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Cooperative binding of KLF4, pELK-1, and HDAC2 to a G/C repressor element in the SM22? promoter mediates transcriptional silencing during SMC phenotypic switching in vivo.

ABSTRACT: We previously identified conserved G/C Repressor elements in the promoters of most smooth muscle cell (SMC) marker genes and demonstrated that mutation of this element within the SM22? promoter nearly abrogated repression of this transgene after vascular wire injury or within lesions of ApoE-/- mice. However, the mechanisms regulating the activity of the G/C Repressor are unknown, although we have previously shown that phenotypic switching of cultured SMC is dependent on Krupple-like factor (KLF)4.The goals of the present studies were to ascertain if (1) injury-induced repression of SM22? gene after vascular injury is mediated through KLF4 binding to the G/C Repressor element and (2) the transcriptional repressor activity of KLF4 on SMC marker genes is dependent on cooperative binding with pELK-1 (downstream activator of the mitogen-activated protein kinase pathway) and subsequent recruitment of histone de-acetylase 2 (HDAC2), which mediates epigenetic gene silencing.Chromatin immunoprecipitation (ChIP) assays were performed on chromatin derived from carotid arteries of mice having either a wild-type or G/C Repressor mutant SM22? promoter-LacZ transgene. KLF4 and pELK-1 binding to the SM22? promoter was markedly increased after vascular injury and was G/C Repressor dependent. Sequential ChIP assays and proximity ligation analyses in cultured SMC treated with platelet-derived growth factor BB or oxidized phospholipids showed formation of a KLF4, pELK-1, and HDAC2 multiprotein complex dependent on the SM22? G/C Repressor element.Silencing of SMC marker genes during phenotypic switching is partially mediated by sequential binding of pELK-1 and KLF4 to G/C Repressor elements. The pELK-1-KLF4 complex in turn recruits HDAC2, leading to reduced histone acetylation and epigenetic silencing.

SUBMITTER: Salmon M

PROVIDER: S-EPMC3517884 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature

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Cooperative binding of KLF4, pELK-1, and HDAC2 to a G/C repressor element in the SM22α promoter mediates transcriptional silencing during SMC phenotypic switching in vivo.

Salmon Morgan M Gomez Delphine D Greene Elizabeth E Shankman Laura L Owens Gary K GK

Circulation research 20120718 6

<h4>Rationale</h4>We previously identified conserved G/C Repressor elements in the promoters of most smooth muscle cell (SMC) marker genes and demonstrated that mutation of this element within the SM22α promoter nearly abrogated repression of this transgene after vascular wire injury or within lesions of ApoE-/- mice. However, the mechanisms regulating the activity of the G/C Repressor are unknown, although we have previously shown that phenotypic switching of cultured SMC is dependent on Kruppl ...[more]

PMID: 22811558

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Project description:BackgroundRupture and erosion of advanced atherosclerotic lesions with a resultant myocardial infarction or stroke are the leading worldwide cause of death. However, we have a limited understanding of the identity, origin, and function of many cells that make up late-stage atherosclerotic lesions, as well as the mechanisms by which they control plaque stability.MethodsWe conducted a comprehensive single-cell RNA sequencing of advanced human carotid endarterectomy samples and compared these with single-cell RNA sequencing from murine microdissected advanced atherosclerotic lesions with smooth muscle cell (SMC) and endothelial lineage tracing to survey all plaque cell types and rigorously determine their origin. We further used chromatin immunoprecipitation sequencing (ChIP-seq), bulk RNA sequencing, and an innovative dual lineage tracing mouse to understand the mechanism by which SMC phenotypic transitions affect lesion pathogenesis.ResultsWe provide evidence that SMC-specific Klf4- versus Oct4-knockout showed virtually opposite genomic signatures, and their putative target genes play an important role regulating SMC phenotypic changes. Single-cell RNA sequencing revealed remarkable similarity of transcriptomic clusters between mouse and human lesions and extensive plasticity of SMC- and endothelial cell-derived cells including 7 distinct clusters, most negative for traditional markers. In particular, SMC contributed to a Myh11-, Lgals3+ population with a chondrocyte-like gene signature that was markedly reduced with SMC-Klf4 knockout. We observed that SMCs that activate Lgals3 compose up to two thirds of all SMC in lesions. However, initial activation of Lgals3 in these cells does not represent conversion to a terminally differentiated state, but rather represents transition of these cells to a unique stem cell marker gene-positive, extracellular matrix-remodeling, "pioneer" cell phenotype that is the first to invest within lesions and subsequently gives rise to at least 3 other SMC phenotypes within advanced lesions, including Klf4-dependent osteogenic phenotypes likely to contribute to plaque calcification and plaque destabilization.ConclusionsTaken together, these results provide evidence that SMC-derived cells within advanced mouse and human atherosclerotic lesions exhibit far greater phenotypic plasticity than generally believed, with Klf4 regulating transition to multiple phenotypes including Lgals3+ osteogenic cells likely to be detrimental for late-stage atherosclerosis plaque pathogenesis.

Project description:The repressor element silencing transcription factor (REST) is a coordinate transcriptional and epigenetic regulator which functions as a tumor suppressor or an oncogene depending on cellular context, and a truncated splice variant REST4 has been linked to various types of cancer. We performed a comprehensive analysis of alternative splicing (AS) of REST by rapid amplification of cDNA ends and PCR amplification of cDNAs from various tissues and cell lines with specific primers. We identified 8 novel alternative exons including an alternate last exon which doubles the REST gene boundary, along with numerous 5'/3' splice sites and ends in the constitutive exons. With the combination of various splicing patterns (e.g. exon skipping and alternative usage of the first and last exons) that are predictive of altered REST activity, at least 45 alternatively spliced variants of coding and non-coding mRNA were expressed in a species- and cell-type/tissue-specific manner with individual differences. By examining the repertoire of REST pre-mRNA splicing in 27 patients with kidney, liver and lung cancer, we found that all patients without exception showed differential expression of various REST splice variants between paired tumor and adjacent normal tissues, with striking cell-type/tissue and individual differences. Moreover, we revealed that exon 3 skipping, which causes no frame shift but loss of a domain essential for nuclear translocation, was affected by pioglitazone, a highly selective activator of the peroxisome proliferator-activated receptor gamma (PPAR?) which contributes to cell differentiation and tumorigenesis besides its metabolic actions. Accordingly, this study demonstrates an extensive AS of REST pre-mRNA which redefines REST gene boundary and structure, along with a general but differential link between REST pre-mRNA splicing and various types of cancer. These findings advance our understanding of the complex, context-dependent regulation of REST gene expression and function, and provide potential biomarkers and therapeutic targets for cancer.

Project description:BackgroundRepressor element 1-silencing transcription (REST)/neuron-restrictive silencer factor is considered a new therapeutic target for neurodegenerative disorders such as Alzheimer's disease (AD). However, the relationship between AD and REST remains unclear. This study aimed to 1) examine plasma REST levels and REST gene levels in AD patients and 2) further explore the pathological relationships between REST protein levels and cognitive decline in clinical conditions, including medial temporal lobe atrophy.MethodsParticipants (n = 252, mean age 68.95 ± 8.78 years) were recruited in Beijing, China, and then divided into a normal cognition (NC) group (n = 89), an amnestic mild cognitive impairment (aMCI) group (n = 79), and an AD dementia group (n = 84) according to diagnostic criteria. All participants underwent neuropsychological assessments, laboratory tests, and neuroimaging scans (magnetic resonance imaging) at baseline. Plasma REST protein levels and the distribution of REST single nucleotide polymorphisms (SNPs) were compared among the three groups. Correlations between cognitive function, neuro-imaging results, and REST levels were determined by a multivariate linear regression analysis.ResultsThe plasma REST levels in both the NC group (430.30 ± 303.43)pg/ml and aMCI group (414.27 ± 263.39)pg/ml were significantly higher than that in the AD dementia group (NC vs AD dementia group, p = 0.034; aMCI vs AD dementia group, p = 0.033). There was no significant difference between the NC and aMCI groups (p = 0.948). No significant difference was found among the three groups regarding the genotype distribution (rs2227902 and rs3976529 SNPs) of the REST gene. The REST level was correlated with the left medial temporal lobe atrophy index (r = 0.306, p = 0.023). After 6 months of follow-up, the REST level in the NC group was positively correlated with the change in the Mini-Mental State Examination score (r = 0.289, p = 0.02).ConclusionThe plasma REST protein level is decreased in AD dementia patients, which is associated with memory impairment and left temporal lobe atrophy and may have potential value for clinical diagnosis of AD dementia.

Dataset Information

Cooperative binding of KLF4, pELK-1, and HDAC2 to a G/C repressor element in the SM22? promoter mediates transcriptional silencing during SMC phenotypic switching in vivo.

Publications

Cooperative binding of KLF4, pELK-1, and HDAC2 to a G/C repressor element in the SM22α promoter mediates transcriptional silencing during SMC phenotypic switching in vivo.

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