Immunohistochemical visualization of wild-type p53 protein in paraffin- embedded rat liver using tyramide amplification: zonal hepatic distribution of p53 protein after N-hydroxy-2-acetylaminofluorene administration

P53 protein plays an important role in regulation of the cell cycle. Recently, a role in tumour genesis has also been suggested. The protein is induced after various forms of DNA damage. Immunohistochemical detection of p53 protein showed positive cells in human skin after UV- irradiation, in mouse skin after benzoa]pyrene treatment and in mouse spleen, thymus and bone after gamma-irradiation. However, no staining was found in mouse and rat liver with traditional immunohistochemical staining methods due to the low amount of p53 present. This seriously hampered studies on the role of p53 in hepatocarcinogenesis. We have developed a more sensitive immunohistochemical method for staining of p53 in paraffin-embedded sections of rat liver using microwave irradiation for antigen retrieval, avidin-biotin complexing and tyramide amplification. A strong, specific fluorescence signal for p53 was found in hepatocytes of rats that had received the hepatocarcinogen N-hydroxy-2-acetylaminofluorene; in control liver no such p53 staining was observed. The fluorescence was located in the nucleus of hepatocytes in zone 1 of the liver. This agrees with the fact that N- hydroxy-2-acetylaminofluorene causes cytotoxicity in this zone.