STATUS OF THE MDM-2 AND WAF-1 GENES IN MOUSE EPIDERMAL JB6 VARIANTS HARBORING WILD-TYPE P53 - A P53-INDEPENDENT INDUCTION OF WAF-1

Mutational inactivation of the p53 tumor suppressor gene has been foun d not to be involved in preneoplastic-to-neoplastic progression in mou se JB6 variants. To examine the role of an inactivated p53 pathway in this tumor promotion/progression model, we have studied the possible a lteration of the MDM-2 oncogene, a gene whose product binds to and ina ctivates p53, and WAF-1 tumor suppressor gene, a gene transcriptionall y controlled by p53 that mediates p53 tumor suppression. Alteration of either of these two genes might mimic p53 inactivation in cells expre ssing wild-type p53. Northern analysis revealed that MDM-2 expression was, in general, upregulated in neoplastic JB6 cells as compared with preneoplastic cells. This higher expression was not due to the gene am plification. Mutational analysis of WAF-1 revealed a) no point mutatio n in neoplastic cells; b) two polymorphic sites; and c) three nucleoti de disagreements with the published sequence. Expression of the WAF-1 gene was also found to be, in general, higher in neoplastic cells, and induced by TPA and/or TNF-alpha in a p53-independent manner. The over all induced level of WAF-1 mRNA was higher in apoptosis sensitive cell s after TPA/TNF-alpha treatment, suggesting a role of WAF-1 in mediati ng apoptosis. We conclude from this study that a) there is no evidence for mutational inactivation of WAF-1 that might mimic p53 inactivatio n in the JB6 model; b) elevated expression of MDM-2 and/or WAF-1 might be involved in neoplastic progression; and c) there is a p53-independ ent pathway controlling WAF-1 expression which may mediate p53-indepen dent apoptosis.