Specific interaction between a subset of the p53 protein family and heat shock proteins hsp72/hsc73 in a human osteosarcoma cell line. We report here immunological evidence for the specific association between p53 and hsp72/hsc73 heat shock proteins in a human cell line derived from an osteosarcoma. The same association between p53 and hsp72/hsc73 was observed in HOS-TE85 clone 5 from which the HOS-SL cell line was derived. This association was indicated by the co-immunoprecipitation from HOS-SL of both p53 and hsp72/hsc73 proteins observed with either an anti-p53 monoclonal antibody (PAb421) or an antiserum specifically reacting with hsp72/hsc73 heat shock proteins. Furthermore, Western blot analysis allowed us to show that hsp72/hsc73 proteins did not share an epitope with p53, confirming that the co-immunoprecipitation of p53 and hsp72/hsc73 was attributable to the physical association of the proteins. Data obtained from SDS-PAGE show that the HOS-SL cells expressed two forms of p53 with distinct molecular weights. Both forms contained several species with different isoelectric points ranging between pH 6.0 and 6.5. The data obtained from both 1D and 2D gel analyses consistently show that the p53 proteins involved in the association with hsp72/hsc73 were mainly the species that migrated with the slower mobility in the SDS dimension. The possibility is discussed that the HOS-SL p53 variant forming a complex with hsp72/hsc73 contains an activating mutation for transformation.