Acetylation at a lysine residue adjacent to the CtBP binding motif within adenovirus 12 E1A causes structural disruption and limited reduction of CtBP binding

Survey of Acetylation for Thermoanaerobacter tengcongensis

Non-histone protein acetylation is involved in key cellular processes both in eukaryotes and prokaryotes. Acetylation in bacteria is used to modify proteins involved in metabolism and allow the bacteria to adapt to their environment. TTE (Thermoanaerobacter tengcongensis) is an anaerobic, thermophilic saccharolytic bacterium that grows at extreme temperature range between 50 and 80 ℃. The annotated TTE proteome contains less than 3000 proteins. We analyzed the proteome and acetylome of TTE using 2DLC-MS/MS (2-dimensional liquid chromatography mass spectrum). We evaluated the ability of mass spectrometry technology to cover a relatively small proteome as much as possible. And we also observed wide spread of acetylation in TTE, which changed under different temperatures. A total of 2082 proteins were identified, which accounts for about 82% of the database. A total of 2050 (~ 98%) proteins were quantified in at least one culture condition and 1818 proteins were quantified in all 4 conditions. The result also consisted 3457 acetylation sites corresponding to 827 distinct proteins, which covered 40% of the proteins identified. Bioinformatics analysis reported that proteins related to replication, recombination, repair, and extracellular structure cell wall biogenesis had more than half members acetylated, while energy production, carbohydrate transport, and metabolism related proteins were least acetylated. Our result suggested that acetylation affects the ATP-related energy metabolism and energy-dependent biosynthesis process. Comparing the enzymes related with lysine acetylation and acetyl-CoA (acetyl-coenzyme A) metabolism, we suggested that the acetylation of TTE took a non-enzymatic mechanism and affected by abundance of acetyl-CoA.

Interplay between sequence, structure and linear motifs in the adenovirus E1A hub protein

E1A is the main transforming protein in mastadenoviruses. This work uses bioinformatics to extrapolate experimental knowledge from Human adenovirus serotype 5 and 12 E1A proteins to all known serotypes. A conserved domain architecture with a high degree of intrinsic disorder acts as a scaffold for multiple linear motifs with variable occurrence mediating the interaction with over fifty host proteins. While linear motifs contribute strongly to sequence conservation within intrinsically disordered E1A regions, motif repertoires can deviate significantly from those found in prototypical serotypes. Close to one hundred predicted residue-residue contacts suggest the presence of stable structure in the CR3 domain and of specific conformational ensembles involving both short- and long-range intramolecular interactions. Our computational results suggest that E1A sequence conservation and co-evolution reflect the evolutionary pressure to maintain a mainly disordered, yet non-random conformation harboring a high number of binding motifs that mediate viral hijacking of the cell machinery.

Site-specific acetylation of the proteasome activator REGγ directs its heptameric structure and functions

The proteasome activator REGγ has been reported to promote degradation of steroid receptor coactivator-3 and cyclin-dependent kinase inhibitors p21, p16, and p19 in a ubiquitin- and ATP-independent manner. A recent comparative analysis of REGγ expression in mouse and human tissues reveals a unique pattern of REGγ in specific cell types, suggesting undisclosed functions and biological importance of this molecule. Despite the emerging progress made in REGγ-related studies, how REGγ function is regulated remains to be explored. In this study, we report for the first time that REGγ can be acetylated mostly on its lysine 195 (Lys-195) residue by CREB binding protein (CBP), which can be reversed by sirtuin 1 (SIRT1) in mammalian cells. Site-directed mutagenesis abrogated acetylation at Lys-195 and significantly attenuated the capability of REGγ to degrade its target substrates, p21 and hepatitis C virus core protein. Mechanistically, acetylation at Lys-195 is important for the interactions between REGγ monomers and ultimately influences REGγ heptamerization. Biological analysis of cells containing REGγ-WT or REGγ-K195R mutant indicates an impact of acetylation on REGγ-mediated regulation of cell proliferation and cell cycle progression. These findings reveal a previously unknown mechanism in the regulation of REGγ assembly and activity, suggesting a potential venue for the intervention of the ubiquitin-independent REGγ proteasome activity.

SIRT1 regulates YAP2-mediated cell proliferation and chemoresistance in hepatocellular carcinoma

The MST/YAP (mammalian Ste20-like kinase/Yes-associated protein 2) pathway plays an important role in hepatocellular carcinoma (HCC). Although post-translational modification-especially MST/Lats (large tumor suppressor)-mediated phosphorylation and PP1 (protein phosphatase-1)-mediated dephosphorylation-has been found to regulate the activity of YAP2, very little is known about its acetylation. In our experiments, we observed that the expression of SIRT1 is significantly upregulated in the tumor samples of the hepatocarcinoma patients, and SIRT1 mRNA level positively correlates with connective tissue growth factor (CTGF) mRNA level. We then found that SIRT1 deacetylates YAP2 protein in HCC cells and SIRT1-mediated deacetylation increases the YAP2/TEAD4 association, leading to YAP2/TEAD4 transcriptional activation and upregulated cell growth in HCC cells. Moreover, knockdown of SIRT1 blocks the cisplatin (CDDP)-induced nuclear translocation of YAP2 and enhances the chemosensitivity of HCC cells to CDDP treatment. Together, our findings reveal a new regulatory mechanism of YAP2 by the SIRT1-mediated deacetylation that may be involved in HCC tumorigenesis and drug resistance.

Nonhistone protein acetylation as cancer therapy targets

Acetylation and deacetylation are counteracting, post-translational modifications that affect a large number of histone and nonhistone proteins. The significance of histone acetylation in the modification of chromatin structure and dynamics, and thereby gene transcription regulation, has been well recognized. A steadily growing number of nonhistone proteins have been identified as acetylation targets and reversible lysine acetylation in these proteins plays an important role(s) in the regulation of mRNA stability, protein localization and degradation, and protein-protein and protein-DNA interactions. The recruitment of histone acetyltransferases (HATs) and histone deacetylases (HDACs) to the transcriptional machinery is a key element in the dynamic regulation of genes controlling cellular proliferation, differentiation and apoptosis. Many nonhistone proteins targeted by acetylation are the products of oncogenes or tumor-suppressor genes and are directly involved in tumorigenesis, tumor progression and metastasis. Aberrant activity of HDACs has been documented in several types of cancers and HDAC inhibitors (HDACi) have been employed for therapeutic purposes. Here we review the published literature in this field and provide updated information on the regulation and function of nonhistone protein acetylation. While concentrating on the molecular mechanism and pathways involved in the addition and removal of the acetyl moiety, therapeutic modalities of HDACi are also discussed.

Acetylation of lysine 564 adjacent to the C-terminal binding protein-binding motif in EVI1 is crucial for transcriptional activation of GATA2

Ecotropic viral integration site 1 (EVI1) is an important transcription factor for leukemogenesis. EVI1 is a member of a group of transcription factors with C-terminal binding protein (CtBP)-binding motifs that act as transcriptional co-repressors; however, we recently found that EVI1 directly activates GATA2 transcription, which is an important gene for the maintenance of hematopoietic stem cells. We show here that EVI1-activated GATA2 transcripts derive from exon 1S of GATA2, which is specifically activated in neural and hematopoietic cells. EVI1 was acetylated by the histone acetyltransferase p300/CBP association factor (P/CAF) in myeloid leukemia cells and hematopoietic progenitor cells. Acetylation at Lys(564), which is adjacent to the CtBP-binding consensus sequence of EVI1, was found to be important for transcriptional activation of GATA2. Mutation of Lys(564) to alanine (K564A) markedly reduced the ability of EVI1 to bind DNA and activate transcription of GATA2. Furthermore, we confirmed that Lys(564) in EVI1 was specifically acetylated in leukemia and primary hematopoietic cells by using an antibody directed against an acetylated Lys(564) EVI1 peptide. Moreover, co-transfection of P/CAF with EVI1 overcame the suppressive effect of the CtBP co-repressor and resulted in GATA2 transcriptional activation; nonetheless, CtBP2 was still included in the protein complex with EVI1 and P/CAF on the EVI1-binding site in the GATA2 promoter region. Thus, acetylation of EVI1 at Lys(564) by P/CAF enhances the DNA binding capacity of EVI1 and thereby contributes to the activation of GATA2.

Acetylation of non-histone proteins modulates cellular signalling at multiple levels

This review focuses on the posttranslational acetylation of non-histone proteins, which determines vital regulatory processes. The recruitment of histone acetyltransferases and histone deacetylases to the transcriptional machinery is a key element in the dynamic regulation of genes controlling cellular proliferation and differentiation. A steadily growing number of identified acetylated non-histone proteins demonstrate that reversible lysine acetylation affects mRNA stability, and the localisation, interaction, degradation and function of proteins. Interestingly, most non-histone proteins targeted by acetylation are relevant for tumourigenesis, cancer cell proliferation and immune functions. Therefore inhibitors of histone deacetylases are considered as candidate drugs for cancer therapy. Histone deacetylase inhibitors alter histone acetylation and chromatin structure, which modulates gene expression, as well as promoting the acetylation of non-histone proteins. Here, we summarise the complex effects of dynamic alterations in the cellular acetylome on physiologically relevant pathways.

PLDLS-dependent interaction of E1A with CtBP: regulation of CtBP nuclear localization and transcriptional functions

C-terminal binding proteins (CtBPs) are cellular corepressors that are targeted by adenovirus E1A. A conserved motif of E1A (PLDLS) interacts with an N-terminal hydrophobic cleft of CtBPs. Many cellular cofactors also interact with CtBPs through PLDLS-like motifs. E1A interaction with CtBP2 changed the composition of the CtBP2 protein complex and enhanced CtBP2 acetylation. We have identified a mutant of CtBP2 (M48A) that fails to interact with cellular cofactors while interacting normally with E1A. Other cleft mutations in CtBP2 affected interaction of both cellular cofactors and E1A. The M48A mutant did not repress the cellular E-cadherin promoter but inhibited transactivation mediated by the E1A N-terminal region through interaction with the E1A PLDLS motif. In vitro, E1A enhanced CtBP2 acetylation by p300 via a mechanism involving dissociation of acetylated CtBP2 from p300. E1A enhanced nuclear localization of CtBP1 as well as a cytoplasmically localized acetylation-deficient mutant of CtBP2 (3KR-CtBP2) through PLDLS-dependent interaction. Chromatin immunoprecipitation assays revealed presence of CtBP2 on E-cadherin and c-fos promoters. While E1A did not significantly alter targeting of CtBP2 to the E-cadherin and c-fos promoters, it dramatically enhanced promoter targeting of 3KR-CtBP2. Our results raise a possibility that E1A may gain access to cellular promoters through PLDLS-dependent interaction with CtBPs.

The effect of CtBP1 binding on the structure of the C-terminal region of adenovirus 12 early region 1A

Adenovirus early region 1A (AdE1A) binds to the C-terminal binding protein 1 (CtBP1) primarily through a highly conserved PXDLS motif located close to its C-terminus. Purified synthetic peptides equivalent to this region of AdE1A have been shown to form a series of beta-turns. In this present study the effect of CtBP1 binding on the conformation of C-terminal region of Ad12E1A has been investigated. Using one- and two-dimensional (1)H NMR spectroscopy, the conformation of 20-residue peptides equivalent to amino acids I(241)-V(260) and E(247)-N(266) of Ad12E1A were examined in the absence of CtBP1. Whilst the latter peptide forms a series of beta-turns in its C-terminal half as reported previously, the former peptide is alpha-helical over the region D(243)-Q(253). Upon interaction with CtBP1 the conformation of the backbone in the region (255)PVDLCVK(261) of the Ad12E1A E(247)-N(266) peptide reorganises from a predominately beta-turn to an alpha-helical conformation. This structural isomerisation is characterised by a shift upfield of 0.318 ppm for the delta-CH(3) proton resonance of V(256). 2-D NOESY experiments showed new signals in the amide-alpha region which correlate to transferred NOEs from the protein to the peptide residues E(251), V(256) and K(261). In further analyses the contribution of individual amino acids within the sequence (254)VPVDLS(259) was assessed for their importance in determining structure and consequently affinity of the peptide for CtBP. It has been concluded that Ad12E1A residues (255)P-V(260) serve initially as a recognition site for CtBP and then as an anchor through a beta-turns-->alpha-helix conformational rearrangement. In addition it has been predicted that regions N-terminal to the PXDLS motif in AdE1As from different virus serotypes and from mammalian proteins form alpha-helices.