SRSF3-regulated miR-132/212 controls cell migration and invasion by targeting YAP1

Intronic miR-6741-3p targets the oncogene SRSF3: Implications for oral squamous cell carcinoma pathogenesis

Epigenetic silencing through methylation is one of the major mechanisms for downregulation of tumor suppressor miRNAs in various malignancies. The aim of this study was to identify novel tumor suppressor miRNAs which are silenced by DNA hypermethylation and investigate the role of at least one of these in oral squamous cell carcinoma (OSCC) pathogenesis. We treated cells from an OSCC cell line SCC131 with 5-Azacytidine, a DNA methyltransferase inhibitor, to reactivate tumor suppressor miRNA genes silenced/downregulated due to DNA methylation. At 5-day post-treatment, total RNA was isolated from the 5-Azacytidine and vehicle control-treated cells. The expression of 2,459 mature miRNAs was analysed between 5-Azacytidine and control-treated OSCC cells by the microRNA microarray analysis. Of the 50 miRNAs which were found to be upregulated following 5-Azacytidine treatment, we decided to work with miR-6741-3p in details for further analysis, as it showed a mean fold expression of >4.0. The results of qRT-PCR, Western blotting, and dual-luciferase reporter assay indicated that miR-6741-3p directly targets the oncogene SRSF3 at the translational level only. The tumor-suppressive role of miR-6741-3p was established by various in vitro assays and in vivo study in NU/J athymic nude mice. Our results revealed that miR-6741-3p plays a tumor-suppressive role in OSCC pathogenesis, in part, by directly regulating SRSF3. Based on our observations, we propose that miR-6741-3p may serve as a potential biological target in tumor diagnostics, prognostic evaluation, and treatment of OSCC and perhaps other malignancies.

circSMARCA5 Is an Upstream Regulator of the Expression of miR-126-3p, miR-515-5p, and Their mRNA Targets, Insulin-like Growth Factor Binding Protein 2 (IGFBP2) and NRAS Proto-Oncogene, GTPase (NRAS) in Glioblastoma

The involvement of non-coding RNAs (ncRNAs) in glioblastoma multiforme (GBM) pathogenesis and progression has been ascertained but their cross-talk within GBM cells remains elusive. We previously demonstrated the role of circSMARCA5 as a tumor suppressor (TS) in GBM. In this paper, we explore the involvement of circSMARCA5 in the control of microRNA (miRNA) expression in GBM. By using TaqMan^® low-density arrays, the expression of 748 miRNAs was assayed in U87MG overexpressing circSMARCA5. Differentially expressed (DE) miRNAs were validated through single TaqMan^® assays in: (i) U87MG overexpressing circSMARCA5; (ii) four additional GBM cell lines (A172; CAS-1; SNB-19; U251MG); (iii) thirty-eight GBM biopsies; (iv) twenty biopsies of unaffected brain parenchyma (UC). Validated targets of DE miRNAs were selected from the databases TarBase and miRTarbase, and the literature; their expression was inferred from the GBM TCGA dataset. Expression was assayed in U87MG overexpressing circSMARCA5, GBM cell lines, and biopsies through real-time PCR. TS miRNAs 126-3p and 515-5p were upregulated following circSMARCA5 overexpression in U87MG and their expression was positively correlated with that of circSMARCA5 (r-values = 0.49 and 0.50, p-values = 9 × 10^-5 and 7 × 10^-5, respectively) in GBM biopsies. Among targets, IGFBP2 (target of miR-126-3p) and NRAS (target of miR-515-5p) mRNAs were positively correlated (r-value = 0.46, p-value = 0.00027), while their expression was negatively correlated with that of circSMARCA5 (r-values = -0.58 and -0.30, p-values = 0 and 0.019, respectively), miR-126-3p (r-value = -0.36, p-value = 0.0066), and miR-515-5p (r-value = -0.34, p-value = 0.010), respectively. Our data identified a new GBM subnetwork controlled by circSMARCA5, which regulates downstream miRNAs 126-3p and 515-5p, and their mRNA targets IGFBP2 and NRAS.

Biological function and molecular mechanism of SRSF3 in cancer and beyond

Serine/arginine-rich splicing factor 3 (SRSF3; also known as SRp20), an important member of the family of SRSFs, is abnormally expressed in tumors, resulting in aberrant splicing of hub genes, such as CD44, HER2, MDM4, Rac family small GTPase 1 and tumor protein p53. Under normal conditions, the splicing and expression of SRSF3 are strictly regulated. However, the splicing, expression and phosphorylation of SRSF3 are abnormal in tumors. SRSF3 plays important roles in the occurrence and development of tumors, including the promotion of tumorigenesis, cellular proliferation, the cell cycle and metastasis, as well as inhibition of cell senescence, apoptosis and autophagy. SRSF3-knockdown significantly inhibits the proliferation and metastatic characteristics of tumor cells. Therefore, SRSF3 may be suggested as a novel anti-tumor target. The other biological functions of SRSF3 and its regulatory mechanisms are also summarized in the current review.

Long Non-coding RNA Rhabdomyosarcoma 2-Associated Transcript Regulates Angiogenesis in Endothelial Cells

Background: Long non-coding RNAs (lncRNAs) are non-coding RNAs that have more than 200 nucleotides. They have recently emerged as important regulators of angiogenesis. To identify novel lncRNAs that may be involved in the regulation of angiogenesis, we detected the mRNA of 84 lncRNAs in human umbilical vein endothelial cells (HUVECs) exposed to hypoxia for 24h. One of these, rhabdomyosarcoma 2-associated transcript (RMST), is significantly upregulated by hypoxia. Little is known about the presence and roles of RMST in EC function. Objective: The main objective of the study was to investigate the regulation of RMST in ECs and to determine its role in EC survival, proliferation, migration, and differentiation. Methods: Using qPCR, basal mRNA levels of 10 RMST isoforms in HUVECs were measured. Levels were then measured in response to 24h of hypoxia, 7days of differentiation in a co-culture assay, and exposure to four different angiogenesis factors. Functional roles of RMST in EC survival, migration, and differentiation were quantified by using a loss-of-function approach (transfection with single-stranded antisense LNA GapmeRs). EC survival was measured using cell counts and crystal violet assays. Cell migration and differentiation were measured using scratch wound healing and Matrigel® differentiation assays, respectively. Results: Five RMST isoforms (RMST-202, -203, -204, -206, and -207) were detected in HUVECs and human microvascular endothelial cells (HMEC-1s). Other types of vascular cells, including human aortic valve interstitial cells and human aortic smooth muscle cells, did not display this expression profile. RMST was significantly upregulated in response to 24h of hypoxia and in response to 7days of HUVEC co-culture with human lung fibroblasts. RMST was significantly downregulated by angiopoietin-2 (Ang-2), but not by VEGF, FGF-2, or angiopoietin-1 (Ang-1). Selective knockdown of RMST demonstrated that it promotes EC survival in response to serum deprivation. It is also required for VEGF- and Ang-1-induced EC survival and migration, but not for differentiation. Conclusion: We conclude that RMST is expressed in human ECs and that this expression is upregulated in response to hypoxia and during differentiation into capillary-like structures. We also conclude that RMST plays important roles in EC survival and migration.

SRp20: A potential therapeutic target for human tumors

As an important member of SR protein family, SRp20 plays a crucial role in alternative splicing. It not only participates in cell cycle regulation, export of mRNA, cleaving of primary microRNAs, homologous recombination-mediated DNA repair, cellular senescence and apoptosis, but also gets involved in the integrity and pluripotency of genome. Alternative splicing maintains a strict balance in the body to ensure the normal physiological function of cells. Once the balance is broken, diseases, even tumors, will follow. Through the analysis of SRp20-related articles, we found that Alzheimer's disease, glaucoma, bipolar disorder and other diseases have a certain relationship with SRp20. More importantly, SRp20 is closely related to the occurrence, proliferation, invasion and metastasis of various tumors, as well as chemotherapy resistance. Some SRp20 inhibitors have shown significant anticancer efficacy, suggesting a potential therapeutic strategy for tumors.

Emerging Roles of SRSF3 as a Therapeutic Target for Cancer

Ser/Arg-rich (SR) proteins are RNA-binding proteins known as constitutive and alternative splicing (AS) regulators that regulate multiple aspects of the gene expression program. Ser/Arg-rich splicing factor 3 (SRSF3) is the smallest member of the SR protein family, and its level is controlled by multiple factors and involves complex mechanisms in eukaryote cells, whereas the aberrant expression of SRSF3 is associated with many human diseases, including cancer. Here, we review state-of-the-art research on SRSF3 in terms of its function, expression, and misregulation in human cancers. We emphasize the negative consequences of the overexpression of the SRSF3 oncogene in cancers, the pathways underlying SRSF3-mediated transformation, and implications of potential anticancer drugs by downregulation of SRSF3 expression for cancer therapy. Cumulative research on SRSF3 provides critical insight into its essential part in maintaining cellular processes, offering potential new targets for anti-cancer therapy.

The roles of microRNA in human cervical cancer

Although a potentially preventable disease, cervical cancer (CC) is the second most commonly diagnosed gynaecological cancer with at least 530,000 new cases annually, and the prognosis with CC is still poor. Studies suggest that aberrant expression of microRNA (miRNA) contributes to the progression of CC. As a group of small non-coding RNA with 18-25 nucleotides, miRNA regulate about one-third of all human genes. They function by repressing translation or inducing mRNA cleavage or degradation, including genes involved in diverse and important cellular processes, including cell cycling, proliferation, differentiation, and apoptosis. Results showed that misexpression of miRNA is closely related to the onset and progression of CC. This review will provide an overview of the function of miRNA in CC and the mechanisms involved in cervical carcinogenesis.

SRSF3: Newly discovered functions and roles in human health and diseases

The serine/arginine rich proteins (SR proteins) are members of a family of RNA binding proteins involved in regulating various features of RNA metabolism, including pre-mRNA constitutive and alternative splicing. In humans, a total of 12 SR splicing factors (SRSFs) namely SRSF1-SRSF12 have been reported. SRSF3, the smallest member of the SR family and the focus of this review, regulates critical steps in mRNA metabolism and has been shown to have mRNA-independent functions as well. Recent studies on SRSF3 have uncovered its role in a wide array of complex biological processes. We have also reviewed the involvement of SRSF3 in disease conditions like cancer, ageing, neurological and cardiac disorders. Finally, we have discussed in detail the autoregulation of SRSF3 and its implications in cancer and commented on the potential of SRSF3 as a therapeutic target, especially in the context of cancer.

Hypoxia-Induced MicroRNA-212/132 Alter Blood-Brain Barrier Integrity Through Inhibition of Tight Junction-Associated Proteins in Human and Mouse Brain Microvascular Endothelial Cells

Blood-brain barrier (BBB) integrity is one of the important elements of central nervous system (CNS) homeostasis. MicroRNAs (miRs) have been demonstrated to play a role in many CNS disorders such as stroke and traumatic brain injury. MiR-212/132 are highly expressed in the CNS but their role at the BBB has not been characterized yet. Thus, we analyzed the expression of miR-212/132 in hypoxic mouse and human brain microvascular endothelial cells (BMEC) as well as in posttraumatic mouse and human brain tissue and serum exosomes. MiR-212/132 expression was detected in brain capillaries by in situ hybridization and was increased up to ten times in hypoxic BMEC. Over-expression of pre-miR-212/132 in BMEC decreased barrier properties and reduced migration of BMEC in the wound healing assay. We identified and validated tight junction proteins claudin-1 (Cldn1), junctional adhesion molecule 3 (Jam3), and tight junction-associated protein 1 (Tjap1) as potential miR-212/132 targets. Over-expression of miRs led to a decrease in mRNA and protein expression of Cldn1, Jam3, and Tjap1, which could be rescued by a respective anti-miR. In conclusion, our study identifies miR-212/132 as critical players at the hypoxic BBB. In addition, we propose three new direct miR-212/132 targets to be involved in miR-212/132-mediated effects on BBB properties.

MicroRNA-212-3p inhibits the Proliferation and Invasion of Human Hepatocellular Carcinoma Cells by Suppressing CTGF expression

MicroRNA-212-3p inhibits several human cancers but its effects on hepatocellular carcinoma (HCC) remain unclear. In this study, we show that miR-212-3p is down-regulated in HCC cell lines and tissues, and correlates with vascular invasion (p = 0.001), and the absence of capsule formation (p = 0.009). We found that miR-212-3p influenced the epithelial to mesenchymal transition (EMT) of HCCLM3 and Huh7 cells. Mechanistically, miR-212-3p repressed cell invasion through the suppression of connective tissue growth factor (CTGF). We therefore validate the anti-HCC effects of miR-212-3p through its ability to suppress CTGF and subsequent EMT.

Clustered miRNAs and their role in biological functions and diseases

MicroRNAs (miRNAs) are endogenous, small non-coding RNAs known to regulate expression of protein-coding genes. A large proportion of miRNAs are highly conserved, localized as clusters in the genome, transcribed together from physically adjacent miRNAs and show similar expression profiles. Since a single miRNA can target multiple genes and miRNA clusters contain multiple miRNAs, it is important to understand their regulation, effects and various biological functions. Like protein-coding genes, miRNA clusters are also regulated by genetic and epigenetic events. These clusters can potentially regulate every aspect of cellular function including growth, proliferation, differentiation, development, metabolism, infection, immunity, cell death, organellar biogenesis, messenger signalling, DNA repair and self-renewal, among others. Dysregulation of miRNA clusters leading to altered biological functions is key to the pathogenesis of many diseases including carcinogenesis. Here, we review recent advances in miRNA cluster research and discuss their regulation and biological functions in pathological conditions.

Predictive value of microRNA-132 and its target gene NAG-1 in evaluating therapeutic efficacy of non-steroidal anti-inflammatory drugs treatment in patients with ankylosing spondylitis

Ankylosing spondylitis (AS) is a common chronic rheumatic disorder, accompanied by the differential expression of various microRNAs (miRNAs) in patients suffering from the condition, some of which have the potential to serve as novel complementary AS biomarkers. During this study, AS patients were recruited in connection with our investigation into the correlation of microRNA-132 (miR-132) in peripheral blood and its target gene NAG-1 expressions in relation with the clinical efficacy of non-steroidal anti-inflammatory drugs (NSAIDs) treatment in patients with AS. A total of 218 AS patients who had been previously treated with oral diclofenac sodium and were placed into either the response (n = 175) or non-response groups (n = 43) following a 16-week period of therapeutic evaluation. An additional 113 healthy patients were also recruited for the purposes of the study. AS patient peripheral blood samples were obtained at the 0th, 8th, and 16th week, with the corresponding samples of the healthy patients collected at week 0. The expressions of miR-132 and NAG-1 were detected by RT-qPCR and analyzed using a ROC curve for the elucidation of the diagnostic value of peripheral blood miR-132 expressions as well as their predictive value among AS patients undergoing NSAIDs treatment. The targeting relations of miR-132 and NAG-1 were validated by microRNA.org and luciferase assay. Greater levels of peripheral blood miR-132 expression were observed among AS patients prior to treatment, in comparison to the healthy patients in the study. Prior to treatment, the area under the miR-132 ROC curve (AUC) of AS patients was 0.965, with a critical point of 2.605. The sensitivity and specificity of miR-132 were 91.7 and 97.3%, respectively, in regard to the AS diagnostic clinical efficacy. In comparison with the non-response group, the miR-132 expression of patients in the response group exhibited descended levels while the mRNA expression of NAG-1 increased. The ROC results indicated that the AUC of miR-132 was 0.876 with its sensitivity and specificity observed to be 95.3 and 80.0%, respectively. The AUC of NAG-1 was 0.912 with its sensitivity and specificity observed to be 76.6 and 79.1%, respectively. In comparison with the high miR-132 expression group and the low NAG-1 mRNA expression group, significantly improved blood biochemistry indexes, sign indexes, blood indexes, and adverse reaction rate were observed among the low miR-132 expression group and the high NAG-1 mRNA expression group. The microRNA.org and luciferase assay revealed NAG-1 to be a target of miR-132. Based on the results of this study, it was concluded that the expressions of MiR-132 and NAG-1 could serve as biological markers in the prediction of the therapeutic efficiency of NSAID treatment in AS patients.

Inhibition of the expression of oncogene SRSF3 by blocking an exonic splicing suppressor with antisense oligonucleotides

Antisense oligonucleotides (ASOs) have been widely used to regulate alternative splicing of pre-mRNA by targeting splice sites, branch points, or exonic splice enhancers to increase exon skipping or intron retention. So far, few studies have used ASOs to block exonic splicing suppressor (ESS) and increase exon inclusion. Previously, we demonstrated that serine and arginine rich splicing factor 3 (SRSF3) (also called SRp20) is an oncogene. The inclusion of its alternative exon 4 down-regulates its expression. An ESS motif is responsible for the skipping of alternative exon 4. Here, we used an economical method to screen effective anti-ESS ASO. We discovered that an ASO targeting the ESS motif can promote the inclusion of exon 4, reduce SRSF3 expression, and inhibit cell growth in oral cancer cells. Our results suggested that using anti-ESS ASOs can efficiently increase exon inclusion and be used as a potential anti-cancer drug.

Inhibition of the expression of oncogene SRSF3 and cancer cell growth by blocking an exonic splicing suppressor in alternative exon 4 of SRSF3 with SR-3 antisense oligonucleotide.