ABSTRACT
Recent studies have identified that first-line renoprotective agents that interrupt the renin-angiotensin system not only reduce BP but also can attenuate advanced glycation end product (AGE) accumulation. This study used in vitro, preclinical, and human approaches to explore the potential effects of these agents on the modulation of the receptor for AGE (RAGE). Bovine aortic endothelial cells that were exposed to the angiotensin-converting enzyme inhibitor (ACEi) ramiprilat in the presence of high glucose demonstrated a significant increase in soluble RAGE (sRAGE) secreted into the medium. In streptozotocin-induced diabetic rats, ramipril treatment (ACEi) at 3 mg/L for 24 wk reduced the accumulation of skin collagen-linked carboxymethyllysine and pentosidine, as well as circulating and renal AGE. Renal gene upregulation of total RAGE (all three splice variants) was observed in ACEi-treated animals. There was a specific increase in the gene expression of the splice variant C-truncated RAGE (sRAGE). There were also increases in sRAGE protein identified within renal cells with ACEi treatment, which showed AGE-binding ability. This was associated with decreases in renal full-length RAGE protein from ACEi-treated rats. Decreases in plasma soluble RAGE that were significantly increased by ACEi treatment were also identified in diabetic rats. Similarly, there was a significant increase in plasma sRAGE in patients who had type 1 diabetes and were treated with the ACEi perindopril. Complexes between sRAGE and carboxymethyllysine were identified in human and rodent diabetic plasma. It is postulated that ACE inhibition reduces the accumulation of AGE in diabetes partly by increasing the production and secretion of sRAGE into plasma.
Subject(s)
Diabetic Nephropathies/metabolism , Peptidyl-Dipeptidase A/metabolism , Receptors, Immunologic/metabolism , Alternative Splicing , Angiotensin-Converting Enzyme Inhibitors/pharmacology , Animals , Aorta/cytology , Arginine/analogs & derivatives , Arginine/chemistry , Blotting, Western , Cattle , Cells, Cultured , Collagen/metabolism , DNA Primers/chemistry , Diabetic Nephropathies/blood , Endothelium, Vascular/cytology , Glycation End Products, Advanced/blood , Glycation End Products, Advanced/metabolism , Humans , Immunohistochemistry , Immunoprecipitation , Kidney Cortex/metabolism , Lysine/analogs & derivatives , Lysine/chemistry , Male , Microscopy, Fluorescence , Molecular Weight , Ramipril/analogs & derivatives , Ramipril/pharmacology , Rats , Rats, Sprague-Dawley , Receptor for Advanced Glycation End Products , Receptors, Immunologic/blood , Reverse Transcriptase Polymerase Chain Reaction , Skin/metabolism , Time Factors , Up-RegulationABSTRACT
Transcriptional repression of methylated genes can be mediated by the methyl-CpG binding protein MeCP2. Here we show that human Brahma (Brm), a catalytic component of the SWI/SNF-related chromatin-remodeling complex, associates with MeCP2 in vivo and is functionally linked with repression. We used a number of different molecular approaches and chromatin immunoprecipitation strategies to show a unique cooperation between Brm, BAF57 and MeCP2. We show that Brm and MeCP2 assembly on chromatin occurs on methylated genes in cancer and the gene FMR1 in fragile X syndrome. These experimental findings identify a new role for SWI/SNF in gene repression by MeCP2.
Subject(s)
Cell Cycle Proteins/physiology , Chromosomal Proteins, Non-Histone/physiology , DNA-Binding Proteins/physiology , Gene Silencing/physiology , Repressor Proteins/physiology , Trans-Activators/physiology , Transcription Factors/physiology , Animals , Drosophila Proteins , Fragile X Mental Retardation Protein , Histones/physiology , Humans , Methyl-CpG-Binding Protein 2 , Mice , Microscopy, Fluorescence , Molecular Sequence Data , NIH 3T3 Cells , Nerve Tissue Proteins/genetics , RNA-Binding Proteins/geneticsABSTRACT
Chromatin is a highly dynamic structure that acts alternately as a substrate and a template in a number of critical biological processes. Modification of chromatin is pertinent and is responsible for a number of nuclear processes, including DNA repair, replication, transcription, and recombination. The purpose of this review is to discuss specific interactions between chromatin remodeling, DNA repair, and transcription. These areas are demonstrated to share commonality, particularly with a number of key molecules that appear to have roles in a number of pathways. The implications of pathway cross-over and communication form a seamless continuation of genomic integrity and stability.
Subject(s)
DNA Damage , DNA Repair , Epigenesis, Genetic , Animals , Chromatin/metabolism , Histones/metabolism , Proliferating Cell Nuclear Antigen/physiology , Transcription Factor TFIIH/metabolism , Transcription, GeneticABSTRACT
The importance of epigenetic modifications in carcinogenesis has been a source of controversy for some time. There is little doubt that changes in genomic hypermethylation contribute to the silencing of tumor suppressor genes. Furthermore, recent studies have also identified the significance of genomic hypomethylation associated with chromosomal instability and tumorigenesis. One of the most perplexing questions regarding epigenetic modifications and leukemogenesis is the relationship with DNA methyltransferases (DNMT's). The primary function of the DNMT enzymes is to methylate genomic DNA, whereas the methyl-CpG binding domain proteins (MBD) interpret this methylation signal and regulate gene expression and chromatin behavior. In this study we analyse these gene families by quantitative real-time PCR to investigate whether expression levels and the B-cell chronic lymphocytic leukemia (B-CLL) phenotype are associated. Furthermore, given the epigenetic crosstalk between genome stability and the histone chromatin code we have analysed eukaryotic histone methyltransferase (Eu-HMTaseI). Surprisingly, we did not observe significant changes in DNMT1 expression in B-CLL cases when compared to normal lymphocytes, regardless of whether we normalise against GAPDH or PCNA as reference standards. Indeed, expression of the maintenance and de novo methylases were independently regulated. Of particular note was the significant down regulation of DNMT3b. Furthermore, we observed a positive correlation between HMTaseI expression levels and stage of leukemia suggesting that changes in the methylation patterns in B-CLL may represent deregulation of the epigenetic repertoire that also include the methylation dependent binding proteins, MBD2 and MeCP2. We envisage changes in the epigenetic program are multifactorial in nature and postulate that the prevalent genomic methylases just one component of a larger epigenetic repertoire.
