Disposable cell culture ware was purchased commercially (Corning Glass Works, Corning, NY; and Zellkulture Flaschen; Techno Plastic Products AG, Trasadingen, Switzerland). Cell culture medium and fetal bovine serum (FBS) were also obtained commercially (Mediatech, Inc., Herndon, VA; and Invitrogen, Long Island, NY), as were permeable supports (Transwell; Corning, Lowell, MA). Other materials, purchased commercially, were: enhanced chemiluminescence (ECL) Western blot detection system (PerkinElmer, Inc., Boston, MA); Phospho-p53 Ser15, Acetyl p53 Lys379, total-p53, cleaved active caspase-3 (Asp 175), phospho-ATM Ser1981, total-ATM, phospho-Rb Ser780, and phospho-H2AX Ser139 antibodies (Cell Signaling Technology, Inc., Beverly, MA); p21Cip1 antibodies (BD Biosciences, San Diego, CA); Nutlin-3 (Sigma, St. Louis, MO); Sirtinol, Resveratrol, MG132, and CGK733 (EMD Biosciences/Millipore Corp., Billerica, MA); p53 small interfering (si)RNA, p53 (DO-1), p53-agarose conjugate, Mdm2 (SMP14), total-Rb, and Nucleolin specific antibodies (Santa Cruz Biotechnology, Santa Cruz, CA); Mdm4 antibody (Millipore Corp., Billerica, MA); Zonula Occludens (ZO-1) and beta-catenin antibodies (Zymed Laboratories Inc., South San Francisco, CA); Alexa-Fluor 488 conjugated and Cy3 conjugated secondary antibodies (Molecular Probes, Eugene, OR); cell death detection ELISA Plus kit (Roche Diagnostics Corp., Indianapolis, IN); mounting medium with 4′,6-diamidino-2-phenylindole (DAPI; Vector Laboratories, Burlingame, CA). All chemicals were of the highest purity commercially available.