Activation of the insulin-like growth factor II transcription by aflatoxin B1 induced p53 mutant 249 is caused by activation of transcription complexes; implications for a gain-of-function during the formation of hepatocellular carcinoma

Abstract

A¯atoxin B1 (AFB1) induced mutation of the p53 gene at codon 249 (p53mt249) is critical during the formation of hepatocellular carcinoma (HCC) following hepatitis B virus (HBV) infection. p53mt249 markedly increases insulin-like growth factor II (IGF-II) transcription largely from promoter 4, accumulating the fetal form of IGF-II. Modulation of the transcription factor binding to IGF-II P4 by wild-type p53 and p53mt249 was identi®ed. Wild-type p53 inhibited binding of transcription factors Sp1 and TBP on the P4 promoter, while p53mt249 enhanced the formation of transcriptional complexes through enhanced DNA-protein (Sp1 or TBP) and protein ± protein (Sp1 and TBP) interactions. p53mt249 stimulates transcription factor Sp1 phosphorylation which might be a cause of increased transcription factor binding on the P4 promoter while wild-type p53 does not. Transfection of hepatocytes with p53mt249 impaired induction of apoptosis by the HBV-X protein and TNF-a. Therefore, the blocking of apoptosis through enhanced production of IGF-II should provide a favorable opportunity for the selection of transformed hepatocytes. These results explain the molecular basis for the genesis of HCC by p53mt249 which was found to be induced by a potent mutagen, AFB1. Oncogene (2000) 19, 3717 ± 3726.

Dysregulation of growth factor signaling in human hepatocellular carcinoma

“…In vitro IGF-II promoter activity and protein biosynthesis is repressed by p53 wt (Zhang et al, 1996;Lee et al, 2000), whereas the aflatoxin-induced p53 mutation (p53 mut(249) ) markedly induces IGF-II accumulation through enhanced formation of transcriptional complexes in HCC cells and increases IGF-1R expression in HCC cells . However, as IGF-1R overexpression was not described in human HCCs, further regulatory elements may inhibit IGF-1R enrichment in vivo.…”

Transcription regulation by mutant p53

“…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). Moreover, Li-Fraumeni syndrome-derived fibroblasts, endogenously expressing mutp53, exhibited increased resistance to apoptosis in response to mitomycin C, UV and IR, relative to p53-null fibroblasts (Gualberto et al, 1998).…”

“…Many subsequent studies have since then confirmed that a variety of p53 mutants can upregulate the expression of genes involved in various cellular processes implicated in cancerous progression, including growth regulation, metabolism, angiogenesis, drug resistance and genomic instability. For instance, the143A, 175H, 248W, 273H and 281G p53 mutants were shown to elevate the expression of EGFR (Ludes-Meyers et al, 1996), the 143A, 248W and 273H mutants were found to increase IGF-I-R expression (Werner et al, 1996), PCNA was reported to be transactivated by the 281G mutant (Lanyi et al, 1998) and c-myc by mutant 143A (Frazier et al, 1998;Matas et al, 2001), whereas 248W upregulated L37, RPP-1, and S2 ribosomal protein gene expression (Loging and Reisman, 1999), 174Y transactivated c-fos (Preuss et al, 2000), 125A, 248W and 249T transactivated the IGF-II gene (Lee et al, 2000), DUTPase was activated by 248W and 175H (Pugacheva et al, 2002), and 281G upregulated hsMAD1 and NFKB2 (Deb et al, 2002;Iwanaga and Jeang, 2002). In some of those cases, the requirement of an intact N terminus for the transcriptional and oncogenic activities of mutp53 could be demonstrated (Lanyi et al, 1998;Matas et al, 2001;Pugacheva et al, 2002), and in several instances, a partial contribution of the C terminus of mutp53 was also reported (Frazier et al, 1998;Lanyi et al, 1998;Deb et al, 2002).…”

Mutant p53: an oncogenic transcription factor

“…Genome-wide approaches have shown that mutant p53 is capable of modulating the expression of large patterns of transcripts (Figure 2). These findings indicate that mutant p53 might function as a transcription factor capable to turn on and off specific set of genes in response to different stimuli (Margulies and Sehgal, 1993;Subler et al, 1994;Tsutsumi-Ishii et al, 1995;Ludes-Meyers et al, 1996;Deb et al, 1998;Frazier et al, 1998;Lee et al, 2000;Iwanaga and Jeang, 2002;Scian et al, 2004Scian et al, , 2005Mizuaray et al, 2006). Consequently, mutant p53 might trigger different pathways that represent the molecular basis of the large spectrum of gain-of-function activities, which ranges from the resistance to anticancer treatments to genomic instability and increased metastasis.…”