Role of Sp1 in the induction of p27 gene expression in vascular smooth muscle cells in vitro and after balloon angioplasty

Role of Sp1 in atherosclerosis

Specificity protein (Sp) is a famous family of transcription factors including Sp1, Sp2 and Sp3. Sp1 is the first one of Sp family proteins to be characterized and cloned in mammalian. It has been proposed that Sp1 acts as a modulator of the expression of target gene through interacting with a series of proteins, especially with transcriptional factors, and thereby contributes to the regulation of diverse biological processes. Notably, growing evidence indicates that Sp1 is involved in the main events in the development of atherosclerosis (AS), such as inflammation, lipid metabolism, plaque stability, vascular smooth muscle cells (VSMCs) proliferation and endothelial dysfunction. This review is designed to provide useful clues to further understanding roles of Sp1 in the pathogenesis of AS, and may be helpful for the design of novel efficacious therapeutics agents targeting Sp1.

The cyclin-dependent kinase inhibitor p27Kip1 interacts with the aryl hydrocarbon receptor and negatively regulates its transcriptional activity

p27^Kip1 functions to coordinate cell cycle progression through the inhibition of cyclin-dependent kinase (CDK) complexes. p27^Kip1 also exerts distinct activities beyond CDK-inhibition, including functioning as a transcriptional regulator. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor with diverse biological roles. The regulatory inputs that control AhR-mediated transcriptional responses are an active area of investigation. AhR was previously established as a direct regulator of p27^Kip1 transcription. Here, we report the physical interaction of AhR and p27^Kip1 and show that p27^Kip1 expression negatively regulates AhR-mediated transcription. p27^Kip1 knockout cells display increased AhR nuclear localisation and significantly higher expression of AhR target genes. This work thus identifies new regulatory cross-talk between p27^Kip1 and AhR.

Valproate and Short-Chain Fatty Acids Activate Transcription of the Human Vitamin D Receptor Gene through a Proximal GC-Rich DNA Region Containing Two Putative Sp1 Binding Sites

The vitamin D receptor (VDR) mediates 1,25-dihydroxyvitamin D3 pleiotropic biological actions through transcription regulation of target genes. The expression levels of this ligand-activated nuclear receptor are regulated by multiple mechanisms both at transcriptional and post-transcriptional levels. Vitamin D3 is the natural VDR activator, but other molecules and signaling pathways have also been reported to regulate VDR expression and activity. In this study, we identify valproic acid (VPA) and natural short-chain fatty acids (SCFAs) as novel transcriptional activators of the human VDR (hVDR) gene. We further report a comprehensive characterization of VPA/SCFA-responsive elements in the 5' regulatory region of the hVDR gene. Two alternative promoter DNA regions (of 2.4 and 3.8 kb), as well as subsequent deletion fragments, were cloned in pGL4-LUC reporter vector. Transfection of these constructs in HepG2 and human Upcyte hepatocytes followed by reporter assays demonstrated that a region of 107 bp (from -107 to -1) upstream of the transcription start site in exon 1a is responsible for most of the increase in transcriptional activity in response to VPA/SCFAs. This short DNA region is GC-rich, does not contain an apparent TATA box, and includes two bona fide binding sites for the transcription factor Sp1. Our results substantiate the hypothesis that VPA and SCFAs facilitate the activity of Sp1 on novel Sp1 responsive elements in the hVDR gene, thus promoting VDR upregulation and signaling. Elevated hepatic VDR levels have been associated with liver steatosis and, therefore, our results may have clinical relevance in epileptic pediatric patients on VPA therapy. Our results could also be suggestive of VDR upregulation by SCFAs produced by gut microbiota.

Amlodipine induces vasodilation via Akt2/Sp1-activated miR-21 in smooth muscle cells

BACKGROUND AND PURPOSE

The calcium antagonist amlodipine exerts important cardioprotective effects by modulating smooth muscle and endothelial functions. However, the mechanisms underlying these effects are incompletely understood.

EXPERIMENTAL APPROACH

Western blotting was used to compare the expression of key genes involved in vascular smooth muscle cell (VSMC) phenotype conversion. Recombinant adeno-associated virus system was used to regulate miRNA expression in rats via tail vein. Bioinformatics was used to predict the transcriptional regulation of miR-21 upstream followed by biochemical validation using quantitative real-time polymerase chain reaction, ChIP-qPCR and EMSA assays.

KEY RESULTS

Only the calcium antagonist amlodipine, and no other type of anti-hypertensive drug, induced miR-21 overexpression in plasma and aortic vessels in the animal model. Real-time PCR and luciferase assays showed that amlodipine induced miR-21 overexpression in vascular smooth muscle cells. Western blot and immunofluorescence assays demonstrated that amlodipine activated Akt2, rather than Akt1, followed by activation of transcription factor Sp1, which regulated VSMC phenotype conversion via binding to the miR-21 promoter. Furthermore, bioinformatic analyses and luciferase assays demonstrated that amlodipine activated miR-21 transcription at the -2034/-2027 Sp1-binding site, which was further demonstrated by ChIP-qPCR and EMSA assays. Consistently, small-interfering RNA-mediated knockdown of Akt2 and Sp1 significantly attenuated the effects of amlodipine on miR-21 expression in smooth muscle cells.

CONCLUSION AND IMPLICATIONS

These results indicate that amlodipine induces smooth muscle cell differentiation via miR-21, which is regulated by p-Akt2 and Sp1 nuclear translocation, thereby providing a novel target for cardiovascular diseases.

Sirtuin 1 Mediates the Actions of Peroxisome Proliferator-Activated Receptor δ on the Oxidized Low-Density Lipoprotein-Triggered Migration and Proliferation of Vascular Smooth Muscle Cells

Peroxisome proliferator-activated receptor δ (PPARδ) has been implicated in vascular pathophysiology. However, its functions in atherogenic changes of the vascular wall have not been fully elucidated. PPARδ activated by GW501516 (2-[2-methyl-4-[[4-methyl-2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-5-yl]methylsulfanyl]phenoxy]acetic acid) significantly inhibited the migration and proliferation of vascular smooth muscle cells (VSMCs) triggered by oxidized low-density lipoprotein (oxLDL). These GW501516-mediated effects were significantly reversed by PPARδ-targeting small-interfering RNA (siRNA), indicating that PPARδ is involved in the action of GW501516. The antiproliferative effect of GW501516 was directly linked to cell cycle arrest at the G₀/G₁ to S phase transition, which was followed by the down-regulation of cyclin-dependent kinase 4 along with increased levels of p21 and p53. In VSMCs treated with GW501516, the expression of sirtuin 1 (SIRT1) mRNA and protein was time-dependently increased. This GW501516-mediated up-regulation of SIRT1 expression was also demonstrated even in the presence of oxLDL. In addition, GW501516-dependent inhibition of oxLDL-triggered migration and proliferation of VSMCs was almost completely abolished in the presence of SIRT1-targeting siRNA. These effects of GW501516 on oxLDL-triggered phenotypic changes of VSMCs were also demonstrated via activation or inhibition of SIRT1 activity by resveratrol or sirtinol, respectively. Finally, gain or loss of SIRT1 function imitated the action of PPARδ on oxLDL-triggered migration and proliferation of VSMCs. Taken together, these observations indicate that PPARδ-dependent up-regulation of SIRT1 contributes to the antiatherogenic activities of PPARδ by suppressing the migration and proliferation of VSMCs linked to vascular diseases such as restenosis and atherosclerosis.

Everolimus (RAD001) inhibits the proliferation of rat vascular smooth muscle cells by up-regulating the activity of the p27/kip1 gene promoter

OBJECTIVE

We investigated whether the inhibitory effect of the immunosuppressant everolimus (RAD001) on vascular smooth muscle cell (VSMC) proliferation is mediated by p27/kip1 gene promoter activity.

METHODS

In this experimental study, cultured rat VSMCs were transiently transfected with a recombinant plasmid (pXp27) containing p27/kip1 gene promoter sequence and a chloramphenicol acetyltransferase (CAT) reporter gene. After stimulation with the mitogen platelet-derived growth factor (PDGF-BB, 10 ng/mL) in the presence or absence of RAD001 (10 nM), the promoter activity, mRNA expression, and protein expression of p27/kip1 were examined by CAT assay, RT-PCR, and immunoblotting, respectively. Cell cycle-related changes were detected by flow cytometry. DNA synthesis was determined using 3H-TdR incorporation.

RESULTS

Compared with the non-stimulation group, PDGF-BB stimulation induced a significant proliferative response in the VSMCs as indicated by decreased p27/kip1 gene promoter activity, decreased p27/kip1 mRNA and protein expression, increased S-phase and G2/M-phase cells, and increased DNA synthesis. RAD001 intervention increased p27/kip1 gene promoter activity 3.5-fold, promoted p27/kip1 mRNA and protein expression, increased G0-phase cells, reduced DNA synthesis, and, overall, inhibited PDGF-BB-stimulated cell proliferation.

CONCLUSION

RAD001 inhibits PDGF-BB-stimulated proliferation of cultured VSMCs by upregulating p27/kip1 gene promoter activity and increasing p27/kip1 mRNA and protein expression.

Prevention of vascular smooth muscle cell proliferation and injury-induced neointimal hyperplasia by CREB-mediated p21 induction: An insight from a plant polyphenol

Cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/cAMP response element (CRE)-binding protein (CREB) signaling cascade negatively regulates platelet-derived growth factor BB (PDGF-BB)-induced smooth muscle cell (SMC) proliferation, which is a critical event in the initiation and development of restenosis and atherosclerotic lesions. Salvianolic acid A (SAA) is one of the most abundant polyphenols extracted from salvia. The aim of this study is to investigate whether SAA exerts an action on PDGF-BB-induced proliferation via cAMP/PKA/CREB mechanism. SAA blunts PDGF-BB-induced human umbilical artery smooth muscle cell (hUASMC) proliferation via p21 induction, as evidenced by its increased mRNA and protein expression levels. The SAA-induced upregulation of p21 involves the cAMP/PKA signaling pathway; a cAMP analog mimicked the effects of SAA and a specific cAMP/PKA inhibitor opposed these effects. SAA also activated CREB, including phosphorylation at Ser133, and induced its nuclear translocation. Deletion and mutational analysis of p21 promoters, co-immunoprecipitation, and western blot analysis showed that CRE is essential for SAA-induced p21 protein expression. Transfection of dominant-negative CREB (mutated Ser133) plasmids into hUASMCs attenuated SAA-stimulated p21 expression. SAA upregulated p21 expression and activated CREB in the neointima of balloon-injured arteries in vivo. Our results indicate that SAA promotes p21 expression in SMCs through the cAMP/PKA/CREB signaling cascade in vitro and prevents injury-induced neointimal hyperplasia.

The microRNA miR-34c inhibits vascular smooth muscle cell proliferation and neointimal hyperplasia by targeting stem cell factor

The fine balance between proliferation and differentiation of vascular smooth muscle cells (VSMCs) is indispensable for the maintenance of healthy blood vessels, whereas an increase in proliferation participates in pathologic cardiovascular events such as atherosclerosis and restenosis. Here we report that microRNA-34c (miR-34c) targets stem cell factor (SCF) to inhibit VSMC proliferation and neointimal hyperplasia. In an animal model, miR-34c was significantly increased in the rat carotid artery after catheter injury. Transient transfection of miR-34c to either VSMCs or A10 cells inhibited cell survival by inducing apoptosis, which was accompanied by an increase in expression of p21, p27, and Bax. Transfection of miR-34c also attenuated VSMC migration. Bioinformatics showed that SCF is a target candidate of miR-34c. miR-34c down-regulated luciferase activity driven by a vector containing the 3'-untranslated region of SCF in a sequence-specific manner. Forced expression of SCF in A10 cells induced proliferation and migration, whereas knocking-down of SCF reduced cell survival and migration. miR-34c antagomir-induced VSMC proliferation was blocked by SCF siRNA. Delivery of miR-34c to rat carotid artery attenuated the expression of SCF and blocked neointimal hyperplasia. These results suggest that miR-34c is a new modulator of VSMC proliferation and that it inhibits neointima formation by regulating SCF.

Histone deacetylase inhibitors modulate the transcriptional regulation of guanylyl cyclase/natriuretic peptide receptor-a gene: interactive roles of modified histones, histone acetyltransferase, p300, AND Sp1

Atrial natriuretic peptide (ANP) binds guanylyl cyclase-A/natriuretic peptide receptor-A (GC-A/NPRA) and produces the intracellular second messenger, cGMP, which regulates cardiovascular homeostasis. We sought to determine the function of histone deacetylases (HDACs) in regulating Npr1 (coding for GC-A/NPRA) gene transcription, using primary mouse mesangial cells treated with class-specific HDAC inhibitors (HDACi). Trichostatin A, a pan inhibitor, and mocetinostat (MGCD0103), a class I HDAC inhibitor, significantly enhanced Npr1 promoter activity (by 8- and 10-fold, respectively), mRNA levels (4- and 5.3-fold, respectively), and NPRA protein (2.7- and 3.5-fold, respectively). However, MC1568 (class II HDAC inhibitor) had no discernible effect. Overexpression of HDAC1 and HDAC2 significantly attenuated Npr1 promoter activity, whereas HDAC3 and HDAC8 had no effect. HDACi-treated cultured cells in vitro and intact animals in vivo showed significantly reduced binding of HDAC1 and -2 and increased accumulation of acetylated H3-K9/14 and H4-K12 at the Npr1 promoter. Deletional analyses of the Npr1 promoter along with ectopic overexpression and inhibition of Sp1 confirmed that HDACi-induced Npr1 gene transcription is accomplished by Sp1 activation. Furthermore, HDACi attenuated the interaction of Sp1 with HDAC1/2 and promoted Sp1 association with p300 and p300/cAMP-binding protein-associated factor; it also promoted the recruitment of p300 and p300/cAMP-binding protein-associated factor to the Npr1 promoter. Our results demonstrate that trichostatin A and MGCD0103 enhanced Npr1 gene expression through inhibition of HDAC1/2 and increased both acetylation of histones (H3-K9/14, H4-K12) and Sp1 by p300, and their recruitment to Npr1 promoter. Our findings define a novel epigenetic regulatory mechanism that governs Npr1 gene transcription.

The microRNA miR-132 targets Lrrfip1 to block vascular smooth muscle cell proliferation and neointimal hyperplasia

OBJECTIVE

The proliferation and remodeling of vascular smooth muscle cells (VSMCs) is an important pathological event in atherosclerosis and restenosis. Here we report that microRNA-132 (miR-132) blocks vascular smooth muscle cells (VSMC) proliferation by inhibiting the expression of LRRFIP1 [leucine-rich repeat (in Flightless 1) interacting protein-1].

METHODS AND RESULTS

MicroRNA microarray revealed that miR-132 was upregulated in the rat carotid artery after catheter injury, which was further confirmed by quantitative real-time RT-PCR. Transfection of a miR-132 mimic significantly inhibited the proliferation of VSMCs, whereas transfection of a miR-132 antagomir increased it. miR-132 mimic inhibited VSMC migration and induced apoptosis. miR-132 mimic increased the protein amounts of both p27 and smooth muscle (SM) α-actin, whereas it decreased SM α-actin and Bcl2. Bioinformatics showed that LRRFIP1 is a target candidate of miR-132. miR-132 down-regulated luciferase activity driven by a vector containing the 3'-untranslated region of Lrrfip1 in a sequence-specific manner. LRRFIP1 induced VSMC proliferation and increased phosphorylation of ERK. Immunohistochemical analysis revealed that Lrrfip1 was clearly expressed along with the basal laminar area of smooth muscle, and its expression pattern was disrupted 7 days after arterial injury. LRRFIP1 mRNA was decreased 14 days after injury. Delivery of miR-132 to rat carotid artery reduced LRRFIP1 expression and attenuated neointimal proliferation in carotid artery injury models.

CONCLUSIONS

Our results suggest that miR-132 is a novel regulator of VSMC proliferation that represses neointimal formation by inhibiting LRRFIP1 expression.

Genome-wide microarray analyses identify the protein C receptor as a novel calcineurin/nuclear factor of activated T cells-dependent gene in vascular smooth muscle cell phenotypic modulation

OBJECTIVE

Calcineurin (Cn) and the nuclear factor of activated T cells (NFAT) family of transcription factors are critical in vascular smooth muscle cell (SMC) development and pathology. Here, we used a genomics approach to identify and validate NFAT gene targets activated during platelet-derived growth factor-BB (PDGF-BB)-induced SMC phenotypic modulation.

METHODS AND RESULTS

Genome-wide expression arrays were used to identify genes both (1) differentially activated in response to PDGF-BB and (2) whose differential expression was reduced by both the Cn inhibitor cyclosporin A and the NFAT inhibitor A-285222. The 20 most pharmacologically sensitive genes were validated by quantitative reverse transcription-polymerase chain reaction analysis of PDGF-BB-stimulated SMCs in the presence of Cn/NFAT inhibitors, including the VIVIT peptide. In all experiments, protein C receptor (PROCR) gene activation was reduced. We showed that PROCR expression was virtually absent in untreated, quiescent SMCs. PDGF-BB stimulation, however, induced significant PROCR promoter activation and downstream protein expression in a Cn/NFAT-dependent manner. Mutation of a species-conserved, NFAT binding motif significantly attenuated PDGF-BB-induced PROCR promoter activity, thereby distinguishing NFAT as the first PROCR transcriptional activator to date. Moreover, SMC PROCR expression was upregulated in the neointima as early as 7 days following acute vascular injury in rat carotid arteries.

CONCLUSION

We hereby report PROCR as a novel, NFAT-dependent gene that may be implicated in vascular restenosis and consequent inward remodeling.

The promoter activity of human Mfn2 depends on Sp1 in vascular smooth muscle cells

AIMS

Mitofusin-2 (Mfn2) expression is dysregulated in vascular proliferative disorders and its overexpression attenuates the proliferation of vascular smooth muscle cells (VSMCs) and neointimal lesion development after balloon angioplasty. We sought to gain insight into the mechanisms that control Mfn2 expression in VSMCs.

METHODS AND RESULTS

We cloned and characterized 2 kb of the 5'-flanking region of the human Mfn2 gene. Its TATA-less promoter contains a CpG island. In keeping with this, 5'-rapid amplification of cDNA ends revealed six transcriptional start sites (TSSs), of which TSS2 and TSS5 were the most frequently used. The strong CpG island was found to be non-methylated under conditions characterized by large differences in Mfn2 gene expression. The proximal Mfn2 promoter contains six putative Sp1 motifs. Sp1 binds to the Mfn2 promoter and its overexpression activates the Mfn2 promoter in VSMCs. Chemical inhibition of Sp1 reduced Mfn2 expression, and Sp1 silencing reduced transcriptional activity of the Mfn2 promoter. In keeping with this view, Sp1 and Mfn2 mRNA levels were down-regulated in the aorta early after an atherogenic diet in apolipoprotein E-knockout mice or in VSMCs cultured in the presence of low serum.

CONCLUSION

Sp1 is a key factor in maintaining basal Mfn2 transcription in VSMCs. Given the anti-proliferative actions of Mfn2, Sp1-induced Mfn2 transcription may represent a mechanism for prevention of VSMC proliferation and neointimal lesion and development.

Specificity protein-1 as a critical regulator of human cystathionine gamma-lyase in smooth muscle cells

Cystathionine γ-lyase (CSE) is the major enzyme in vascular smooth muscle cells (SMCs) that catalyzes the endogenous production of H(2)S. Phenotypic switching of SMCs is affected by endogenous H(2)S level and alterations of this switching may result in vascular disorders. To date, the mechanisms underlying the alteration of CSE expression and H(2)S production in vascular proliferative diseases have been unclear. In the present study, we found that serum deprivation induced SMC differentiation marker gene expressions and increased CSE expression and H(2)S production in cultured human aorta SMCs (HASMCs). Carotid artery ligation in mice resulted in enhanced neointima formation and down-regulation of CSE expression, suggesting an important role of CSE in SMC differentiation. Transient transfection of HASMCs with human CSE (hCSE) promoter/luciferase reporter revealed that the region between -226 to +140 base pair contains the core promoter for the hCSE gene. Deletion and mutation analysis demonstrated that two specificity protein-1 (Sp1) consensus binding sites were present in the core promoter region of the hCSE gene. Incubation of HASMCs with Sp1 binding inhibitor mithramycin inhibited CSE mRNA expression in a dose-dependent manner. Overexpression of Sp1 alone was sufficient to increase the activity of the hCSE core promoter and CSE protein expression. Chromatin immunoprecipitation assay showed that the binding of Sp1 to the hCSE promoter was increased in differentiated HASMCs compared with that in proliferated HASMCs. Exogenously applied H(2)S at 100 μM stimulated SMC differentiation, which was reversed by p38 MAPK inhibitor SB203580. These results suggest that transcript factor Sp1 is a critical regulator of the hCSE expression during SMC differentiation, and CSE/H(2)S system is essential for maintenance of SMC phenotype.

Interactive roles of Ets-1, Sp1, and acetylated histones in the retinoic acid-dependent activation of guanylyl cyclase/atrial natriuretic peptide receptor-A gene transcription

Cardiac hormones atrial and brain natriuretic peptides activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), which plays a critical role in reduction of blood pressure and blood volume. Currently, the mechanisms responsible for regulating the Npr1 gene (coding for GC-A/NPRA) transcription are not well understood. The present study was conducted to examine the interactive roles of all-trans retinoic acid (ATRA), Ets-1, Sp1, and histone acetylation on the transcriptional regulation and function of the Npr1 gene. Deletion analysis of the Npr1 promoter and luciferase assays showed that ATRA enhanced a 16-fold Npr1 promoter activity and greatly stimulated guanylyl cyclase (GC) activity of the receptor protein in both atrial natriuretic peptide (ANP)-dependent and -independent manner. As confirmed by gel shift and chromatin immunoprecipitation assays, ATRA enhanced the binding of both Ets-1 and Sp1 to the Npr1 promoter. The retinoic acid receptor α (RARα) was recruited by Ets-1 and Sp1 to form a transcriptional activator complex with their binding sites in the Npr1 promoter. Interestingly, ATRA also increased the acetylation of histones H3 and H4 and enhanced their recruitment to Ets-1 and Sp1 binding sites within the Npr1 promoter. Collectively, the present results demonstrate that ATRA regulates Npr1 gene transcription and GC activity of the receptor by involving the interactive actions of Ets-1, Sp1, and histone acetylation.

Baicalin inhibits PDGF-BB-stimulated vascular smooth muscle cell proliferation through suppressing PDGFRβ-ERK signaling and increase in p27 accumulation and prevents injury-induced neointimal hyperplasia

The increased proliferation and migration of vascular smooth muscle cells (VSMCs) are key events in the development of atherosclerotic lesions. Baicalin, an herb-derived flavonoid compound, has been previously shown to induce apoptosis and growth inhibition in cancer cells through multiple pathways. However, the potential role of baicalin in regulation of VSMC proliferation and prevention of cardiovascular diseases remains unexplored. In this study, we show that pretreatment with baicalin has a dose-dependent inhibitory effect on PDGF-BB-stimulated VSMC proliferation, accompanied with the reduction of proliferating cell nuclear antigen (PCNA) expression. We also show that baicalin-induced growth inhibition is associated with a decrease in cyclin E-CDK2 activation and increase in p27 level in PDGF-stimulated VSMCs, which appears to be at least partly mediated by blockade of PDGF receptor β (PDGFRβ)-extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. In addition, baicalin was also found to inhibit adhesion molecule expression and cell migration induced by PDGF-BB in VSMCs. Furthermore, using an animal carotid arterial balloon-injury model, we found that baicalin significantly inhibited neointimal hyperplasia. Taken together, our results reveal a novel function of baicalin in inducing growth arrest of PDGF-stimulated VSMCs and suppressing neointimal hyperplasia after balloon injury, and suggest that the underlying mechanism involves the inhibition of cyclin E-CDK2 activation and the increase in p27 accumulation via blockade of the PDGFRβ-ERK1/2 signaling cascade.

Tissue inhibitor of metalloproteinase-3 inhibits neonatal mouse cardiomyocyte proliferation via EGFR/JNK/SP-1 signaling

We have recently demonstrated that tissue inhibitor of metalloproteinase-3 (TIMP-3) decreases neonatal cardiomyocyte proliferation (Hammoud L, Xiang F, Lu X, Brunner F, Leco K, Feng Q. Cardiovasc Res 75: 359–368, 2007). The aim of the present study was to delineate a pathway through which TIMP-3 exerts its antiproliferative effect. Experiments were conducted on neonatal cardiomyocyte cultures and heart tissues isolated from wild-type (WT) and TIMP-3−/− mice. Deficiency in TIMP-3 decreased p27 expression and increased cardiomyocyte proliferation in cardiomyocytes and neonatal hearts. A TIMP-3/epidermal growth factor (EGF) receptor (EGFR)/c-Jun NH2-terminal kinase (JNK)/SP-1/p27 pathway was investigated. JNK phosphorylation and EGFR protein levels were increased in TIMP-3−/− cardiomyocytes and heart tissues. Treatment with recombinant TIMP-3 decreased JNK phosphorylation and EGFR expression/phosphorylation. Inhibition of JNK activity using SP-600125 decreased SP-1 phosphorylation, increased p27 expression, and decreased cardiomyocyte proliferation. Furthermore, treatment with the EGFR specific inhibitor PD-168393 or the EGF-neutralizing antibody decreased cardiomyocyte proliferation as well as phosphorylation of JNK and SP-1 in both WT and TIMP-3−/− cardiomyocytes. We conclude that TIMP-3 inhibits neonatal mouse cardiomyocyte proliferation by upregulating p27 expression. The effects of TIMP-3 are mediated via inhibition of EGFR expression/phosphorylation, and decreases in JNK and SP-1 signaling.

Sp1-dependent activation of KLF4 is required for PDGF-BB-induced phenotypic modulation of smooth muscle

There is clear evidence that the phenotypic modulation of smooth muscle cells (SMCs) contributes to the pathophysiology of vascular disease. Phenotypic modulation refers to the unique ability of SMCs to alter their phenotype in response to extracellular stimuli and is hallmarked by the loss of SMC marker gene expression. The transcription factor Krüppel-like factor 4 (KLF4) is a known powerful negative regulator of SMC marker gene expression that works, in part, by decreasing the expression of the serum response factor (SRF) myocardin. KLF4 is not expressed in healthy adult SMCs but is increased in SMCs in response to vascular injury in vivo or PDGF-BB treatment in vitro. The aim of the present study was to determine the molecular mechanisms that regulate the expression of KLF4 in phenotypically modulated SMCs. The results demonstrated that the transcription factor stimulating protein-1 (Sp1) regulated the expression of KLF4 in SMCs. The KLF4 promoter contains three consensus Sp1 binding sites. Using a series of truncated KLF4 promoters, we showed that only fragments containing these Sp1 sites could be activated by PDGF-BB. In addition, overexpression of Sp1 alone was sufficient to increase the activity of the KLF4 promoter. Moreover, inhibiting Sp1 expression with small-interfering RNA attenuated the effects of PDGF-BB on KLF4 expression. Mutation of the three Sp1 sites within the KLF4 promoter abolished both baseline and PDGF-BB-induced activity. Finally, the results demonstrated enhanced Sp1 binding to the KLF4 promoter in SMCs treated with PDGF-BB in vitro and following vascular injury in vivo. Taken together, the results suggest a novel role for Sp1 in increasing the expression of KLF4 in phenotypically modulated SMCs.

Neutrophil elastase inhibition of cell cycle progression in airway epithelial cells in vitro is mediated by p27kip1

Neutrophil elastase (NE), a serine protease present in high concentrations in the airways of cystic fibrosis patients, injures the airway epithelium. We examined the epithelial response to NE-mediated proteolytic injury. We have previously reported that NE treatment of airway epithelial cells causes a marked decrease in epithelial DNA synthesis and proliferation. We hypothesized that NE inhibits DNA synthesis by arresting cell cycle progression. Progression through the cell cycle is positively regulated by cyclin complexes and negatively regulated by cyclin-dependent kinase inhibitors (CKI). To test whether NE arrests cell cycle progression, we treated normal human bronchial epithelial (NHBE) cells with NE (50 nM) or control vehicle for 24 h and assessed the effect of treatment on the cell cycle by flow cytometry. NE treatment resulted in G(1) arrest. Arrest in G(1) phase may be the result of CKI inhibition of the cyclin E complex; therefore, we evaluated whether NE upregulated CKI expression and/or affected the interaction of CKIs with the cyclin E complex. Following NE or control vehicle treatment, expression of p27(Kip1), a member of the Cip/Kip family, was evaluated. NE increased p27(Kip1) gene and protein expression. NE increased the coimmunoprecipitation of p27(Kip1) with cyclin E complex, suggesting that p27(Kip1) inhibited cyclin E complex activity. Our results demonstrate that p27 is regulated by NE and is critical for NE-induced cell cycle arrest.

Expression of Cell-Cycle-Regulating Genes in the Development of Atherosclerosis in Japanese Quail (Coturnix japonica)

The levels of mRNA expression in regulatory genes that are involved in the pathological changes of aortic atherosclerotic and fibroblastic intimal thickening was investigated in Japanese quail. The quail were divided into a control diet group and an atherogenic diet group. The quail were euthanized at 2, 4, 8, and 12 wk after consuming either a control diet or an atherogenic diet. Thereafter, both histological and immunohistochemical studies and mRNA expression analysis of the cell-cycle-regulating genes in aortic atherosclerotic lesions were performed on selected ascending aortas and their large branches. In the atherogenic diet group, aortic lipid-containing intimal and atheromatous lesions were seen mainly at 8 and 12 wk, respectively. Semiquantitative reverse-transcription PCR was used to analyze the alterations of mRNA expression on the development of atherosclerotic lesions. Messenger RNA expression of the c-fos and c-src genes showed peak levels at 8 wk in the atherogenic diet group. However, no significant alteration of c-jun mRNA expression was noted during the entire experimental period. According to the progression of aortic atherosclerotic lesions, c-myc mRNA expression in the atherogenic diet group increased chronologically, and the highest level was observed at 12 wk. Alterations in mRNA expression of proliferating cell nuclear antigen and the p27 gene were similar to that of c-myc. The levels of c-myc, proliferating cell nuclear antigen, and p27 mRNA expression was significantly correlated with the degree of aortic atherosclerotic lesion development at 12 wk in our experiment.

Beneficial effect of atorvastatin on left ventricular remodeling in spontaneously hypertensive rats

This study was designed to investigate whether atorvastatin has a beneficial effect on left ventricular (LV) remodeling in spontaneously hypertensive rats (SHR), and then explore the underlying mechanisms involved. 12 SHRs were randomized to receive either distilled water (SHR group, n = 6) or atorvastatin (ATV group, n = 6) for 10 weeks. Age-matched Wistar-Kyoto rats (WKY) gavaged by distilled water were used as normal controls (WKY group, n = 6). By using these rats, we observed the effects of atorvastatin on LV hypertrophy and fibrosis, and investigated atorvastatin-induced cell apoptosis and p27 protein expression. In addition, the serum lipid concentration and blood pressure level were also measured in this study. 10 weeks later, a significant decrease in the cardiosomatic ratio, LV weight to body weight ratio and cardiomyocyte transverse diameter, as well as myocardial hydroxyproline and collagen content was observed in the atorvastatin-treated SHR. In addition, atorvastatin increased the positive rate of cell apoptosis and p27 protein expression. A decreased serum lipid concentration and a reduced systolic blood pressure level were also found in the atorvastatin-treated SHR. These findings demonstrated a beneficial effect of atorvastatin on adverse LV remodeling in SHR, and the induction of cell apoptosis and upregulation of p27 protein may serve as the underlying mechanisms of this action.