Abstract 3973: MiR-21 modulates hTERT through a STAT3-dependent manner on glioblastoma cell growth

MiRNAs, are small noncoding RNA molecules of approximately 20-22 nucleotides in length, regulate protein expression by cleaving or repressing the translation of targets mRNA. MiR-21, as an oncogene, has been reported to be dyregulated in a variety of cancer. Our recent data have verified that miR-21 is one of the most frequently over-expressed miRNA in human glioblastoma (GBM) cell lines. However, the mechanism of miR-21 involved in gliomagenesis is still unknown. In this study, reduction of miR-21 by antisense oligonucleotide induced cell apoptosis and inhibited cell growth in U87 and LN229 GBM cells, with a decreased expression of human telomerase reverse transcriptase (hTERT). Knockdown of hTERT expression using lentiviral vector mediated delivery of hTERT-siRNA triggered cell apoptosis and cell cycle G1/G0 arrest in U87 and LN229 cells. In order to explore the molecular regulation of hTERT by miR-21, we found that STAT3 could be an important mediator between miR-21 and hTERT. Reduction of miR-21 repressed STAT3 expression and STAT3 phosphorylation. STAT3 inhibitor WP1066 led to a remarkable depletion of hTERT both at mRNA and protein levels. To determine the functional interaction between STAT3 and hTERT, ChIP showed the presence of STAT3-binding sites in the hTERT gene. Luciferase reporter assay revealed that the hTERT gene promoter was direct bound by STAT3. Furthermore, we evaluated the status of STAT3 in hTERT regulation by miR-21. U87 and LN229 cells that treated with miR-21 antisense oligonucleotide and IL-6 which could elevate the expression of STAT3 showed a significant increase of hTERT expression, whereas cells that treated with miR-21 oligonucleotide and STAT3 inhibitor WP1066 displayed a reduction of hTERT expression. Finally, knockdown of miR-21 considerably inhibited tumor growth and diminished the expression of STAT3, pSTAT3 and hTERT in xenograft model. Taken together, we have demonstrated that miR-21 inhibits cell growth through regulating hTERT expression in a STAT3-dependent pathway in GBM cells. These results suggest that modulation of the mechanism responsible for miR-21 in GBM could be used as a therapeutic strategy for GBM treatment and warrants further investigation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3973. doi:10.1158/1538-7445.AM2011-3973