MCP-1 Promoter Research Articles

Cooperative interaction of C/EBPβ and Tat modulates MCP-1 gene transcription in astrocytes

The chemoattractant protein 1 (MCP-1) is one of the most potent monocyte chemoattractants whose level is elevated during the course of AIDS dementia. Earlier studies showed that HIV-1 Tat protein is able to induce transcription of the MCP-1 promoter in astrocytic cells. Furthermore, the TGFβ-1 signaling pathway through its regulatory proteins, Smads, modulates Tat activation of MCP-1. Here, we demonstrate that C/EBPβ, whose activity is enhanced by a variety of cytokines during the course of viral infection, can stimulate basal- and Tat-mediated transcription of MCP-1 in human astrocytic cells. Results using promoter deletion mutants suggested the importance of multiple C/EBPβ binding sites scattered within −200 to +1 of the MCP-1 promoter in the observed activity. Results from DNA binding studies have shown that the interaction of C/EBPβ with its DNA motif is diminished by the C/EBPβ homologous protein, CHOP, which possesses the ability to suppress the stimulatory effect of C/EBPβ on MCP-1 transcription. Tat, which possesses the ability to interact with C/EBPβ, alleviates the negative effect of CHOP and restores C/EBPβ interaction with the DNA. Furthermore, Smad3 and its C-terminal regulatory motif, MH2, interact with C/EBPβ and modulate its DNA binding and transcriptional activity on the MCP-1 promoter. Our results show that the physical and functional interactions of C/EBPβ and Tat are severely affected by the presence of Smad3 and MH2. Altogether, these observations identify C/EBPβ as a new partner for Tat in stimulating MCP-1 transcription in astrocytes and suggest that the delicate balance among the downstream regulatory proteins of several cytokines and immunomodulators can dictate the level of expression of chemoattractants, including MCP-1. Hence, inappropriate expression and function of regulatory proteins such as C/EBPβ and Smads by Tat may induce MCP-1 production in astrocytes and contribute to the neuropathogenesis of AIDS through stimulation of inflammation in the CNS.

The correlation between monocyte chemoattractant protein-1 and the arthritis of systemic lupus erythematosus among Chinese

Monocyte chemoattractant protein-1 (MCP1) polymorphism has been reported to be associated with systemic lupus erythematosus (SLE). However, the correlation between the polymorphism and SLE is poorly understood. In this study we investigated the role of this polymorphism together with that of chemokine SDF1-3'A and chemokine receptor CCR2-V64I. The association between gene polymorphism and SLE was explored by way of a case-control study. In 143 patients with SLE and 157 healthy controls, the polymorphisms of SDF1-3'A, -2518MCP-1 and CCR2-V64I were determined using PCR-RFLP and an amplification-refractory mutation system, respectively. No significant difference was found in allelic and genotype frequency of SDF1-3'A, CCR2-V64I and -2518MCP-1 between SLE patients and controls. However, a significant increase in the frequency of the AG genotype of MCP-1 was found among patients with arthritis (P(c)=0.003, OR 3.08, 95%CI 1.27-7.57). The frequency of individuals having G at position -2518 of the MCP-1 gene was also increased among patients with arthritis (P(c)=0.028, OR 2.99, 95%CI 1.13-8.08). It is noteworthy that the frequency of -2518MCP-1G in the Chinese Han population was 64%. The results indicate an association between the presence of G at position -2518 in the MCP-1 promoter region and the presence of arthritis in patients with SLE.

The monocyte chemotactic protein-1 -2578G allele is associated with elevated MCP-1 concentrations in cerebrospinal fluid

Because monocyte chemotactic protein (MCP)-1 is an important cofactor in HIV neuropathogenesis, we investigated the relationship between MCP-1 genotype and expression in cerebrospinal fluid (CSF). We evaluated a genetic polymorphism in the MCP-1 promoter at position -2578 (alternatively designated -2518) in 98 HIV-infected subjects who had contemporaneously collected plasma and CSF. CSF MCP-1 levels were highest in the G/G genotype group, intermediate in the G/A group, and lowest in the A/A group. MCP-1 levels in plasma only differed by genotype after adjusting for HIV-related factors. Our findings suggest that this MCP-1 promoter polymorphism influences HIV neuropathogenesis by regulating MCP-1 protein expression in the central nervous system (CNS).

MCP-1 in Alzheimer’s disease patients: A-2518G polymorphism and serum levels

MCP-1 levels are increased in CSF of patients with Alzheimer’s disease (AD) compared with controls, suggesting a role in the development of dementia. Recently, a biallelic A/G polymorphism in the MCP-1 promoter at position −2518 has been found, influencing the level of MCP-1 expression in response to an inflammatory stimulus. The distribution of the A-2518G SNP was determined in 269 AD patients and in 203 healthy age matched controls, showing no differences between the two groups. On the contrary, a significant increase of MCP-1 serum levels in AD patients carrying at least one G mutated allele was observed. Moreover, the highest peaks of MCP-1 serum levels were present in patients carrying two G alleles. Stratifying by ApoE genotype, gender or age at onset, no differences in both allele frequency and MCP-1 serum concentration were observed. The A-2518G polymorphism in MCP-1 gene does not seem to be a risk factor for the development of AD, but its presence correlates with higher levels of serum MCP-1, which can contribute to increase the inflammatory process occurring in AD.

Short CommunicationThe MCP-1 Promoter -2518 Polymorphism in Behcet's Disease: Correlation Between Allele Types, MCP-1 Production and Clinical Symptoms among Korean Patients

Objective: To compare the G vs. A variation at the MCP-1 promoter -2518 position among normal Koreans and Behcet patients, and to investigate possible association of this polymorphism with disease pathogenesis.Methods: The allele type of -2518 polymorphism was determined by restriction fragment length polymorphism of Pvu II. The level of MCP-1 in serum and culture supernatent was measured by sandwich ELISA.Results: The average serum level of MCP-1 in Behcet patients was 2.37 times higher than in normal controls. The serum MCP-1 concentration was higher in G-allele carriers than in AA homozygotes, and symptoms accompanying graver cases of Behcet's disease, such as gastrointestinal inflammation and uveitis, were more frequent in patients with the G-allele. However, the frequency of G-allele in patient group was not higher than that in healthy Koreans, probably due to the dominance of G-allele in general Korean population. When stimulated in vitro with IL-1β and LPS, the mononuclear cells from patients carrying the G-allele showed a steeper increase in MCP-1 production than the boost observed in AA homozygotes.Conclusion: Although the allele frequency of MCP-1 promoter -2518 polymorphism is not likely to be the reason for the elevated serum MCP-1 level in Korean patients with Behcet's disease, it is possible that proinflammatory factors induced in patients' serum cause stronger activation of MCP-1 expression from the G-type promoter, as well as increased incidence of uveitis and gastric ulcer, among carriers of the G-allele.

MCP-1-MCP-3-Eotaxin gene cluster influences HIV-1 transmission.

MCP-1 (CCL2), MCP-3 (CCL7), and eotaxin (CCL11) are genes for CC chemokines clustered on the long arm of chromosome 17. Previous studies have implicated these chemokines in monocyte recruitment, viral replication, and anti-HIV cytotoxic T cell responses. An epidemiological analysis identified genetic variants influencing HIV-1 transmission and disease progression. Genomic DNA from over 3000 participants enrolled in five natural history cohorts in the United States were analyzed. Nine single nucleotide polymorphisms (SNP) covering 33 kb containing these three genes were genotyped using the polymerase chain reaction. Distortions in allele, genotype, and haplotype frequencies were assessed with respect to HIV-1 transmission and rates of disease progression using categorical and survival analyses. Extensive linkage disequilibrium was observed. Three SNP (-2136T located in the MCP-1 promoter region, 767G in intron 1 of MCP-1, and -1385A in the Eotaxin promoter) were nearly always found together on a 31 kb haplotype (H7) containing the three genes. Frequencies of the three variants and the H7 haplotype were significantly elevated (odds ratio, 0.6; P = 0.005-0.01) in uninfected European-Americans repeatedly exposed to HIV-1 through high-risk sexual behavior or contaminated blood products. Although the extensive linkage disequilibrium precludes positive identification of the causal variant, the results suggest that genetic variation in the H7 region influences susceptibility to HIV-1 infection. Since these chemokines do not bind the primary HIV-1 coreceptors CCR5 or CXCR4, the observed influence on transmission may result from activation of the immune system in response to infection rather than receptor blockage.

Regulation of MCP-1 gene transcription by Smads and HIV-1 Tat in human glial cells

Expression of several cytokines involved in signal transduction such as TGFβ-1 and the inflammatory chemokines including MCP-1 is elevated during the course of AIDS progression. The enhancement of these cellular proteins in astrocytic cells is mediated, at least in part, by HIV-1 Tat protein. Here, we investigate the possible regulation of MCP-1 transcription by Tat and the Smad family of transcription factors whose activities are induced by the TGFβ-1 pathway. Results from transfection studies revealed that Smad-3 stimulates basal and Tat-mediated transcription of MCP-1 in human astrocytic cells. Smad-4, on the other hand, had no effect on the basal activity of the MCP-1 promoter, but showed the ability to decrease both Smad-3 and Tat-induced transcription of the MCP promoter. Results from protein-binding studies revealed the ability of both Smad-3 and Smad-4 to associate with the region of Tat spanning residues 1–40. Examination of the transcriptional activity of the various domains of Smad including MH1, at the N-terminus, and MH2, at the C-terminus of the protein indicated that neither MH1 or MH2 alone positively cooperate with Tat in modulating MCP-1 transcription. However, ectopic expression of MH1 and, more notably, MH2 severely suppressed transcriptional activation of MCP-1 by Tat in astrocytic cells. Binding studies revealed that similar to the full-length Smad protein, both MH1 and MH2 associate with Tat protein and that the residues between 1 and 40 of Tat are important for their interaction. These observations reveal a novel mechanism for Tat-mediated transcriptional activation via TGFβ signaling pathway and provide evidence for regulation of MCP-1 gene transcription by this signaling pathway in human astrocytic cells.

Expression of a Full-Length Hepatitis C Virus cDNA Up-Regulates the Expression of CC Chemokines MCP-1 and RANTES

We had previously reported the cloning of the complete genome of an isolate of hepatitis C virus (HCV), HCV-S1, of genotype 1b. We have constructed a full-length complementary DNA (cDNA) clone of HCV-S1 using nine overlapping cDNA clones that encompassed its entire genome. HCV core, E1, E2, NS-3, -4B, -5A, and -5B proteins were detected in 293T cells by immunoblot analyses when expression of the full-length HCV-S1 was driven under a CMV promoter. Expression of full-length HCV-S1 led to induction of the CC chemokines RANTES and MCP-1 at both the mRNA and the protein levels in HeLa, Huh7, and HepG2 cells. Reporter gene assays showed that a minimal MCP-1 promoter construct containing 128 nucleotides upstream of its translational start site was sufficient for optimal HCV-mediated activation. HCV induced AP-1 binding activities to this region, as determined from electrophoretic mobility shift assays and supershifts with anti-AP-1 antibodies. Transfection of full-length HCV-S1 up-regulated both AP-1 binding activities as well as c- jun transcripts. A minimal promoter construct containing 181 nucleotides upstream of the RANTES translational start site was sufficient for maximal HCV-mediated induction. Gel mobility shift and supershift assays showed that HCV induced NF-κB and other unknown binding activities to the A/B-site within this region. In HeLa cells, HCV core and NS5A could separately augment promoter activities of both MCP-1 and RANTES. In Huh7 cells, only NS5A produced a similar effect, while rather surprisingly, HCV core induced a dramatic reduction in promoter activities of these two genes. This study provides the first direct evidence for the induction of CC chemokines in HCV infection and draws attention to their roles in affecting the progress and outcome of HCV-associated liver diseases.

Lysophosphatidylcholine stimulates monocyte chemoattractant protein-1 gene expression in rat aortic smooth muscle cells.

Monocyte chemoattractant protein (MCP)-1 is a proatherogenic factor that is responsible for approximately 60% of plaque macrophages in mouse models of atherosclerosis. We investigated whether lysophosphatidylcholine (LPC), enriched in oxidized low density lipoprotein, can modulate the expression of MCP-1 in arterial wall cells. LPC induced a 3-fold increase in MCP-1 mRNA in rat vascular smooth muscle cells (VSMCs) in a time- and dose-dependent manner. Nuclear runon analysis showed that this increase was attributable to increased MCP-1 gene transcription. There was a 2-fold increase in MCP-1 protein in the conditioned media of cells treated with LPC. LPC-associated increases of MCP-1 mRNA and protein were similar to those produced by platelet-derived growth factor-BB, a known inducer of MCP-1. Analyses of the MCP-1 promoter in transiently transfected VSMCs indicated an LPC-responsive element(s) between base pairs -146 and -261 (relative to transcription initiation). Further studies suggested that LPC-induced MCP-1 expression partially involves mitogen-activated protein kinase/extracellular signal-regulated kinase, a tyrosine kinase(s), and (to a lesser extent) protein kinase C but not the activation of the platelet-derived growth factor receptor. LPC stimulates MCP-1 expression at the transcriptional level in VSMCs, suggesting a molecular mechanism by which LPC contributes to the atherogenicity of oxidized low density lipoprotein.

NO modulates monocyte chemotactic protein-1 expression in endothelial cells under cyclic strain.

Endothelial cells (ECs) under hemodynamic forces increase intracellular reactive oxygen species (ROS) that modulate gene expression. We previously showed that NO attenuated the shear flow-induced gene level. The present study explored the role of endothelial NO in cyclic strain-treated ECs. Treatment of ECs with S-nitroso-N-acetylpenicillamine (SNAP), an NO donor, reduced cyclic strain-induced monocyte chemotactic protein (MCP)-1 expression. Conversely, exposure of ECs to an NO synthase inhibitor augmented MCP-1 mRNA levels. NO attenuated the binding of activator protein-1 to the 12-O-tetradecanoylphobol-13-acetate-responsive element (TRE) in the MCP-1 promoter region. ECs overexpressed with endothelial NO synthase (eNOS) inhibited cyclic strain-induced MCP-1 expression and MCP-1 promoter (-540 bp) activity. Consistently, ECs treated with SNAP or infected with adenovirus carrying eNOS reduced strain-induced superoxide levels. These strain-induced superoxide and MCP-1 expressions were greatly blunted by treating ECs with an NADPH oxidase inhibitor, diphenyleneiodonium chloride or apocynine, but not with a xanthine oxidase inhibitor. ECs infected with adenovirus carrying the dominant-negative mutant of Rac (RacN17), a component of NADPH oxidase, reduced the strain-induced superoxide and MCP-1 expression. In contrast, ECs transfected with a constitutively active Rac (RacV12) increased MCP-1 and 4x TRE promoter activities. However, ECs cotransfected with eNOS and RacV12 reduced those promoter activities. Consistently, the increases of superoxide levels and MCP-1 expression by overexpression of RacV12 were abolished after infecting ECs with eNOS. Our results show that NO from eNOS-inhibiting redox-sensitive MCP-1 expression is mediated via Rac-dependent NADPH oxidase by reducing ROS. This study provides a molecular basis to support the notion that endothelial NO acts as an antioxidant by negatively regulating redox-sensitive gene expression in ECs constantly under hemodynamic influence.

Inhibition of Monocyte Chemoattractant Protein-1 Expression in Cytokine-Treated Human Lung Epithelial Cells by Thiazolidinedione

Several lung diseases are characterized by the presence of increased numbers of activated macrophages. The recruitment and activation of peripheral blood monocytes are potentially critical regulatory events for the control of pulmonary inflammation. The chemokine monocyte chemoattractant protein (MCP)-1 is a potent chemoattractant for monocytes. MCP-1 is produced by lung epithelial cells during the course of inflammatory lung diseases. In the present study, we examined the effects of a thiazolidinedione (TZD), which is used to improve the insulin resistance of individuals with diabetes mellitus, on MCP-1 expression in a human lung epithelial cell line, A549. In A549 cells, interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha induced endogenous MCP-1 protein secretion and messenger RNA expression. The TZD inhibited the increase of MCP-1 secretion by IL-1beta and TNF-alpha treatment. The TZD inhibited the expression of MCP-1 messenger RNA with IL-1beta treatment, but not with TNF-alpha treatment. This observation was confirmed by the results of a monocyte chemotactic assay. The transcriptional activity of human MCP-1 promoter in A549 cells paralleled the endogenous messenger RNA expression by cytokines and TZD treatment. Our findings indicated that the suppression of the expression of MCP-1 could be accomplished by TZD treatment, raising the possibility that TZD may be of therapeutic value in several lung diseases in which MCP-1 plays an important role.

New Single Nucleotide Polymorphisms in the Shear Responsive MCP-1 Promoter Region in Atherosclerosis.

P160 Background: Atherosclerosis represents a complex chronic inflammatory process influenced in part by genetic factors. Polymorphisms in the key regulators of inflammation are hypothesized to increase the susceptibility for the development of atheroma. Single nucleotide polymorphisms (SNPs) affect the secretion of inflammatory mediators such as monocyte chemoattractant protein one (MCP-1). MCP-1 has been shown to affect atherosclerosis development and SNPs affecting its secretion may affect the occurrence of atherosclerosis in humans. The aim of this study is to examine the frequency of SNPs in the promoter region of MCP-1 in patients with atherosclerosis versus controls. Methods: DNA was obtained from patients presenting for carotid endarterectomy and controls. A region of the MCP-1 promoter spanning -2746 to +440 bases relative to the transcriptional start site was sequenced. Results: The MCP-1 distal regulatory region was sequenced and two known SNPs were identified at base -2518 and base -2076 from the transcriptional start site. A “G” substitution at -2518 is associated with increased secretion of MCP-1. No association between atherosclerosis and these two SNP’s was observed. Two new SNPs consisting of a C/G substitution at bases -302 and -868 from the transcriptional start site were discovered. Allele frequency for the C -301 SNP represented 33%% of the control population and 61% of the atherosclerotic population. There was a trend toward higher C allele frequency in the atherosclerotic population (P=0.10). The power of this analysis (0.35) was limited by the relatively small control sample size (n=16). Conclusion: We report the discovery of two novel SNPs in the MCP-1 promoter region. The SNP at the -301 base site that is activated by shear forces such as elevated blood pressure. This region is a highly conserved region with a high prevalence of the -301 polymorphism suggesting some effect on gene function. Work is on going to characterize the frequency of the C allele in populations with atherosclerosis as well as its effect on MCP-1 secretion.

TNF-α Stimulation of MCP-1 Expression Is Mediated by the Akt/PKB Signal Transduction Pathway in Vascular Endothelial Cells

MCP-1 is expressed in a variety of cell types including vascular endothelial cells following induction by different stimuli such as tumor necrosis factor (TNF)-α. Although TNF-α stimulates MCP-1 expression and secretion, the mechanism by which TNF-α stimulates expression of the MCP-1 gene is not known. In this study, we examine the involvement of the phosphatidylinositol-3-OH kinase (PI3-kinase)-Akt/PKB pathway. Exposure of human umbilical vein endothelial cells (HUVECs) to TNF-α elicited the rapid phosphorylation of Akt/PKB. In HUVECs, wortmannin, a PI3-kinase inhibitor, inhibits TNF-α-mediated MCP-1 secretion at a dose-dependent manner. Constitutively active form of Akt/PKB induces transcription of the MCP-1 gene, and cotransfection of dominant negative Akt/PKB suppressed the activation of the MCP-1 promoter induced by TNF-α. These findings show that Akt/PKB participates in the TNF-α induction of MCP-1 gene transcription in endothelial cells.

New Single Nucleotide Polymorphisms in the Shear Responsive MCP-1 Promoter Region in Atherosclerosis.

P160 Background: Atherosclerosis represents a complex chronic inflammatory process influenced in part by genetic factors. Polymorphisms in the key regulators of inflammation are hypothesized to increase the susceptibility for the development of atheroma. Single nucleotide polymorphisms (SNPs) affect the secretion of inflammatory mediators such as monocyte chemoattractant protein one (MCP-1). MCP-1 has been shown to affect atherosclerosis development and SNPs affecting its secretion may affect the occurrence of atherosclerosis in humans. The aim of this study is to examine the frequency of SNPs in the promoter region of MCP-1 in patients with atherosclerosis versus controls. Methods: DNA was obtained from patients presenting for carotid endarterectomy and controls. A region of the MCP-1 promoter spanning -2746 to +440 bases relative to the transcriptional start site was sequenced. Results: The MCP-1 distal regulatory region was sequenced and two known SNPs were identified at base -2518 and base -2076 from the transcriptional start site. A “G” substitution at -2518 is associated with increased secretion of MCP-1. No association between atherosclerosis and these two SNP’s was observed. Two new SNPs consisting of a C/G substitution at bases -302 and -868 from the transcriptional start site were discovered. Allele frequency for the C -301 SNP represented 33%% of the control population and 61% of the atherosclerotic population. There was a trend toward higher C allele frequency in the atherosclerotic population (P=0.10). The power of this analysis (0.35) was limited by the relatively small control sample size (n=16). Conclusion: We report the discovery of two novel SNPs in the MCP-1 promoter region. The SNP at the -301 base site that is activated by shear forces such as elevated blood pressure. This region is a highly conserved region with a high prevalence of the -301 polymorphism suggesting some effect on gene function. Work is on going to characterize the frequency of the C allele in populations with atherosclerosis as well as its effect on MCP-1 secretion.

Differential Regulation of CC Chemokine Gene Expression in Human Immunodeficiency Virus-Infected Myeloid Cells

The importance of chemokine expression on HIV infection has been emphasized by the discovery that infection of CD4+ T cells by M-tropic strains of HIV-1 is antagonized by the chemokines RANTES, MIP-1α, and MIP-1β, which are natural ligands of CCR5, a major coreceptor for macrophagetropic (M-tropic) isolates of HIV-1. Similarly, the CCR2b ligands MCP-1 and MCP-3 inhibit productive infection of PBMCs by both CCR5- and CXCR4-dependent strains of HIV-1, suggesting that expression of the MCP-1 chemokine may affect HIV infection via signaling through the CCR2 receptor and subsequent desensitization of the CCR5 and/or CXCR4 signaling pathway. Given the major role played by chemokine receptors in HIV-1 fusion/entry and the regulatory effects of chemokines on HIV-1 infection, we examined the pattern of chemokine gene expression in HIV-1-infected myeloid cells and in primary monocyte/macrophages. Chronic HIV-1 infection of U937 monocytic cells increased the expression of RANTES, MIP-1α, MIP-1β, and IL-8 chemokine genes, but strongly inhibited PMA/PHA- and TNFα-induced MCP-1 gene transcription. HIV-1-mediated inhibition of MCP-1 transcription and secretion was further confirmed in de novo HIV-1-infected U937 cells and correlated with a delay in HIV- and signal-induced NF-κB binding to the MCP-1 promoter. The inhibition of MCP-1 gene expression may provide a mechanism by which HIV-1 escapes the early influence of chemokine expression in monocytic cells.

Nitric oxide regulates monocyte chemotactic protein-1.

Monocyte chemotactic protein-1 (MCP-1) is a 76-amino-acid chemokine thought to be the major chemotactic factor for monocytes. We and others have demonstrated that NO inhibits monocyte-endothelial cell interactions and atherogenesis. We hypothesize that the antiatherogenic effect of NO may be due in part to its inhibition of MCP-1 expression. Smooth muscle cells (SMCs) were isolated from normal rabbit aortas by the explant method. Cells were then exposed to LPS (10 microg/mL), native LDL, or oxidized LDL (30 microg/mL) for 6 hours. The expression of MCP-1 in SMCs and chemotactic activity in the conditioned medium were induced by lipopolysaccharide (LPS) or by oxidized LDL but not native LDL. The induction of MCP-1 by cytokines or oxidized lipoproteins was associated with an increased generation of superoxide anion by the SMCs and increased activity of the transcriptional protein nuclear factor-kappaB (NFkappaB). The induced expression of MCP-1 and activation of NFkappaB were reduced by previous exposure of the SMCs to the NO donor DETA-NONOate (100 micromol/L) (P<.05). To determine whether NO exerted its effect at a transcriptional level, SMCs and COS cells were transfected with a 400-bp fragment of the MCP-1 promoter. Promoter activity was enhanced by oxidized LDL, and LPS was inhibited by DETA-NO. Nuclear run-on assays confirmed that the effect of NO occurred at a transcriptional level. To investigate the role of endogenous NO in the regulation of MCP-1 in vivo, New Zealand White rabbits were fed normal chow, normal chow plus nitro-L-arginine (LNA), high-cholesterol diet (Chol), or high-cholesterol diet supplemented with L-arginine (Arg). After 2 weeks, thoracic aortas were harvested and total RNA was isolated. Northern analysis using full-length MCP-1 cDNA demonstrated increased expression in Chol and LNA aortas; this expression was decreased in aortas from Arg animals. These studies indicate that the antiatherogenic effect of NO may be mediated in part by its inhibition of MCP-1 expression.