Downregulation of miR-21 inhibits EGFR pathway and suppresses the growth of human glioblastoma cells independent of PTEN status

Abstract

MicroRNAs (miRNAs) are a class of endogenous small noncoding RNAs that regulate gene expression after transcription. Aberrant expression of miRNAs has been shown to be involved in tumorigenesis. We showed that miR-21 was one of the most frequently overexpressed miRNA in human glioblastoma (GBM) cell lines. To explore whether miR-21 can serve as a therapeutic target for glioblastoma, we downregulated miR-21 with a specific antisense oligonucleotide and found that apoptosis was induced and cell-cycle progression was inhibited in vitro in U251 (PTEN mutant) and LN229 (PTEN wildtype) GBM cells; xenograft tumors from antisense-treated U251 cells were suppressed in vivo. Antisense-miR-21-treated cells showed a decreased expression of EGFR, activated Akt, cyclin D, and Bcl-2. Although miR-21 is known to regulate PTEN and downregulation of miR-21 led to increased PTEN expression both endogenously and in a reporter gene assay, the GBM suppressor effect of antisense-miR-21 is most likely independent of PTEN regulation because U251 has mutant PTEN. Microarray analysis showed that the knockdown of miR-21 significantly altered expression of 169 genes involved in nine cell-cycle and signaling pathways. Taken together, our studies provide evidence that miR-21 may serve as a novel therapeutic target for malignant gliomas independent of PTEN status. Malignant gliomas are the most common primary brain tumors with high mortality and morbidity. The prognosis for malignant gliomas has not significantly improved in the last four decades. A recent meta-analysis of 12 randomized clinical trials showed that the overall survival rate of highgrade gliomas was 40% at 1 year after surgical removal and only slightly higher, 46%, after combined radiotherapy and chemotherapy. 1 To develop more optimized and effective treatment strategies for malignant gliomas, it is critical to gain deeper understanding of the molecular mechanisms underlying gliomagenesis and to identify targets for therapeutic intervention.The microRNAs (miRNAs) are a class of highly conserved small non-coding RNAs, approximately 22 nucleotides in length, that control gene expression through binding to the seed sequence at the 3 0 -UTR (untranslated region) of target mRNAs, resulting in translational repression or mRNA degradation. 2 This regulatory mechanism was first shown in the developmental processes in worms, flies, and plants. [3][4][5] Subsequently, miRNAs have been shown to have important roles in many physiological processes of mammalian systems by influencing cell apoptosis, proliferation, differentiation, development, and metabolism through regulation of critical signaling molecules including cytokines, growth factors, transcription factors, and pro-apoptotic and anti-apoptotic proteins. [6][7][8] Increasing number of miRNAs have been identified in the human genome and they are collectively called the miRNome. 9 Accumulating evidence shows the potential

Identification of Novel miR-21 Target Proteins in Multiple Myeloma Cells by Quantitative Proteomics

“…15,42 Recently, miR-21 was reported to upregulate STAT3 expression in a positive feedback loop. 43 miR-21 is overexpressed in all types of human cancers.…”

miRNA-182 and the regulation of the glioblastoma phenotype - toward miRNA-based precision therapeutics

“…miR-21 has oncogenic functions and promotes cell proliferation by targeting the phosphatase and tensin homolog (PTEN), sprouty RTK signaling antagonist 2 (SPRY2) tumor suppressor pathways, and by activating the nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-kB) and rat sarcoma viral oncogene (Ras)-signaling. 26,27 Further molecular analyses revealed that miR-21 promoted cell invasion by targeting the matrix metaloproteinase regulators reversion-inducing cysteine-rich protein with kazal motifs (RECK) and tissue inhibitor of metallopeptidase 3 (TIMP3), 28 and inhibited apoptosis via repression of heterogeneous nuclear ribonucleoprotein K (HNRPK) and programmed cell death 4 (PDCD4). 29 miR-10b and -26a represent additional tumor-promoting miRNAs.…”

HBx-induced miR-21 suppresses cell apoptosis in hepatocellular carcinoma by targeting interleukin-12

“…Previous studies have shown that HBx inhibits apoptosis and enhances cellular proliferation in hepatoma cells (34,35), while the mechanism is unknown. Thus, further validation by MTT assay and FCM analysis showed that the proliferation ability of the HepG2 cells was increased when HBx was overexpressed (Fig.…”