Phosphorylation of Mxi1 at Ser160 by S6K1 promotes Myc activation and cell radioresistance in lung cancer. A. A549 and H1299 cells stably expressing empty vector (EV), wild-type Mxi1, or Mxi1 S160A mutant were collected and analyzed by Western blotting using indicated antibodies (n=4). The ratio shows relative Mxi1 protein expression normalized for GAPDH (control, set at 1). B. The mRNA levels of the indicated genes were analyzed by Real time-PCR in A549 and H1299 cells stably expressing wild-type or mutant Mxi1. * P < 0.05, ** P < 0.01, *** P <0.001 (n=4). C. A549 and H1299 cells stably expressing wild-type or mutant Mxi1 were seeded and cultured for two weeks. The colonies were stained by crystal violet and then counted. Representative pictures are shown. * P < 0.05, ** P < 0.01, *** P <0.001 (n=3). D. A549 and H1299 cells stably expressing wild-type or mutant Mxi1 were irradiated with indicated doses. After two weeks, the colonies contained more than 50 cells were counted. ** P < 0.01, *** P <0.001 (n=3).