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Bromodomain containing 7 (BRD7) was identified as a nuclear transcriptional regulatory factor. BRD7 functions as a tumor suppressor in multiple cancers, including nasopharyngeal carcinoma (NPC). In this study, we reported a novel mechanism of BRD7 in NPC progression. We demonstrated that the expression of miR-141 was remarkably increased in NPC tissues and was negatively correlated with the expression of BRD7 and the survival rate of NPC patients. Decreased expression levels of miR-141, including the primary, the precursor and the mature forms of miR-141, were found in BRD7-overexpressing HEK293, 5-8F and HNE1 cells compared the control cells, while there was no obvious effect on the expression levels of the two critical enzymes Drosha and Dicer. BRD7 can negatively regulate the promoter activity of miR-141, while no obvious binding site of BRD7 was found in the potential promoter region of miR-141. Moreover, ectopic expression of miR-141 can significantly promote cell proliferation and inhibit apoptosis in NPC, and rescuing the expression of miR-141 in BRD7-overexpressing NPC cells could partially reverse the tumor suppressive effect of BRD7 on cell proliferation and tumor growth in vitro and in vivo. Furthermore, the activation of the PTEN/AKT pathway mediated by the overexpression of BRD7 could be inhibited by rescuing the expression of miR-141, which accordingly results in the partial restoration of cell proliferation and tumor growth. Our findings demonstrate that the BRD7/miR-141/PTEN/AKT axis has critical roles in the progression of NPC and provide some promising targets for the diagnosis and treatment of NPC.
BACKGROUND:
MicroRNAs (miRNAs) are frequently dysregulated in human cancers and can act as either potent oncogenes or tumor suppressor genes. In the present study, we intend to prove that the gene PTEN (phosphatase and tensin homolog deleted on chromosome ten) is a target gene of miR-205 and to investigate the suppressive effects on PTEN transcriptional activity by enhancing miR-205 expression in endometrial cancer Ishikawa cells.
METHODS:
Using Ishikawa cells as model systems, we up-regulated miR-205 expression by transient transfection with miR-205 mimics. A luciferase reporter assay, qRT-PCR and western blotting assays were used to verify whether PTEN is a direct target of miR-205. Meanwhile, the modulatory role of miR-205 in the AKT (protein kinase B) pathway was evaluated by determining the AKT phosphorylation. As a biological counterpart, we investigated cell apoptosis using flow cytometry.
RESULTS:
Our data indicate that miR-205 down-regulates the expression of PTEN through direct interaction with the putative binding site in the 3'-untranslated region (3'-UTR) of PTEN. Moreover, we documented the functional interactions of miR-205 and PTEN, which have a downstream effect on the regulation of the AKT pathway, explaining, at least in part, the inhibitory effects on Ishikawa cell apoptosis of enhancing miR-205 expression.
CONCLUSIONS:
For the first time, we demonstrate that the expression of PTEN is directly regulated by miR-205 in endometrial cancer cells and leads the inhibition of cellular apoptosis. This relationship could be targeted for new therapeutic strategies for endometrial cancer.
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