P53 GENE DOSAGE MODIFIES GROWTH AND MALIGNANT PROGRESSION OF KERATINOCYTES EXPRESSING THE V-RAS(HA) ONCOGENE

Epidermal keratinocyte cultures were established from newborn mice exp ressing a null mutation in the p53 gene to explore the contribution of p53 to epidermal growth regulation and neoplasia. Keratinocytes were initiated by transduction with a replication-defective retrovirus enco ding the v-ras(Ha) oncogene and grafted onto nude mouse hosts. Tumors arising from keratinocytes heterozygous or null for functional p53 in the presence of v-ras(Ha) have growth rates approximately 5-fold highe r than those derived from p53(+/+) controls and rapidly form carcinoma s, in contrast to the benign phenotype observed in p53(+/+)/v-ras(Ha) grafts. In vitro, p53-deficient keratinocytes with and without v-ras(H a) expression display decreased responsiveness to the negative growth regulators transforming growth factors beta(1) and beta(2). In combina tion with v-ras(Ha), p53-deficient keratinocytes also exhibit decrease d responsiveness to elevated Ca2+. These differences between genotypes cannot be attributed to changes in transforming growth factor beta re ceptor types present or altered levels of epidermal growth factor rece ptor and are independent of c-myc transcript levels. mRNA expression f or the p-53 inducible protein WAF1 correlates with p53 gene dosage, bu t low levels are still detectable in p53(-/-) keratinocytes. The alter ed responsiveness of p53 deficient keratinocytes to negative growth re gulators may provide a growth advantage to such cells in vivo and rend er them more susceptible to genetic alterations and malignant conversi on.