Background: microRNAs (miRNAs) are non-coding RNAs that alter the stability and translation efficiency of messenger RNAs. Ionizing radiation (IR) induces rapid and selective changes in miRNA expression. Depletion of the miRNA processing enzymes Dicer or Ago2 reduces the capacity of cells to survive radiation exposure. Elucidation of critical radiation-regulated miRNAs and their target proteins offers a promising approach to identify new targets to increase the therapeutic effectiveness of the radiation treatment of cancer.
Principal findings: Expression of miR-525-3p is rapidly up-regulated in response to radiation. Manipulation of miR-525-3p expression in irradiated cells confirmed that this miRNA mediates the radiosensitivity of a variety of non-transformed (RPE, HUVEC) and tumor-derived cell lines (HeLa, U2-Os, EA.hy926) cell lines. Thus, anti-miR-525-3p mediated inhibition of the increase in miR-525-3p elevated radiosensitivity, while overexpression of precursor miR-525-3p conferred radioresistance. Using a proteomic approach we identified 21 radiation-regulated proteins, of which 14 were found to be candidate targets for miR-525-3p-mediated repression. Luciferase reporter assays confirmed that nine of these were indeed direct targets of miR-525-3p repression. Individual analysis of these direct targets by RNAi-mediated knockdown established that ARRB1, TXN1 and HSPA9 are essential miR-525-3p-dependent regulators of radiation sensitivity.
Conclusion: The transient up-regulation of miR-525-3p, and the resultant repression of its direct targets ARRB1, TXN1 and HSPA9, is required for cell survival following irradiation. The conserved function of miR-525-3p across several cell types makes this microRNA pathway a promising target for modifying the efficacy of radiotherapy.