Persistent high glucose induced EPB41L4A-AS1 inhibits glucose uptake via GCN5 mediating crotonylation and acetylation of histones and non-histones.

BACKGROUND: Persistent hyperglycemia decreases the sensitivity of insulin-sensitive organs to insulin, owing to which cells fail to take up and utilize glucose, which exacerbates the progression of type 2 diabetes mellitus (T2DM). lncRNAs' abnormal expression is reported to be associated with the progression of diabetes and plays a significant role in glucose metabolism. Herein, we study the detailed mechanism underlying the functions of lncRNA EPB41L4A-AS1in T2DM. METHODS: Data from GEO datasets were used to analyze the expression of EPB41L4A-AS1 between insulin resistance or type 2 diabetes patients and the healthy people. Gene expression was evaluated by qRT-PCR and western blotting. Glucose uptake was measured by Glucose Uptake Fluorometric Assay Kit. Glucose tolerance of mice was detected by Intraperitoneal glucose tolerance tests. Cell viability was assessed by CCK-8 assay. The interaction between EPB41L4A-AS1 and GCN5 was explored by RNA immunoprecipitation, RNA pull-down and RNA-FISH combined immunofluorescence. Oxygen consumption rate was tested by Seahorse XF Mito Stress Test. RESULTS: EPB41L4A-AS1 was abnormally increased in the liver of patients with T2DM and upregulated in the muscle cells of patients with insulin resistance and in T2DM cell models. The upregulation was associated with increased TP53 expression and reduced glucose uptake. Mechanistically, through interaction with GCN5, EPB41L4A-AS1 regulated histone H3K27 crotonylation in the GLUT4 promoter region and nonhistone PGC1ß acetylation, which inhibited GLUT4 transcription and suppressed glucose uptake by muscle cells. In contrast, EPB41L4A-AS1 binding to GCN5 enhanced H3K27 and H3K14 acetylation in the TXNIP promoter region, which activated transcription by promoting the recruitment of the transcriptional activator MLXIP. This enhanced GLUT4/2 endocytosis and further suppressed glucose uptake. CONCLUSION: Our study first showed that the EPB41L4A-AS1/GCN5 complex repressed glucose uptake via targeting GLUT4/2 and TXNIP by regulating histone and nonhistone acetylation or crotonylation. Since a weaker glucose uptake ability is one of the major clinical features of T2DM, the inhibition of EPB41L4A-AS1 expression seems to be a potentially effective strategy for drug development in T2DM treatment.

The histone acetylase activator pentadecylidenemalonate 1b rescues proliferation and differentiation in the human cardiac mesenchymal cells of type 2 diabetic patients.

This study investigates the diabetes-associated alterations present in cardiac mesenchymal cells (CMSC) obtained from normoglycemic (ND-CMSC) and type 2 diabetic patients (D-CMSC), identifying the histone acetylase (HAT) activator pentadecylidenemalonate 1b (SPV106) as a potential pharmacological intervention to restore cellular function. D-CMSC were characterized by a reduced proliferation rate, diminished phosphorylation at histone H3 serine 10 (H3S10P), decreased differentiation potential, and premature cellular senescence. A global histone code profiling of D-CMSC revealed that acetylation on histone H3 lysine 9 (H3K9Ac) and lysine 14 (H3K14Ac) was decreased, whereas the trimethylation of H3K9Ac and lysine 27 significantly increased. These observations were paralleled by a downregulation of the GCN5-related N-acetyltransferases (GNAT) p300/CBP-associated factor and its isoform 5-α general control of amino acid synthesis (GCN5a), determining a relative decrease in total HAT activity. DNA CpG island hypermethylation was detected at promoters of genes involved in cell growth control and genomic stability. Remarkably, treatment with the GNAT proactivator SPV106 restored normal levels of H3K9Ac and H3K14Ac, reduced DNA CpG hypermethylation, and recovered D-CMSC proliferation and differentiation. These results suggest that epigenetic interventions may reverse alterations in human CMSC obtained from diabetic patients.

Oestrogen-receptor-mediated transcription and the influence of co-factors and chromatin state.

Oestrogen receptor-alpha (ERalpha)-regulated transcription in breast cancer cells involves protein co-factors that contribute to the regulation of chromatin structure. These include co-factors with the potential to regulate histone modifications such as acetylation or methylation, and therefore the transcriptional state of target genes. Although much of the information regarding the interaction of specific co-factors with ER has been generated by studying specific promoter regions, we now have an improved understanding of the nature of these interactions and are better placed to relate these with ER activity and potentially with the activity of breast cancer drugs, including tamoxifen.

p300 modulates HIV-1 gp120-induced apoptosis in human proximal tubular cells: associated with alteration of TGF-beta and Smad signaling.

p300 is a key protein, which determines acceleration or deceleration of signal transduction. Recently, renal proximal tubular cells have not only been found to be a harboring site for HIV-1 but have also been shown to undergo apoptosis in response to HIV-1 exposure. Both HIV-1 and its envelop glycoprotein, i.e. gp120, triggered tubular cell apoptosis in the same magnitude. In the present study, we evaluated the role of p300 in gp120-induced tubular cell apoptosis and associated downstream signaling. We have demonstrated that by transient transfection assays, p300 significantly increases susceptibility of human proximal renal tubular HK-2 cells to apoptosis triggered by HIV-1 gp120. A mutant p300, missing the E1A/TFIIB binding site, fails to produce such sensitization potential. Smad7 and an anti-TGF-beta antibody rescue the p300 sensitization. Furthermore, p300 and HIV-1 gp120 synergistically increase TGF-beta, ATF-2 and activating protein-1 (AP-1) expression. In addition, HIV-1 gp120 results in phosphorylation of Smad2 and decreases c-Jun. These findings suggest that p300 acts as a potent transcriptional cofactor in HIV-1 gp120-induced apoptosis via TGF-beta and Smad signaling.

Interactions with p300 enhance transcriptional activation by the PDZ-domain coactivator Bridge-1.

Transcriptional coactivators are essential mediators of signal amplification in the regulation of gene expression in response to hormones and extracellular signals. We previously identified Bridge-1 (PSMD9) as a PDZ-domain coregulator that augments insulin gene transcription via interactions with the basic helix-loop-helix transcription factors E12 and E47, and that increases transcriptional activation by the homeodomain transcription factor PDX-1. In these studies, we find that transcriptional activation by Bridge-1 can be regulated via interactions with the histone acetyltransferase and nuclear receptor coactivator p300. In transfection assays, transcriptional activation by Bridge-1 is increased by the inhibition of endogenous histone deacetylase activity with trichostatin A, indicating that the transcriptional activation function of Bridge-1 can be regulated by histone modifications. The exogenous expression of p300 enhances the transcriptional activation by Bridge-1 in a dose-dependent manner. In contrast, the sequestration of p300 by the overexpression of the adenoviral protein E1A, but not by an E1A mutant protein that is unable to interact with p300, suppresses the transcriptional activation by Bridge-1. We demonstrate that p300 and Bridge-1 proteins interact in immunopre-cipitation and glutathione-S-transferase (GST) pull-down assays. Bridge-1 interacts directly with multiple regions within p300 that encompass C/H1 or C/H2 cysteine- and histidine-rich protein interaction domains and the histone acetyltransferase domain. Deletion or point mutagenesis of the Bridge-1 PDZ domain substantially reduces transcriptional activation by Bridge-1 and interrupts interactions with p300. We propose that p300 interactions with Bridge-1 can augment the transcriptional activation of regulatory target genes by Bridge-1.