Imiquimod activates p53-dependent apoptosis in a human basal cell carcinoma cell line.
BACKGROUND
The tumor suppressor p53 controls DNA repair, cell cycle, apoptosis, autophagy and numerous other cellular processes. Imiquimod (IMQ), a synthetic toll-like receptor (TLR) 7 ligand for the treatment of superficial basal cell carcinoma (BCC), eliminates cancer cells by activating cell-mediated immunity and directly inducing apoptosis and autophagy in cancer cells.


OBJECTIVE
To evaluate the role of p53 in IMQ-induced cell death in skin cancer cells.


METHODS
The expression, phosphorylation and subcellular localization of p53 were detected by real-time PCR, luciferase reporter assay, cycloheximide chase analysis, immunoblotting and immunocytochemistry. Using BCC/KMC1 cell line as a model, the upstream signaling of p53 activation was dissected by over-expression of TLR7/8, the addition of ROS scavenger, ATM/ATR inhibitors and pan-caspase inhibitor. The role of p53 in IMQ-induced apoptosis and autophagy was assessed by genetically silencing p53 and evaluated by a DNA content assay, immunoblotting, LC3 puncta detection and acridine orange staining.


RESULTS
IMQ induced p53 mRNA expression and protein accumulation, increased Ser15 phosphorylation, promoted nuclear translocation and up-regulated its target genes in skin cancer cells in a TLR7/8-independent manner. In BCC/KMC1 cells, the induction of p53 by IMQ was achieved through increased ROS production to stimulate the ATM/ATR-Chk1/Chk2 axis but was not mediated by inducing DNA damage. The pharmacological inhibition of ATM/ATR significantly suppressed IMQ-induced p53 activation and apoptosis. Silencing of p53 significantly decreased the IMQ-induced caspase cascade activation and apoptosis but enhanced autophagy. Mutant p53 skin cancer cell lines were more resistant to IMQ-induced apoptosis than wildtype p53 skin cancer cell lines.


CONCLUSION
IMQ induced ROS production to stimulate ATM/ATR pathways and contributed to p53-dependent apoptosis in a skin basal cell carcinoma cell line BCC/KMC1.
['Huang|Shi-Wei|SW|', 'Chang|Shu-Hao|SH|', 'Mu|Szu-Wei|SW|', 'Jiang|Hsin-Yi|HY|', 'Wang|Sin-Ting|ST|', 'Kao|Jun-Kai|JK|', 'Huang|Jau-Ling|JL|', 'Wu|Chun-Ying|CY|', 'Chen|Yi-Ju|YJ|', 'Shieh|Jeng-Jer|JJ|']
D021581:Active Transport, Cell Nucleus D000634:Aminoquinolines D000970:Antineoplastic Agents D017209:Apoptosis D064007:Ataxia Telangiectasia Mutated Proteins D001343:Autophagy D002280:Carcinoma, Basal Cell D045744:Cell Line, Tumor D004305:Dose-Response Relationship, Drug D015972:Gene Expression Regulation, Neoplastic D006801:Humans D000077271:Imiquimod D009154:Mutation D010766:Phosphorylation D034622:RNA Interference D017382:Reactive Oxygen Species D015398:Signal Transduction D012878:Skin Neoplasms D013997:Time Factors D014162:Transfection D016159:Tumor Suppressor Protein p53
Imiquimod Apoptosis p53 Autophagy