Function, oligomerization, and conformation of tumor-associated p53 proteins with mutated C-terminus

Mutations that affect the oligomerization domain (OD) of the p53 tumor suppressor may be of particular interest because of the remarkable contradiction between the conservation of the OD and its relative functional resistance to amino acid substitutions, and because of recent hints that cellular protein factors may interact with the OD. Both point to the possibility that this domain fulfills tasks beyond oligomerization. We report that the tumor-associated mutants 330H, 334V, and 337C are defective for homo-oligomerization by three criteria. Accordingly, 330H and 337C failed to bind to a p53 recognition motif in gel-shift assays and to stimulate reporter genes efficiently in transient transfections. 334V retained some activity in both assays despite being oligomerization-defective. The ability of the mutants to induce apoptosis correlated with their performance in the DNA binding and transactivation assays. However, mutants 330H and 337C were able to provoke cell death when overexpressed, which in combination with their failure to transactivate genes suggests competence for the induction of transactivation-independent apoptosis at high protein levels. Although 334V and 337C failed to homo-oligomerize, they were able to hetero-oligomerize with a p53 with wild-type OD, and 334V was able to interfere with transactivation by wt p53. All mutants showed a reduced reactivity with antibody PAb421 and a distinct calpain cleavage pattern indicative of conformational alterations. In conclusion, tumor-associated OD mutants of p53 can be functionally competent to different degrees despite of being oligomerization defective.