Srinivas Mummidi

HIV-1 infection and AIDS dementia are influenced by a mutant MCP-1 allele linked to increased monocyte infiltration of tissues and MCP-1 levels

Studies in humans and in experimental models of HIV-1 infection indicate an important role for monocyte chemoattractant protein-1 (MCP-1; also known as CC chemokine ligand 2), a potent chemoattractant and activator of mononuclear phagocytes (MP) in the pathogenesis of HIV-associated dementia (HAD). We determined the influence of genetic variation in MCP-1 on HIV-1 pathogenesis in large cohorts of HIV-1-infected adults and children. In adults, homozygosity for the MCP-1 –2578G allele was associated with a 50% reduction in the risk of acquiring HIV-1. However, once HIV-1 infection was established, this same MCP-1 genotype was associated with accelerated disease progression and a 4.5-fold increased risk of HAD. We examined the molecular and cellular basis for these genotype–phenotype associations and found that the mutant MCP-1 –2578G allele conferred greater transcriptional activity via differential DNA–protein interactions, enhanced protein production in vitro, increased serum MCP-1 levels, as well as MP infiltration into tissues. Thus, MCP-1 expression had a two-edged role in HIV-1 infection: it afforded partial protection from viral infection, but during infection, its proinflammatory properties and ability to up-regulate HIV-1 replication collectively may contribute to accelerated disease progression and increased risk of dementia. Our findings suggest that MCP-1 antagonists may be useful in HIV-1 infection, especially for HAD, and that HIV+ individuals possessing the MCP-1 –2578G allele may benefit from early initiation of antiretroviral drugs that effectively cross the blood–brain barrier. In a broader context, the MCP-1 –2578G allele may serve as a genetic determinant of outcome of other disease states in which MP-mediated tissue injury is central to disease pathogenesis.

Global survey of genetic variation in CCR5, RANTES, and MIP-1α: Impact on the epidemiology of the HIV-1 pandemic

Expression of CC chemokine receptor 5 (CCR5), the major coreceptor for HIV-1 cell entry, and its ligands (e.g., RANTES and MIP-1α) is widely regarded as central to the pathogenesis of HIV-1 infection. By surveying nearly 3,000 HIV+ and HIV− individuals from worldwide populations for polymorphisms in the genes encoding RANTES, MIP-1α, and CCR5, we show that the evolutionary histories of human populations have had a significant impact on the distribution of variation in these genes, and that this may be responsible, in part, for the heterogeneous nature of the epidemiology of the HIV-1 pandemic. The varied distribution of RANTES haplotypes (AC, GC, and AG) associated with population-specific HIV-1 transmission- and disease-modifying effects is a striking example. Homozygosity for the AC haplotype was associated with an increased risk of acquiring HIV-1 as well as accelerated disease progression in European Americans, but not in African Americans. Yet, the prevalence of the ancestral AC haplotype is high in individuals of African origin, but substantially lower in non-Africans. In a Japanese cohort, AG-containing RANTES haplotype pairs were associated with a delay in disease progression; however, we now show that their contribution to HIV-1 pathogenesis and epidemiology in other parts of the world is negligible because the AG haplotype is infrequent in non-Far East Asians. Thus, the varied distribution of RANTES, MIP-1α, and CCR5 haplotype pairs and their population-specific phenotypic effects on HIV-1 susceptibility and disease progression results in a complex pattern of biological determinants of HIV-1 epidemiology. These findings have important implications for the design, assessment, and implementation of effective HIV-1 intervention and prevention strategies.

A strong signature of balancing selection in the 5' cis-regulatory region of CCR5.

CCR5 encodes a cell surface chemokine receptor molecule that serves as the principal coreceptor, with CD4, for HIV-type 1 (HIV-1). Varied HIV-1 susceptibility and time to progression to AIDS have been associated with polymorphisms in CCR5. Many of these polymorphisms are located in the 5′ cis-regulatory region of CCR5, suggesting that it may have been a target of natural selection. We characterized CCR5 sequence variation in this region in 400 chromosomes from worldwide populations and compared it to a genome-wide analysis of 100 Alu polymorphisms typed in the same populations. Variation was substantially higher than expected and characterized by an excess of intermediate-frequency alleles. A genealogy of CCR5 haplotypes had deep branch lengths despite markedly little differentiation among populations. This finding suggested a deviation from neutrality not accounted for by population structure, which was confirmed by tests for natural selection. These results are strong evidence that balancing selection has shaped the pattern of variation in CCR5 and suggest that HIV-1 resistance afforded by CCR5 5′ cis-regulatory region haplotypes may be the consequence of adaptive changes to older pathogens.

Interleukin-18-induced human coronary artery smooth muscle cell migration is dependent on NF-κB- and AP-1-mediated matrix metalloproteinase-9 expression and is inhibited by atorvastatin

The proliferation and migration of arterial smooth muscle cells (SMCs) are key events in the vascular restenosis that frequently follows angioplasty. Furthermore, SMC migration and neointimal hyperplasia are promoted by degradation of the extracellular matrix by matrix metalloproteinases (MMPs). Because we demonstrated previously that the proinflammatory and proatherogenic cytokine interleukin-18 (IL-18) stimulates SMC proliferation (Chandrasekar, B., Mummidi, S., Valente, A. J., Patel, D. N., Bailey, S. R., Freeman, G. L., Hatano, M., Tokuhisa, T., and Jensen, L. E. (2005) J. Biol. Chem. 280, 26263–26277), we investigated whether IL-18 induces SMC migration in an MMP-dependent manner and whether the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor atorvastatin can inhibit this response. IL-18 treatment increased both mRNA and protein expression of MMP9 in human coronary artery SMCs. Gel shift, enzyme-linked immunosorbent, and chromatin immunoprecipitation assays revealed a strong induction of IL-18-mediated AP-1 (c-Fos, c-Jun, and Fra-1) and NF-κB (p50 and p65) activation and stimulation of MMP9 promoter-dependent reporter gene activity in an AP-1- and NF-κB-dependent manner. Ectopic expression of p65, c-Fos, c-Jun, and Fra-1 induced MMP9 promoter activity. Specific antisense or small interfering RNA reagents for these transcription factors reduced IL-18-mediated MMP9 transcription. Furthermore, IL-18 stimulated SMC migration in an MMP9-dependent manner. Atorvastatin effectively suppressed IL-18-mediated AP-1 and NF-κB activation, MMP9 expression, and SMC migration. Together, our results indicate for the first time that the proatherogenic cytokine IL-18 induces human coronary artery SMC migration in an MMP9-dependent manner. Atorvastatin inhibits IL-18-mediated aortic SMC migration and has therapeutic potential for attenuating the progression of atherosclerosis and restenosis.

The human CC chemokine receptor 5 (CCR5) gene. Multiple transcripts with 5'-end heterogeneity, dual promoter usage, and evidence for polymorphisms within the regulatory regions and noncoding exons

Human CC chemokine receptor 5 (CCR5), mediates the activation of cells by the chemokines macrophage inflammatory protein-1α, macrophage inflammatory protein-1β, and RANTES, and serves as a fusion cofactor for macrophage-tropic strains of human immunodeficiency virus type 1. To understand the molecular mechanisms that regulate human CCR5 gene expression, we initiated studies to determine its genomic and mRNA organization. Previous studies have identified a single CCR5 mRNA isoform whose open reading frame is intronless. We now report the following novel findings. 1) Complex alternative splicing and multiple transcription start sites give rise to several distinct CCR5 transcripts that differ in their 5′-untranslated regions (UTR). 2) The gene is organized into four exons and two introns. Exons 2 and 3 are not interrupted by an intron. Exon 4 and portions of exon 3 are shared by all isoforms. Exon 4 contains the open reading frame, 11 nucleotides of the 5′-UTR and the complete 3′-UTR. 3) The transcripts appear to be initiated from two distinct promoters: an upstream promoter (PU), upstream of exon 1, and a downstream promoter (PD), that includes the “intronic” region between exons 1 and 3. 4) PU and PD lacked the canonical TATA or CAAT motifs, and are AT-rich. 5) PD demonstrated strong constitutive promoter activity, whereas PU was a weak promoter in all three leukocyte cell environments tested (THP-1, Jurkat, and K562). 6) We provide evidence for polymorphisms in the noncoding sequences, including the regulatory regions and 5′-UTRs. The structure of CCR5 was strikingly reminiscent of the overall structure of other chemokine/chemoattractant receptors, underscoring an important evolutionarily conserved function for a prototypical gene structure. This is the first description of functional promoters for any CC chemokine receptor gene, and we speculate that the complex pattern of splicing events and dual promoter usage may function as a versatile mechanism to create diversity and flexibility in the regulation of CCR5 expression.

Fractalkine (CX3CL1) stimulated by nuclear factor κB (NF-κB)-dependent inflammatory signals induces aortic smooth muscle cell proliferation through an autocrine pathway

Fractalkine (also known as CX3CL1), a CX3C chemokine, activates and attracts monocytes/macrophages to the site of injury/inflammation. It binds to CX3C receptor 1 (CX3CR1), a pertussis toxin-sensitive G-protein-coupled receptor. In smooth muscle cells (SMCs), fractalkine is induced by proinflammatory cytokines [tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma)], which may mediate monocyte adhesion to SMCs. However, the mechanisms underlying its induction are unknown. In addition, it is unlear whether SMCs express CX3CR1. TNF-alpha activated nuclear factor kappaB (NF-kappaB) and induced fractalkine and CX3CR1 expression in a time-dependent manner in rat aortic SMCs. Transient transfections with dominant-negative (dn) inhibitory kappaB (IkappaB)-alpha, dnIkappaB-beta, dnIkappaB kinase (IKK)-gamma, kinase-dead (kd) NF-kappaB-inducing kinase (NIK) and kdIKK-beta, or pretreatment with wortmannin, Akt inhibitor, pyrrolidinecarbodithioc acid ammonium salt (PDTC) or MG-132, significantly attenuated TNF-alpha-induced fractalkine and CX3CR1 expression. Furthermore, expression of dn TNF-alpha-receptor-associated factor 2 (TRAF2), but not dnTRAF6, inhibited TNF-alpha signal transduction. Pretreatment with pertussis toxin or neutralizing anti-CX3CR1 antibodies attenuated TNF-alpha-induced fractalkine expression, indicating that fractalkine autoregulation plays a role in TNF-alpha-induced sustained fractalkine expression. Fractalkine induced its own expression, via pertussis toxin-sensitive G-proteins, phosphoinositide 3-kinase (PI 3-kinase), phosphoinositide-dependent kinase 1 (PDK1), Akt, NIK, IKK and NF-kappaB activation, and induced SMC cell-cell adhesion and cellular proliferation. Taken together, our results demonstrate that TNF-alpha induces the expression of fractalkine and CX3CR1 in rat aortic SMCs and that this induction is mediated by NF-kappaB activation. We also show that fractalkine induces its own expression, which is mediated by the PI 3-kinase/PDK1/Akt/NIK/IKK/NF-kappaB signalling pathway. More importantly, fractalkine increased cell-cell adhesion and aortic SMC proliferation, indicating a role in initiation and progression of atherosclerotic vascular disease.

Resveratrol inhibits high glucose-induced PI3K/Akt/ERK-dependent interleukin-17 expression in primary mouse cardiac fibroblasts

We investigated the expression of the proinflammatory cytokine interleukin (IL)-17 in cardiac fibroblasts and its induction by high glucose (HG). Our results show that primary mouse cardiac fibroblasts (mCFs) secrete low basal levels of IL-17 and that HG (25 mM D-glucose) as opposed to low glucose (5 mM D-glucose + 20 mM mannitol) significantly enhances its secretion. HG induces IL-17 mRNA expression by both transcriptional and posttranscriptional mechanisms. HG induces phosphoinositide 3- kinase [PI3K; inhibited by adenoviral (Ad).dominant negative (dn)PI3Kp85], Akt (inhibited by Ad.dnAkt1), and ERK (inhibited by PD-98059) activation and induces IL-17 expression via PI3K-->Akt-->ERK-dependent signaling. Moreover, mCFs express both IL-17 receptors A and C, and although IL-17RA is upregulated, HG fails to modulate IL-17RC expression. Furthermore, IL-17 stimulates net collagen production by mCFs. Pretreatment with the phytoalexin resveratrol blocks HG-induced PI3K-, Akt-, and ERK-dependent IL-17 expression. These results demonstrate that 1) cardiac fibroblasts express IL-17 and its receptors; 2) HG upregulates IL-17 and IL-17RA, suggesting a positive amplification loop in IL-17 signaling in hyperglycemia; 3) IL-17 enhances net collagen production; and 4) resveratrol can inhibit these HG-induced changes. Thus, in hyperglycemic conditions, IL-17 may potentiate myocardial inflammation, injury, and remodeling through autocrine and paracrine mechanisms, and resveratrol has therapeutic potential in ameliorating this effect.

Concordance between the CC chemokine receptor 5 genetic determinants that alter risks of transmission and disease progression in children exposed perinatally to human immunodeficiency virus

If CC chemokine receptor 5 (CCR5)-dependent mechanisms at the time of initial virus exposure are important determinants of virus entry and disease outcome, then the polymorphisms in CCR5 that influence risk of transmission and disease progression should be similar; this hypothesis was tested in a cohort of 649 Argentinean children exposed perinatally to human immunodeficiency virus type 1 (HIV-1). Two lines of evidence support this hypothesis. First, CCR5 haplotype pairs associated with enhanced risk of transmission were the chief predictors of a faster disease course. Second, some of the haplotype pairs associated with altered rates of transmission and disease progression in children were similar to those that we previously found influenced outcome in European American adults. This concordance suggests that CCR5 haplotypes may serve as genetic rheostats that influence events occurring shortly after initial virus exposure, dictating not only virus entry but, by extension, also the extent of early viral replication.

CC Chemokine Receptor 5-Mediated Signaling and HIV-1 Co-receptor Activity Share Common Structural Determinants CRITICAL RESIDUES IN THE THIRD EXTRACELLULAR LOOP SUPPORT HIV-1 FUSION

There is a close correspondence between the ability of RANTES and macrophage inflammatory proteins 1α and 1β to activate CC chemokine receptor 5 (CCR5) and the ability to inhibit CCR5-dependent membrane fusion mediated by the envelope glycoprotein of human immunodeficiency virus (HIV), type 1. This finding suggests that some of the structural determinants for CC chemokine/CCR5 interactions and CCR5 HIV-1 fusion co-receptor activity may be shared. Recent studies using human CCR5/CCR2B chimeras have suggested that the determinants of CCR5 co-receptor activity are complex and may involve multiple extracellular receptor domains and that viral co-receptor activity is dissociable from ligand-dependent signaling responses. However, conclusive evidence demonstrating an important role for the second and third extracellular regions of human CCR5 is lacking. Furthermore, to determine whether the determinants for CCR5 co-receptor activity overlap with those required for agonist activity, studies that compare the chemokine specificity for inhibition of envelope-mediated cell fusion and the agonist profile of chimeric receptors are necessary. In the present report, using a series of CCR5/CCR2B chimeras we ascribe an important role for the second and third extracellular loop of CCR5 in supporting the co-receptor activity of CCR5. We also provide evidence that the intracytoplasmic tail of CCR5 does not play an important role in supporting HIV-1 entry. The hypothesis that the structural determinants for CC chemokine/CCR5 interactions and CCR5 HIV-1 fusion co-receptor activity may be shared was confirmed by two novel observations: first, the fusion activity supported by two hybrid receptors could be inhibited by both RANTES and monocyte chemoattractant protein-1, chemokines specific to CCR5 and CCR2B, respectively; and second, the chemokine specificity for inhibition of envelope-mediated cell fusion matched the agonist profile of these hybrid receptors. These data shed new light on the structural determinants involved in these distinct activities of CCR5 and may have important implications for the development of CCR5-targeted anti-viral compounds.

WNT1-inducible signaling pathway protein-1 activates diverse cell survival pathways and blocks doxorubicin-induced cardiomyocyte death

The anthracycline antibiotic doxorubicin (DOX) is a potent cancer chemotherapeutic agent that exerts both acute and chronic cardiotoxicity. Here we show that in adult mouse cardiomyocytes, DOX activates (i) the pro-apoptotic p53, (ii) p38MAPK and JNK, (iii) Bax translocation, (iv) cytochrome c release, and (v) caspase 3. Further, it (vi) inhibits expression of anti-apoptotic Akt, Bcl-2 and Bcl-xL, and (vii) induces internucleosomal degradation and cell death. WNT1-inducible signaling pathway protein-1 (WISP1), a CCN family member and a matricellular protein, inhibits DOX-mediated cardiomyocyte death. WISP1 inhibits DOX-induced p53 activation, p38 MAPK and JNK phosphorylation, Bax translocation to mitochondria, and cytochrome c release into cytoplasm. Additionally, WISP1 reverses DOX-induced suppression of Bcl-2 and Bcl-xL expression and Akt inhibition. The pro-survival effects of WISP1 were recapitulated by the forced expression of mutant p53, wild-type Bcl-2, wild-type Bcl-xL, or constitutively active Akt prior to DOX treatment. WISP1 also induces the pro-survival factor Survivin via PI3K/Akt signaling. Overexpression of wild-type, but not mutant Survivin, blunts DOX cytotoxicity. Further, WISP1 stimulates PI3K-Akt-dependent GSK3beta phosphorylation and beta-catenin nuclear translocation. Importantly, WISP1 induces its own expression. Together, these results provide important insights into the cytoprotective effects of WISP1 in cardiomyocytes, and suggest a potential therapeutic role for WISP1 in DOX-induced cardiotoxicity.