Dual Regulation of c-Myc by p300 via Acetylation-Dependent Control of Myc Protein Turnover and Coactivation of Myc-Induced Transcription

Abstract

The c-Myc oncoprotein (Myc) controls cell fate by regulating gene transcription in association with a DNA-binding partner, Max. While Max lacks a transcription regulatory domain, the N terminus of Myc contains a transcription activation domain (TAD) that recruits cofactor complexes containing the histone acetyltransferases (HATs) GCN5 and Tip60. Here, we report a novel functional interaction between Myc TAD and the p300 coactivator-acetyltransferase. We show that p300 associates with Myc in mammalian cells and in vitro through direct interactions with Myc TAD residues 1 to 110 and acetylates Myc in a TAD-dependent manner in vivo at several lysine residues located between the TAD and DNA-binding domain. Moreover, the Myc:Max complex is differentially acetylated by p300 and GCN5 and is not acetylated by Tip60 in vitro, suggesting distinct functions for these acetyltransferases. Whereas p300 and CBP can stabilize Myc independently of acetylation, p300-mediated acetylation results in increased Myc turnover. In addition, p300 functions as a coactivator that is recruited by Myc to the promoter of the human telomerase reverse transcriptase gene, and p300/CBP stimulates Myc TAD-dependent transcription in a HAT domain-dependent manner. Our results suggest dual roles for p300/CBP in Myc regulation: as a Myc coactivator that stabilizes Myc and as an inducer of Myc instability via direct Myc acetylation.The c-Myc oncoprotein (Myc) is the ubiquitous member of a small family of highly related DNA-binding transcription factors (including L-Myc and N-Myc) that regulate a wide variety of genes involved in the control of cell growth, proliferation, differentiation, and apoptotic cell death. Myc is essential for embryonic development and both Myc expression and activity are tightly regulated by mitogens and other physiological stimuli in normal somatic cells. Notably, unregulated Myc expression is tumorigenic in mice and has been associated with most types of cancer in humans. Myc binds to E-box DNA elements having the core consensus sequence CACGTG as a heterodimer with an obligatory partner protein called Max. Myc and Max dimerize and bind DNA via their respective basic-helix-loop-helix-leucine zipper (bHLHZip) domains. While Max does not have a transcription regulatory domain, Myc has a phylogenetically conserved N-terminal transcription activation domain (TAD) that is also essential for oncogenic cellular transformation (reviewed in reference 10).Several proteins have been shown to interact with Myc N-terminal TAD and are potential regulators or mediators of Myc transactivating and transforming activities (10,30). Among these, the TRRAP protein has been shown to contribute to the transformation activity of Myc through interactions with the conserved Myc box 1 (MB1) and MB2 regions within the TAD (23) and is a subunit of various transcription regulatory cofactors complexes that have histone acetyltransferase (HAT) activity. These TRRAP-HAT complexes include the GCN5 HAT-containing complexes STAGA (21, 22) and TFTC (3), the rela...

CITED2 functions as a molecular switch of cytokine-induced proliferation and quiescence

“…31 Consistently, we observed that p300 enhanced MYC-mediated transactivation of E2F3 promoter, and CITED2 expression boosted MYC-p300-mediated transactivation of E2F3 promoter (Figure 3e). We found that MYC bound CITED2 through its C-terminus, and knocking down CITED2 attenuated MYC-p300 interaction.…”

Glucose-stimulated Expression of Txnip Is Mediated by Carbohydrate Response Element-binding Protein, p300, and Histone H4 Acetylation in Pancreatic Beta Cells

“…The transcriptional co-activator and histone acetyltransferase (HAT) p300 has been shown to regulate the expression of other glucose-responsive genes, such as insulin and fibronectin (21)(22)(23), and to physically interact with other E-box-binding basic helix-loop-helix proteins, such as NeuroD (21), USF2 (24), MyoD (25), SREBP (26), and Myc (27). Moreover, p300 is one of the major HATs (in addition to HAT1 and TIP 60) that acetylate H4.…”

Reprogramming to pluripotency: stepwise resetting of the epigenetic landscape

“…In ES cells, Myc interacts with a histone acetyltransferase protein complex, the NuA4 histone acetyltransferase, and its target promoters have abundant histone acetylation levels [32]. In somatic cells, c-Myc is known to recruit p300 [88], another histone acetyltransferase; however, in ES cells, p300 does not appear to get recruited to c-Myc targets, rather p300 is targeted to enhancers with the help of Oct4-Sox2-Nanog [29]. Thus, specific reprogramming factors may exert some of their functions by modulating histone acetylation levels and are required less when acetylation levels are raised in cells by other means.…”