Background: Nuclear accumulation of p53 protein in breast cancer cells is generally accepted as a marker for the presence of p53 gene mutation and as an indicator of poor prognosis. Mutation in the p53 gene has been shown to cause conformational change in the p53 protein, which gives rise to a complex with heat shock protein 70 (hsp70).
Experimental design: To clarify whether the p53 protein that accumulates in the nuclei of human cancer cells is bound to hsp70 in vivo, we compared the immunohistochemical localization of both p53 and hsp70 in 65 surgically resected cases of primary breast cancer. In four cases showing both nuclear accumulation of p53 protein and mutation of the p53 gene, identified by single-strand conformation polymorphism and direct sequence analysis, the presence of the p53-hsp70 complex was examined by coimmunoprecipitation assay. In 12 human cancer cell lines showing nuclear accumulation of the p53 protein, the presence of the p53-hsp70 complex was also examined by immunoprecipitation with two anti-p53 Ab after labeling with [35S]methionine.
Results: Among the 65 cases, p53 and hsp70 immunoreaction in cancer cell nuclei was detected immunohistochemically in 16 (25%) and 23 (35%) cases, respectively. The localizations of the two proteins were significantly correlated, but there was a discrepancy in the localization patterns in 23 cases. Although the p53-hsp70 complex was detected in all of the four cases in which the p53 mutation was identified, the expression levels of hsp70 detected by coimmunoprecipitation assay were much weaker than those of p53 protein. In all of the 12 cancer cell lines with nuclear accumulation of p53, no distinct 70-kDa bands were immunoprecipitated with the p53 protein.
Conclusions: In human breast cancer tissue, only part of the pool of p53 is bound to hsp70.