p53 from complexity to simplicity: mutant p53 stabilization, gain-of-function, and dominant-negative effect

Increasing the complexity of their models, p53s are stabilized either in order to function (wt p53) or due to the loss of function (mutant p53) with acquiring a mysterious prion-like ability to drive the normal p53 into the abnormal conformation to gain new functions. As already recognized, the loss of trans-activating function leads to a stabilization of mutant p53 because of the disappearance of the p53-inducible proteins, which otherwise directly (Mdm-2) or indirectly (p21) target p53 for degradation. Simplifying further, I will discuss that the loss of function results in a dominant-negative effect and gain-of-function (a dominant-positive effect). Thus, mutant p53 lacking trans-activation function nevertheless may retain the ability to repress transcription due to its competition with numerous transcription factors for their coactivators. When mutant p53 competes with wt p53, the inhibition of the wt p53-dependent transcription is perceived as a dominant-negative effect. Just like trans-repression, a dominant-negative effect requires an excess of p53 and, therefore, a 'dominant'-negative effect is not dominant. Furthermore, the stabilization of an endogenous mt p53 due to the loss of wt functions cannot occur in the presence of the wt p53 allele. Given the inability of mutant p53 to accumulate in the presence of wt p53, a dominant-negative effect does not naturally occur and, not surprisingly, heterozygous mt/wt cells are rare. The detection of a dominant-negative effect simply indicates that mutant p53 indeed has lost its function. Last, since mutant p53 loses some or most but not all activities and accumulates in the absence of wt allele, gain-of-function can be considered as an exaggeration of the remaining functions. Applications to cancer therapy are discussed.