Ras mutation promotes p53 activation and apoptosis of skin keratinocytes

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Research

Background:

• Previous studies showed 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate (DMBA/TPA) induces apoptosis and p53 mitochondrial translocation in mouse skin carcinogenesis.
• Oncogenic Ras mutations are early events critical in skin carcinogenesis.

Purpose of the Study:

• To investigate the role of Ras mutation and NADPH oxidase (NOX) in p53 activation and apoptosis during chemical-induced skin carcinogenesis.
• To elucidate the signaling pathway bridging oncogenic activation to cell death.

Main Methods:

• Utilized a H-ras mutated malignant skin keratinocyte cell line (308) and its non-malignant counterpart (C50).
• Inhibited NADPH oxidase (NOX) using diphenyleneiodonium (DPI) and employed small interfering RNA (siRNA) for Rac1.
• Applied DPI to DMBA-initiated mouse skin tissue.

Main Results:

• Ras-mutated 308 cells exhibited elevated p53, increased caspase 3 activity, and enhanced apoptosis after TPA treatment compared to C50 cells.
• NOX inhibition by DPI suppressed p53 activation and apoptosis in 308 cells.
• siRNA to Rac1 also inhibited p53 activation post-TPA treatment.
• DPI application to skin tissue blocked TPA-mediated p53 increase and reduced apoptosis.

Conclusions:

• Ras mutation is linked to NOX-induced p53 activation in skin carcinogenesis.
• NOX acts as a mediator bridging oncogenic Ras activation to p53 mitochondrial translocation and apoptosis.
• This pathway is a key component of multistage chemical-induced skin carcinogenesis.