MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate gene expression at the transcriptional and post-transcriptional levels. Here we show that miR-30e, which was previously identified as an ionizing radiation-inducible miRNA, enhances cellular invasion by promoting secretion of the matrix metalloproteinase MMP-2. The enhancement of cellular invasion by miR-30e involved up-regulation of the epidermal growth factor receptor (EGFR) and subsequent activation of its downstream signaling mediators, AKT and extracellular signal-regulated kinase. EGFR up-regulation by miR-30e occurred due to stabilization of the EGFR protein. The E3 ubiquitin ligase casitas B-lineage lymphoma B (CBL-B) was down-regulated by miR-30e, and this led to increased EGFR abundance. A 3 0 UTR reporter assay confirmed that CBL-B is a direct target of miR-30e. Knocking down CBL-B expression phenocopied the effects of miR-30e, whereas ectopic expression of CBL-B suppressed miR-30e-induced EGFR up-regulation and invasion. Collectively, our results suggest that targeting miR-30e may limit the invasiveness induced during glioma radiotherapy.

In response to genotoxic stress, the tumor suppressor protein p73 induces apoptosis and cell cycle arrest. Despite extensive studies on p73-mediated apoptosis, little is known about the cytoplasmic apoptotic function of p73. Here, using H1299 lung cancer cells and diverse biochemical approaches, including colony formation, DNA fragmentation, GST pulldown, and apoptosis assays along with NMR spectroscopy, we show that p73 induces transcription-independent apoptosis via its transactivation domain (TAD) through a mitochondrial pathway and that this apoptosis is mediated by the interaction between p73-TAD and the anti-apoptotic protein B-cell lymphoma-extra large (Bcl-X L or BCL2L1). This binding disrupted an interaction between Bcl-X L and the pro-apoptotic protein BH3-interacting domain death agonist (Bid). In particular, we found that a 16-mer p73-TAD peptide motif (p73-TAD16) mediates transcription-independent apoptosis, accompanied by cytochrome c release from the mitochondria, by interacting with Bcl-X L. Interestingly, the structure of the Bcl-X L-p73-TAD16 peptide complex revealed a novel mechanism of Bcl-X L recognition by p73-TAD. We observed that the ␣-helical p73-TAD16 peptide binds to a noncanonical site in Bcl-X L , comprising the BH1, BH2, and BH3 domains in an orientation opposite to those of pro-apoptotic BH3 peptides. Taken together, our results indicate that the cytoplasmic apoptotic function of p73 is mediated through a noncanonical mode of Bcl-X L recognition. This finding sheds light on a critical transcription-independent, p73-mediated mechanism for apoptosis induction, which has potential implications for anticancer therapy.