Published online before print July 3, 2008, doi: 10.1161/CIRCRESAHA.108.174607
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© 2008 American Heart Association, Inc.
Molecular Medicine |
Involvement of Heat Shock Factor 1 in Statin-Induced Transcriptional Upregulation of Endothelial Thrombomodulin
From the Departments of Microbiology and Immunology (Q.F.), Surgery (J.W., M.B., X.Q., M.H.-J.), Pharmaceutical Sciences (M.B.), and Pathology (M.H.-J.), University of Arkansas for Medical Sciences, Little Rock, Ark; Nevada Cancer Institute (L.M.F.), Las Vegas, Nev; and the Surgery Service (M.H.-J.), Central Arkansas Veterans Healthcare System, Little Rock, Ark.
Correspondence to Martin Hauer-Jensen, MD, PhD, Winthrop P. Rockefeller Cancer Institute, 4301 West Markham, Slot 725, Little Rock, AR 72205. E-mail mhjensen{at}life.uams.edu
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Abstract |
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Statins upregulate endothelial thrombomodulin (TM) by mechanisms that involve members of the Kruppel-like factor family. Although Kruppel-like factors are unequivocally implicated in this process, experimental evidence points to additional mechanisms. Deletion/mutation analysis of reporter constructs was used to demonstrate that mutation of the SP1/Kruppel-like factor element in the TM promoter only partially abolishes statin-induced TM upregulation, whereas simultaneous mutation of relevant heat shock elements and SP1/Kruppel-like factor element completely prevents statin-induced TM upregulation, thus demonstrating a role for heat shock factors (HSFs). We further identified the pathway by which statins increase binding of HSF1 to heat shock elements in the TM promoter. Specifically, statins caused NO-dependent dissociation of HSF1 from heat shock protein 90, nuclear translocation of HSF1, and binding to heat shock elements in the TM promoter. Statins also decreased nuclear content of the HSF1 chaperone 14-3-3β. In addition to reducing TM upregulation, inhibition of HSF1 reduced statin-induced upregulation of tissue plasminogen activator, whereas downregulation of thrombomospondin, plasminogen activator inhibitor 1, or connective tissue growth factor was unaffected. Knockdown of 14-3-3β or inhibition of HSF1 phosphorylation enhanced the effect of statins on TM and tissue plasminogen activator, but did not influence thrombomospondin, plasminogen activator inhibitor 1, or connective tissue growth factor. These data demonstrate that HSF1 is involved in statin-induced regulation of TM. They also suggest that analogous mechanisms may apply to genes that are upregulated by statins, but not to downregulated genes. These results may have broad implications and suggest the use of heat shock protein modulators to selectively regulate pleiotropic statin effects.
Key Words: endothelial cells • heat shock proteins • thrombomodulin • transcriptional regulation
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Introduction |
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Inhibitors of 3-hydroxy-3-methylglutaryl reductase, statins, reduce cholesterol biosynthesis and are widely used in the treatment of hyperlipidemia disorders. In addition, statins also have many so-called pleiotropic (nonlipid-related) properties. Most pleiotropic effects are mediated through reduced levels of cholesterol biosynthesis pathway intermediates that serve as lipid attachments for posttranslational modification (isoprenylation) of proteins, including Ras and Ras-like proteins such as Rho and Rac.1
Vascular endothelium is a major target for the pleiotropic effects of statins. Statins exert anti-inflammatory, anticoagulant, and fibrinolytic properties by upregulating and enhancing the activity of endothelial nitric oxide synthase.2 This results in, for example, downregulation of connective tissue growth factor (CTGF), thrombospondin (TSP-1), and plasminogen activator inhibitor-1 (PAI-1)3 and upregulation of tissue plasminogen activator (tPA),4 and thrombomodulin (TM).5,6
TM is expressed on the luminal surface of endothelial cells where it forms a complex with thrombin. Thrombin, when bound to TM, loses its ability to cleave fibrinogen and activate cellular thrombin receptors, but instead acquires the ability to activate the "natural anticoagulant," protein C. Restoration of the TM–thrombin–protein C pathway has potential therapeutic benefits in many disorders associated with endothelial dysfunction, including sepsis,7 adult respiratory distress syndrome,8 coagulation disorders,9 and radiation injury.10
Several transcription factor binding sites in the 5'-flanking region of the TM promoter regulate TM expression.11,12 The SP1/KLF binding site (at -207), to which Kruppel-like factor 2 and 4 (KLF2 and KLF4) bind, appears particularly important for upregulating TM, and forced overexpression of KLF2 or KLF4 substantially increases TM expression.13,14 Despite the clear role for KLF2 and KLF4, however, several lines of evidence point to additional mechanisms. First, TM is downregulated by inflammatory cytokines,13 some of which induce KLF4.15,16 Second, KLF2 is induced by mevastatin, simvastatin, and lovastatin, but not by pravastatin,17,18 although pravastatin strongly upregulates TM.19
Conway and coworkers reported in 1994 that exposure of endothelial cells to heat shock increased the expression of TM, suggesting that heat shock proteins (HSPs), heat shock factors (HSFs), and/or heat shock elements (HSEs) may be involved in transcriptional regulation of TM.20 More recent data suggest that statin-induced improvement of endothelial function may be related to activation of heat shock factor 1 (HSF1).21,22 However, a firm relationship among HSF1, endothelial nitric oxide synthase activity, and TM expression has not been established.
The present study clarifies how HSF1 participates in statin-induced upregulation of endothelial TM at the transcriptional level. Analogous mechanisms may apply to other, but not all, pleiotropic effects of statins. Hence, these findings provide a potential basis for differential regulation of pleiotropic statin effects and thus may have wide-ranging implications for selective regulation of such effects for therapeutic purposes.
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Materials and Methods |
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Cell Culture and Reagents
Cell cultures were performed as described previously.23 Human umbilical vein endothelial cells (HUVECs) and human coronary artery endothelial cells (HCAECs) were cultured in EGM-2 and EGM-2 MV medium, respectively (Lonza, Walkersville, Md). Atorvastatin was from Pfizer (New York, NY), pravastatin from TRC (North York, Ontario, Canada), simvastatin from Spectrum Laboratory Product (Gardena, Calif), and geldanamycin, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine, 3-morpholinosydnonimine hydrochloride, mevalonate, PD98059, and U0126 from Sigma Chemical Co (St Louis, Mo). KNK437 was from EMD Biosciences (San Diego, Calif). All experiments in the present study were performed at least 5 times. The bars showing the real-time polymerase chain reaction (PCR) results and the densitometric data represent means of 5 independent experiments±SDs. Statistical comparisons against vehicle-treated control samples were performed with Student t test for samples with unequal variances. A 2-sided significance level of 0.05 was used throughout.
Reporter Construct Assays
TM reporter constructs were created by PCR amplification from a PAC clone containing the human TM gene (RP4–753D; BACPAC Resources, Oakland, Calif) and inserted into the Nhe I and Hind III site of the pGL3.0 basic luciferase reporter vector (Promega, Madison, Wis). The first untranscribed base -1 was defined as the -169 base from the ATG codon of the TM translation site. Luciferase reporter constructs and the pRL-TK vector (Promega) were cointroduced into cells by transient transfection using Lipofectamine 2000 (Invitrogen, Carlsbad, Calif). A dual-Luciferase reporter assay system (Promega) was used to measure firefly and Renilla luciferase activity of cell lysates. Firefly luciferase values were normalized to Renilla luciferase values. Site-specific mutations of HSEs and SP1/KLF elements were created with the QuikChange Site Directed Mutagenesis Kit (Stratagene, La Jolla, Calif) (supporting information).
RNAi
Interference transfections were performed with the silencer siRNA Starter Kit (Ambion, Austin, Texas). The Ambion predesigned 14-3-3β siRNA and HSF1 siRNA duplex oligonucleotide sense sequence were as follows: 5'-GCAGAAAACAGAGAGGAAUtt-3' (14-3-3β, siRNA ID 41953) and 5'-GCUUCCACGUGUUCGACCAtt-3' (HSF1, siRNA ID s6951), respectively. The Ambion negative control siRNA #1 (catalog 4611) was used for a negative control; nontransfected cells were used as a positive control. Cells were incubated with siRNA for 48 hours and then treated with atorvastatin for 24 hours. Total RNA was extracted at 24 hours and analyzed by real-time PCR.
Chromatin Immunoprecipitation Assay
Chromatin immunoprecipitation assays (ChIP) assays were performed with the ChIP-IT Enzymatic Kit (Active Motif, Carlsbad, Calif). Briefly, cells were crosslinked with 1% formaldehyde and chromatin was sheared with an enzymatic Shearing Cocktail. Chromatin containing DNA fragments with average size 500 bp were immunoprecipitated with anti-HSF1 monoclonal antibody (sc-13516 X; Santa Cruz Biotechnology, Santa Cruz, Calif) with mouse IgG and anti-RNA polymerase II antibody (Active Motif) as negative and positive controls, respectively. DNA fragments were amplified using primers designed around the HSE sites in the TM 5'-flanking region. Primer sets were as follows: 5'-CTGATTCAGCCTAGGCAGC-3' and 5'- GCTGAGTTGAGCTCTTCGCTG-3' (HSE1, -1721 to -1709, PCR product 209 bp); 5'-AGAAGGAGGACTCTGTGCTCCTA-3' and 5'-CATAATGGTGAGAGGCAAAC-3' (HSE2, -1310 to -1301, chain product 168 bp); 5'-GTCTTGCAGGTCCTGTGCAC-3' and 5'-CTGTAACAAGACGACTGTC-3' (HSE3, -332 to -321, PCR product 208 bp); 5'-CAATCCGAGTATGCGGCATC-3' and 5'-GATCTCGAGTTTATAAGTGCCCG-3' (HSE4, -71 to -54, PCR product 98 bp). Positive control PCR primers amplified a region of the constitutively active glyceraldehyde-3-phosphate dehydrogenase promoter; primer set was: 5'-TACTAGCGGTTTTACGGGCG-3' and 5'-TCGAACAGGAGGAGCAGAGAGCGA-3' (PCR product 166 bp). Negative control primers amplified a region of genomic DNA between the glyceraldehyde-3-phosphate dehydrogenase gene and the chromosome condensation-related SMC-associated protein gene; the sequences were: 5'-ATGGTTGCCACTGGGGATCT-3' and 5'-TGCCAAAGCCTAGGGGAAGA-3' (PCR product 174 bp). PCR products were resolved on a 2% agarose gel and visualized by ethidium bromide staining.
Electrophoretic Mobility Shift Assays
Cells were treated with 1x10–5 M atorvastatin for 6 hours, and nuclear extracts were prepared with the Nuclear Extraction Kit (Active Motif). Electrophoretic mobility shift assay (EMSA) analysis was performed with the LightShift Chemiluminescent EMSA Kit (Pierce, Rockford, Ill). The following double-stranded oligonucleotides were used (only top strands are shown): 5'-TGTGCATTCCGGGAGCTTCAGACCC-3' (HSE1, -1721 to -1709); 5'-TTAGCCCGAAACTTCTCCAACTTCC-3 (HSE2, -1310 to -1301); 5'-CATGTATGAAAAGAAAGAAAGGAGGACC-3' (HSE3, -332 to -321); 5'-GGCACTTCCTTCCTTTTCCCGAACGTCC-3' (HSE4: -71 to -54). Oligonucleotides were labeled with the Biotin3' End DNA Labeling Kit (Pierce).
Immunoprecipitation
Cells were lysed in modified RIPA lysis buffer (Upstate, Temecula, Calif). Lysate (500 µg total protein) was incubated with 2 µg of HSP90 monoclonal antibody (SPA-835; Stressgen, British Columbia, Canada) and 50 µL of protein G-agarose beads (Upstate) overnight at 4°C on a rotating platform. Beads were washed extensively in lysis buffer, proteins were eluted with 2x Laemmli sample buffer, and the amount of bound protein was measured by Western blotting.
Western Blots
Total cytoplasmic and nuclear protein was isolated with the Nuclear Extract Kit (Active Motif) and run on 7% to 10% SDS/PAGE gels. After blotting to PVDF membranes (Invitrogen), membranes were blocked for 60 minutes at room temperature and incubated overnight at 4°C in buffer (TBS with 0.1% Tween 20 and 5% milk power) containing 1:1000 diluted Santa Cruz antibodies against HSF1 (sc-13516 X), 14-3-3β (sc-629), β-actin (sc-10731), Lamin B (sc-6217), or HSP90 (SPA-835; Stressgen). Detection of primary antibodies was performed with HRP-conjugated goat antirat/rabbit or rabbit antigoat secondary antibody (Santa Cruz Biotechnology) diluted 1:2500. Immunoreactive bands were visualized with Chemiluminescent substrate (Pierce). All films presented in this article were scanned in a Lexmark X73 (Lexmark International, Lexington, Ky) scanner. The images were not enhanced or altered with any software. Densitometric analysis was performed using Quantity One software (Bio-Rad, Hercules, Calif).
RNA Analysis
Total RNA was isolated using Ultraspec reagent (Biotecx Laboratories, Houston, Texas) and cDNA was generated with the cDNA Archive Kit (Applied Biosystems, Foster, Calif). Gene expression levels were measured with TaqMan real-time quantitative PCR using Applied Biosystems predesigned primer/probe sets: TM, Hs00264920_s1; tPA, Hs00263492_m1; TSP-1, Hs00170236_m1; PAI-1, Hs00167155_m1; CTGF, Hs00170014_m1; and S27, Hs01378332_g1. PCR amplification and detection were carried out on an ABI Prism 7000 Sequence Detection System (Applied Biosystems) and values were normalized to ribosomal protein S27 mRNA.
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Results |
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Binding of Heat Shock Protein 1 to Heat Shock Element Contributes to Statin-Induced Thrombomodulin Upregulation
Analysis of the TM promoter with rVista 2.0 (Lawrence Livermore National Laboratory, www.dcode.org) revealed several potential transcription factor binding sites. Besides the 4 SP1 and SP1/KLF sites and one DR4 site described previously, one binding site for STATx (-1153 to -1142) and 4 HSE sites (HSE1: -1721 to -1709, HSE2: -1310 to -1301, HSE3: -332 to -321, and HSE4: -71 to -54) were identified. Primary HUVEC cultures were transiently transfected with reporter constructs containing a firefly luciferase gene under control of the human TM promoter. The constructs had various parts of the TM promoter either deleted or mutated. Cells were treated for 24 hours with vehicle or atorvastatin or pretreated with mevalonate for 30 minutes before treatment with atorvastatin.
Deletion of HSE1 or HSE3 significantly reduced the atorvastatin-induced luciferase signal, whereas deletion of HSE2 or DR4 had no effect. Deletion of the sequence -333 to -1154, which contains the STATx binding site, increased the atorvastatin-induced luciferase signal. Interestingly, mutation of the STATx binding site did not change the luciferase signal significantly (Figure 1A), suggesting the presence of a repressor element distinct from the STATx site. Mutation of the SP1/KLF binding site on -207 partly reduced baseline and atorvastatin-induced luciferase reporter signal. Simultaneous deletion of HSE3 and SP1/KLF, however, completely abolished the effect of atorvastatin as well as the effect of the non-KLF2 dependent pravastatin (Figure 1B).
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ChIP assays confirmed binding of HSF1 to the TM promoter. Atorvastatin induced binding of HSF1 to HSE1 and HSE3, but not to HSE2 or HSE4 (Figure 2A). EMSA analysis confirmed the results of the ChIP assay. Furthermore, EMSA showed statin-induced binding of HSF1 to HSE 1 and HSE3 to be decreased by pretreatment with KNK437 (Figure 2B). KNK437 has low toxicity, is a highly selective inhibitor of HSF1 activity, does not inhibit constitutive expression of HSP, inhibits induced synthesis of HSP, and reduces formation of HSF1/HSE complexes.24 Atorvastatin did not induce binding of STAT1/STAT3 to the STATx site (data not shown).
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To support that atorvastatin-induced binding of HSF1 to HSE was indeed involved in upregulation of TM, we investigated the effects of siRNA HSF1 knockdown and KNK437 on statin-induced TM expression in HUVECs and HCAECs. HSF1 knockdown significantly reduced atorvastatin-induced TM and tPA expression (Figure 2C), but did not reverse the effect of statin on TSP-1, CTGF, or PAI-1 (data not shown). Similarly, KNK437 blocked statin-induced upregulation of TM and tPA, but not downregulation of TSP-1, CTGF, or PAI-1 (Figure 2D). Taken together, these data are consistent with the notion that HSF1 binding to HSE is involved in the statin-induced regulation of certain genes such as TM and tPA, but not in the regulation of others.
Atorvastatin Induces Nitric Oxide-Dependent Dissociation of Heat Shock Protein 1 From Heat Shock Protein 90 and Nuclear Translocation of Heat Shock Protein 1
In normal cells, most HSF1 is retained in the cytoplasm as transcriptionally inactive monomers bound to HSP90 in a multichaperone complex. Various stimulants and cellular stresses induce dissociation of HSF1 from this complex, causing activation and nuclear translocation of HSF1.25,26 Significant reductions in the amount of HSF1 immunoprecipitated by the HSP90 antibody were observed after 30 minutes of atorvastatin treatment (Figure 3A), indicating rapid dissociation of HSF1 from HSP90. This effect was reversed by a nitric oxide (NO) scavenger (Figure 3B) and mimicked by slow and rapid NO donors (Figure 3C–D), indicating that statin-induced dissociation of HSF1 from HSP90 is NO-mediated.
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To further support the putative effect of HSP90/HSF1 dissociation on HSE-dependent TM expression, we used geldanamycin, a commonly used inhibitor of HSP90 reported to stimulate HSF1 dissociation from HSP90.25 EMSA confirmed binding of HSF1 to HSE1 and HSE3 after geldanamycin treatment (Figure 2B). Furthermore, geldanamycin alone or in combination with statins significantly upregulated TM in HUVECs and HCAECs (Figure 3E).
The effect of atorvastatin on nuclear translocation of HSF1 in HUVECs was studied with Western blotting. Decreased cytoplasmic levels and increased nuclear levels of HSF1 were found starting 4 hours after atorvastatin treatment (Figure 3F–G), consistent with rapid nuclear translocation of HSF1 after dissociation of the HSF1–HSP90 complex.
The Mitogen-Activated Protein Kinase Pathway and Protein 14-3-3 Are Involved in Statin-Induced Upregulation of Endothelial Thrombomodulin
HSF1 transcriptional activation is negatively regulated by phosphorylation of serine residues 303 and 307 by mitogen-activated protein kinase.27,28 Phosphorylation converts HSF1 to a form recognized and bound by the intracellular regulatory proteins, 14-3-3.29
Western blot analysis of 14-3-3 proteins in HUVECs revealed that atorvastatin substantially decreased nuclear content of 14-3-3β with a concomitant increase in cytoplasmic levels 4 to 8 hours after treatment (Figure 4A–B). Atorvastatin did not significantly change nuclear and cytoplasmic levels of 14-3-3
and 14-3-3
(data not shown).
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To confirm that negative regulation of HSF1 by mitogen-activated protein kinase and 14-3-3β does indeed reduce statin-induced TM upregulation, MEK inhibition and silencing of the 14-3-3β gene were used. HUVECs were pretreated with inhibitors of MEK activation, PD98059, or U012630,31 for 30 minutes. MEK inhibition enhanced atorvastatin-induced upregulation of TM and tPA (Figure 4C), consistent with the notion that the mitogen-activated protein kinase pathway acts to repress genes that are upregulated by statins. Moreover, siRNA knockdown of 14-3-3β enhanced atorvastatin-induced overexpression of TM and tPA (Figure 4D). Taken together, these results suggest that the mitogen-activated protein kinase pathway, by phosphorylating HSF1 to allow subsequent association of HSF1 with 14-3-3β, counteracts the effects of atorvastatin on TM expression. Interestingly, downregulation of TSP, CTGF, and PAI-1 by atorvastatin was unaffected by MEK inhibition or silencing of 14-3-3β (data not shown), again indicating that downregulation of these genes by statins occurs through other pathways.
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Discussion |
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The present study shows that both KLF and HSF1 contribute to achieve maximal statin-induced activation of TM gene expression and that the mechanism involves binding of HSF1 to specific HSE sites in the TM promoter. The proposed pathway by which HSF1 contributes to statin-induced upregulation of TM is depicted in Figure 5. Statins increase production of NO by endothelial NO synthase. NO induces dissociation of HSF1 from the HSP90-containing multichaperone complex. HSF1 subsequently translocates into the nucleus and binds to 2 of 4 HSE elements in the TM promoter, resulting in increased TM expression. Subsequent phosphorylation of HSF1 promotes its binding to protein 14-3-3β, facilitating nuclear export of HSF1 to end the stimulation of TM transcription. Our results suggest that upregulation of other endothelial genes by statins may be mediated through similar pathways, whereas downregulated genes are regulated by different mechanisms.
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HSPs and HSF1 are presumed to play roles in the pathogenesis of and/or protection against atherosclerosis and other cardiovascular disorders.32 Interestingly, Uchiyama et al have suggested the involvement of HSF1 in pleiotropic effects of statins, including upregulation of TM and downregulation of PAI-1, through upregulation of HSPs.21,22 Their findings are somewhat in conflict with data from our and other laboratories. We and others have shown that statins consistently downregulate heat shock proteins, notably HSP70 and HSP90, in endothelial cells and other cells.23,33 We show here that the TM promoter contains specific HSE sites and that HSF1 induces TM transcription in a direct manner by binding to these HSE sites. Moreover, in contrast to genes that are upregulated by statins such as TM and tPA, downregulation of CTGF, TSP, and PAI-1 appears to be mediated by other mechanisms. This finding is also somewhat in contrast to Uchiyama et al, who reported that an HSE oligonucleotide inhibited simvastatin-induced downregulation of PAI-1.22 It is conceivable that the observed differences between their study and ours relate to differential inactivation/inhibition of nuclear versus cytoplasmic HSF1.
It is well known that statins increase the activity of endothelial NO synthase, that NO triggers various physiological responses, and that many of the antiproliferative, anti-inflammatory and vasculoprotective effects of statins are mediated by this mechanism. In unstressed cells, HSF1 exists in the cytoplasm associated with HSP90. The HSP90–HSF1 complex dissociates in response to various cellular stresses.25 We show here that NO causes dissociation of HSF1 from HSP90, a finding that may explain previous observations that NO induces nuclear translocation and functional activation of HSF1.34 Because HSP90 functions as part of a large complex with other proteins,35 NO effects may not only be directed toward HSF1 or HSP90, but also toward other proteins within the HSP90 complex. Interestingly, NO-mediated activation of HSF1 was blocked by DTT, a disulfide-reducing agent.34 NO may induce S-nitrosylation of proteins; 2 sulfhydryl groups in close proximity may form a disulfide bond on S-nitrosylation.36 The blocking effect of DTT on NO-mediated activation of HSF1 indicates that protein S-nitrosylation may be involved in the mechanism of HSF1 activation. Further studies are needed to examine the effects of S-nitrosylation on HSF1 dissociation from HSP90.
In vivo, endothelial KLF2 is associated with resistance to atherogenesis. KLF2 is regulated by shear stress and atheroprotective wave forms upregulate KLF2.37 Overexpression of KLF2 in vitro induces TM and endothelial NO synthase expression in endothelial cells.38 Interestingly, KLF2 expression is induced by a number of statins, but not by pravastatin,17,18 despite the fact that pravastatin upregulates TM,19 suggesting that other transcription factor(s) besides KLF2 may induce TM expression.
Our data showed that when only the KLF2 binding site in the TM promoter was mutated, atorvastatin and pravastatin retained the ability to increase luciferase activity in HUVECs transfected with the reporter construct. Conversely, mutation of HSE3 alone did not completely abolish statin-induced luciferase activity. When both HSE3 and the SP1/KLF element were mutated, however, statin-induced luciferase activity was completely abolished, suggesting that both KLF2 and HSF1 participate in statin-dependent TM upregulation.
Although HSF1 binds to the distal (HSE1) and proximal (HSE3) HSE elements and both elements play a role in statin-induced TM promoter activity, the relative importance of HSE1and HSE3 remains to be elucidated. The reporter construct assays revealed that sequence -333 to -1154 in the 5'-flanking region of the human TM gene may have a repressor function, which appears not to be mediated through the STAT1/STAT3 binding site in this part of the TM promoter. It is conceivable that binding of HSF1 to the distal HSE (HSE1) is necessary to overrule the effect of that repressor domain.
In conclusion, this study demonstrates that 1) statins upregulate endothelial TM by a mechanism that involves NO-dependent dissociation of HSF1 from HSP90, nuclear translocation of HSF1, and activation of specific HSEs in the TM promoter; 2) Erk-dependent phosphorylation of HSF1 and subsequent nuclear export of HSF1, facilitated by protein 14-3-3β, contributes to the termination of statin-induced TM upregulation; and 3) analogous HSF1-dependent mechanisms may apply to genes that are upregulated by statins, but not to genes that are downregulated. These findings have broad implications and point to the opportunity to selectively regulate specific pleiotropic statin effects by modulating heat shock proteins.
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Acknowledgments |
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Sources of Funding
Supported by grants from the National Institutes of Health (CA83719), the Veterans Administration, and the Defense Threat Reduction Agency (HDTRA1–07-C-0028).
Disclosures
None.
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Footnotes |
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Original received February 26, 2008; revision received June 2, 2008; accepted June 24, 2008.
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References |
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