PGP and cancer: Since the expression of DNA-PKcs regulates MDR1 gene [12] and cellular c-Myc protein levels [28], which can affect TRAIL sensitivity in cancer cells as described above, we showed that knockdown of DNA-PKcs with specific siRNA led to the increased expression of DR5 and the decreased expression of c-FLIP and caused the reduction of pAkt, pGSK-3β and P-gp levels in CEM/VBL100 cells.