Mutant p53 Protects Cells from 12-O-Tetradecanoylphorbol-13-Acetate–Induced Death by Attenuating Activating Transcription Factor 3 Induction

Yosef Buganim,Marina Kalis,Ran Brosh,Naomi Goldfinger,Ido Nachmany,Varda Rotter,Xiaohu Tang,Yoach Rais,Michael Milyavsky,Perry Stambolsky,Eyal Kalo,Igor Shats,Hila Besserglick

doi:10.1158/0008-5472.can-06-0916

Abstract

Mutations in p53 are ubiquitous in human tumors. Some p53 mutations not only result in loss of wild-type (WT) activity but also grant additional functions, termed "gain of function." In this study, we explore how the status of p53 affects the immediate response gene activating transcription factor 3 (ATF3) in the 12-O-tetradecanoylphorbol-13-acetate (TPA)-protein kinase C (PKC) pathway. We show that high doses of TPA induce ATF3 in a WT p53-independent manner correlating with PKCs depletion and cell death. We show that cells harboring mutant p53 have attenuated ATF3 induction and are less sensitive to TPA-induced death compared with their p53-null counterparts. Mutagenesis analysis of the ATF3 promoter identified the regulatory motifs cyclic AMP-responsive element binding protein/ATF and MEF2 as being responsible for the TPA-induced activation of ATF3. Moreover, we show that mutant p53 attenuates ATF3 expression by two complementary mechanisms. It interacts with the ATF3 promoter and influences its activity via the MEF2 site, and additionally, it attenuates transcriptional expression of the ATF3 activator MEF2D. These data provide important insights into the molecular mechanisms that underlie mutant p53 gain of function.

Highlights

Multiple stress responses are regulated by the p53 tumor suppressor gene [1]. p53 is a transcription factor that activates specific target genes through direct binding to a p53 consensus sequence [2]. p21WAF1 and GADD45 are activated transcriptionally by p53 in response to DNA damage, and this activation is involved in the control of cell cycle checkpoints [3, 4]
Because p53 and activating transcription factor 3 (ATF3) are cross-talking regulators of cell fate decisions, we decided to explore further the molecular relationships between these two transcription factors. As both p53 and cyclic AMP-responsive element binding protein (CREB)/activating transcription factor (ATF) are involved in the protein kinase C (PKC) pathway that has been implicated in malignant progression, we focused on p53-ATF3 cross-talk following treatment with three compounds that modulate PKC activity: Transforming growth factor h (TGFh), Tumor necrosis factor a (TNFa), and TPA
We explore how mutant p53 affects the immediate early response gene ATF3 and exerts its gain of function in the TPA-PKC pathway

Summary

Introduction

Multiple stress responses are regulated by the p53 tumor suppressor gene [1]. p53 is a transcription factor that activates specific target genes through direct binding to a p53 consensus sequence [2]. p21WAF1 and GADD45 are activated transcriptionally by p53 in response to DNA damage, and this activation is involved in the control of cell cycle checkpoints [3, 4]. The predominant mode of p53 inactivation is by point mutation rather than by deletion or truncation These data coupled with the observation that mutant p53 is generally highly overexpressed in tumors have led to the hypothesis that mutant p53 possesses gain-of-function activities. One putative mechanism is that mutant p53 alters the expression of specific genes and interferes with the onset of the apoptotic process This is supported by recent data showing that the EGR1 and NFjB2 genes can be activated and the CD95 and MSP-1 genes repressed by mutant p53 [14,15,16,17]. We report here that expression of mutant p53 results in reduced sensitivity to cell death induced by high doses of TPA We show that this protection is mediated by attenuation of p53-independent ATF3 induction. This study provides novel insights into the molecular mechanisms by which mutant p53 exerts gain-of-function activity

Materials and Methods

Results

Discussion