Induction of high mobility group I architectural transcription factors in proliferating vascular smooth muscle in vivo and in vitro

Integrative analysis of transcriptome-wide association study and mRNA expression profile identified candidate genes and pathways associated with aortic aneurysm and dissection

BACKGROUND

Aortic aneurysm and dissection (AAD) are a set of life-threatening diseases. This study aimed to investigate the genetic mechanisms of AAD by integrating transcriptome-wide association study (TWAS) and mRNA expression profile.

METHODS

The genome-wide association study (GWAS) summary data of AAD was obtained from the UK Biobank, which contains 452,264 White British individuals, including 1470 AAD patients. The TWAS analysis was performed by integrating expression quantitative trait loci (eQTL) data of aorta and the GWAS dataset of AAD using the FUSION software. The TWAS significant genes and differentially expressed genes (DEGs) identified by mRNA expression profile of aortic dissection were integrated to find common genes and biological process. For TWAS significant genes, protein-protein interaction (PPI) network analysis was further conducted based on STRING database.

RESULTS

TWAS identified 423 genes with P < 0.05. After comparing the results of TWAS and mRNA expression profile, 11 overlapping genes (PDE8B, IKBKE, HMGA1, PKM, CHST1, DUS3L, S100A16, PTGS1, RAB38, PDLIM5, NOL6) and 15 common gene ontology (GO) terms (including extracellular matrix organization, external encapsulating structure organization, cell-substrate adhesion, actin filament-based process, focal adhesion, protein kinase activity) were identified. 9 hub genes of the TWAS results were identified via PPI network analysis, including RPS9, RPS18, RSRC1, DNAJC3, HBS1L, PRKCA, NCAM1, ITGB3, FTSJ3.

CONCLUSION

Multiple candidate genes and biological processes associated with AAD were identified by the present integrative study of TWAS and mRNA expression profile. Further studies are needed to elucidate the genetic mechanisms of AAD.

Mesenchymal stromal cells expressing a dominant-negative high mobility group A1 transgene exhibit improved function during sepsis

High mobility group (HMG)A proteins are nonhistone chromatin proteins that bind to the minor groove of DNA, interact with transcriptional machinery, and facilitate DNA-directed nuclear processes. HMGA1 has been shown to regulate genes involved with systemic inflammatory processes. We hypothesized that HMGA1 is important in the function of mesenchymal stromal cells (MSCs), which are known to modulate inflammatory responses due to sepsis. To study this process, we harvested MSCs from transgenic (Tg) mice expressing a dominant-negative (dn) form of HMGA1 in mesenchymal cells. MSCs harvested from Tg mice contained the dnHMGA1 transgene, and transgene expression did not change endogenous HMGA1 levels. Immunophenotyping of the cells, along with trilineage differentiation revealed no striking differences between Tg and wild-type (WT) MSCs. However, Tg MSCs growth was decreased compared with WT MSCs, although Tg MSCs were more resistant to oxidative stress-induced death and expressed less IL-6. Tg MSCs administered after the onset of Escherichia coli-induced sepsis maintained their ability to improve survival when given in a single dose, in contrast with WT MSCs. This survival benefit of Tg MSCs was associated with less tissue cell death, and also a reduction in tissue neutrophil infiltration and expression of neutrophil chemokines. Finally, Tg MSCs promoted bacterial clearance and enhanced neutrophil phagocytosis, in part through their increased expression of stromal cell-derived factor-1 compared with WT MSCs. Taken together, these data demonstrate that expression of dnHMGA1 in MSCs provides a functional advantage of the cells when administered during bacterial sepsis.

HMGA1 Mediated High-Glucose-Induced Vascular Smooth Muscle Cell Proliferation in Diabetes Mellitus: Association Between PI3K/Akt Signaling and HMGA1 Expression

High-mobility group protein A1 (HMGA1), an architectural transcription factor, was found to regulate multiple gene expression in mammals. Recent studies firmly indicate an association between HMGA1 and type 2 diabetes. However, the presence and function of HMGA1 in diabetic vasculopathy has not been substantiated. in this study, we first determined the HMGA1 changes in aorta tissue of diabetic rats. In streptozotocin-induced diabetic rats, a higher level of blood glucose and plasma lipids, an increase of intima-media thickness, and a significant upregulation and accumulation of HMGA1, mainly in the nucleus and around the nuclear membrane of vascular smooth muscle cells (VSMCs), were detected. In vitro, high glucose increased HMGA1 expression and promoted proliferation of VSMCs, which could be blunted by Wortmannin and LY294002, inhibitors of PI3K/Akt pathway, and specificity protein 1 (SP1) siRNA. Moreover, knockdown of HMGA1 could weaken the upregulation of cyclin D1 accompanied by high-glucose-induced HMGA1 in VSMCs. Taken together, these findings demonstrate the vital role of PI3K/Akt-SP1-HMGA1 pathway in high-glucose-induced VSMCs proliferation.

Repression of smooth muscle differentiation by a novel high mobility group box-containing protein, HMG2L1

The molecular mechanisms regulating smooth muscle-specific gene expression during smooth muscle development are poorly understood. Myocardin is an extraordinarily powerful cofactor of serum response factor (SRF) that stimulates expression of smooth muscle-specific genes. In an effort to search for proteins that regulate myocardin function, we identified a novel HMG box-containing protein HMG2L1 (high mobility group 2 like 1). We found that HMG2L1 expression is correlated with the smooth muscle cell (SMC) synthetic phenotype. Overexpression of HMG2L1 in SMCs down-regulated smooth muscle marker expression. Conversely, depletion of endogenous HMG2L1 in SMCs increases smooth muscle-specific gene expression. Furthermore, we found HMG2L1 specifically abrogates myocardin-induced activation of smooth muscle-specific genes. By GST pulldown assays, the interaction domains between HMG2L1 and myocardin were mapped to the N termini of each of the proteins. Finally, we demonstrated that HMG2L1 abrogates myocardin function through disrupting its binding to SRF and abolishing SRF-myocardin complex binding to the promoters of smooth muscle-specific genes. This study provides the first evidence of this novel HMG2L1 molecule playing an important role in attenuating smooth muscle differentiation.

Transcription factor CHF1/Hey2 regulates the global transcriptional response to platelet-derived growth factor in vascular smooth muscle cells

The cardiovascular restricted transcription factor CHF1/Hey2 has been previously shown to regulate the smooth muscle response to growth factors. To determine how CHF1/Hey2 affects the smooth muscle response to growth factors, we performed a genomic screen for transcripts that are differentially expressed in wild-type and knockout smooth muscle cells after stimulation with platelet-derived growth factor. We screened 45,101 probes representing >39,000 transcripts derived from at least 34,000 genes, at eight different time points. We analyzed the expression data utilizing an algorithm based on Bayesian statistics to derive the best polynomial clustering model to fit the expression data. We found that in a total of 9,827 transcripts the normalized ratio of knockout to wild-type expression diverged more than threefold from baseline in at least one time point, and these transcripts separated into 17 distinct clusters. Further analysis of each cluster revealed distinct alterations in gene expression patterns for immediate early genes, transcription factors, matrix metalloproteinases, signaling molecules, and other molecules important in vascular biology. Our findings demonstrate that CHF1/Hey2 profoundly affects vascular smooth muscle phenotype by altering both the absolute expression level of a variety of genes and the kinetics of growth factor-induced gene expression.

Transcription Factor SOX18 Is Expressed in Human Coronary Atherosclerotic Lesions and Regulates DNA Synthesis and Vascular Cell Growth

OBJECTIVE

SOX18, a member of the SOX gene family (SRY-like 3-hydroxy-3-methylglutaryl box gene), is a transcription factor expressed in the development of blood vessels during embryogenesis. We analyzed SOX18 expression in human coronary atherosclerotic lesions and investigated its potential function in vascular cells.

METHODS AND RESULTS

In advanced human coronary atherosclerotic lesions, SOX18 immunostaining was localized in endothelial cells (on the luminal surface, in vasa vasorum, and in intimal neovessels) and in vascular smooth muscle cells (VSMCs) scattered in the intima, colocalizing with proliferating cell nuclear antigen. In cell cultures, SOX18 was mainly localized in subconfluent and denuded areas. Significant SOX18 mRNA levels (by Northern blot analysis and reverse transcription-polymerase chain reaction) were detected in cell cultures from human umbilical vein endothelial cells and human VSMCs. Antisense SOX18 inhibited DNA synthesis ([3H]thymidine incorporation) and vascular cell growth. Antisense SOX18 also significantly reduced VSMC regrowth after injury in an in vitro model of wound repair.

CONCLUSIONS

Our results indicate that SOX18 is involved in vascular cell growth and suggest that this transcription factor may play a role in atherosclerosis.

HMGA1 proteins in human atherosclerotic plaques

One of the major characteristics of atherosclerosis is the migration of smooth muscle cells (SMC) from the tunica media to the intima, caused by alterations in the environment, e.g. mechanical, chemical, or immunologic injuries of the arterial walls. A group of molecules that may act as a main regulator of SMC phenotype switching is formed by the so-called HMGA1 high-mobility group proteins. One target gene of the HMGA1 protein, playing a major role in the development of atherosclerotic lesions, is CD44. The expression of CD44 is regulated by IL-1beta, but binding of HMGA1 potentiates the transactivation of the CD44 promoter. In this study, the HMGA1 expression of human atherosclerotic plaque samples was examined. Compared to the non-active components, all major components of the well-developed atherosclerotic plaques showed strong positivity of the high-mobility group protein HMGA1 in their activated areas, e.g. neointimal SMCs, macrophages, newly built blood vessels. This report is the first to describe HMGA1 as one of the first mediators in the development of human atherosclerotic plaques.

High mobility group A2 protein and its derivatives bind a specific region of the promoter of DNA repair gene ERCC1 and modulate its activity

High mobility group A2 (HMGA2) chromosomal non-histone protein and its derivatives play an important role in development and progression of benign and malignant tumors, obesity and arteriosclerosis, although the underlying mechanisms of these conditions are poorly understood. Therefore, we tried to identify target genes for this transcriptional regulator and to provide insights in the mechanism of interaction to its target. Multiple genes have been identified by microarray experiments as being transcriptionally regulated by HMGA2. Among these we chose the ERCC1 gene, encoding a DNA repair protein, for this study. DNA-binding studies were performed using HMGA2 and C-terminally truncated DeltaHMGA2, a derivative that is frequently observed in a variety of tumors. A unique high affinity HMGA2 binding site was mapped to a specific AT-rich region located -323 to -298 upstream of the ERCC1 transcription start site, distinguishing it from other potential AT-rich binding sites. The observed 1:1 stoichiometry for the binding of wild-type HMGA2 to this region was altered to 1:2 upon binding of truncated DeltaHMGA2, causing DNA bending. Furthermore, the regulatory effect of HMGA2 was confirmed by luciferase promoter assays showing that ERCC1 promoter activity is down-regulated by all investigated HMGA2 forms, with the most striking effect exerted by DeltaHMGA2. Our results provide the first insights into how HMGA2 and its aberrant forms bind and regulate the ERCC1 promoter.

Regulation of smooth muscle phenotype

Differentiated smooth muscle cells (SMCs) remain highly plastic, enabling them to alter their phenotype in response to environmental and pathologic stimuli. SMCs in vascular pathologies such as atherosclerosis exhibit phenotypes clearly different from those of the mature cells in normal blood vessels. These phenotypically modulated SMCs play an integral role in the development of vascular diseases. This review addresses recent progress in our understanding of the mechanisms that control SMC phenotype during vascular development and in vascular disease. A particular focus is on the transcriptional control programs of the differentiated state of SMCs.

Egr1 promotes growth and survival of prostate cancer cells. Identification of novel Egr1 target genes

In the majority of aggressive tumorigenic prostate cancer cells, the transcription factor Egr1 is overexpressed. We provide new insights of Egr1 involvement in proliferation and survival of TRAMP C2 prostate cancer cells by the identification of several new target genes controlling growth, cell cycle progression, and apoptosis such as cyclin D2, P19ink4d, and Fas. Egr1 regulation of these genes, identified by Affymetrix microarray, was confirmed by real-time PCR, immunoblot, and chromatin immunoprecipitation assays. Furthermore we also showed that Egr1 is responsible for cyclin D2 overexpression in tumorigenic DU145 human prostate cells. The regulation of these genes by Egr1 was demonstrated using Egr1 antisense oligonucleotides that further implicated Egr1 in resistance to apoptotic signals. One mechanism was illustrated by the ability of Egr1 to inhibit CD95 (Fas/Apo) expression, leading to insensitivity to FasL. The results provide a mechanistic basis for the oncogenic role of Egr1 in TRAMP C2 prostate cancer cells.

Human HMGA2 promoter is coregulated by a polymorphic dinucleotide (TC)-repeat

HMGA proteins are thought to be causally involved in the progression of different diseases, including benign and malignant tumors, obesity, arteriosclerosis, and restenosis. As HMGA proteins are architectural transcription factors, their binding to DNA leads to changes in DNA-conformation modulating the environment for the assembly and function of transcriptional complexes, thus influencing the expression of a huge variety of genes. Despite the emerging role of HMGA proteins for important diseases, only limited information is available about mechanisms regulating the expression of the HMGA2 gene. In this report, 2240 bp of the 5' flanking region of the HMGA2 gene were functionally analyzed by luciferase assay experiments. Besides the identification of novel positive and negative regulatory elements, it was shown that transcription is initiated from two independent promoter regions within cell lines HeLa, MCF7, and L14TSV40. Furthermore, a functional polymorphic dinucleotide repeat (TCTCT(TC)(n)) 500 bp upstream of the ATG translational start codon was found to regulate strongly the human HMGA2 promoter with an activation pattern that correlates to its TC-repeat length.

The HMG I proteins: dynamic roles in gene activation, development, and tumorigenesis

The high mobility group I, Y, and I-C proteins are low-molecular-weight, nonhistone chromosomal proteins that play a general role modulating gene expression during development and the immune response. Consistent with their role in early development, all three proteins are expressed at high levels during embryogenesis, and their expression is markedly diminished in differentiated cells. Exceptions to the general repression of these genes in adult tissues involve (1) A burst of synthesis of the HMG I protein during the immune response (during lymphocyte activation and preceding cytokine/adhesion molecule gene expression), (2) A constitutive expression of the HMG I and Y proteins in photoreceptor cells, and (3) Derepression of HMG I, Y, and often I-C expression in neoplastic cells. Work from several laboratories has now uncovered how these proteins participate in gene activation: (1) By altering the chromatin structure around an inducible gene-and thus influencing accessibility of the locus to regulatory proteins-(2) By facilitating the loading of transcription factors onto the promoters, and (3) By bridging adjacent transcription factors on a promoter via protein/protein interactions. Despite the similar structures and biochemical properties of the three proteins, the work has also provided clues to a division of labor between these proteins. HMG I and Y have demonstrable roles in enhanceosome formation, whereas HMG I-C has a specific role in adipogenesis. C-terminal truncations of HMG I-C and wild-type HMG Y appear to function in a manner analogous to oncogenes, as assessed by cellular transforation assays and transgenic mice. Future work should clearly define the similarities and differences in the biological roles of the three proteins, and should evolve to include attempts at pharmaceutical intervention in disease, based upon structural information concerning HMG I interactions with DNA and with regulatory proteins.

Striated muscle preferentially expressed genes alpha and beta are two serine/threonine protein kinases derived from the same gene as the aortic preferentially expressed gene-1

Aortic preferentially expressed gene (APEG)-1 is a 1.4-kilobase pair (kb) mRNA expressed in vascular smooth muscle cells and is down-regulated by vascular injury. An APEG-1 5'-end cDNA probe identified three additional isoforms. The 9-kb striated preferentially expressed gene (SPEG)alpha and the 11-kb SPEGbeta were found in skeletal muscle and heart. The 4-kb brain preferentially expressed gene was detected in the brain and aorta. We report here cloning of the 11-kb SPEGbeta cDNA. SPEGbeta encodes a 355-kDa protein that contains two serine/threonine kinase domains and is homologous to proteins of the myosin light chain kinase family. At least one kinase domain is active and capable of autophosphorylation. In the genome, all four isoforms share the middle three of the five exons of APEG-1, and they differ from each other by using different 5'- and 3'-ends and alternative splicing. We show that the expression of SPEGalpha and SPEGbeta is developmentally regulated in the striated muscle during C2C12 myoblast to myotube differentiation in vitro and cardiomyocyte maturation in vivo. This developmental regulation suggests that both SPEGalpha and SPEGbeta can serve as sensitive markers for striated muscle differentiation and that they may be important for adult striated muscle function.