Ionizing radiation-inducible miR-494 promotes glioma cell invasion through EGFR stabilization by targeting p190B rhoGAP.

MicroRNAs (miRNAs) play an important role in various stages of tumor progression. miR-494, which we had previously identified as a miRNA induced by ionizing radiation (IR) in the glioma cell line U-251, was observed to enhance invasion of U-251 cells by activating MMP-2. The miR-494-induced invasive potential was accompanied by, and dependent on, epidermal growth factor receptor (EGFR) upregulation and the activation of its downstream signaling constituents, Akt and ERK. The upregulation of EGFR by miR-494 involved the suppression of lysosomal protein turnover. Among the putative target proteins tested, p190B RhoGAP (p190B) was downregulated by miR-494, and its reduced expression was responsible for the increase in EGFR expression. A reporter assay using a luciferase construct containing p190B 3'-untranslated region (3'UTR) confirmed that p190B is a direct target of miR-494. Downregulation of p190B by small interfering RNA (siRNA) transfection closely mimicked the outcomes of miR-494 transfection, and showed increased EGFR expression, MMP-2 secretion, and invasion. Ectopic expression of p190B suppressed the miR-494-induced EGFR upregulation and invasion promotion, thereby suggesting that p190B depletion is critical for the invasion-promoting action of miR-494. Collectively, our results suggest a novel function for miR-494 and its potential application as a target to control invasiveness in cancer therapy.

Mercury accumulation in hydrothermal vent mollusks from the southern Tonga Arc, southwestern Pacific Ocean.

We provide the mercury (Hg) and monomethylmercury (MMHg) levels of the plume water, sulfide ore, sediment, and mollusks located at the hydrothermal vent fields of the southern Tonga Arc, where active volcanism and intense seismic activity occur frequently. Our objectives were: (1) to address the potential release of Hg from hydrothermal fluids and (2) to examine the distribution of Hg and MMHg levels in hydrothermal mollusks (mussels and snails) harboring chemotrophic bacteria. While high concentrations of Hg in the sediment and Hg, As, and Sb in the sulfide ore indicates that their source is likely hydrothermal fluids, the MMHg concentration in the sediment was orders of magnitude lower than the Hg (<0.001%). It suggests that Hg methylation may have not been favorable in the vent field sediment. In addition, Hg concentrations in the mollusks were much higher (10-100 times) than in other hydrothermal vent environments, indicating that organisms located at the Tonga Arc are exposed to exceedingly high Hg levels. While Hg concentration was higher in the gills and digestive glands than in the mantles and residues of snails and mussels, the MMHg concentrations in the gills and digestive glands were orders of magnitude lower (0.004-0.04%) than Hg concentrations. In summary, our results suggest that the release of Hg from the hydrothermal vent fields of the Tonga Arc and subsequent bioaccumulation are substantial, but not for MMHg.

Phosphorylation and stabilization of c-Myc by NEMO renders cells resistant to ionizing radiation through up-regulation of γ-GCS.

The transcription factor c-Myc has been previously shown to be phosphorylated and stabilized by NEMO through direct interaction in the nucleus. Here, we show that NEMO induces up-regulation of the c-Myc target protein, γ-glutamyl-cysteine synthetase (γ-GCS), leading to an increase of intracellular glutathione (GSH) levels and simultaneous enhancement of redox-controlling capacity. NEMO enhanced c-Myc recruitment to γ-GCS promoters and c-Myc was essential for NEMO-mediated γ-GCS up-regulation. The phosphorylation and stabilization of c-Myc by NEMO rendered cells more resistant to ionizing radiation (IR). Thus, the interaction between NEMO and c-Myc may be targeted for the development of strategies to overcome the resistance to radiotherapy.

NEMO stabilizes c-Myc through direct interaction in the nucleus.

The transcription factor c-Myc is a cellular oncoprotein generally upregulated in most of human cancers. NF-κB essential modulator (NEMO) caused phosphorylation and stabilization of c-Myc protein in the nucleus through direct interaction. The interaction caused reduced ubiquitination of c-Myc by inhibiting ubiquitinating activity of Fbw7 without blocking the interaction between c-Myc and Fbw7. As a consequence, NEMO enhanced the expression of several selected c-Myc targets. Compared to the classical role as an essential subunit for the activity of IKK complex, stabilization of c-Myc by direct interaction is a unique function of NEMO, representing a new mechanism to regulate c-Myc activity.