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Evolution of CCR5 use before and during coreceptor switching.

ABSTRACT: The envelope gene (env) of human immunodeficiency virus type 1 (HIV-1) undergoes rapid divergence from the transmitted sequence and increasing diversification during the prolonged course of chronic infection in humans. In about half of infected individuals or more, env evolution leads to expansion of the use of entry coreceptor from CCR5 alone to CCR5 and CXCR4. The stochastic nature of this coreceptor switch is not well explained by host selective forces that should be relatively constant between infected individuals. Moreover, differences in the incidence of coreceptor switching among different HIV-1 subtypes suggest that properties of the evolving virus population drive the switch. We evaluated the functional properties of sequential env clones from a patient with evidence of coreceptor switching at 5.67 years of infection. We found an abrupt decline in the ability of viruses to use CCR5 for entry at this time, manifested by a 1- to 2-log increase in susceptibility to CCR5 inhibitors and a reduced ability to infect cell lines with low CCR5 expression. There was an abnormally rapid 5.4% divergence in env sequences from 4.10 to 5.76 years of infection, with the V3 and V4/V5 regions showing the greatest divergence and evidence of positive selection. These observations suggest that a decline in the fitness of R5 virus populations may be one driving force that permits the emergence of R5X4 variants.

SUBMITTER: Coetzer M

PROVIDER: S-EPMC2583682 | biostudies-literature | 2008 Dec

REPOSITORIES: biostudies-literature

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Evolution of CCR5 use before and during coreceptor switching.

Coetzer Mia M Nedellec Rebecca R Salkowitz Janelle J McLaughlin Sherry S Liu Yi Y Heath Laura L Mullins James I JI Mosier Donald E DE

Journal of virology 20080924 23

The envelope gene (env) of human immunodeficiency virus type 1 (HIV-1) undergoes rapid divergence from the transmitted sequence and increasing diversification during the prolonged course of chronic infection in humans. In about half of infected individuals or more, env evolution leads to expansion of the use of entry coreceptor from CCR5 alone to CCR5 and CXCR4. The stochastic nature of this coreceptor switch is not well explained by host selective forces that should be relatively constant betwe ...[more]

PMID: 18815295

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Project description:Entry of human immunodeficiency virus type 1 (HIV-1) requires CD4 and one of a family of related seven-transmembrane-domain coreceptors. Macrophage-tropic HIV-1 isolates are generally specific for CCR5, a receptor for the CC chemokines RANTES, MIP-1alpha, and MIP-1beta, while T-cell line-tropic viruses tend to use CXCR4 (also known as fusin, LESTR, or HUMSTR). Like HIV-1, simian immunodeficiency virus (SIV) requires CD4 on the target cell surface; however, whether it also requires a coreceptor is not known. We report here that several genetically divergent SIV isolates, including SIVmac, SIVsmSL92a, SIVsmLib-1, and SIVcpzGAB, can use human and rhesus CCR5 for entry. CXCR4 did not facilitate entry of any of the simian viruses tested, nor did any of the other known chemokine receptors. Moreover, SIVmac251 that had been extensively passaged in a human transformed T-cell line retained its use of CCR5. Rhesus and human CCR5 differed at only eight amino acid residues, four of which were in regions of the receptor that could be exposed, two in the amino-terminal extracellular region and two in the second extracellular loop. The human coreceptor was as active as the simian for SIV entry. In addition, HIV-1 was able to use the rhesus homologs of the human coreceptors, CCR5 and CXCR4. The SIV strains tested were specific for CCR5 regardless of whether they were able to replicate in transformed T-cell lines or macrophages and whether they were phenotypically syncytium inducing or noninducing in MT-2 cells. However, SIV replication was not restricted to cells expressing CCR5. SIV strains replicated efficiently in the human transformed lymphoid cell line CEMx174, which does not express detectable amounts of transcripts of CCR5. SIV also replicated in human peripheral blood mononuclear cells that were genetically deficient in CCR5. These findings indicated that, in addition to CCR5, SIV can use one or more unknown coreceptors that are expressed on human PBMCs and CEMx174 cells.

Project description:The chemokine receptor CCR5 is a cofactor for the entry of R5 tropic strains of human immunodeficiency viruses (HIV)-1 and -2 and simian immunodeficiency virus. Cells susceptible to infection by these viruses can be protected by treatment with the CCR5 ligands regulated on activation, normal T cell expressed and secreted (RANTES), MIP-1alpha, and MIP-1beta. A major component of the mechanism through which chemokines protect cells from HIV infection is by inducing endocytosis of the chemokine receptor. Aminooxypentane (AOP)-RANTES, an NH(2)-terminal modified form of RANTES, is a potent inhibitor of infection by R5 HIV strains. AOP-RANTES efficiently downmodulates the cell surface expression of CCR5 and, in contrast with RANTES, appears to prevent recycling of CCR5 to the cell surface. Here, we investigate the cellular basis of this effect. Using CHO cells expressing human CCR5, we show that both RANTES and AOP-RANTES induce rapid internalization of CCR5. In the absence of ligand, CCR5 shows constitutive turnover with a half-time of 6-9 h. Addition of RANTES or AOP-RANTES has little effect on the rate of CCR5 turnover. Immunofluorescence and immunoelectron microscopy show that most of the CCR5 internalized after RANTES or AOP-RANTES treatment accumulates in small membrane-bound vesicles and tubules clustered in the perinuclear region of the cell. Colocalization with transferrin receptors in the same clusters of vesicles indicates that CCR5 accumulates in recycling endosomes. After the removal of RANTES, internalized CCR5 recycles to the cell surface and is sensitive to further rounds of RANTES-induced endocytosis. In contrast, after the removal of AOP-RANTES, most CCR5 remains intracellular. We show that these CCR5 molecules do recycle to the cell surface, with kinetics equivalent to those of receptors in RANTES-treated cells. However, these recycled CCR5 molecules are rapidly reinternalized. Our results indicate that AOP-RANTES-induced changes in CCR5 alter the steady-state distribution of the receptor and provide the first evidence for G protein-coupled receptor trafficking through the recycling endosome compartment.

Project description:In contrast to HIV infection in humans and SIV in macaques, SIV infection of natural hosts including sooty mangabeys (SM) is non-pathogenic despite robust virus replication. We identified a novel SM CCR5 allele containing a two base pair deletion (?2) encoding a truncated molecule that is not expressed on the cell surface and does not support SIV entry in vitro. The allele was present at a 26% frequency in a large SM colony, along with 3% for a CCR5?24 deletion allele that also abrogates surface expression. Overall, 8% of animals were homozygous for defective CCR5 alleles and 41% were heterozygous. The mutant allele was also present in wild SM in West Africa. CD8+ and CD4+ T cells displayed a gradient of CCR5 expression across genotype groups, which was highly significant for CD8+ cells. Remarkably, the prevalence of natural SIVsmm infection was not significantly different in animals lacking functional CCR5 compared to heterozygous and homozygous wild-type animals. Furthermore, animals lacking functional CCR5 had robust plasma viral loads, which were only modestly lower than wild-type animals. SIVsmm primary isolates infected both homozygous mutant and wild-type PBMC in a CCR5-independent manner in vitro, and Envs from both CCR5-null and wild-type infected animals used CXCR6, GPR15 and GPR1 in addition to CCR5 in transfected cells. These data clearly indicate that SIVsmm relies on CCR5-independent entry pathways in SM that are homozygous for defective CCR5 alleles and, while the extent of alternative coreceptor use in SM with CCR5 wild type alleles is uncertain, strongly suggest that SIVsmm tropism and host cell targeting in vivo is defined by the distribution and use of alternative entry pathways in addition to CCR5. SIVsmm entry through alternative pathways in vivo raises the possibility of novel CCR5-negative target cells that may be more expendable than CCR5+ cells and enable the virus to replicate efficiently without causing disease in the face of extremely restricted CCR5 expression seen in SM and several other natural host species.

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Evolution of CCR5 use before and during coreceptor switching.

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Evolution of CCR5 use before and during coreceptor switching.

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