Early p53 alterations in mouse skin carcinogenesis by UVB radiation: immunohistochemical detection of mutant p53 protein in clusters of preneoplastic epidermal cells.

Abstract

High levels of the p53 protein are immunohistochemically detectable in a majority of human nonmelanoma skin cancers and UVB-induced murine skin tumors. These increased protein levels are often associated with mutations in the conserved domains of the p53 gene. To investigate the timing of the p53 alterations in the process of UVB carcinogenesis, we used a well defined murine model (SKH:HR1 hairless mice) in (1), and from animal studies it appeared that the UVB part of the solar spectrum is the most carcinogenic (2). This has been substantiated by detection of mutations in the p53 tumor-suppressor gene in human SCCs (3) and basal cell carcinomas (4) that are characteristic for UVB radiation: i.e., mainly C T transitions at dipyrimidine sites among which are CC TT tandem mutations. There are indications that p53 is involved in the earliest stages of human nonmelanoma skin cancer. Recently, it has been reported that p53 mutations are already present in a benign precursor of SCC, actinic keratosis (5), and in skin adjacent to basal cell carcinomas (6). Furthermore, it has been shown that CC --TT tandem mutations in the p53 gene are detectable in biopsies from nonneoplastic skin of sun-exposed sites from Australian skin cancer patients (7).The suspected causal relationship between chronic UV exposure and p53 mutation and their relation to tumor forThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. mation can most directly and unequivocally be established in an animal model in which UV exposure is the only well controlled carcinogenic agent. A robust model is the SKH:HR1 hairless mouse for which the relationship between UVB exposure and carcinogenic response is well established (8, 9) and for which the pathogenesis of UVB-induced SCC shows close similarities with that of human SCC (10).Under physiological circumstances, the wild-type p53 protein has a very short half-life and is present in such small quantities that it is not immunohistochemically detectable (11,12). There are different pathways that lead to accumulation of the p53 protein up to immunohistochemically detectable levels. (i) DNA damage gives rise to a temporary accumulation of the wild-type p53 protein resulting in an arrest of the cell cycle assumed to prevent replication of damaged DNA (13). (ii) Missense mutations in the p53 gene in general lead to a dramatic increase in half-life of the p53 protein (11). In contrast to the transient accumulation of wild-type p53, the latter can lead to a constitutively high p53 level in the cell. We have recently reported that >75% of UVB-induced murine skin carcinomas show immunostaining with the p53-specific polyclonal antiserum CM-5, which was primarily confined to the proliferative compartments of the tumors. A substantial part of the p53-positive staining was associated with point mutations in the conserved domains of the p53 gene (14). Subsequ...

Fate of UVB-induced p53 mutations in SKH-hr1 mouse skin after discontinuation of irradiation: relationship to skin cancer development

“…In hairless mouse skin, UV-induced p53 mutations could be detected by AS-PCR as early as 1 week after the first UV radiation exposure, with 80-90% of animals incurring p53 mutations after 8 weeks of UV treatment (Ouhtit et al, 2000a). Clones of keratinocytes carrying mutant p53 have also been detected in mouse skin within 2-3 weeks after UV treatment (Berg et al, 1996;Rebel et al, 2001;Remenyik et al, 2003). In this study, we investigated the fate of p53 mutations and the development of skin cancer after discontinuation of UV treatment.…”

“…This acute regression phase may be followed by a significantly slower second phase (Berg et al, 1996). Berg et al (1996) found that more than 50% of p53-positive patches induced in Skhhr1 mouse skin by exposure to 39 kJ/m 2 of total UV radiation over a period of 30 days disappeared within the first 2 weeks after discontinuation of UV irradiation. The rate of disappearance of p53-positive patches was significantly higher (85%) when the total dose of UV radiation was decreased to 22 kJ/m 2 (Berg et al, 1996).…”

“…shown that the number and size of p53-positive cell clones in mouse epidermis decrease within 2 weeks after the discontinuation of chronic UV treatment (Berg et al, 1996;Remenyik et al, 2003). This acute regression phase may be followed by a significantly slower second phase (Berg et al, 1996).…”

“…While evidence supports the role of mutant p53 in enabling apoptosis resistance in keratinocytes (Ziegler et al, 1994;Tron et al, 1998;Zhang et al, 2001;Mudgil et al, 2003), the possibility that mutant p53 provides keratinocyte progenitors with proliferative advantages remains largely unexplored, even though two phenotypes may be related to the same underlying molecular changes (Kuhn et al, 1999;van Hogerlinden et al, 1999;Peus et al, 2000;Marconi et al, 2003). Nevertheless, discontinuation of UV irradiation has been shown to result in the fast spontaneous regression of some mutant p53 clones in mouse skin, although the mechanisms involved in this process are unclear (Berg et al, 1996;Rebel et al, 2001;Remenyik et al, 2003).…”

“…In addition, cell survival and growth following UV irradiation involves activation of NF-kB, mitogen-activated protein kinase, and phosphoinositide-3 0 -kinase/Akt pathways (Coffer et al, 1995;De-Metys et al, 1995;Rosette and Karin, 1996;Bender et al, 1997). Repeated exposure of skin to UV radiation results in the clonal expansion of p53-mutant cells (Ziegler et al, 1994;Berg et al, 1996;Rebel et al, 2001;Zhang et al, 2001). Two mechanisms are believed to contribute to the selective expansion of p53-mutant cells: their resistance to UV-induced apoptosis and their proliferative advantage over normal keratinocytes in response to stimulation with UV radiation.…”