Competitive ubiquitination activates the tumor suppressor p53

Xingyao Li,Mengqi Guo,Han-Fei Ding,Hongbo Wang,Chunhong Yan,Xiaoguang Chen,Lun Cai,Junran Zhang,Ying Liu,Tingting Du

doi:10.1038/s41418-019-0463-x

Abstract

Blocking p53 ubiquitination through disrupting its interaction with MDM2 or inhibiting the MDM2 catalytic activity is the central mechanism by which the tumor suppressor p53 is activated in response to genotoxic challenges. Although MDM2 is first characterized as the major E3 ubiquitin ligase for p53, it can also catalyze the conjugation of ubiquitin moieties to other proteins (e.g., activating transcription factor 3, or ATF3). Here we report that ATF3 can act as an ubiquitin “trap” and competes with p53 for MDM2-mediated ubiquitination. While ATF3-mediated p53 stabilization required ATF3 binding to the MDM2 RING domain, we demonstrated that ATF3 ubiquitination catalyzed by MDM2 was indispensable for p53 activation in response to DNA damage. Moreover, a cancer-derived ATF3 mutant (R88G) devoid of ubiquitination failed to prevent p53 from MDM2-mediated degradation and thus was unable to activate the tumor suppressor. Therefore, we have identified a previously-unknown mechanism that can activate p53 in the genotoxic response.

Highlights

The tumor suppressor p53 is the guardian of the genome, and maintains genetic integrity by regulating expression of an array of genes involved in a variety of cellular events
We have shown that MDM2mediated ubiquitination of ATF3 is required for p53 activation
As an array of proteins can interact with MDM2 and are ubiquitinated by MDM2 [41], competitive ubiquitination could be used as a common mechanism for p53 activation upon genotoxic stress

Summary

Introduction

The tumor suppressor p53 is the guardian of the genome, and maintains genetic integrity by regulating expression of an array of genes involved in a variety of cellular events ATF3 directly binds p53 at its C-terminus, and blocks its ubiquitination mediated by MDM2 [18]. While genetic evidence has confirmed that ATF3 can activate p53 upon γ-irradiation (IR) or oncogenic stress [16, 20], how ATF3 prevents p53 from MDM2-mediated ubiquitination remains unclear. ATF3 binds to the MDM2 RING domain responsible for the recruitment of E2-Ub [21]. As spatial proximity of E2s to substrates is important for ubiquitin transfer and ubiquitin chain elongation [25, 26], the binding of ATF3 directly to the MDM2 RING domain raises an intriguing possibility that ATF3 might compete with p53 for MDM2-mediated ubiquitination thereby activating the tumor suppressor. We present evidence supporting the notion that ATF3 can serve as an “ubiquitin trap” that activates p53 by competitive inhibition of p53 ubiquitination

Methods and materials

Results

Discussion

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