All proteins were extracted with RIPA lysis buffer and protein concentrations were determined using the BCA assay (Pierce, Rockford, IL, USA). For mouse skin, the tissue was homogenized in liquid nitrogen and then lysed in RIPA lysis buffer. Equal amounts of protein were subjected to electrophoresis. Western blotting was performed as described previously (32 (link), 33 (link)). Antibodies used included COX-2, AKT, p53, p21, Chk1, Chk2, XPC, DDB1, DDB2, γH2AX, β-actin, GAPDH (Santa Cruz), SIRT6, p-AKT (serine 473), Cleaved-caspase3, p-AMPK, p-Chk1, p-Chk2 (Cell Signal), acetylated k382 p53 (ac-p53,Abcam), and ac-H3K9 (Sigma).