miR-497/Wnt3a/c-jun feedback loop regulates growth and epithelial-to-mesenchymal transition phenotype in glioma cells
Introduction
As one of the most common forms of brain cancer in adults, high-grade gliomas are notorious for its diffuse infiltrative growth as well as for its notorious resistance to different treatment strategies. Although improvements have been made by combining neurosurgery, chemotherapy, and radiotherapy, the prognosis and survival rate for glioma patients is still poor [1], and the 5-year survival rate is <5% [2]. It is therefore important to elucidate the molecular mechanisms involved in glioma progression and to develop new strategies for glioma treatment.
Over the past decade, microRNA (miRNA) expression has been a hot topic in cancer biology. MiRNAs are a class of endogenous non-coding RNAs that are 19–25 nucleotides in length. MiRNAs interact with mRNAs through complementary base-pairing with their 3′-untranslated region and thereby influence the translation or stability of the target mRNA molecule [3,4]. MiRNAs contribute to diverse biological processes and their dysregulation is linked to the progression and metastasis of human cancers [5,6]. These insights have made miRNAs targets for novel therapeutic approaches and recently several miRNA-targeted therapeutics have reached clinical development [7]. In glioma's abnormal miRNA expression can affect cell proliferation, invasion, and chemo- and radio-resistance [8,9].
The Wnt3a gene is clustered on human chromosome 1q42 and contributes to the accumulation of β-catenin, thereby activating the canonical Wnt signaling pathway, which usually contributes to cancer progression or chemoresistance [[10], [11], [12]]. The Wnt3a protein is often highly expressed in tumor tissues [13,14]. A list of studies demonstrate that elevated expression of Wnt3a is correlated with a worse clinical outcome in cancer [15,16].Wnt3a can also trigger epithelial-mesenchymal transition (EMT) phenotype, which is vital during cancer metastasis [[17], [18], [19], [20]]. Interestingly, Wnt3a expression is associated with the clinical grade and aggressiveness of gliomas [21]. However, the biological role of Wnt3a in glioma is seldom reported.
In the present study, we explored the role of miR-497 in glioma cells and investigated the underlying mechanism. We revealed that miR-497 expression was significantly down-regulated in glioma tissues and cell lines. The Wnt3a protein was identified as a down-stream target of miR-497 and mediated miR-497's function in cell growth and invasion. In addition, Wnt3a promoted c-jun expression and thereby negatively modulated miR-497 expression.
Section snippets
Sample collection
The glioma tissues (77 samples) and normal brain samples (77 samples) (formalin-fixed and embedded in paraffin) were obtained from patients of the Zhujiang Hospital. Written informed consent was obtained from all patients. All experimental protocols were approved by the Ethical Committee of Southern Medical University.
Cell culture
The glioma cell lines were maintained in our lab. Glioma cells were cultured in DMEM medium supplemented with 10% fetal bovine serum. Normal brain cells (NBC) were cultured
miR-497 expression was down-regulated in glioma tissues and cell lines
We measured the miR-497 expression in glioma tissues and normal brain tissues by the use of RT-PCR assay. It was revealed that the expression level of miR-497 was significantly down-regulated in glioma tissues when compared with that in normal brain tissues (Fig. 1A). In parallel, the expression level of miR-497 was significantly down-regulated in glioma cell lines when compared with that in normal brain cell line (NBC) (Fig. 1B). Interestingly, glioma patients with high miR-497 expression had
Discussion
MiRNAs contribute to the development and metastasis of glioma and have been suggested as novel therapeutic targets to treat glioma [26,27]. The role of miR-497 in the development of cancer has been documented. In non-small cell lung cancer, miR-497 expression is down-regulated and able to inhibit cell growth and invasion by targeting VEGF-A and YAP1 [28,29]. Similar results were found in a serious of studies, which revealed that miR-497 functioned as a tumor suppressor [[30], [31], [32], [33],
Acknowledgement
The research was funded by National Natural Science Foundation of China (81560220), Youth Science Foundation of Jiangxi Province (20151BAB215014) and Key projects of Youth Science Foundation of Jiangxi Province (20171ACB21054).
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These authors contributed equally to this work.