A gain of function p53 mutant promotes both genomic instability and cell survival in a novel p53‐null mammary epithelial cell mode.

Abstract

Approximately 40% of human breast cancers contain alterations in the tumor suppressor p53. The p53 172R-H gain-of-function mutant (equivalent to the common 175R-H human breast cancer mutant) has been shown to promote aneuploidy and tumorigenesis in the mammary gland in transgenic mice and may affect genomic stability in part by causing centrosome abnormalities. The precise mechanism of action of these gain-of-function mutants is not well understood, and has been studied primarily in fibroblast cell lines. A novel p53-null mouse mammary epithelial cell line developed from p53-null mice has been used in adenovirus-mediated transient transfection experiments to study the properties of this p53 mutant. Marked centrosome amplification and an increased frequency of aberrant mitoses were observed within 72 h of introduction of p53 172R-H. However, few cells with aberrant centrosome numbers were observed in cells stably expressing the p53 172R-H mutant. Furthermore, stable expression of this p53 mutant reduced both basal and DNA damage-induced apoptosis. This result may be mediated in part through abrogation of p73 function. The p53 172R-H mutant, therefore, appears to influence tumorigenesis at the molecular level in two distinct ways: promoting the development of aneuploidy in cells while also altering their apoptotic response after DNA damage.

Mutant p53 drives multinucleation and invasion through a process that is suppressed by ANKRD11

“…Our findings are consistent with observations of mutant p53 GOF in mouse models where expression of the mouse R172H mutant (equivalent to human R175H) results in tumours showing centrosome amplification and an associated aneuploidy (Murphy et al, 2000;Hingorani et al, 2005;Caulin et al, 2007). However, these previous reports are confounded as they use a K-Ras G12D mutation as an initiating oncogenic event (Hingorani et al, 2005;Caulin et al, 2007).…”

Difference in the centrosome duplication regulatory activity among p53 ‘hot spot’ mutants: potential role of Ser 315 phosphorylation-dependent centrosome binding of p53

“…Expression of R175H mutant exacerbated the abnormal centrosome pro®le as seen in both p537/7(R175H)-1 and p537/7(R175H)-2 lines with a decrease in the per cent of cells with one centrosome (12 ± 13%), and an increase in the per cent of cells with 53 centrosomes (34 ± 37%). The`gain-of-function' property of R175H in centrosome hyperampli®cation has recently been reported also by Wang et al (1998) and Murphy et al (2000). In contrast, expression of R249S greatly restored the centrosome numerality with an increase in the per cent of cells with one centrosome (40 ± 46%), and a decrease in the per cent of cells with 53 centrosomes (5 ± 6%), which is similar to normal p53+/+ MEFs (Fukasawa et al, 1996).…”

Transcription regulation by mutant p53

“…Mutp53 was shown to increase genomic instability in Li-Fraumeni syndrome-derived fibroblasts in conjunction with disruption of the mitotic spindle checkpoint (Gualberto et al, 1998), in Jurkat cells following X-irradiation as measured by altered T-cell receptor surface expression (Iwamoto et al, 1996), in mammary mouse fibroblasts following ultraviolet (UV) and ionizing radiation (IR) as reflected by aberrant centrosome numbers (Murphy et al, 2000) and in Saos-2 human osteosarcoma cells as assessed by gene amplification (El-Hizawi et al, 2002). Mutp53 was also shown to enhance colony formation when overexpressed in p53-null mouse fibroblasts and human lung cancer-derived cells (Murphy et al, 2000;Deb et al, 2002;Weisz et al, 2004;Scian et al, 2004a). Furthermore, exogenous mutp53 was found to enhance the growth rate of such cells (Deb et al, 2002;Scian et al, 2004b).…”

“…Particular attention was devoted to the ability of mutp53 to impinge upon apoptotic pathways, primarily as this might be important in the context of efficient killing of tumor cells by chemotherapy and radiotherapy. Here, mutp53 gain of oncogenic function was manifested as the ability of various p53 mutants to interfere with apoptotic cell death upon treatment with various stress inducers, including growth factor deprivation and genotoxic agents such as IR, UV radiation, cisplatin, etoposide, doxorubicin, and a-amanitin (Peled et al, 1996;Li et al, 1998;Blandino et al, 1999;Murphy et al, 2000;Matas et al, 2001;Sigal et al, 2001;Yap et al, 2004). Mutp53 was also reported to protect hepatocytes from a combination of HBV-X protein and TNFa (Lee et al, 2000).…”