DNA-PKcs regulates c-Myc stability. (A) Silencing DNA-PKcs promoted c-Myc destruction. Cells were treated with cycloheximide for the given times to inhibit novel protein synthesis, then the cell extracts were prepared, followed by immunoblotting analysis of c-Myc. (B) Quantification of c-Myc destruction following CHX treatment based on densitometrical scanning of the immunohybridization signals of c-Myc protein shown in panel A. The data are the means with standard deviation from three independent experiments. (C) Silencing DNA-PKcs promoted ubiquitination of c-Myc. CoIP product (IP) of c-Myc was detected by immunoblotting (IB) with anti-ubquitin antibody (upper panel), while 1/2 the amount of c-Myc immunoprecipitates were subjected to immunoblotting analysis with c-Myc antibody as a control (lower panel).