Induction of invasive mouse skin carcinomas in transgenic mice with mutations in both H-ras and p53

Synergistic interaction between H-ras and p53 were systematically examined during skin tumorigenesis. Concurrent expression of an activated H-ras gene and a mutant p53 gene was accomplished by crossing p53^Val135/wt mice with TG·AC mice. Topical application to wild-type mice with benzo(a)pyrene (BaP) alone produced ∼26% skin tumor incidence, whereas BaP treatment of p53^wt/wtHras^TG·AC/wt, p53 ^Val135/wtHras^wt/wt, and p53^Val135/wtHras ^TG·AC/wt mice produced a 75%, 77%, and 100% incidence of skin tumors, respectively. An average of 0.33 tumor per mouse was observed in wild-type (p53^wt/wtHras^wt/wt) mice, whereas ∼1.54, 1.96, and 3.08 tumors per mouse were seen in BaP-treated p53 ^wt/wtHras^TG·AC/wt, p53^Val135/wtHras ^wt/wt, and p53^Val135/wtHras^TG·AC/wt mice, respectively. The effects on total tumor volume were even more striking with 7-, 48-, and 588-fold increases in tumor volume compared with wild-type (p53^wt/wtHras^wt/wt) in p53^wt/wtHras ^TG·AC/wt, p53^Val135/wtHras^wt/wt, and p53^Val135/wtHras^TG·AC/wt mice respectively. Histopathologically, all tumors from p53^wt/wtHras^wt/wt mice were either papillomas or well-differentiated squamous cell carcinomas, whereas the tumors in p53^wt/wtHras^TG·AC/wt, p53^Val135/wtHras^wt/wt, and p53 ^Val135/wtHras^TG·AC/wt mice were principally squamous cell carcinomas with varying degree of invasiveness. Particularly, tumors in p53^Val135/wtHras^TG·AC/wt mice exhibited the most rapid growth and the extreme form of tumor invasion. Microarray analysis revealed that dominant-negative p53 (Val¹³⁵) and activated H-ras affected several cellular processes involved in tumorigenesis possibly through its effects on apoptosis, cell cycle arrest, and Ras-mitogen-activated protein kinase pathways. The present study provides the first in vivo evidence that a germ line p53 mutation and activated H-ras act synergistically to profoundly enhance tumor progression.