P53 MUTATIONS - GAINS OR LOSSES

Although the case for p53 as a tumor suppressor gene appears very strong, one should still keep an open eye for the possibility that mutations in p53 do not necessarily imply a mere loss of "suppressor" activity. It is still possible that the presence of a p53 mutation in a tumor contributes, in a dominant positive manner, to tumorigenesis. In other words, certain p53 mutants may well be oncogenic in their own right, and carry distinct activities that promote growth deregulation and malignant progression. Elucidating this issue also has practical implications, since the nature of the resident mutations may greatly dictate the consequences of attempts to reintroduce wild-type (wt) p53 into particular types of tumor cells. There are two major obstacles along the road to meaningful answers: the limitations of the experimental systems used for evaluating the biological activities of wt and mutant p53 and a fundamental lack of knowledge about the relevant biochemistry of the p53 protein. These two aspects constitute primary experimental challenges for investigators in the field.