SIAH-mediated ubiquitination and degradation of acetyl-transferases regulate the p53 response and protein acetylation

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Abstract

Posttranslational modification of proteins by lysine acetylation regulates many biological processes ranging from signal transduction to chromatin compaction. Here we identify the acetyl-transferases CBP/p300, Tip60 and PCAF as new substrates for the ubiquitin E3 ligases SIAH1 and SIAH2. While CBP/p300 can undergo ubiquitin/proteasome-dependent degradation by SIAH1 and SIAH2, the two other acetyl-transferases are exclusively degraded by SIAH2. Accordingly, SIAH-deficient cells show enhanced protein acetylation, thus revealing SIAH proteins as indirect regulators of the cellular acetylation status. Functional experiments show that Tip60/PCAF-mediated acetylation of the tumor suppressor p53 is antagonized by the p53 target gene SIAH2 which mediates ubiquitin/proteasome-mediated degradation of both acetyl-transferases and consequently diminishes p53 acetylation and transcriptional activity. The p53 kinase HIPK2 mediates hierarchical phosphorylation of SIAH2 at 5 sites, which further boosts its activity as a ubiquitin E3 ligase for several substrates and therefore dampens the late p53 response.

Graphical abstract

Highlights

► The ubiquitin E3 ligase Siah controls the stability of various acetyl-transferases. ► HIPK2-mediated phosphorylation of Siah2 regulates its ubiquitinating activity. ► Siah2 contributes to the downregulation of the p53 response.

Keywords

SIAH
Ubiquitin E3 ligase
p53
Protein acetylation
HIPK2

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