Tumor-derived p53 mutants induce oncogenesis by transactivating growth-promoting genes

Abstract

We have studied the mechanism of mutant p53-mediated oncogenesis using several tumor-derived mutants. Using a colony formation assay, we found that the majority of the mutants increased the number of colonies formed compared to the vector. Expression of tumor-derived p53 mutants increases the rate of cell growth, suggesting that the p53 mutants have 'gain of function' properties. We have studied the gene expression profile of cells expressing tumor-derived p53-D281G to identify genes transactivated by mutant p53. We report the transactivation of two genes, asparagine synthetase and human telomerase reverse transcriptase. Quantitative real-time PCR confirms this upregulation. Transient transfection promoter assays verify that tumor-derived p53 mutants transactivate these promoters significantly. An electrophoretic mobility shift assay shows that tumor-derived p53-mutants cannot bind to the wild-type p53 consensus sequence. The results presented here provide some evidence of a possible mechanism for mutant p53-mediated transactivation.

Transcription regulation by mutant p53

“…The long lists of mutp53-regulated genes obtained by these studies included some that had already been reported previously, along with many novel mutp53 targets, unraveling the potential involvement of mutp53 in additional cellular processes such as transcriptional and translational regulation, signal transduction, cell motility, DNA repair, proteolysis and more. For some of those genes, regulation by mutp53 was confirmed also at the protein level and functional oncogenic relevance of this regulation by mutp53 was assigned; these include Cam2 (Knaup and Roemer, 2004), ASNS and hTERT (Scian et al, 2004a), EGR1 (Weisz et al, 2004), MSP (Zalcenstein et al, 2006), GEF-H1 (Mizuarai et al, 2006) and ATF3 (Buganim et al, 2006). These studies also allowed the comparison of the transcriptional programs of different p53 mutants, confirming that individual p53 mutants share some but not all transcriptional targets, compatible with the notion that they may possess distinct GOF phenotypes.…”

“…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).…”

Circulating tumour cells demonstrate an altered response to hypoxia and an aggressive phenotype

“…Under conditions of hypoxia and/or glucose deprivation, cells can switch to ATF4-mediated ASNS expression as a protective mechanism (Cui et al, 2007). Furthermore, ASNS is also known to be associated with drug resistance in leukaemia (Williams, 2007) and oncogenesis triggered by mutated p53 (Scian et al, 2004).…”

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

“…Loss of function is largely due to the inability of mutant p53 to bind to the canonical wild-type p53-binding site, resulting in an inability to transactivate its target genes (Kato et al, 2003;Scian et al, 2004), an attenuated tumoursuppressive function and, consequently, deregulated cellular growth and apoptosis. By contrast, GOF characteristics of mutant p53 are critical for tumour progression and metastasis (Brosh and Rotter, 2009;Oren and Rotter, 2010).…”