The growth suppressor protein p53 is abnormally expressed in a variety of different human tumor cells. We have analyzed the expression of p53 in cell cultures derived from tissues of radical prostatectomies and in the permanent prostate carcinoma cell line PC-3 using two different p53 specific monoclonal antibodies. With the wild-type specific monoclonal antibody PAb1620 we found p53 localized in nucleoli whereas only a few cells were positively stained in the nucleus with the mutant specific monoclonal antibody PAb240. Control experiments with p53 from SV80 cells which express wild-type p53 and HT29 cells expressing mutant p53 documented the specificity of the monoclonal antibodies. The specificity of the antibodies in recognizing indeed p53 was demonstrated further by immunoprecipitation analysis of p53 from the same cell cultures. Since p53 is usually localized to the nucleus our results may represent a specific feature of the wild-type phenotype of p53 in prostate carcinoma cells. The localization of p53 in nucleoli may be another mechanism of the inactivation of wild-type p53.

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