Study of p53 Gain of Function Mutations in p53-null Astrocytes

A number of recent studies suggest that expression of mutant p53 with mutations in certain codons show a gain of function and some of the characteristics of an oncoprotein. In order to study gain of function mutation and eliminate the potential of a dominant negative interaction with endogenous wild type p53 protein, p53 knockout mouse astrocytes were used. A retrovirus system was used to introduce mutant p53 genes into these p53-null astrocytes. Immunohistochemical staining and western blot experiments showed the expression of mutant p53 protein in these cells after infection with the mutant p53 retroviruses. Cell growth experiment did not suggest growth advantages for mutant p53 expressing astrocytes over vector control cells. Data from clonogenic survival assays following exposure to etoposide or cisplatin suggested that mutant p53 expressing cells with a point mutation at codon 273 may be resistant to apoptosis induced by etoposide. In contrast, p53 with a point mutation at codon 248 may sensitize cells to the apoptotic effects of etoposide and cisplatin