O-GlcNAc modified-TIP60/KAT5 is required for PCK1 deficiency-induced HCC metastasis.

Aberrant glucose metabolism and elevated O-linked ß-N-acetylglucosamine modification (O-GlcNAcylation) are hallmarks of hepatocellular carcinoma (HCC). Loss of phosphoenolpyruvate carboxykinase 1 (PCK1), the major rate-limiting enzyme of hepatic gluconeogenesis, increases hexosamine biosynthetic pathway (HBP)-mediated protein O-GlcNAcylation in hepatoma cell and promotes cell growth and proliferation. However, whether PCK1 deficiency and hyper O-GlcNAcylation can induce HCC metastasis is largely unknown. Here, gain- and loss-of-function studies demonstrate that PCK1 suppresses HCC metastasis in vitro and in vivo. Specifically, lysine acetyltransferase 5 (KAT5), belonging to the MYST family of histone acetyltransferases (HAT), is highly modified by O-GlcNAcylation in PCK1 knockout hepatoma cells. Mechanistically, PCK1 depletion suppressed KAT5 ubiquitination by increasing its O-GlcNAcylation, thereby stabilizing KAT5. KAT5 O-GlcNAcylation epigenetically activates TWIST1 expression via histone H4 acetylation, and enhances MMP9 and MMP14 expression via c-Myc acetylation, thus promoting epithelial-mesenchymal transition (EMT) in HCC. In addition, targeting HBP-mediated O-GlcNAcylation of KAT5 inhibits lung metastasis of HCC in hepatospecific Pck1-deletion mice. Collectively, our findings demonstrate that PCK1 depletion increases O-GlcNAcylation of KAT5, epigenetically induces TWIST1 expression and promotes HCC metastasis, and link metabolic enzyme, post-translational modification (PTM) with epigenetic regulation.

Structural and histone binding studies of the chromo barrel domain of TIP60.

Tat-interactive protein 60 consists of an N-terminal chromo barrel domain (TIP60-CB) and a C-terminal acetyltransferase domain and acetylates histone and nonhistone proteins in diverse cellular processes. While TIP60-CB is thought to recognize histone tails, molecular details of this interaction remain unclear. Here, we attempted a quantitative analysis of the interaction between the human TIP60-CB and histone peptides, but did not observe any detectable binding by either fluorescence polarization or isothermal titration calorimetry assays. We also determined the crystal structure of the TIP60-CB alone. Analysis of the apo-structure reveals a putative peptide-binding site that might be occluded by the basic side chain of a residue in a unique ß hairpin between the two N-terminal strands of the ß barrel, leading to the inability of TIP60-CB to bind histones.

CDK9-mediated phosphorylation controls the interaction of TIP60 with the transcriptional machinery.

The acetyltransferase TIP60 is regulated by phosphorylation, and we have previously shown that phosphorylation of TIP60 on S86 by GSK-3 promotes p53-mediated induction of the BCL-2 protein PUMA. TIP60 phosphorylation by GSK-3 requires a priming phosphorylation on S90, and here, we identify CDK9 as a TIP60S90 kinase. We demonstrate that a phosphorylation-deficient mutant, TIP60S90A, exhibits reduced interaction with chromatin, histone 3 and RNA Pol II, while its association with the TIP60 complex subunit EPC1 is not affected. Consistently, we find a diminished association of TIP60S90A with the MYC gene. We show that cells expressing TIP60S90A, but also TIP60S86A, which retains S90 phosphorylation, exhibit reduced histone 4 acetylation and proliferation. Thus, our data indicate that, during transcription, phosphorylation of TIP60 at two sites has different regulatory effects on TIP60, whereby S90 phosphorylation controls association with the transcription machinery, and S86 phosphorylation is regulating TIP60 HAT activity.

Interaction of the epigenetic integrator UHRF1 with the MYST domain of TIP60 inside the cell.

BACKGROUND: The nuclear epigenetic integrator UHRF1 is known to play a key role with DNMT1 in maintaining the DNA methylation patterns during cell division. Among UHRF1 partners, TIP60 takes part in epigenetic regulations through its acetyltransferase activity. Both proteins are involved in multiple cellular functions such as chromatin remodeling, DNA damage repair and regulation of stability and activity of other proteins. The aim of this work was to investigate the interaction between UHRF1 and TIP60 in order to elucidate the dialogue between these two proteins. METHODS: Biochemical (immunoprecipitation and pull-down assays) and microscopic (confocal and fluorescence lifetime imaging microscopy; FLIM) techniques were used to analyze the interaction between TIP60 and UHRF1 in vitro and in vivo. Global methylation levels were assessed by using a specific kit. The results were statistically analyzed using Graphpad prism and Origin. RESULTS: Our study shows that UHRF1, TIP60 and DNMT1 were found in the same epigenetic macro-molecular complex. In vitro pull-down assay showed that deletion of either the zinc finger in MYST domain or deletion of whole MYST domain from TIP60 significantly reduced its interaction with UHRF1. Confocal and FLIM microscopy showed that UHRF1 co-localized with TIP60 in the nucleus and confirmed that both proteins interacted together through the MYST domain of TIP60. Moreover, overexpression of TIP60 reduced the DNA methylation levels in HeLa cells along with downregulation of UHRF1 and DNMT1. CONCLUSION: Our data demonstrate for the first time that TIP60 through its MYST domain directly interacts with UHRF1 which might be of high interest for the development of novel oncogenic inhibitors targeting this interaction.