Cross-Talk Between circRNAs and mRNAs Modulates MiRNA-mediated Circuits and Affects Melanoma Plasticity

Circular RNAs in stem cells: from basic research to clinical implications

Circular RNAs (circRNAs) are a special class of endogenous RNAs with a wide variety of pathophysiological functions via diverse mechanisms, including transcription, microRNA (miRNA) sponge, protein sponge/decoy, and translation. Stem cells are pluripotent cells with unique properties of self-renewal and differentiation. Dysregulated circRNAs identified in various stem cell types can affect stem cell self-renewal and differentiation potential by manipulating stemness. However, the emerging roles of circRNAs in stem cells remain largely unknown. This review summarizes the major functions and mechanisms of action of circRNAs in stem cell biology and disease progression. We also highlight circRNA-mediated common pathways in diverse stem cell types and discuss their diagnostic significance with respect to stem cell-based therapy.

Long noncoding RNA HOXC-AS3 enhances the progression of cervical cancer via activating ErbB signaling pathway

Emerging evidence reveals that long noncoding RNAs (lncRNAs) contribute to human tumorigenesis. Nevertheless, the function of HOXC cluster antisense RNA 3 (HOXC-AS3) in human cervical cancer (CC) remains largely unknown. The levels of HOXC-AS3, miR-105-5p and SOS1 in CC tissues and cells were monitored by reverse transcription-polymerase chain reaction (RT-PCR) and western blot (WB). Gain- and loss-of-function experiments were conducted to verify the function of HOXC-AS3 and miR-105-5p in CC cells. Meanwhile, cell proliferation, apoptosis, migration and invasion were examined by the cell counting kit-8 (CCK8) experiment, colony formation assay, flow cytometry and Transwell assay. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were carried out to test the regulatory interaction of HOXC-AS3, miR-105-5p and SOS1. In addition, in vivo experiment was performed to certain the role of HOXC-AS3 in tumorigenesis of CC. HOXC-AS3 was overexpressed in CC tissues (vs. adjacent normal tissues) and CC cells. Besides, the higher HOXC-AS3 profile was associated with the poorer clinical prognosis of CC patients. Overexpression of HOXC-AS3 promoted cell growth, migration and invasion, hampered apoptosis, whereas knocking down HOXC-AS3 exhibited the reverse effects. MiR-105-5p was a downstream target of HOXC-AS3, and it mediated the HOXC-AS3-induced oncogenic effects. Mechanistically, the bioinformatic analysis illustrated that SOS1 was targeted by miR-105-5p. Up-regulating SOS1 heightened the growth, migration and invasion of CC cells by enhancing the ErbB signaling pathway, which was reversed by miR-105-5p. Up-regulated HOXC-AS3 aggravates CC by promoting SOS1 expression via targeting miR-105-5p.

CircRNA-1967 participates in the differentiation of goat SHF-SCs into hair follicle lineage by sponging miR-93-3p to enhance LEF1 expression

Circular RNAs (circRNAs), a novel class of non-coding RNAs, can interact with miRNAs through a sequence-driven sponge mechanism, thereby regulating the expression of their downstream target genes. CircRNA-1967 was found in secondary hair follicles (SHFs) of cashmere goats, but its functions are not clear. Here, we showed that both circRNA-1967 and its host gene BNC2 had significantly higher expression in SHF bulge at anagen than those at telogen of cashmere goats. Also, circRNA-1967 participates in the differentiation of SHF stem cells (SHF-SCs) into hair follicle lineage in cashmere goats. RNA pull-down assay verified that circRNA-1967 interacts with miR-93-3p. We also indicated that circRNA-1967 promoted LEF1 expression in SHF-SCs of cashmere goats. By dual-luciferase reporter analysis, we found that circRNA-1967 up-regulated LEF1 expression through the miR-93-3p-mediated pathway. The results from this study demonstrated that circRNA-1967 participated in the differentiation of goat SHF-SCs into hair follicle lineage by sponging miR-93-3p to enhance LEF1 expression. Our founding might constitute a novel pathway for revealing the potential mechanism of the differentiation of SHF-SCs into hair follicle lineage in cashmere goats. Also, these results provided a valuable basis for further enhancing the intrinsic regeneration of cashmere goat SHFs with the formation and growth of cashmere fibers.

Novel Regulators of the IGF System in Cancer

The insulin-like growth factor (IGF) system is a dynamic network of proteins, which includes cognate ligands, membrane receptors, ligand binding proteins and functional downstream effectors. It plays a critical role in regulating several important physiological processes including cell growth, metabolism and differentiation. Importantly, alterations in expression levels or activation of components of the IGF network are implicated in many pathological conditions including diabetes, obesity and cancer initiation and progression. In this review we will initially cover some general aspects of IGF action and regulation in cancer and then focus in particular on the role of transcriptional regulators and novel interacting proteins, which functionally contribute in fine tuning IGF1R signaling in several cancer models. A deeper understanding of the biological relevance of this network of IGF1R modulators might provide novel therapeutic opportunities to block this system in neoplasia.

Circular RNA circ_0079593 enhances malignant melanoma progression by the regulation of the miR-573/ABHD2 axis

BACKGROUND

Malignant melanoma is the most fatal type of skin tumor. Circular RNAs (circRNAs) have been implicated in the malignant progression of melanoma.

OBJECTIVE

The main purpose of this paper was to identify the precise parts of circ_0079593 in the malignant progression of melanoma.

METHODS

The levels of circ_0079593, miR-573 and abhydrolase domain containing 2 (ABHD2) were determined by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot. Cell proliferation, colony formation, cell cycle progression, apoptosis, migration, and invasion were evaluated using the Cell Counting Kit-8 (CCK-8), colony formation, flow cytometry, and transwell assays, respectively. Targeted correlations among circ_0079593, miR-573 and ABHD2 were confirmed by dual-luciferase reporter, RNA immunoprecipitation (RIP) and RNA pull-down assays. Animal studies were performed to assess the role of circ_0079593 in vivo.

RESULTS

Our data showed that circ_0079593 level was up-regulated in melanoma tissues and cells. The knockdown of circ_0079593 suppressed cell proliferation, cell cycle progression, migration, invasion, and enhanced apoptosis in vitro and inhibited tumor growth in vivo. Mechanistically, circ_0079593 directly targeted miR-573, and circ_0079593 controlled ABHD2 expression by miR-573. MiR-573 mediated the regulation of circ_0079593 on melanoma cell progression in vitro. Moreover, ABHD2 was a functional target of miR-573 in regulating melanoma cell progression in vitro.

CONCLUSION

Our findings identified that the knockdown of circ_0079593 suppressed melanoma progression at least partially through targeting the miR-573/ABHD2 axis, providing evidence for developing circ_0079593 as a promising therapeutic target for melanoma treatment.

MicroRNA-633 enhances melanoma cell proliferation and migration by suppressing KAI1

The aim of the present study was to determine the impact of microRNA (miRNA/miR)-633 on the biological properties of malignant melanoma cells. Kang-Ai 1 (KAI1), also known as cluster of differentiation 82, is an important transcriptional regulator and tumor suppressor gene present in different types of tumors. miRNAs that potentially bind with KAI1 were predicted via bioinformatics analyses. In total, six putative miRNA regulators of KAI1 were identified in the present analysis, among which miR-633 was upregulated the most in melanoma tissues compared with the control group. The expression levels of miR-633 and KAI1 in melanoma tissues compared with adjacent normal tissues were then assessed. It was found that miR-633 was significantly upregulated in melanoma cells compared with the control group, whereas the expression levels of KAI1 showed the opposite results. miR-633 was predicted to target the 3'-untranslated region of KAI1 using predictive online tools, and results from luciferase reporter assays confirmed the direct regulation of KAI1 promoter activity by miR-633. Furthermore, miR-633 mimics over expression was shown to suppress both mRNA and protein expression of KAI1, while miR-633 inhibition resulted in decreased viability and migrationin melanoma cells in vitro. Taken together, the present study demonstrated, to the best of the authors' knowledge for the first time, that miR-633 exerts an important role in melanoma through targeting KAI1.

Integrative analysis of the circRNA-miRNA regulatory network in atrial fibrillation

We aimed to investigate the circRNA-miRNA regulatory network in atrial fibrillation (AF) by using Cytoscape and HMDD v3.0. Finally, 120 differentially expressed circRNAs in peripheral blood monocytes of 4 AF patients were preliminarily screened by circRNA microarray. circRNA_4648, circRNA_4631, and circRNA_2875 were the first four circRNAs with the most binding nodes in the circRNA-miRNA network. The top three most frequent miRNAs for up-regulated circRNAs were hsa-miR-328 that interacted with 5 up-regulated circRNAs, hsa-miR-4685-5p with 4 up-regulated circRNAs, hsa-miR-3150a-3p, hsa-miR-4649-5p, hsa-miR-4783-3p, and hsa-miR-8073 with 3 up-regulated circRNAs,, while the top three most frequent miRNAs for down-regulated circRNAs were hsa-miR-328 that interacted with 14 down-regulated circRNAs, hsa-miR-4685-5p with 11 down-regulated circRNAs and hsa-miR-661 with 9 down-regulated circRNAs. According to HMDD v3.0, five up-regulated and eleven down-regulated circRNAs were found to interact with AF related miRNAs. These results indicated the possible regulatory network between circRNAs and miRNAs in the pathogenesis of AF.

Identifying inhibitors of epithelial-mesenchymal plasticity using a network topology-based approach

Metastasis is the cause of over 90% of cancer-related deaths. Cancer cells undergoing metastasis can switch dynamically between different phenotypes, enabling them to adapt to harsh challenges, such as overcoming anoikis and evading immune response. This ability, known as phenotypic plasticity, is crucial for the survival of cancer cells during metastasis, as well as acquiring therapy resistance. Various biochemical networks have been identified to contribute to phenotypic plasticity, but how plasticity emerges from the dynamics of these networks remains elusive. Here, we investigated the dynamics of various regulatory networks implicated in Epithelial–mesenchymal plasticity (EMP)—an important arm of phenotypic plasticity—through two different mathematical modelling frameworks: a discrete, parameter-independent framework (Boolean) and a continuous, parameter-agnostic modelling framework (RACIPE). Results from either framework in terms of phenotypic distributions obtained from a given EMP network are qualitatively similar and suggest that these networks are multi-stable and can give rise to phenotypic plasticity. Neither method requires specific kinetic parameters, thus our results emphasize that EMP can emerge through these networks over a wide range of parameter sets, elucidating the importance of network topology in enabling phenotypic plasticity. Furthermore, we show that the ability to exhibit phenotypic plasticity correlates positively with the number of positive feedback loops in a given network. These results pave a way toward an unorthodox network topology-based approach to identify crucial links in a given EMP network that can reduce phenotypic plasticity and possibly inhibit metastasis—by reducing the number of positive feedback loops.

Circ_0002770, acting as a competitive endogenous RNA, promotes proliferation and invasion by targeting miR-331-3p in melanoma

Melanoma is a kind of tumor that originates from melanocytes and is characterized by chemoresistance and distant metastasis. Although the complete pathogenesis of melanoma remains unclear, increasing evidence suggests that circular RNAs (circRNAs) may be involved. In the present study, we identified a circular RNA, circ_0002770, which is produced from the well-known oncogene MDM2, and was sharply increased in melanoma and correlated with a poor prognosis. Knockdown of circ_0002770 suppressed melanoma cell invasion, migration and proliferation. Mechanistically, circ_0002770 acted as a sponge of miR-331-3p and could indirectly regulate DUSP5 and TGFBR1. Inhibition of miR-331-3p reversed the inhibitory effect of si-circ_0002770 on melanoma cell proliferation and invasion. In vivo evidence further confirmed that silencing circ_0002770 inhibited melanoma tumor formation. In conclusion, circ_0002770 facilitated melanoma cell proliferation, invasion and migration by sponging miR-331-3p and modulating DUSP5 and TGFBR1.

Interplay among SNAIL Transcription Factor, MicroRNAs, Long Non-Coding RNAs, and Circular RNAs in the Regulation of Tumor Growth and Metastasis

SNAIL (SNAI1) is a zinc finger transcription factor that binds to E-box sequences and regulates the expression of genes. It usually acts as a gene repressor, but it may also activate the expression of genes. SNAIL plays a key role in the regulation of epithelial to mesenchymal transition, which is the main mechanism responsible for the progression and metastasis of epithelial tumors. Nevertheless, it also regulates different processes that are responsible for tumor growth, such as the activity of cancer stem cells, the control of cell metabolism, and the regulation of differentiation. Different proteins and microRNAs may regulate the SNAIL level, and SNAIL may be an important regulator of microRNA expression as well. The interplay among SNAIL, microRNAs, long non-coding RNAs, and circular RNAs is a key event in the regulation of tumor growth and metastasis. This review for the first time discusses different types of regulation between SNAIL and non-coding RNAs with a focus on feedback loops and the role of competitive RNA. Understanding these mechanisms may help develop novel therapeutic strategies against cancer based on microRNAs.