ANALYSIS OF CENTROSOME ABNORMALITIES AND ANGIOGENESIS IN EPIDERMAL-TARGETED P53(172H) MUTANT AND P53-KNOCKOUT MICE AFTER CHEMICAL CARCINOGENESIS - EVIDENCE FOR A GAIN OF FUNCTION

We previously developed a transgenic mouse model that expresses in the epidermis a murine p53(172-->H) mutant (p53(m)) under the control of a human keratin-l-based vector (HK1.p53(m)). In contrast to mice with wild-type p53 and p53-knockout mice, HK1.p53(m) mice exhibit increased susceptibility to chemical carcinogenesis, with greatly accelerated b enign papilloma formation, malignant conversion, and metastasis. In th e study presented here, we examined the expression pattern of several differentiation markers and observed that p53(m) tumors exhibited a le ss differentiated phenotype than tumors elicited in non-transgenic mic e. Metastasis in p53m tumors was also associated with a poorly differe ntiated phenotype. To determine whether genomic instability was associ ated with a putative gain-of-function role for this p53(m), in situ ex amination of centrosomes was performed in HK1.p53(m) and equivalent p5 3-null papillomas. In contrast to HK1.p53(m) papillomas, wh ich had ce ntrosome abnormalities at high frequencies (75% of cells contained mor e than three centrosomes/cell), p53-null tumors exhibited few abnormal centrosomes (4% of cells contained more than three centrosomes/cell). To determine whether angiogenesis played a role in the rapid progress ion of p53(m) tumors, the expression of vascular endothelial growth fa ctor, a promoter of angiogenesis, and thrombospondin-l, an inhibitor o f angiogenesis, was examined in tumors derived from either p53(m) or p 53-knockout mice. Regardless of their p53 status (wild type, p53(m), p 53(-/-)), all of the papillomas exhibited similar levels of vascular e ndothelial growth factor expression and decreased expression of thromb ospondin-l as did normal epidermis. In addition, tumors from different p53 genotypes showed a similar density of blood vessels. Because p53 status did not appear to play an overt role in angiogenesis, these dat a suggest that p53(m) accelerates tumorigenesis primarily by exerting a gain of function associated with genomic instability. (C) 1998 Wiley -Liss, Inc.