The effect of miR-375 on MYCN IRES activity and MYCN expression in the presence of IR. A, co-transfection of SK-N-SH cells with 5 μg MYCN IRES (pRL-100-FL) plasmid and either increasing concentrations (50, 100 and 200 nM) of miR-375 alone or in the presence of 4 Gy IR. MYCN IRES-transfected cells alone treated with increasing doses (2, 4 and 6 Gy) of IR served as control. Data represent the mean (±SD) of luciferase activity of FL versus RL in three independent experiments, *p<0.01. B, NB-1643 and MYCN-transfected SH-Tet/21N cells were treated with increasing amounts (50, 100 and 200 nM) of miR-375 in the absence or presence of an increasing dose (2, 4 and 6 Gy) of IR, with controls being untreated cells and cells treated with 6 Gy only. Detection of MYCN expression in NB-1643 (native) and in SHEP-Tet/21N (ectopic) shown by Western blot.