Analysis of centrosome abnormalities and angiogenesis in epidermal-targetedp53172H mutant andp53-knockout mice after chemical carcinogenesis: Evidence for a gain of function

Abstract

We previously developed a transgenic mouse model that expresses in the epidermis a murine p53172R-->H mutant (p53m) under the control of a human keratin-1-based vector (HK1.p53m). In contrast to mice with wild-type p53 and p53-knockout mice, HK1.p53m mice exhibit increased susceptibility to chemical carcinogenesis, with greatly accelerated benign papilloma formation, malignant conversion, and metastasis. In the study presented here, we examined the expression pattern of several differentiation markers and observed that p53m tumors exhibited a less differentiated phenotype than tumors elicited in non-transgenic mice. Metastasis in p53m tumors was also associated with a poorly differentiated phenotype. To determine whether genomic instability was associated with a putative gain-of-function role for this p53m, in situ examination of centrosomes was performed in HK1.p53m and equivalent p53-null papillomas. In contrast to HK1.p53m papillomas, which had centrosome abnormalities at high frequencies (75% of cells contained more 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 progression of p53m tumors, the expression of vascular endothelial growth factor, a promoter of angiogenesis, and thrombospondin-1, an inhibitor of angiogenesis, was examined in tumors derived from either p53m or p53-knockout mice. Regardless of their p53 status (wild type, p53m, p53-/-), all of the papillomas exhibited similar levels of vascular endothelial growth factor expression and decreased expression of thrombospondin-1 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 data suggest that p53m accelerates tumorigenesis primarily by exerting a gain of function associated with genomic instability.

Aberrant cell cycle progression contributes to the early-stage accelerated carcinogenesis in transgenic epidermis expressing the dominant negative TGFβRII

“…Therefore, perturbation of cell cycle control appears to be a primary mechanism whereby DbRII accelerates tumorigenesis; whereas chromosome instability may be a direct e ect of p53 m . Secondly, increased angiogenesis in ML.DbRII tumors correlated with their earlier metastatic invasion (Go et al, 1999); whereas p53 m tumors did not exhibit an increase in angiogenesis (Wang et al, 1998b). These results highlight the importance of using transgenic models to investigate di erent molecular mechanisms leading to distinct alterations in cancer development.…”

“…Total RNA was isolated from chemically-induced tumors with RNAzol B (Tel-Test, Inc.) as previously described (Wang et al, 1998b). RNase protection assays (RPA) were performed using the RPA II kit (Ambion, TX, USA) and 32 Plabeled riboprobes.…”

Mutant p53 (G199V) Gains Antiapoptotic Function through Signal Transducer and Activator of Transcription 3 in Anaplastic Thyroid Cancer Cells

“…In addition, several mutants (p53-His175, p53-Gln213, and p53-Gln248) have been shown to enhance metastatic capacity when injected into severe combined immunodeficiency mice, whereas other mutants (p53-Cys273 and p53-His234) had no effect on metastatic capacity in this same model (18). Furthermore, transgenic mice designed to express murine p53-His172 exhibit increased susceptibility to chemical carcinogenesis (19).…”

The P53 pathway: what questions remain to be explored?

“…The p53 knockout mouse produces cells with abnormal numbers of centrosomes. 60 The way in which the p53 pathway brings about cellular senescence is completely unknown. Just which p53-regulated genes initiate this state remain unclear.…”