All-trans retinoic acid (ATRA), a derivative of retinoid, is involved in the onset of differentiation and apoptosis in a wide variety of normal and cancer cells. MicroRNAs (miRNAs) are small non-coding RNAs that control gene expression. Several miRNAs were identified to participate in ATRA-mediated cell differentiation. However, no studies have demonstrated whether miRNA can enhance ATRA cytotoxicity, thereby resulting in cell apoptosis. This study investigated the effects of ATRA-mediated miRNA expression in activating apoptotic pathways in glioblastoma. First, we found that high-dose ATRA treatment significantly reduced cell viability, caspase-dependent apoptosis, endoplasmic reticular (ER) stress activation, and intracellular reactive oxygen species accumulation. From microarray data, miR-302b was analyzed as a putative downstream regulator upon ATRA treatment. Furthermore, we found that ATRA up-regulated miR-302b expression in a dose- and time-dependent manner through retinoic acid receptor α-mediated pathway. Overexpression and knockdown of miR-302b significantly influenced ATRA-mediated cytotoxicity. E2F3, an important transcriptional regulator of glioma proliferation, was validated to be a direct target gene of miR-302b. The miR-302b-reduced E2F3 levels were also identified to be associated with ATRA-mediated glioma cell death. These results emphasize that an ATRA-mediated miR-302b network may provide novel therapeutic strategies for glioblastoma therapy.
We propose that high-dose all-trans retinoic acid (ATRA) treatment, a derivative of retinoid, significantly induces glioblastoma cell apoptosis via caspase-dependent apoptosis, endoplasmic reticular (ER) stress, and intracellular reactive oxygen species (ROS) accumulation. The miR-302b overexpression enhanced by ATRA-mediated retinoic acid receptor (RAR)α pathway was also identified. The E2F3 repression, a novel target gene of miR-302b, was involved in ATRA-induced glioblastoma cell cytotoxicity.