Partially transformed T3T3 cells express high levels of mutant p53 in the 'wild-type' immunoreactive form with defective oligomerization.

High levels of wild-type p53 suppress transformed growth of many cell lines and yet murine T3T3 cells shown partially transformed growth despite high endogenous levels of phenotypically 'wild-type' p53. On sequencing T3T3 p53 was found to encode missense mutations at codons 230 and 287 and, although endogenous T3T3 p53 is 'wild type', the protein adopted the mutant phenotype when expressed in vitro. Size fractionation of T3T3 cell lysate indicated monomeric p53 possibly in complex with a low molecular weight protein. When expressed in vitro T3T3 p53 formed dimers and higher order structures. Thus T3T3 cells appear (i) to drive endogenous mutant p53 to adopt conformational epitopes characteristic of the 'wild-type' protein, and (ii) to interfere with normal assembly of p53 quaternary structure. Phosphopeptide mapping of p53 from 3T3x cells, T3T3 cells and SV3T3 cells indicated reduced amino terminal phosphorylation of the mutant p53 phenotype. Alternative splicing of p53 was also detected in 3T3x cells; similar splicing occurs in wild-type p53 (Han & Kulesz-Martin, 1992; Nucl. Acids Res., 20, 1979-1981) and a possible regulatory function is discussed.