THE P53-MEDIATED G(1) CHECKPOINT IS RETAINED IN TUMORIGENIC RAT EMBRYO FIBROBLAST CLONES TRANSFORMED BY THE HUMAN PAPILLOMAVIRUS TYPE-16 E7GENE AND EJ-RAS

Rat embryo fibroblast clones transformed with the human papillomavirus type 16 E7 gene and the H-ras oncogene (ER clones) fall into two grou ps on the basis of endogenous p53 genotype, wild type or mutant, We ha ve compared these clones,vith the aim of identifying physiological dif ferences that could be attributed to p53 protein function, We show tha t all ER clones, regardless of p53 gene status, are tumorigenic and me tastatic in severe combined immunodeficiency mice, We demonstrate that only the wild-type p53 protein expressed in ER clones is functional o n the basis of its site-specific double-stranded DNA-binding activity and its ability to confer a G(1) delay on cells following treatment wi th ionizing radiation, These data indicate that disruption of the p53 growth-regulatory pathway is not a prerequisite for the malignant conv ersion of rat embryo fibroblasts expressing the E7 gene and mutant ras , Differences in phenotype that were correlated with loss of p53 prote in function included the following: serum-independent growth of ER clo nes in culture, decreased tumor doubling time in vivo, and increased r adioresistance. In addition, we demonstrate the p53-dependent G(1) che ckpoint alone does not determine radiosensitivity,