Ionizing radiation (IR) activates cell-cycle regulatory proteins in lung cancer tumour xenographts. ( A) Tumour tissue extracted from Control and IR–treated animals were subjected to immunoblotting analysis using p53, P-p53 (Ser15), p27kip, and p21waf/cip antibodies. Anti-actin immunoblotting was used as a loading control. A representative immunoblot from 6 independent experiments is shown. (B) Immunoblot densitometric values are shown as percent change in protein expression relative to the control group (*p < 0.05; **p < 0.001).