Brief communication, P53 accumulation in N-methyl-N-nitrosourea-induced rat mammary tumors.

P53 aberrant protein expression and mutation is a component of many human tumors but less information is available regarding involvement in relevant animal models. We have examined invasive mammary epithelial neoplasms for p53 aberrant protein expression from Sprague-Dawley rats induced by two intrajugular injections of N-methyl-N-nitrosourea (NMU, 50 mg/kg), 7 days apart, beginning at 44-49 days of age. Positive nuclear staining was observed in 8/10 mammary tumor frozen sections using PAb 421, a mouse monoclonal antibody, compared to a mixed mouse IgG negative control antibody. Paraffin sections from two additional sets of similarly induced rat mammary tumors also showed positive nuclear staining (22/37 tumors) with CM-5, a rabbit polyclonal antibody. Our results indicate that elevated cellular content of p53 is a common event in invasive palpable mammary tumors induced by NMU in this dual-injection model system.