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.

Myc, Aurora Kinase A, and mutant p53R172H co-operate in a mouse model of metastatic skin carcinoma

“…The enhanced genomic instability in GOF p53 SCCs led to the retention of specific genomic alterations targeting powerful oncogenes as Myc and Aurora-A. Furthermore, the presence of metastatic and EMT signatures coupled with the absence of genomic instability signatures suggests that GOF p53 SCCs acquired genomic instability at an early stage of tumor evolution, consistent with the presence of centrosome amplification, a hallmark feature of genomic instability in cancer (Fukasawa, 2005), previously observed in papillomas that expressed the GOF p53 mutant (Caulin et al , 2007; Wang et al , 1998). Taken together our results indicate that LOF p53 SCCs acquire genomic instability at a late stage in their tumor development, thereby delaying the emergence of metastases which is consistent with previous reports for p53 -null skin tumors (Caulin et al , 2007; Kemp et al , 1993), whereas GOF p53 tumors acquire genomic instability at an early stage of cancer progression.…”

Hetero-oligomerization does not compromise ‘gain of function’ of tumor-derived p53 mutants

“…Interestingly, expression of`gain of function' mutants of p53 has also been shown to enhance drug resistance, interfere with p53-independent apoptosis, and induce centrosome abnormalities in cells expressing them (Blandino et al, 1999;Li et al, 1998;Murphy et al, 2000;Sigal and Rotter, 2000;Wang et al, 1998). It is not known whether mutant p53-mediated transactivation is involved as the etiologic agent for these phenotypes.…”

Comparison of the Effect of Mutant and Wild-Type p53 on Global Gene Expression

“…These are phenotypes not caused by WT p53 that are seen when mutant p53s are expressed in p53 null cells. Several gain-of-function phenotypes have been found for various p53 mutants such as increased cell growth (10,11), enhanced tumorigenicity (11)(12)(13)(14)(15) and invasiveness (11,13,16), disturbed spindle checkpoint (17,18), and resistance to cytotoxic agents (19). Furthermore, it was shown that the expression of p53 mutants V134A and C132F caused cells to become resistant to transforming growth factor (TGF)-␤-mediated growth suppression (12,20).…”