and could promote angiogenesis in osteosarcoma through upregulating CDKN2AIP expression. Moreover, circFOXP1 could directly bind to miR-127-5p, which further targets CDKN2AIP directly. In conclusion, circFOXP1 promoted angiogenesis by regulating miR-127-5p/CDKN2AIP signaling pathway in osteosarcoma.

Upregulation of miR‑335 exerts protective effects against sepsis‑induced myocardial injury

Septicemia is associated with excessive inflammation, oxidative stress and apoptosis, causing myocardial injury that results in high mortality and disability rates worldwide. The abnormal expression of multiple microRNAs (miRNAs/miRs) is associated with more severe sepsis-induced myocardial injury (SIMI) and miR-335 has been shown to protect cardiomyocytes from oxidative stress. The present study aimed to investigate the role of miR-335 in SIMI. An SIMI model was established by cecal ligation and puncture (CLP) in mice. An miRNA-335 precursor (pre-miR-335) was transfected to accelerate miR-335 expression and an miR-335 inhibitor (anti-miR-335) was used to inhibit miR-335 expression. CLP or sham surgery was performed on pre-miR-335, anti-miR-335 and wild-type mice and miR-335 expression was determined by reverse transcription-quantitative PCR. Inflammatory factors (TNF-α, IL-6 and IL-10) and troponin (cTNI), brain natriuretic peptide (BNP), creatine kinase (CK), lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) were assessed using commercial kits. Apoptosis was detected by flow cytometry and cardiac function was assessed using a Langendorff isolated cardiac perfusion system. miR-335 expression was upregulated and an elevation in inflammatory factors and cTNI, BNP, CK, LDH and AST was observed. Compared with the wild-type control group, pre-miR-335 mice treated with CLP exhibited significantly reduced left ventricular development pressure, maximum pressure increased reduction rates, as well as decreased levels of TNF-α, IL-6 and IL-10, myocardial injury and apoptosis; by contrast, these features were amplified in CLP-treated anti-miR-335 mice. In conclusion, the upregulation of miR-335 exerted ameliorative effects on myocardial injury following sepsis and may indicate a novel therapeutic intervention for SIMI.

Functional characterization of miR-708 microRNA in telomerase positive and negative human cancer cells

Activation of a telomere length maintenance mechanism (TMM), including telomerase and alternative lengthening of telomeres (ALT), is essential for replicative immortality of tumor cells, although its regulatory mechanisms are incompletely understood. We conducted a microRNA (miRNA) microarray analysis on isogenic telomerase positive (TEP) and ALT cancer cell lines. Amongst nine miRNAs that showed difference in their expression in TEP and ALT cancer cells in array analysis, miR-708 was selected for further analysis since it was consistently highly expressed in a large panel of ALT cells. miR-708 in TEP and ALT cancer cells was not correlated with C-circle levels, an established feature of ALT cells. Its overexpression induced suppression of cell migration, invasion, and angiogenesis in both TEP and ALT cells, although cell proliferation was inhibited only in TEP cells suggesting that ALT cells may have acquired the ability to escape inhibition of cell proliferation by sustained miR-708 overexpression. Further, cell proliferation regulation in TEP cells by miR708 appears to be through the CARF-p53 pathway. We demonstrate here that miR-708 (i) is the first miRNA shown to be differentially regulated in TEP and ALT cancer cells, (ii) possesses tumor suppressor function, and (iii) deregulates CARF and p21^WAF1-mediated signaling to limit proliferation in TEP cells.

Long non‑coding RNA SNHG20 promotes cell proliferation, migration and invasion in retinoblastoma via the miR‑335‑5p/E2F3 axis

Current therapies for retinoblastoma (RB) are unsatisfactory and there is an urgent need for the development of new treatment modalities. Small nucleolar RNA host gene 20 (SNHG20) has been reported to serve a key oncogenic role in the development of various types of cancer, but its role in RB tumorigenesis remains to be fully determined. The present study aimed to investigate the expression patterns and biological roles of SNHG20 in RB. The expression levels of SNHG20 were measured via reverse transcription‑quantitative PCR in RB tissues and cell lines. The impact of SNHG20 status on cell proliferation, survival, migration and invasion was determined using small interfering RNA and a range of established experimental assays. The SNHG20/microRNA (miR)‑335‑5p/E2F transcription factor 3 (E2F3) signaling axis was further investigated using a dual‑luciferase activity reporter system and an RNA pull‑down assay combined with bioinformatics analyses. SNHG20 expression was significantly increased in RB tissues and cell lines. Silencing of SNHG20 in RB cells was shown to inhibit cell proliferation, clonogenic survival, migration and invasion. Moreover, mechanistic investigations demonstrated that SNHG20 could enhance the expression of E2F3 by sponging of miR‑335‑5p. These data suggested that the long non‑coding RNA SNHG20 may promote cell proliferation, migration and invasion in RB via the miR‑335‑5p/E2F3 axis.

Inhibition of MicroRNA-302c on Stemness of Colon Cancer Stem Cells via the CARF/Wnt/β-Catenin Axis

BACKGROUND

Even though the relevance of microRNA (miR)-302c has been studied, little is known about its involvement in colon cancer (CC).

AIMS

Our aim here was to investigate the role of miR-302c in the cancer stem cells (CSCs) of CC.

METHODS

Firstly, the CSCs were screened out from cultured SW1116 and SW480 cells by flow cytometry, and the differentially expressed miRNAs in cell were obtained by microarray analysis. The expression of miR-302c, collaborator of ARF (CARF), and Wnt/β-catenin-related genes in CSCs was determined by means of RT-qPCR and Western blot. A dual-luciferase reporter assay was conducted to authenticate the binding relationship between miR-302c and CARF. Proliferation, migration, invasion, sphere formation as well as apoptosis of CSCs were assessed by cell counting kit-8, Transwell assay, sphere formation assay as well as flow cytometric analysis, respectively. The roles of miR-302c and CARF in tumor growth were determined in vivo.

RESULTS

The expression of miR-302c in CC cells was reduced versus that in normal cells. The overexpression of miR-302c weakened the stemness, proliferation, invasion, and migration abilities while induced apoptosis of CSCs in CC. Also, miR-302c reduced tumor size and weight in mice, accompanied with lowered CARF expression. The mechanistic analysis manifested that miR-302c bound to CARF and suppressed its expression and disrupted the Wnt/β-catenin signaling.

CONCLUSION

This study offers a novel characterization of miR-302c function in CSCs in CC, which may be beneficial to the development of capable therapeutic options for CC.

Genes and pathways involved in senescence bypass identified by functional genetic screens

Cellular senescence is a state of stable and irreversible cell cycle arrest with active metabolism, that normal cells undergo after a finite number of divisions (Hayflick limit). Senescence can be triggered by intrinsic and/or extrinsic stimuli including telomere shortening at the end of a cell's lifespan (telomere-initiated senescence) and in response to oxidative, genotoxic or oncogenic stresses (stress-induced premature senescence). Several effector mechanisms have been proposed to explain senescence programmes in diploid cells, including the induction of DNA damage responses, a senescence-associated secretory phenotype and epigenetic changes. Senescent cells display senescence-associated-β-galactosidase activity and undergo chromatin remodeling resulting in heterochromatinisation. Senescence is established by the pRb and p53 tumour suppressor networks. Senescence has been detected in in vitro cellular settings and in premalignant, but not malignant lesions in mice and humans expressing mutant oncogenes. Despite oncogene-induced senescence, which is believed to be a cancer initiating barrier and other tumour suppressive mechanisms, benign cancers may still develop into malignancies by bypassing senescence. Here, we summarise the functional genetic screens that have identified genes, uncovered pathways and characterised mechanisms involved in senescence evasion. These include cell cycle regulators and tumour suppressor pathways, DNA damage response pathways, epigenetic regulators, SASP components and noncoding RNAs.

Sp1 promotes ovarian cancer cell migration through repressing miR-335 expression

Decreased miR-335 has been reported in a variety of cancers. We previously showed that miR-335 played an important role in ovarian cancer metastasis and prognosis. However, miR-335 is down-regulated in ovarian cancer by mechanisms that remain unclear. In silico analysis identified putative transcription factor specificity protein 1 (SP1) transcription factor binding sites in the miR-335 promoter. To investigate the relation between SP1 and miR-335, qRT-PCR was performed. Our results showed both Sp1 knockdown and mithramycin A increased miR-335 expression in ovarian cancer cell lines. Luciferase reporter assays indicated that Sp1 knockdown increased miR-335 transcriptional activity. ChIP experiments showed that Sp1 bound directly to miR-335 promoter. Moreover, transwell migration and wound-healing assays showed that Sp1 knockdown resulted in inhibited cell migration, which was in turn mitigated by miR-335 inhibitor. We propose that miR-335 was negatively regulated by SP1, which in turn contributes to miR-335 deregulation and tumor cells migration.

Current Smoking is Associated with Decreased Expression of miR-335-5p in Parenchymal Lung Fibroblasts

Cigarette smoking causes lung inflammation and tissue damage. Lung fibroblasts play a major role in tissue repair. Previous studies have reported smoking-associated changes in fibroblast responses and methylation patterns. Our aim was to identify the effect of current smoking on miRNA expression in primary lung fibroblasts. Small RNA sequencing was performed on lung fibroblasts from nine current and six ex-smokers with normal lung function. MiR-335-5p and miR-335-3p were significantly downregulated in lung fibroblasts from current compared to ex-smokers (false discovery rate (FDR) <0.05). Differential miR-335-5p expression was validated with RT-qPCR (p-value = 0.01). The results were validated in lung tissue from current and ex-smokers and in bronchial biopsies from non-diseased smokers and never-smokers (p-value <0.05). The methylation pattern of the miR-335 host gene, determined by methylation-specific qPCR, did not differ between current and ex-smokers. To obtain insights into the genes regulated by miR-335-5p in fibroblasts, we overlapped all proven miR-335-5p targets with our previously published miRNA targetome data in lung fibroblasts. This revealed Rb1, CARF, and SGK3 as likely targets of miR-335-5p in lung fibroblasts. Our study indicates that miR-335-5p downregulation due to current smoking may affect its function in lung fibroblasts by targeting Rb1, CARF and SGK3.

MicroRNA controls of cellular senescence

Cellular senescence is a state of permanent cell-cycle arrest triggered by different internal and external stimuli. This phenomenon is considered to be both beneficial and detrimental depending on the cell types and biological contexts. During normal embryonic development and after tissue injury, cellular senescence is critical for tissue remodeling. In addition, this process is useful for arresting growth of tumor cells, particularly during early onset of tumorigenesis. However, accumulation of senescent cells decreases tissue regenerative capabilities and induces inflammation, which is responsible for cancer and organismal aging. Therefore cellular senescence has to be tightly regulated, and dysregulation might lead to the aging and human diseases. Among many regulators of cellular senescence, in this review, I will focus on microRNAs, small non-coding RNAs playing critical roles in diverse biological events including cellular senescence. [BMB Reports 2018; 51(10): 494-500].

Identification of H2O2 induced oxidative stress associated microRNAs in HLE-B3 cells and their clinical relevance to the progression of age-related nuclear cataract

BACKGROUND

This study is aimed to screen out the microRNAs (miRNAs) associated with H₂O₂ induced oxidative stress in human lens epithelial B3 (HLE-B3) cell lines and investigate their relations with the progression of age-related nuclear cataract.

METHODS

H₂O₂ was used to induce oxidative stress in HLE-B3 cells. A genome-wide expression profiling of miRNAs in HLE-B3 cells was performed to select the differentially expressed miRNAs before and after H₂O₂ treatment. The selected miRNAs were validated by RT-PCR and fluorescence in situ hybridization (FISH). Clinical specimens were divided into three groups according to the Lens Opacities Classification System III (LOCSIII) and the expression levels of the selected miRNAs were tested by RT-PCR in the three groups. Bioinformatics analyses were applied to predict the target genes of the miRNA hits and construct the miRNA regulatory network. The expression level of MAPK14 was analyzed by Western blot.

RESULTS

The H₂O₂ induced oxidative stress model of HLE-B3 cells was established. Nineteen upregulated and 30 downregulated miRNAs were identified as differentially expressed miRNAs. Seven of the total 49 were validated in the cell model. RT-PCR of the clinical samples showed that the expression levels of miR-34a-5p, miR-630 and miR-335-3p were closely related with the severity of nuclear opacity. The images taken from FISH confirmed the results of RT-PCR. There were 172 target genes of the three miRNAs clustered in the category of response to stress. The regulatory network demonstrated that 23 target genes were co-regulated by multiple miRNAs. MAPK14 was the target gene of three miRNAs and the result were verified by Western blot.

CONCLUSION

Up-regulation of miR-34a-5p and miR-630 and down-regulation of miR-335-3p are related with the progression of age-related nuclear cataract and the underlying mechanism awaits further functional research to reveal.

Tumor suppressor activity of miR-451: Identification of CARF as a new target

microRNAs (miRs) have recently emerged as small non-coding regulators of gene expression. We performed a loss-of-function screening by recruiting retrovirus mediated arbitrary manipulation of genome coupled with escape of cells from 5-Aza-2′-deoxycytidine (5-Aza-dC)-induced senescence. miRNA pool from cells that emerged from 5-Aza-dC-induced senescence was subjected to miR-microarray analysis with respect to the untreated control. We identified miR-451 as one of the upregulated miRs and characterized its functional relevance to drug resistance, cell growth, tumor suppressor proteins p53 and pRb, and stress response. We report that miR-451 caused growth arrest in cells leading to their resistance to 5-Aza-dC-induced senescence. Decrease in cyclin D1, CDK4 and phosphorylated pRB supported the growth arrest in miR-451 transfected cells. We demonstrate that Collaborator of ARF (CARF) protein is a new target of miR-451 that intermediates its function in tumor suppressor and stress signaling.