miR-9 and let-7g enhance the sensitivity to ionizing radiation by suppression of $NF{\kappa}B1

The activation of nuclear factor-kappa B1 ($NF{\kappa}B1$) in cancer cells may confer resistance to ionizing radiation (IR). To enhance the therapeutic efficiency of IR in lung cancer, we screened for microRNAs (miRNAs) that suppress $NF{\kappa}B1$ and observed their effects on radiosensitivity in a human lung cancer cell line. From time series data of miRNA expression in ${\gamma}$-irradiated H1299 human lung cancer cells, we found that the expression of miR-9 was inversely correlated with that of $NF{\kappa}B1$. Overexpression of miR-9 down-regulated the level of $NF{\kappa}B1$ in H1299 cells, and the surviving fraction of ${\gamma}$-irradiated cells was decreased. Interestingly, let-7g also suppressed the expression of $NF{\kappa}B1$, although there was no canonical target site for let-7g in the $NF{\kappa}B1$ 3' untranslated region. From these results, we conclude that the expression of miR-9 and let-7g could enhance the efficiency of radiotherapy for lung cancer treatment through the inhibition of $NF{\kappa}B1$.