Determinants of the trans-dominant negative effect of truncated forms of the CCR5 chemokine receptor

The multilayered complexity of the chemokine receptor system

The chemokines receptor family are membrane-expressed class A-specific seven-transmembrane receptors linked to G proteins. Through interaction with the corresponding ligands, the chemokines, they induce a wide variety of cellular responses including cell polarization, movement, immune and inflammatory responses, as well as the prevention of HIV-1 infection. Like a Russian matryoshka doll, the chemokine receptor system is more complex than initially envisaged. This review focuses on the mechanisms that contribute to this dazzling complexity and how they modulate the signaling events triggered by chemokines. The chemokines and their receptors exist as monomers, dimers and oligomers, their expression pattern is highly regulated, and the ligands can bind distinct receptors with similar affinities. The use of novel imaging-based technologies, particularly real-time imaging modalities, has shed new light on the very dynamic conformations that chemokine receptors adopt depending on the cellular context, and that affect chemokine-mediated responses. This complex scenario presents both challenging and exciting opportunities for drug discovery.

CCR5 and CXCL12 allelic variants: Possible association with childhood neuroblastoma susceptibility?

Neuroblastoma (NB) is a heterogeneous and particularly malignant childhood neoplasm in its higher stages, prone to form metastasis in selected organs and for which there is still no efficient treatment available beyond surgery. Evidence indicates that chemokines and their receptors present involvement as mediators of neuroinflammation and have a neurophysiological role. In the present study, we aimed to verify if CCR5 (rs333) and CXCL12 (rs1801157) allelic variants were associated with NB. For CCR5 (rs333) D32 carriers (OR: 5.96, IC: 2.21-16.06) and for CXCL12 genotype 3'A/3'A (OR:26.18, IC:6.15-111.4) there were statistically significant differences as well to allelic frequency (OR:4.20, IC: 2.19-8.03). Although no correlation was verified regarding prognostic parameters for both CCR5 and CXCL12 polymorphic variants, these polymorphisms may be associated with NB susceptibility which deserve attention for future investigations.

Predominance of the heterozygous CCR5 delta-24 deletion in African individuals resistant to HIV infection might be related to a defect in CCR5 addressing at the cell surface

INTRODUCTION

The chemokine receptor CCR5 is the main co-receptor for R5-tropic HIV-1 variants. We have previously described a novel 24-base pair deletion in the coding region of CCR5 among individuals from Rwanda. Here, we investigated the prevalence of hCCR5Δ24 in different cohorts and its impact on CCR5 expression and HIV-1 infection in vitro.

METHODS

We screened hCCR5Δ24 in a total of 3232 individuals which were either HIV-1 uninfected, high-risk HIV-1 seronegative and seropositive partners from serodiscordant couples, Long-Term Survivors, or HIV-1 infected volunteers from Africa (Rwanda, Kenya, Guinea-Conakry) and Luxembourg, using a real-time PCR assay. The role of the 24-base pair deletion on CCR5 expression and HIV infection was assessed in cell lines and PBMC using mRNA quantification, confocal analysis, flow and imaging cytometry.

RESULTS AND DISCUSSION

Among the 1661 patients from Rwanda, 12 individuals were heterozygous for hCCR5Δ24 but none were homozygous. Although heterozygosity for this allele may not confer complete resistance to HIV-1 infection, the prevalence of the mutation was 2.41% (95%CI: 0.43; 8.37) in 83 Long-Term Survivors (LTS) and 0.99% (95%CI: 0.45; 2.14) in 613 HIV-1 exposed seronegative members as compared with 0.35% (95% Cl: 0.06; 1.25) in 579 HIV-1 seropositive members. The prevalence of hCCR5Δ24 was 0.55% (95%CI: 0.15; 1.69) in 547 infants from Kenya but the mutation was not detected in 224 infants from Guinea-Conakry nor in 800 Caucasian individuals from Luxembourg. Expression of hCCR5Δ24 in cell lines and PBMC showed that the hCCR5Δ24 protein is stably expressed but is not transported to the plasma membrane due to a conformational change. Instead, the mutant receptor was retained intracellularly, colocalized with an endoplasmic reticulum marker and did not mediate HIV-1 infection. Co-transfection of hCCR5Δ24 and wtCCR5 did not indicate a transdominant negative effect of CCR5Δ24 on wtCCR5.

CONCLUSIONS

Our findings indicate that hCCR5Δ24 is not expressed at the cell surface. This could explain the higher prevalence of the heterozygous hCCR5Δ24 in LTS and HIV-1 exposed seronegative members from serodiscordant couples. Our data suggest an East-African localization of this deletion, which needs to be confirmed in larger cohorts from African and non-African countries.

West Nile Virus Encephalitis in Haematological Setting: Report of Two Cases and a Brief Review of the Literature

West Nile virus is a zoonotic agent causing life-threatening encephalitis in a proportion of infected patients. Older age, immunosuppression, and mutations in specific host genes (e.g., CCR5 delta-32 mutation) predispose to neuroinvasive infection. We report on two cases of severe West Nile encephalitis in recently-treated, different-aged, chronic lymphocytic leukemia patients. Both patients developed high-grade fever associated with severe neurological impairment. The younger one harboured germ-line CCR5 delta-32 mutation, which might have played a role in the pathogenesis of its neuroinvasive manifestations.

Engineered zinc-finger nuclease to generate site-directed modification in the KLF1 gene for fetal hemoglobin induction

Elevation of hemoglobin F (HbF) ameliorates symptoms of β-thalassemia, as a common autosomal recessive disorder. In this study, the ability of an engineered zinc-finger nuclease (ZFN) system was assesed to disrupt the KLF1 gene to inhibit the γ to β hemoglobin switching in K562 cells. This study was performed using a second generation integration-deficient lentiviral vector assigned to transient gene targeting. The sequences coding for zinc finger protein arrays were designed and subcloned in TDH plus as a transfer vector. Transduction of K562 cells was performed with the integrase minus lentivirus containing ZFN. The indel percentage of the transducted cells with lentivirus containing ZFN was about 29%. Differentiation of K562 cell line into erythroid cell lineage was induced with cisplatin concentration of 15 µg/mL. After differentiation, γ-globin and HbF expression were evaluated using real-time reverse-transcription polymerase chain reaction and hemoglobin electrophoresis methods. The levels of γ-globin messenger RNA were nine-fold higher in the ZFN treated cells compared with untreated cells 5 days after differentiation. Hemoglobin electrophoresis method showed the same results for HbF level measurement. Application of the ZFN tool to induce KLF1 gene mutation in adult erythroid progenitors might be a candidate to stimulate HbF expression in β-thalassemia patients.

CCR5 Revisited: How Mechanisms of HIV Entry Govern AIDS Pathogenesis

The chemokine receptor CCR5 has been the focus of intensive studies since its role as a coreceptor for HIV entry was discovered in 1996. These studies lead to the development of small molecular drugs targeting CCR5, with maraviroc becoming in 2007 the first clinically approved chemokine receptor inhibitor. More recently, the apparent HIV cure in a patient transplanted with hematopoietic stem cells devoid of functional CCR5 rekindled the interest for inactivating CCR5 through gene therapy and pharmacological approaches. Fundamental research on CCR5 has also been boosted by key advances in the field of G-protein coupled receptor research, with the realization that CCR5 adopts a variety of conformations, and that only a subset of these conformations may be targeted by chemokine ligands. In addition, recent genetic and pathogenesis studies have emphasized the central role of CCR5 expression levels in determining the risk of HIV and SIV acquisition and disease progression. In this article, we propose to review the key properties of CCR5 that account for its central role in HIV pathogenesis, with a focus on mechanisms that regulate CCR5 expression, conformation, and interaction with HIV envelope glycoproteins.

Remodeling our concept of chemokine receptor function: From monomers to oligomers

The chemokines direct leukocyte recruitment in both homeostatic and inflammatory conditions, and are therefore critical for immune reactions. By binding to members of the class A G protein-coupled receptors, the chemokines play an essential role in numerous physiological and pathological processes. In the last quarter century, the field has accumulated much information regarding the implications of these molecules in different immune processes, as well as mechanistic insight into the signaling events activated through their binding to their receptors. Here, we will focus on chemokine receptors and how new methodological approaches have underscored the role of their conformations in chemokine functions. Advances in biophysical-based techniques show that chemokines and their receptors act in very complex networks and therefore should not be considered isolated entities. In this regard, the chemokine receptors can form homo- and heterodimers as well as oligomers at the cell surface. These findings are changing our view as to how chemokines influence cell biology, identify partners that regulate chemokine function, and open new avenues for therapeutic intervention.

Inducing indel mutation in the SOX6 gene by zinc finger nuclease for gamma reactivation: An approach towards gene therapy of beta thalassemia

β-thalassemia is a common autosomal recessive disorder characterized by a deficiency in the synthesis of β-chains. Evidences show that increased HbF levels improve the symptoms in patients with β-thalassemia or sickle cell anemia. In this study, ZFN technology was applied to induce a mutation in the binding domain region of SOX6 to reactivate γ-globin expression. The sequences coding for ZFP arrays were designed and sub cloned in TDH plus as a transfer vector. The ZFN expression was confirmed using Western blot analysis. In the next step, using the site-directed mutagenesis strategy through the overlap PCR, a missense mutation (D64V) was induced in the catalytic domain of the integrase gene in the packaging plasmid and verified using DNA sequencing. Then, the integrase minus lentivirus containing ZFN cassette was packaged. Transduction of K562 cells with this virus was performed. Mutation detection assay was performed. The indel percentage of the cells transducted with lenti virus containing ZFN was 31%. After 5 days of erythroid differentiation with 15 μg/mL cisplatin, the levels of γ-globin mRNA were sixfold in the cells treated with ZFN compared to untreated cells. In the meantime, the measurement of HbF expression levels was carried out using hemoglobin electrophoresis and showed the same results. Integrase minus lentivirus can provide a useful tool for efficient transient gene expression and helps avoid disadvantages of gene targeting using the native virus. The ZFN strategy applied here to induce indel on SOX6 gene in adult erythroid progenitors may provide a method to activate fetal hemoglobin expression in individuals with β-thalassemia.

CCR5 gene disruption via lentiviral vectors expressing Cas9 and single guided RNA renders cells resistant to HIV-1 infection

CCR5, a coreceptor for HIV-1 entry, is a major target for drug and genetic intervention against HIV-1. Genetic intervention strategies have knocked down CCR5 expression levels by shRNA or disrupted the CCR5 gene using zinc finger nucleases (ZFN) or Transcription activator-like effector nuclease (TALEN). In the present study, we silenced CCR5 via CRISPR associated protein 9 (Cas9) and single guided RNAs (sgRNAs). We constructed lentiviral vectors expressing Cas9 and CCR5 sgRNAs. We show that a single round transduction of lentiviral vectors expressing Cas9 and CCR5 sgRNAs into HIV-1 susceptible human CD4+ cells yields high frequencies of CCR5 gene disruption. CCR5 gene-disrupted cells are not only resistant to R5-tropic HIV-1, including transmitted/founder (T/F) HIV-1 isolates, but also have selective advantage over CCR5 gene-undisrupted cells during R5-tropic HIV-1 infection. Importantly, using T7 endonuclease I assay we did not detect genome mutations at potential off-target sites that are highly homologous to these CCR5 sgRNAs in stably transduced cells even at 84 days post transduction. Thus we conclude that silencing of CCR5 via Cas9 and CCR5-specific sgRNAs could be a viable alternative strategy for engineering resistance against HIV-1.

Chemokine receptor oligomerization and allostery

Oligomerization of chemokine receptors has been reported to influence many aspects of receptor function through allosteric communication between receptor protomers. Allosteric interactions within chemokine receptor hetero-oligomers have been shown to cause negative cooperativity in the binding of chemokines and to inhibit receptor activation in the case of some receptor pairs. Other receptor pairs can cause enhanced signaling and even activate entirely new, hetero-oligomer-specific signaling complexes and responses downstream of receptor activation. Many mechanisms contribute to these effects including direct allosteric coupling between the receptors, G protein-mediated allostery, G protein stealing, ligand sequestration, and recruitment of new intracellular proteins by exposing unique binding interfaces on the oligomerized receptors. These effects present both challenges as well as exciting opportunities for drug discovery. One of the most difficult challenges will involve determining if and when hetero-oligomers versus homomeric receptors are involved in specific disease states.

Absence of Association between CCR5 rs333 Polymorphism and Childhood Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is a malignant disorder that originates from one single hematopoietic precursor committed to B- or T-cell lineage. Ordinarily, these cells express CCR5 chemokine receptor, which directs the immune response to a cellular pattern and is involved in cancer pathobiology. The genetic rs333 polymorphism of CCR5 (Δ32), results in a diminished receptor expression, thus leading to impaired cell trafficking. The objective of the present study was to investigate the effect of CCR5 chemokine receptor rs333 polymorphism in the pathogenesis of ALL. The genotype distribution was studied in 79 patients and compared with 80 control subjects, in a childhood population of Southern Brazil. Genotyping was performed using DNA samples amplified by polymerase chain reaction with sequence-specific primers (PCR-SSP). The homozygous (Δ32/Δ32) deletion was not observed in any subject involved in the study. Heterozygous genotype was not associated with ALL risk (OR 0.7%; 95% CI 0.21–2.32; P > 0.05), nor recurrence status of ALL (OR 0.86; 95% CI 0.13–5.48; P > 0.05). This work demonstrated, for the first time, no significant differences in the frequency of the CCR5/Δ32 genotype between ALL and control groups, indicating no effect of this genetic variant on the ALL susceptibility and recurrence risk.

CC chemokine receptor 5: the interface of host immunity and cancer

Solid tumors are embedded in a stromal microenvironment consisting of immune cells, such as macrophages and lymphocytes, as well as nonimmune cells, such as endothelial cells and fibroblasts. Chemokines are a type of small secreted chemotactic cytokine and together with their receptors play key roles in the immune defense. Critically, they regulate cancer cellular migration and also contribute to their proliferation and survival. The CCR5 chemokine receptor is involved in leucocytes chemotaxis to sites of inflammation and plays an important role in the macrophages, T cells, and monocytes recruitment. Additionally, CCR5 may have an indirect effect on cancer progression by controlling the antitumor immune response, since it has been demonstrated that its expression could promote tumor growth and contribute to tumor metastasis, in different types of malignant tumors. Furthermore, it was demonstrated that a CCR5 antagonist may inhibit tumor growth, consisting of a possible therapeutic target. In this context, the present review focuses on the establishment of CCR5 within the interface of host immunity, tumor microenvironment, and its potential as a targeting to immunotherapy.

C-C chemokine receptor type five (CCR5): An emerging target for the control of HIV infection

When HIV was initially discovered as the causative agent of AIDS, many expected to find a vaccine within a few years. This has however proven to be elusive; it has been approximately 30 years since HIV was first discovered, and a suitable vaccine is still not in effect. In 2009, a paper published by Hutter et al. reported on a bone marrow transplant performed on an HIV positive individual using stem cells that were derived from a donor who was homozygous for a mutation in the CCR5 gene known as CCR5 delta-32 (Δ32) (Hütter et al., 2009). The HIV positive individual became HIV negative and remained free of viral detection after transplantation despite having halted anti-retroviral (ARV) treatment. This review will focus on CCR5 as a key component in HIV immunity and will discuss the role of CCR5 in the control of HIV infection.

Chemokine receptor oligomerization: a further step toward chemokine function

A broad array of biological responses including cell polarization, movement, immune and inflammatory responses, as well as prevention of HIV-1 infection, are triggered by the chemokines, a family of secreted and structurally related chemoattractant proteins that bind to class A-specific seven-transmembrane receptors linked to G proteins. Chemokines and their receptors should not be considered isolated entities, as they act in complex networks. Chemokines bind as oligomers, or oligomerize after binding to glycosaminoglycans on endothelial cells, and are then presented to their receptors on target cells, facilitating the generation of chemoattractant gradients. The chemokine receptors form homo- and heterodimers, as well as higher order structures at the cell surface. These structures are dynamic and are regulated by receptor expression and ligand levels. Complexity is even greater, as in addition to regulation by cytokines and decoy receptors, chemokine and receptor levels are affected by proteolytic cleavage and other protein modifications. This complex scenario should be considered when analyzing chemokine biology and the ability of their antagonists to act in vivo. Strategies based on blocking or stabilizing ligand and receptor dimers could be alternative approaches that might have broad therapeutic potential.

Chemokine polymorphisms and lymphoma: a pooled analysis

Polymorphisms in chemokine genes have been associated with human immunodeficiency virus (HIV)-related non-Hodgkin lymphoma (NHL) but are understudied in non-HIV-related NHL. Associations of NHL and NHL subtypes with polymorphisms and haplotypes in CCR5, CCR2, CCL5, CXCL12, and CX(3)CR(1) were explored in a pooled analysis of three case-control studies (San Francisco Bay Area, California; United Kingdom; total: cases N = 1610, controls N = 1992). Adjusted unconditional logistic regression was used to estimate relative risks among HIV-negative non-Hispanic Caucasians. The CCR5 Delta32 deletion reduced the risk of NHL (odds ratio = 0.56, 95% confidence interval = 0.38-0.83) in men but not women with similar effects observed for diffuse large-cell and follicular lymphoma (FL). NHL risk also was reduced in men with the CCR2/CCR5 haplotype characterized by the CCR5 Delta32 deletion. The CCL5 -403A allele conferred reduced risks of FL and chronic lymphocytic leukemia/small lymphocytic lymphoma. Results should be interpreted conservatively. Continued investigation is warranted to confirm these findings.

Targeted chromosomal deletions in human cells using zinc finger nucleases

We present a novel approach for generating targeted deletions of genomic segments in human and other eukaryotic cells using engineered zinc finger nucleases (ZFNs). We found that ZFNs designed to target two different sites in a human chromosome could introduce two concurrent DNA double-strand breaks (DSBs) in the chromosome and give rise to targeted deletions of the genomic segment between the two sites. Using this method in human cells, we were able to delete predetermined genomic DNA segments in the range of several-hundred base pairs (bp) to 15 mega-bp at frequencies of 10(-3) to 10(-1). These high frequencies allowed us to isolate clonal populations of cells, in which the target chromosomal segments were deleted, by limiting dilution. Sequence analysis revealed that many of the deletion junctions contained small insertions or deletions and microhomologies, indicative of DNA repair via nonhomologous end-joining. Unlike other genome engineering tools such as recombinases and meganucleases, ZFNs do not require preinsertion of target sites into the genome and allow precise manipulation of endogenous genomic scripts in animal and plant cells. Thus, ZFN-induced genomic deletions should be broadly useful as a novel method in biomedical research, biotechnology, and gene therapy.

Targeted genome editing in human cells with zinc finger nucleases constructed via modular assembly

Broad applications of zinc finger nuclease (ZFN) technology-which allows targeted genome editing-in research, medicine, and biotechnology are hampered by the lack of a convenient, rapid, and publicly available method for the synthesis of functional ZFNs. Here we describe an efficient and easy-to-practice modular-assembly method using publicly available zinc fingers to make ZFNs that can modify the DNA sequences of predetermined genomic sites in human cells. We synthesized and tested hundreds of ZFNs to target dozens of different sites in the human CCR5 gene-a co-receptor required for HIV infection-and found that many of these nucleases induced site-specific mutations in the CCR5 sequence. Because human cells that harbor CCR5 null mutations are functional and normal, these ZFNs might be used for (1) knocking out CCR5 to produce T-cells that are resistant to HIV infection in AIDS patients or (2) inserting therapeutic genes at "safe sites" in gene therapy applications.

Resistance to human immunodeficiency virus type 1 (HIV-1) generated by lentivirus vector-mediated delivery of the CCR5{Delta}32 gene despite detectable expression of the HIV-1 co-receptors

It has previously been demonstrated that there are two distinct mechanisms for genetic resistance to human immunodeficiency virus type 1 (HIV-1) conferred by the CCR5Delta32 gene: the loss of wild-type CCR5 surface expression and the generation of CCR5Delta32 protein, which interacts with CXCR4. To analyse the protective effects of long-term expression of the CCR5Delta32 protein, recombinant lentiviral vectors were used to deliver the CCR5Delta32 gene into human cell lines and primary peripheral blood mononuclear cells that had been immortalized by human T-cell leukemia virus type 1. Blasticidin S-resistant cell lines expressing the lentivirus-encoded CCR5Delta32 showed a significant reduction in HIV-1 Env-mediated fusion assays. It was shown that CD4(+) T lymphocytes expressing the lentivirus-encoded CCR5Delta32 gene were highly resistant to infection by a primary but not by a laboratory-adapted X4 strain, suggesting different infectivity requirements. In contrast to previous studies that analysed the CCR5Delta32 protective effects in a transient expression system, this study showed that long-term expression of CCR5Delta32 conferred resistance to HIV-1 despite cell-surface expression of the HIV co-receptors. The results suggest an additional unknown mechanism for generating the CCR5Delta32 resistance phenotype and support the hypothesis that the CCR5Delta32 protein acts as an HIV-suppressive factor by altering the stoichiometry of the molecules involved in HIV-1 entry. The lentiviral-CCR5Delta32 vectors offer a method of generating HIV-resistant cells by delivery of the CCR5Delta32 gene that may be useful for stem cell- or T-cell-based gene therapy for HIV-1 infection.

Common CCR5-del32 frameshift mutation associated with serum levels of inflammatory markers and cardiovascular disease risk in the Bruneck population

BACKGROUND AND PURPOSE

Atherosclerosis is a progressive inflammatory disease and can develop in large arteries such as carotid and femoral arteries or medium-sized muscular arteries of the heart. Previous predominantly experimental studies suggested an important role of chemokines in the development of atherosclerosis. The main aim of this study was to examine potential effect of the CCR5-del32 mutation on systemic inflammation, intima-media thickness in carotid and femoral arteries, and on the indices of cardiovascular disease.

METHODS

In the present study, we have examined the association of a common functional 32-bp frameshift deletion mutation in a chemokine receptor (CCR5) in relation to inflammation and atherosclerosis. CCR5 is a G protein-coupled receptor involved in inflammatory response and regulation of leukocytes activation and migration. Genetic screening of this mutation was carried out on a well-known and previously described cohort of Bruneck (n=826) using polymerase chain reaction.

RESULTS

Screening was successful in 810 subjects of whom 7 were homozygous, 102 were heterozygous, and 701 were normal. The mutation was associated with significantly lower levels of C-reactive protein in a dose-dependent manner. Moreover, CCR5-del32 was associated with a significantly lower carotid intima-media thickness in the common carotid artery (del32/del32, 837+/-8 microm; wt/del32, 909+/-21 microm; wt/wt, 958+/-8 microm; P=0.007 after multivariable adjustment). Furthermore, incident cardiovascular disease (1995 to 2005) was markedly reduced in del32 homozygotes and heterozygotes subjects compared with wild-type homozygotes (del32/del32=0%, wt/del32=7.8%, wt/wt=14.8%, P=0.020). Findings equally applied to coronary artery and cerebrovascular disease.

CONCLUSIONS

The chemokine receptor CCR5-del32 frameshift mutation is associated with low levels of C-reactive protein, decreased intima-media thickness, and cardiovascular disease risk. These findings are consistent with the hypothesis that the chemokine receptor CCR5 is involved in the mediation of low-grade systemic inflammation and may play a role in human atherosclerosis and cardiovascular disease.

Two amino acid substitutions within the first external loop of CCR5 induce human immunodeficiency virus-blocking antibodies in mice and chickens

Antibodies to the first loop (ECL1) of CCR5 have been identified in human immunodeficiency virus (HIV)-exposed uninfected individuals (ESN) and in HIV-positive nonprogressing subjects. Thus, these antibodies may confer resistance against HIV infection. To define which amino acids are involved in antibody binding to CCR5, we performed a peptide-scanning assay and studied the immunogenicity of peptides in animal models. A panel of synthetic peptides spanning the CCR5-ECL1 region and displaying glycine or alanine substitutions was assayed for antibody binding with a pool of natural anti-CCR5 antibodies. We used mice and chickens to study the immunogenicity of mutagenized peptide. Structural characterization by nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics simulations were performed to better understand the structural and conformational features of the mutagenized peptide. Amino acid substitutions in positions Ala95 and Ala96 (A(95)-A(96)) increased antibody-peptide binding compared to that of the wild-type peptide (Asp(95)-Phe(96)). The Ala95-96 peptide was shown to induce, in mice and chickens, antibodies displaying biological activity at very low concentrations. Strikingly, chicken antibodies to the Ala95-96 peptide specifically recognize human CCR5 molecules, downregulate receptors from lymphocytes, inhibit CCR5-dependent chemotaxis, and prevent infection by several R5 viruses, displaying 50% inhibitory concentrations of less than 3 ng/ml. NMR spectroscopy and molecular dynamics simulations proved the high flexibility of isolated epitopes and suggested that A(95)-A(96) substitutions determine a slightly higher tendency to generate helical conformations combined with a lower steric hindrance of the side chains in the peptides. These findings may be relevant to the induction of strong and efficient HIV-blocking antibodies.

CCR5Delta32 59537-G/A promoter polymorphism is associated with low translational efficiency and the loss of CCR5Delta32 protective effects

We have recently demonstrated that the CCR5Delta32 protein interacts with CCR5 and CXCR4 and down-modulates their cell surface expression. We have also reported the absence of detectable expression of the truncated CCR5Delta32 protein in four out of six human immunodeficiency virus-infected (HIV(+)) CCR5(-/-) individuals. To explain the defect in protein expression in these samples, we cloned and sequenced the promoter regions of the six HIV(+) individuals. We have identified several polymorphisms in the CCR5Delta32 promoter region, but these polymorphisms were not associated with significant differences in mRNA levels. Coupled in vitro transcription/translation and polyribosome analysis demonstrated a strong association between a variant genotype designated CCR5Delta32 59537-A/A and a low translation efficiency. Protein analysis indicated that the peripheral blood mononuclear cells from two of the HIV(+) CCR5(-/-) individuals carrying the CCR5Delta32 59537-A/A variant expressed trace amounts of CCR5Delta32 protein compared to the individuals carrying the CCR5Delta32 59537-G/G genotype. The results imply that the absence of CCR5Delta32 protein in two HIV(+) individuals is due to a genetic defect in the translation of the protein. Together, these results highlight the importance of the CCR5Delta32 protein as an HIV suppressive factor and provide further insight into the mechanism of the protective effect of the CCR5Delta32 mutation.

CCR5Delta32 protein expression and stability are critical for resistance to human immunodeficiency virus type 1 in vivo

Human immunodeficiency virus type 1 (HIV-1) infection of individuals carrying the two alleles of the CCR5Delta32 mutation (CCR5(-/-)) has rarely been reported, but how the virus overcomes the CCR5Delta32 protective effect in these cases has not been delineated. We have investigated this in 6 infected (HIV(+)) and 25 HIV(-) CCR5(-/-) individuals. CD4(+) T lymphocytes isolated from HIV(-) CCR5(-/-) peripheral blood mononuclear cells (PBMCs) showed lower levels of CXCR4 expression that correlated with lower X4 Env-mediated fusion. Endogenous CCR5Delta32 protein was detected in all HIV(-) CCR5(-/-) PBMC samples (n = 25) but not in four of six unrelated HIV(+) CCR5(-/-) PBMC samples. Low levels were detected in another two HIV(+) CCR5(-/-) PBMC samples. The expression of adenovirus 5 (Ad5)-encoded CCR5Delta32 protein restored the protective effect in PBMCs from three HIV(+) CCR5(-/-) individuals but failed to restore the protective effect in PBMCs isolated from another three HIV(+) CCR5(-/-) individuals. In the latter samples, pulse-chase analyses demonstrated the disappearance of endogenous Ad5-encoded CCR5Delta32 protein and the accumulation of Ad5-encoded CCR5 during the chase periods. PBMCs isolated from CCR5(-/-) individuals showed resistance to primary X4 but were readily infected by a lab-adapted X4 strain. Low levels of Ad5-encoded CCR5Delta32 protein conferred resistance to primary X4 but not to lab-adapted X4 virus. These data provide strong support for the hypothesis that the CCR5Delta32 protein actively confers resistance to HIV-1 in vivo and suggest that the loss or reduction of CCR5Delta32 protein expression may account for HIV-1 infection of CCR5(-/-) individuals. The results also suggest that other cellular or virally induced factors may be involved in the stability of CCR5Delta32 protein.

Persistent resistance to HIV-1 infection in CD4 T cells from exposed uninfected Vietnamese individuals is mediated by entry and post-entry blocks

BACKGROUND

We have previously reported that CD4 T cells from some exposed uninfected (EU) Vietnamese intravenous drug users are relatively resistant to HIV infection in vitro. Here, we further characterized the restriction of viral replication in CD4 T cells from five EUs and assessed its persistence in serial samples.

RESULTS

CD4 T cells and/or PBMC sampled during a period of between 2 and 6 years were challenged with replication-competent HIV-1 and other retroviral particles pseudotyped with envelope proteins of various tropisms. CCR5 expression and function in resistant CD4 T cells was evaluated. The step at which HIV-1 replication is restricted was investigated by real-time PCR quantification of HIV-1 reverse transcripts. We identified three patterns of durable HIV-1 restriction in EU CD4 T cells. CD4 T cells from four of the five EU subjects were resistant to HIV-1 R5 infection. In two cases this resistance was associated with low CCR5 surface expression, which was itself associated with heterozygous CCR5 mutations. In the other two cases, CD4 T cells were resistant to HIV-1 R5 infection despite normal CCR5 expression and signaling function, and normal beta-chemokine secretion upon CD4 T cell activation. Instead, restriction appeared to be due to enhanced CD4 T cell sensitivity to beta-chemokines in these two subjects. In the fifth EU subject the restriction involved post-entry steps of viral replication and affected not only HIV-1 but also other lentiviruses. The restriction was not overcome by a high viral inoculum, suggesting that it was not mediated by a saturable inhibitory factor.

CONCLUSION

Various constitutive mechanisms of CD4 T cell resistance to HIV-1 infection, affecting entry or post-entry steps of viral replication, are associated with resistance to HIV-1 in subjects who remain uninfected despite long-term high-risk behavior.

Discovery of naturally occurring splice variants of the rat histamine H3 receptor that act as dominant-negative isoforms

We described previously the cDNA cloning of three functional rat histamine H3 receptor (rH3R) isoforms as well as the differential brain expression patterns of their corresponding mRNAs and signaling properties of the resulting rH3A, rH3B, and rH3C receptor isoforms (Mol Pharmacol 59:1-8). In the current report, we describe the cDNA cloning, mRNA localization in the rat central nervous system, and pharmacological characterization of three additional rH3R splice variants (rH3D, rH3E, and rH3F) that differ from the previously published isoforms in that they result from an additional alternative-splicing event. These new H3R isoforms lack the seventh transmembrane (TM) helix and contain an alternative, putatively extracellular, C terminus (6TM-rH3 isoforms). After heterologous expression in COS-7 cells, radioligand binding or functional responses upon the application of various H3R ligands could not be detected for the 6TM-rH3 isoforms. In contrast to the rH3A receptor (rH3AR), detection of the rH3D isoform using hemagglutinin antibodies revealed that the rH3D isoform remains mainly intracellular. The expression of the rH3D-F splice variants, however, modulates the cell surface expression-levels and subsequent functional responses of the 7TM H3R isoforms. Coexpression of the rH3AR and the rH3D isoforms resulted in the intracellular retention of the rH3AR and reduced rH3AR functionality. Finally, we show that in rat brain, the H3R mRNA expression levels are modulated upon treatment with the convulsant pentylenetetrazole, suggesting that the rH3R isoforms described herein thus represent a novel physiological mechanism for controlling the activity of the histaminergic system.

Novel down-regulatory mechanism of the surface expression of the vasopressin V2 receptor by an alternative splice receptor variant

In rat kidney, two alternatively spliced transcripts are generated from the V2 vasopressin receptor gene. The large transcript (1.2 kb) encodes the canonical V2 receptor, whereas the small transcript encodes a splice variant displaying a distinct sequence corresponding to the putative seventh transmembrane domain and the intracellular C terminus of the V2 receptor. This work showed that the small spliced transcript is translated in the rat kidney collecting tubules. However, the protein encoded by the small transcript (here called the V2b splice variant) is retained inside the cell, in contrast to the preferential surface distribution of the V2 receptor (here called the V2a receptor). Cells expressing the V2b splice variant do not exhibit binding to 3H-labeled vasopressin. Interestingly, we found that expression of the splice variant V2b down-regulates the surface expression of the V2a receptor, most likely via the formation of V2a.V2b heterodimers as demonstrated by co-immunoprecipitation and fluorescence resonance energy transfer experiments between the V2a receptor and the V2b splice variant. The V2b splice variant would then be acting as a dominant negative. The effect of the V2b splice variant is specific, as it does not affect the surface expression of the G protein-coupled interleukin-8 receptor (CXCR1). Furthermore, the sequence encompassing residues 242-339, corresponding to the C-terminal domain of the V2b splice variant, also down-regulates the surface expression of the V2a receptor. We suggest that some forms of nephrogenic diabetes insipidus are due to overexpression of the splice variant V2b, which could retain the wild-type V2a receptor inside the cell via the formation of V2a.V2b heterodimers.

Homodimerization of the β2-Adrenergic Receptor as a Prerequisite for Cell Surface Targeting

Although homodimerization has been demonstrated for a large number of G protein-coupled receptors (GPCRs), no general role has been attributed to this process. Because it is known that oligomerization plays a key role in the quality control and endoplasmic reticulum (ER) export of many proteins, we sought to determine if homodimerization could play such a role in GPCR biogenesis. Using the beta2-adrenergic receptor (beta2AR) as a model, cell fractionation studies revealed that receptor homodimerization is an event occurring as early as the ER. Supporting the hypothesis that receptor homodimerization is involved in ER processing, beta2AR mutants lacking an ER-export motif or harboring a heterologous ER-retention signal dimerized with the wild-type receptor and inhibited its trafficking to the cell surface. Finally, in addition to inhibiting receptor dimerization, disruption of the putative dimerization motif, 276GXXXGXXXL284, prevented normal trafficking of the receptor to the plasma membrane. Taken together, these data indicate that beta2AR homodimerization plays an important role in ER export and cell surface targeting.

Role for CCR5Delta32 protein in resistance to R5, R5X4, and X4 human immunodeficiency virus type 1 in primary CD4+ cells

CCR5Delta32 is a loss-of-function mutation that abolishes cell surface expression of the human immunodeficiency virus (HIV) coreceptor CCR5 and provides genetic resistance to HIV infection and disease progression. Since CXCR4 and other HIV coreceptors also exist, we hypothesized that CCR5Delta32-mediated resistance may be due not only to the loss of CCR5 function but also to a gain-of-function mechanism, specifically the active inhibition of alternative coreceptors by the mutant CCR5Delta32 protein. Here we demonstrate that efficient expression of the CCR5Delta32 protein in primary CD4(+) cells by use of a recombinant adenovirus (Ad5/Delta32) was able to down-regulate surface expression of both wild-type CCR5 and CXCR4 and to confer broad resistance to R5, R5X4, and X4 HIV type 1 (HIV-1). This may be important clinically, since we found that CD4(+) cells purified from peripheral blood mononuclear cells of individuals who were homozygous for CCR5Delta32, which expressed the mutant protein endogenously, consistently expressed lower levels of CXCR4 and showed less susceptibility to X4 HIV-1 isolates than cells from individuals lacking the mutation. Moreover, CD4(+) cells from individuals who were homozygous for CCR5Delta32 expressed the mutant protein in five of five HIV-exposed, uninfected donors tested but not in either of two HIV-infected donors tested. The mechanism of inhibition may involve direct scavenging, since we were able to observe a direct interaction of CCR5 and CXCR4 with CCR5Delta32, both by genetic criteria using the yeast two-hybrid system and by biochemical criteria using the coimmunoprecipitation of heterodimers. Thus, these results suggest that at least two distinct mechanisms may account for genetic resistance to HIV conferred by CCR5Delta32: the loss of wild-type CCR5 surface expression and the generation of CCR5Delta32 protein, which functions as a scavenger of both CCR5 and CXCR4.

CCR5 expression influences the progression of human breast cancer in a p53-dependent manner

Chemokines are implicated in tumor pathogenesis, although it is unclear whether they affect human cancer progression positively or negatively. We found that activation of the chemokine receptor CCR5 regulates p53 transcriptional activity in breast cancer cells through pertussis toxin–, JAK2-, and p38 mitogen–activated protein kinase–dependent mechanisms. CCR5 blockade significantly enhanced proliferation of xenografts from tumor cells bearing wild-type p53, but did not affect proliferation of tumor xenografts bearing a p53 mutation. In parallel, data obtained in a primary breast cancer clinical series showed that disease-free survival was shorter in individuals bearing the CCR5Δ32 allele than in CCR5 wild-type patients, but only for those whose tumors expressed wild-type p53. These findings suggest that CCR5 activity influences human breast cancer progression in a p53-dependent manner.

Novel interfering bifunctional molecules against the CCR5 coreceptor are efficient inhibitors of HIV-1 infection

CCR5 is the major coreceptor for the HIV-1 strains responsible for primary infection. Individuals homozygous for a 32-bp deletion in the CCR5 coding region are resistant to HIV-1 infection. Strategies to delete CCR5 functionally could thus be of substantial benefit in preventing HIV-1 infection or delaying disease. We evaluated new molecules for their ability to inhibit cell membrane CCR5 expression and to prevent HIV-1 infection. These inhibitors include several truncated forms of CCR5 that may act as negative transdominants, as well as bifunctional molecules resulting from the combination of a previously described anti-CCR5 ribozyme or a truncated CCR5 variant with an intracellular chemokine (RANTES-KDEL). These constructs efficiently blocked membrane CCR5 expression when cotransfected into HEK 293 cells. When expressed by retroviral transduction, some of these molecules significantly inhibited CCR5-dependent chemotaxis in the MCF-7 cell line and reduced CCR5 expression and HIV-1 infection in human T cells. Analysis of inhibitors with different efficiencies showed a strong linear correlation between CCR5 expression inhibition and prevention of HIV-1 infection. This study indicates the potential clinical application of several new CCR5 inhibitory molecules for HIV-1 gene therapy.

Novel truncated isoform of SK3 potassium channel is a potent dominant-negative regulator of SK currents: implications in schizophrenia

The small-conductance calcium-activated K(+) channel SK3 (SKCa3/KCNN3) regulates electrical excitability and neurotransmitter release in monoaminergic neurons, and has been implicated in schizophrenia, ataxia and anorexia nervosa. We have identified a novel SK3 transcript, SK3-1B that utilizes an alternative first exon (exon 1B), but is otherwise identical to SK3. SK3-1B, mRNA is widely distributed in human tissues and is present at 20-60% of SK3 in the brain. The SK3-1B protein lacks the N-terminus and first transmembrane segment, and begins eight residues upstream of the second transmembrane segment. When expressed alone, SK3-1B did not produce functional channels, but selectively suppressed endogenous SK3 currents in the pheochromocytoma cell line, PC12, in a dominant-negative fashion. This dominant inhibitory effect extended to other members of the SK subfamily, but not to voltage-gated K(+) channels, and appears to be due to intracellular trapping of endogenous SK channels. The effect of SK3-1B expression is very similar to that produced by expression of the rare SK3 truncation allele, SK3-Delta, found in a patient with schizophrenia. Regulation of SK3 and SK3-1B levels may provide a potent mechanism to titrate neuronal firing rates and neurotransmitter release in monoaminergic neurons, and alterations in the relative abundance of these proteins could contribute to abnormal neuronal excitability, and to the pathogenesis of schizophrenia.

Rescue of HIV-1 receptor function through cooperation between different forms of the CCR5 chemokine receptor

Interaction of the human immunodeficiency virus (HIV-1) envelope glycoproteins with the CCR5 chemokine receptor, a G-protein-coupled receptor, triggers a membrane fusion process and virus entry. Cooperation for HIV-1 receptor activity was observed when two forms of CCR5 were coexpressed, either the wild-type (WT) receptor and a defective mutant with deletion of the amino-terminal (NT) extracellular domain or the latter deltaNT mutant and a human-mouse CCR5 chimera bearing the NT domain from human CCR5. Cooperation was most efficient when the two forms of CCR5 were in a 1:1 ratio. It was not observed between the CCR5 deltaNT mutant and a chimeric receptor (5444) in which the NT domain of CCR5 was in the context of another G-protein-coupled receptor, the HIV-1 receptor CXCR4. These results suggested that physical association between two forms of CCR5 was required for their cooperation. Coimmunoprecipitation experiments in transfected cell lysates indeed showed that the deltaNT CCR5 mutant formed oligomeric complexes with the WT CCR5 or the HMMM chimera but not with the CXCR4-derived chimera 5444. These observations suggest that the formation of CCR5 oligomers is a constitutive process independent from activation by chemokine ligands. The interaction of HIV-1 with independent subunits of CCR5 oligomers could favor the local recruitment of fusiogenic proteins and the formation of a fusion pore.