Ionizing radiation affects miRNA composition in both young and old mice.

Purpose: Humans are exposed to both natural (e.g. soil, cosmic rays) and human-made radiation sources (e.g. medical devices, nuclear energy production) on a daily basis. The use of medical radiation sources such as Computed Tomography (CT) scans and X-ray has increased rapidly, especially in the treatment of older populations. Micro Ribonucleic Acids (miRNAs) are the major regulators of multiple low-dose radiation-induced biological processes through post-translational inhibition. As a result, understanding age-related changes of miRNA profiles that may compromise the population after low dose radiation exposure has become increasingly important. Materials and methods: In this study, we irradiated both young (2 months) and old (26 months) C57BL/6J mice with low dose radiation (10 mGy and 100 mGy at 1 mGy/min using an open beam 60Co gamma source) and checked the miRNA expression profiles. Results: The global miRNA expression of old mice was significantly reduced compared to that of young mice. Low dose radiation at 10 mGy significantly increased the global miRNA expression in both old and young mice one week following irradiation, which suggests that 10 mGy low dose radiation may reverse the global inhibition effects of aging on miRNA expression. Higher 100 mGy radiation slightly reduced the global expression of miRNAs. We also identified several miRNAs that were elevated or reduced in all of the radiation treatment groups; these can be further explored as candidates for the radiation-induced bio-markers. Conclusions: The results of our study demonstrate that both radiation and aging can influence the global expression of miRNAs, while low dose radiation modulates the expression of miRNAs in a dose-, time-, and age-dependent manner.

Activation of Endosome-Associated Inert EGF Receptor Following Internalization.

Our current understanding of endosomal signaling is incomplete given our inability to generate endosomal signals in isolation from plasma membrane signals. We present a novel method to specifically activate epidermal growth factor (EGF) receptor (EGFR) following its internalization into endosomes. This method will allow us to address questions such as whether endosomal signaling is sufficient to activate signal transduction pathways and produce biological responses. In this method, the cells are treated with EGF in the presence of AG1478, a specific EGFR tyrosine kinase inhibitor, and monensin, which blocks recycling of EGFR. The treatment results in the internalization of nonactivated EGF-EGFR complex into endosomes. Next, the removal of AG1478 and monensin causes endosome-associated EGFR activation. Phosphorylated surface EGFR levels are undetectable during the treatment. This is a unique and novel approach to study endosomal signaling and its physiological relevance. The protocol is transferable to study endosomal signaling of other receptor tyrosine kinases.

Two-Pulse Endosomal Stimulation of Receptor Tyrosine Kinases Induces Cell Proliferation.

Signals transduced from ligand-activated receptor tyrosine kinases (RTKs) lead to a diverse array of biological outcomes, such as cell proliferation. Strict regulation of RTK activity is therefore necessary to prevent aberrancies in cell signaling that can lead to diseases such as cancer. RTKs are activated at the plasma membrane (PM) upon ligand binding. Contrary to the initial belief, RTK activity does not terminate immediately following endocytosis, instead RTKs remain active while being trafficked in endosomes. Here we describe a two-pulse endosomal stimulation approach which can specifically activate endosome-accumulated EGFR and drive cell proliferation.