Identification of the 15FRFG domain in HIV-1 Gag p6 essential for Vpr packaging into the virion

The HIV-1 gag p6: a promising target for therapeutic intervention

The p6 domain of the Gag precursors (Gag p6) in human immunodeficiency virus type 1 (HIV-1) plays multifunctional roles in the viral life cycle. It utilizes the endosomal sorting complex required for transport (ESCRT) system to facilitate viral budding and release from the plasma membrane through the interactions with the ESCRT-I component tumor susceptibility gene 101 (TSG101) and with the ALG-2 interacting protein X (ALIX). Moreover, Gag p6 contributes to viral replication by a range of posttranslational modifications such as SUMOylation, ubiquitination and phosphorylation. Additionally, Gag p6 also mediates the incorporation of the accessory protein Vpr into virions, thereby promoting Vpr-induced viral replication. However, less attention is focused on Gag p6 as therapeutic intervention. This review focuses on the structures and diverse functions of Gag p6 in viral replication, host cells, and pathogenesis. Additionally, several challenges were also discussed in studying the structure of Gag p6 and its interactions with partners. Consequently, it concludes that the Gag p6 represents an attractive target for the development of antiretroviral drugs, and efforts to develop p6-targeted antiretrovirals are expected to undergo significant growth in the forthcoming years.

Advances in HIV-1 Assembly

The assembly of HIV-1 particles is a concerted and dynamic process that takes place on the plasma membrane of infected cells. An abundance of recent discoveries has advanced our understanding of the complex sequence of events leading to HIV-1 particle assembly, budding, and release. Structural studies have illuminated key features of assembly and maturation, including the dramatic structural transition that occurs between the immature Gag lattice and the formation of the mature viral capsid core. The critical role of inositol hexakisphosphate (IP6) in the assembly of both the immature and mature Gag lattice has been elucidated. The structural basis for selective packaging of genomic RNA into virions has been revealed. This review will provide an overview of the HIV-1 assembly process, with a focus on recent advances in the field, and will point out areas where questions remain that can benefit from future investigation.

HIV-1 Gag Recruits Oligomeric Vpr via Two Binding Sites in p6, but Both Mature p6 and Vpr Are Rapidly Lost upon Target Cell Entry

The p12 region of murine leukemia virus (MLV) Gag and the p6 region of HIV-1 Gag contain late domains required for virus budding. Additionally, the accessory protein Vpr is recruited into HIV particles via p6. Mature p12 is essential for early viral replication events, but the role of mature p6 in early replication is unknown. Using a proviral vector in which the gag and pol reading frames are uncoupled, we have performed the first alanine-scanning mutagenesis screens across p6 to probe its importance for early HIV-1 replication and to further understand its interaction with Vpr. The infectivity of our mutants suggests that, unlike p12, p6 is not important for early viral replication. Consistent with this, we observed that p6 is rapidly lost upon target cell entry in time course immunoblot experiments. By analyzing Vpr incorporation into p6 mutant virions, we identified that the 15-FRFG-18 and 41-LXXLF-45 motifs previously identified as putative Vpr-binding sites are important for Vpr recruitment but that the 34-ELY-36 motif also suggested to be a Vpr-binding site is dispensable. Additionally, disrupting Vpr oligomerization together with removing either binding motif in p6 reduced Vpr incorporation ∼25- to 50-fold more than inhibiting Vpr oligomerization alone and ∼10- to 25-fold more than deleting each p6 motif alone, implying that multivalency/avidity is important for the interaction. Interestingly, using immunoblotting and immunofluorescence, we observed that most Vpr is lost concomitantly with p6 during infection but that a small fraction remains associated with the viral capsid for several hours. This has implications for the function of Vpr in early replication. IMPORTANCE The p12 protein of MLV and the p6 protein of HIV-1 are both supplementary Gag cleavage products that carry proline-rich motifs that facilitate virus budding. Importantly, p12 has also been found to be essential for early viral replication events. However, while Vpr, the only accessory protein packaged into HIV-1 virions, is recruited via the p6 region of Gag, the function of both mature p6 and Vpr in early replication is unclear. Here, we have systematically mutated the p6 region of Gag and have studied the effects on HIV infectivity and Vpr packaging. We have also investigated what happens to p6 and Vpr during early infection. We show that, unlike p12, mature p6 is not required for early replication and that most of the mature p6 and the Vpr that it recruits are lost rapidly upon target cell entry. This has implications for the role of Vpr in target cells.

HIV-1 Vpr antagonizes innate immune activation by targeting karyopherin-mediated NF-κB/IRF3 nuclear transport

HIV-1 must replicate in cells that are equipped to defend themselves from infection through intracellular innate immune systems. HIV-1 evades innate immune sensing through encapsidated DNA synthesis and encodes accessory genes that antagonize specific antiviral effectors. Here, we show that both particle associated, and expressed HIV-1 Vpr, antagonize the stimulatory effect of a variety of pathogen associated molecular patterns by inhibiting IRF3 and NF-κB nuclear transport. Phosphorylation of IRF3 at S396, but not S386, was also inhibited. We propose that, rather than promoting HIV-1 nuclear import, Vpr interacts with karyopherins to disturb their import of IRF3 and NF-κB to promote replication in macrophages. Concordantly, we demonstrate Vpr-dependent rescue of HIV-1 replication in human macrophages from inhibition by cGAMP, the product of activated cGAS. We propose a model that unifies Vpr manipulation of nuclear import and inhibition of innate immune activation to promote HIV-1 replication and transmission.

How HIV-1 Gag Manipulates Its Host Cell Proteins: A Focus on Interactors of the Nucleocapsid Domain

The human immunodeficiency virus (HIV-1) polyprotein Gag (Group-specific antigen) plays a central role in controlling the late phase of the viral lifecycle. Considered to be only a scaffolding protein for a long time, the structural protein Gag plays determinate and specific roles in HIV-1 replication. Indeed, via its different domains, Gag orchestrates the specific encapsidation of the genomic RNA, drives the formation of the viral particle by its auto-assembly (multimerization), binds multiple viral proteins, and interacts with a large number of cellular proteins that are needed for its functions from its translation location to the plasma membrane, where newly formed virions are released. Here, we review the interactions between HIV-1 Gag and 66 cellular proteins. Notably, we describe the techniques used to evidence these interactions, the different domains of Gag involved, and the implications of these interactions in the HIV-1 replication cycle. In the final part, we focus on the interactions involving the highly conserved nucleocapsid (NC) domain of Gag and detail the functions of the NC interactants along the viral lifecycle.

HIV-1 Vpr Abrogates the Effect of TSG101 Overexpression to Support Virus Release

HIV-1 budding requires interaction between Gag and cellular TSG101 to initiate viral particle assembly and release via the endosomal sorting complexes required for transport (ESCRT) pathway. However, some reports show that overexpression of TSG101 inhibits virus release by disruption of Gag targeting process. Since a HIV-1 accessory protein, Vpr binds to Gag p6 domain at the position close to the binding site for TSG101, whether Vpr implicates TSG101 overexpression effect has not been investigated. Here, we found that Vpr abrogates TSG101 overexpression effect to rescue viral production. Co-transfection of TSG101 and Gag with Vpr prevented TSG101-induced Gag accumulation in endosomes and lysosomes. In addition, Vpr rescued virus-like particle (VLP) production in a similar manner as a lysosomal inhibitor, Bafilomycin A1 indicating that Vpr inhibits TSG101-induced Gag downregulation via lysosomal pathway. Vpr and Gag interaction is required to counteract TSG101 overexpression effect since Vpr A30F mutant which is unable to interact with Gag and incorporate into virions, reduced ability to prevent Gag accumulation and to rescue VLP production. In addition, GST pull-down assays and Biacore analysis revealed that Vpr competed with TSG101 for Gag binding. These results indicate that Vpr overcomes the effects of TSG101 overexpression to support viral production by competing with TSG101 to bind Gag.

HIV Genome-Wide Protein Associations: a Review of 30 Years of Research

The HIV genome encodes a small number of viral proteins (i.e., 16), invariably establishing cooperative associations among HIV proteins and between HIV and host proteins, to invade host cells and hijack their internal machineries. As a known example, the HIV envelope glycoprotein GP120 is closely associated with GP41 for viral entry. From a genome-wide perspective, a hypothesis can be worked out to determine whether 16 HIV proteins could develop 120 possible pairwise associations either by physical interactions or by functional associations mediated via HIV or host molecules. Here, we present the first systematic review of experimental evidence on HIV genome-wide protein associations using a large body of publications accumulated over the past 3 decades. Of 120 possible pairwise associations between 16 HIV proteins, at least 34 physical interactions and 17 functional associations have been identified. To achieve efficient viral replication and infection, HIV protein associations play essential roles (e.g., cleavage, inhibition, and activation) during the HIV life cycle. In either a dispensable or an indispensable manner, each HIV protein collaborates with another viral protein to accomplish specific activities that precisely take place at the proper stages of the HIV life cycle. In addition, HIV genome-wide protein associations have an impact on anti-HIV inhibitors due to the extensive cross talk between drug-inhibited proteins and other HIV proteins. Overall, this study presents for the first time a comprehensive overview of HIV genome-wide protein associations, highlighting meticulous collaborations between all viral proteins during the HIV life cycle.

HIV Genome-Wide Protein Associations: a Review of 30 Years of Research

The HIV genome encodes a small number of viral proteins (i.e., 16), invariably establishing cooperative associations among HIV proteins and between HIV and host proteins, to invade host cells and hijack their internal machineries. As a known example, the HIV envelope glycoprotein GP120 is closely associated with GP41 for viral entry. From a genome-wide perspective, a hypothesis can be worked out to determine whether 16 HIV proteins could develop 120 possible pairwise associations either by physical interactions or by functional associations mediated via HIV or host molecules. Here, we present the first systematic review of experimental evidence on HIV genome-wide protein associations using a large body of publications accumulated over the past 3 decades. Of 120 possible pairwise associations between 16 HIV proteins, at least 34 physical interactions and 17 functional associations have been identified. To achieve efficient viral replication and infection, HIV protein associations play essential roles (e.g., cleavage, inhibition, and activation) during the HIV life cycle. In either a dispensable or an indispensable manner, each HIV protein collaborates with another viral protein to accomplish specific activities that precisely take place at the proper stages of the HIV life cycle. In addition, HIV genome-wide protein associations have an impact on anti-HIV inhibitors due to the extensive cross talk between drug-inhibited proteins and other HIV proteins. Overall, this study presents for the first time a comprehensive overview of HIV genome-wide protein associations, highlighting meticulous collaborations between all viral proteins during the HIV life cycle.

Short Communication: Phylogenetic and Molecular Characterization of Six Full-Length HIV-1 Genomes from India Reveals a Monophyletic Lineage of Indian Sub-Subtype A1

Although HIV-1 epidemic in India is mainly driven by subtype C, subtype A has been reported for over two decades. This is the first comprehensive analysis of sequences of HIV-1 subtype A from India, based on the near full-length genome sequences of six different HIV-1 subtype A Indian isolates along with available partial gene sequences from India and global sequences. The phylogenetic analyses revealed the convergence of all Indian whole-genome sequences and majority of the partial gene sequences to a single node with the sequences most closely related to African sub-subtype A1. The presence of the signature motifs consistent with those observed in subtype A and CTL epitopes characterized specifically for subtype A1 were observed among the study sequences. Deletion of LY amino acid of LYPXnL motif of p6gag and one amino acid in V3 loop have been observed among the study isolates, which have also been observed in a few sequences from East Africa. Overall, the results are indicative of a monophyletic lineage or founder effect of the Indian epidemic due to sub-subtype A1 and supportive of a possible migration of subtype A1 into India from East Africa.

The APPEESFRS Peptide, Restricted by the HLA-B*35:01 Molecule, and the APPEESFRF Variant Derived from an Autologous HIV-1 Strain Induces Polyfunctional Responses in CD8+ T Cells

Numerous reports have focused on consensus peptides to determine CD8+ T-cell responses; however, few studies evaluated the functional profile using peptides derived from circulating strains of a specific region. We determined the effector profile and maturation phenotype of CD8+ T-cells targeting the consensus APPEESFRS (AS9) epitope and its variant APPEESFRF (AF9), previously identified. The free energy of binding, maturation phenotype, and polyfunctional profile of both peptides were similar. The magnitude of CD8+ T-cell responses to AF9 was greater than the one elicited by AS9, although the difference was not significant. The polyfunctional profile of AF9 was characterized by CD107a/interleukin-2 (IL-2)/macrophage inflammatory protein beta (MIP1β) and by interferon gamma (IFNγ)/MIP1β/tumor necrosis factor alpha (TNFα) in response to AS9. TNFα production was significantly higher in response to AF9 than to AS9, and there was a negative correlation between the absolute number of CD8+ T-cell-producing TNFα and the plasma human immunodeficiency virus (HIV) load, suggesting a role of this cytokine in the control of HIV replication.

Distinct nucleic acid interaction properties of HIV-1 nucleocapsid protein precursor NCp15 explain reduced viral infectivity

During human immunodeficiency virus type 1 (HIV-1) maturation, three different forms of nucleocapsid (NC) protein—NCp15 (p9 + p6), NCp9 (p7 + SP2) and NCp7—appear successively. A mutant virus expressing NCp15 shows greatly reduced infectivity. Mature NCp7 is a chaperone protein that facilitates remodeling of nucleic acids (NAs) during reverse transcription. To understand the strict requirement for NCp15 processing, we compared the chaperone function of the three forms of NC. NCp15 anneals tRNA to the primer-binding site at a similar rate as NCp7, whereas NCp9 is the most efficient annealing protein. Assays to measure NA destabilization show a similar trend. Dynamic light scattering studies reveal that NCp15 forms much smaller aggregates relative to those formed by NCp7 and NCp9. Nuclear magnetic resonance studies suggest that the acidic p6 domain of HIV-1 NCp15 folds back and interacts with the basic zinc fingers. Neutralizing the acidic residues in p6 improves the annealing and aggregation activity of NCp15 to the level of NCp9 and increases the protein–NA aggregate size. Slower NCp15 dissociation kinetics is observed by single-molecule DNA stretching, consistent with the formation of electrostatic inter-protein contacts, which likely contribute to the distinct aggregate morphology, irregular HIV-1 core formation and non-infectious virus.

HIV-1 p6 - a structured to flexible multifunctional membrane-interacting protein

The human immunodeficiency virus type 1 (HIV-1) p6 protein has recently been recognized as a docking site for several cellular and viral binding partners and is important for the formation of infectious viruses. Most of its known functions are suggested to occur under hydrophobic conditions near the cytoplasmic membrane, where the protein is presumed to exist in its most structured state. Although p6 is involved in manifold specific interactions, the protein has previously been considered to possess a random structure in aqueous solution. We show that p6 exhibits a defined structure with N- and C-terminal helical domains, connected by a flexible hinge region in 100mM dodecylphosphocholine micelle solution at pH 7 devoid of any organic co-solvents, indicating that this is a genuine limiting structural feature of the molecule in a hydrophobic environment. Furthermore, we show that p6 directly interacts with a cytoplasmic model membrane through both N-terminal and C-terminal regions by use of surface plasmon resonance (SPR) spectroscopy. Phosphorylation of Ser-40 located in the center of the C-terminal α-helix does not alter the secondary structure of the protein but amplifies the interaction with membranes significantly, indicating that p6 binds to the polar head groups at the surface of the cytoplasmic membrane. The increased hydrophobic membrane interaction of p6(23-52) S40F correlated with the observed increased amount of the polyprotein Gag in the RIPA insoluble fraction when Ser40 of p6 was mutated with Phe indicating that p6 modulates the membrane interactions of HIV-1 Gag.

Human immunodeficiency virus type 1 modified to package Simian immunodeficiency virus Vpx efficiently infects macrophages and dendritic cells

The lentiviral accessory protein Vpx is thought to facilitate the infection of macrophages and dendritic cells by counteracting an unidentified host restriction factor. Although human immunodeficiency virus type 1 (HIV-1) does not encode Vpx, the accessory protein can be provided to monocyte-derived macrophages (MDM) and monocyte-derived dendritic cells (MDDC) in virus-like particles, dramatically enhancing their susceptibility to HIV-1. Vpx and the related accessory protein Vpr are packaged into virions through a virus-specific interaction with the p6 carboxy-terminal domain of Gag. We localized the minimal Vpx packaging motif of simian immunodeficiency virus SIVmac(239) p6 to a 10-amino-acid motif and introduced this sequence into an infectious HIV-1 provirus. The chimeric virus packaged Vpx that was provided in trans and was substantially more infectious on MDDC and MDM than the wild-type virus. We further modified the virus by introducing the Vpx coding sequence in place of nef. The resulting virus produced Vpx and replicated efficiently in MDDC and MDM. The virus also induced a potent type I interferon response in MDDC. In a coculture system, the Vpx-containing HIV-1 was more efficiently transmitted from MDDC to T cells. These findings suggest that in vivo, Vpx may facilitate transmission of the virus from dendritic cells to T cells. In addition, the chimeric virus could be used to design dendritic cell vaccines that induce an enhanced innate immune response. This approach could also be useful in the design of lentiviral vectors that transduce these relatively resistant cells.

Highly conserved serine residue 40 in HIV-1 p6 regulates capsid processing and virus core assembly

Background

The HIV-1 p6 Gag protein regulates the final abscission step of nascent virions from the cell membrane by the action of two late assembly (L-) domains. Although p6 is located within one of the most polymorphic regions of the HIV-1 gag gene, the 52 amino acid peptide binds at least to two cellular budding factors (Tsg101 and ALIX), is a substrate for phosphorylation, ubiquitination, and sumoylation, and mediates the incorporation of the HIV-1 accessory protein Vpr into viral particles. As expected, known functional domains mostly overlap with several conserved residues in p6. In this study, we investigated the importance of the highly conserved serine residue at position 40, which until now has not been assigned to any known function of p6.

Results

Consistently with previous data, we found that mutation of Ser-40 has no effect on ALIX mediated rescue of HIV-1 L-domain mutants. However, the only feasible S40F mutation that preserves the overlapping pol open reading frame (ORF) reduces virus replication in T-cell lines and in human lymphocyte tissue cultivated ex vivo. Most intriguingly, L-domain mediated virus release is not dependent on the integrity of Ser-40. However, the S40F mutation significantly reduces the specific infectivity of released virions. Further, it was observed that mutation of Ser-40 selectively interferes with the cleavage between capsid (CA) and the spacer peptide SP1 in Gag, without affecting cleavage of other Gag products. This deficiency in processing of CA, in consequence, led to an irregular morphology of the virus core and the formation of an electron dense extra core structure. Moreover, the defects induced by the S40F mutation in p6 can be rescued by the A1V mutation in SP1 that generally enhances processing of the CA-SP1 cleavage site.

Conclusions

Overall, these data support a so far unrecognized function of p6 mediated by Ser-40 that occurs independently of the L-domain function, but selectively affects CA maturation and virus core formation, and consequently the infectivity of released virions.

HIV-1 viral protein r: from structure to function

The viral protein r (Vpr) of HIV-1 binds several host proteins leading to pleiotropic functions, such as G2/M cell cycle arrest, apoptosis induction and gene transactivation. Vpr is encapsidated through the Gag C-terminus into the nascent viral particles, suggesting that Vpr plays several important functions in the early stages of the viral lifecycle. In this regard, Vpr interacts with nucleic acids and membranes to facilitate the preintegration complex migration and incorporation into the nucleus of nondividing cells. Thus, Vpr has to recruit several host and viral factors to promote its functions during HIV-1 pathogenesis. This article focuses on its interacting partners by giving an overview of the functional outcome of the different Vpr complexes, as well as the structural determinants of Vpr required for its binding properties.

Human immunodeficiency virus type 1 Vpr: oligomerization is an essential feature for its incorporation into virus particles

HIV-1 Vpr, a nonstructural viral protein associated with virus particles, has a positive role in the efficient transport of PIC into the nucleus of non-dividing target cells and enhances virus replication in primary T cells. Vpr is a 96 amino acid protein and the structure by NMR shows three helical domains. Vpr has been shown to exist as dimers and higher order oligomers. Considering the multifunctional nature of Vpr, the contribution of distinct helical domains to the dimer/oligomer structure of Vpr and the relevance of this feature to its functions are not clear. To address this, we have utilized molecular modeling approaches to identify putative models of oligomerization. The predicted interface residues were subjected to site-directed mutagenesis and evaluated their role in intermolecular interaction and virion incorporation. The interaction between Vpr molecules was monitored by Bimolecular Fluorescence complementation (BiFC) method. The results show that Vpr forms oligomers in live cells and residues in helical domains play critical roles in oligomerization. Interestingly, Vpr molecules defective in oligomerization also fail to incorporate into the virus particles. Based on the data, we suggest that oligomerization of Vpr is essential for virion incorporation property and may also have a role in the events associated with virus infection.

HIV-1 Vpr oligomerization but not that of Gag directs the interaction between Vpr and Gag

During HIV-1 assembly, the viral protein R (Vpr) is incorporated into newly made viral particles via an interaction with the C-terminal domain of the Gag polyprotein precursor Pr55(Gag). Vpr has been implicated in the nuclear import of newly made viral DNA and subsequently in its transcription. In addition, Vpr can affect the cell physiology by causing G(2)/M cell cycle arrest and apoptosis. Vpr can form oligomers, but their roles have not yet been investigated. We have developed fluorescence lifetime imaging microscopy-fluorescence resonance energy transfer-based assays to monitor the interaction between Pr55(Gag) and Vpr in HeLa cells. To that end, we used enhanced green fluorescent protein-Vpr that can be incorporated into the virus and tetracysteine (TC)-tagged Pr55(Gag)-TC. This TC motif is tethered to the C terminus of Pr55(Gag) and does not interfere with Pr55(Gag) trafficking and the assembly of virus-like particles (VLPs). Results show that the Pr55(Gag)-Vpr complexes accumulated mainly at the plasma membrane. In addition, results with Pr55(Gag)-TC mutants confirm that the (41)LXXLF domain of Gag-p6 is essential for Pr55(Gag)-Vpr interaction. We also report that Vpr oligomerization is crucial for Pr55(Gag) recognition and its accumulation at the plasma membrane. On the other hand, Pr55(Gag)-Vpr complexes are still formed when Pr55(Gag) carries mutations impairing its multimerization. These findings suggest that Pr55(Gag)-Vpr recognition and complex formation occur early during Pr55(Gag) assembly.

An integrative bioinformatic approach for studying escape mutations in human immunodeficiency virus type 1 gag in the Pumwani Sex Worker Cohort

Human immunodeficiency virus type 1 (HIV-1) is able to evade the host cytotoxic T-lymphocyte (CTL) response through a variety of escape avenues. Epitopes that are presented to CTLs are first processed in the presenting cell in several steps, including proteasomal cleavage, transport to the endoplasmic reticulum, binding by the HLA molecule, and finally presentation to the T-cell receptor. An understanding of the potential of the virus to escape CTL responses can aid in designing an effective vaccine. To investigate such a potential, we analyzed HIV-1 gag from 468 HIV-1-positive Kenyan women by using several bioinformatic approaches that allowed the identification of positively selected amino acids in the HIV-1 gag region and study of the effects that these mutations could have on the various stages of antigen processing. Correlations between positively selected residues and mean CD4 counts also allowed study of the effect of mutation on HIV disease progression. A number of mutations that could create or destroy proteasomal cleavage sites or reduce binding affinity of the transport antigen processing protein, effectively hindering epitope presentation, were identified. Many mutations correlated with the presence of specific HLA alleles and with lower or higher CD4 counts. For instance, the mutation V190I in subtype A1-infected individuals is associated with HLA-B*5802 (P = 4.73 x 10(-4)), a rapid-progression allele according to other studies, and also to a decreased mean CD4 count (P = 0.019). Thus, V190I is a possible HLA escape mutant. This method classifies many positively selected mutations across the entire gag region according to their potential for immune escape and their effect on disease progression.

HIV-1 Vpr potently induces programmed cell death in the CNS in vivo

The human immunodeficiency virus type I (HIV-1) accessory protein Vpr has been associated with the induction of programmed cell death (apoptosis) and cell-cycle arrest. Studies have shown the apoptotic effect of Vpr on primary and established cell lines and on diverse tissues including the central nervous system (CNS) in vitro. However, the relevance of the effect of Vpr observed in vitro to HIV-1 neuropathogenesis in vivo, remains unknown. Due to the narrow host range of HIV-1 infection, no animal model is currently available. This has prompted us to consider a small animal model to evaluate the effects of Vpr on CNS in vivo through surrogate viruses expressing HIV-1Vpr. A single round of replication competent viral vectors, expressing Vpr, were used to investigate the apoptosis-inducing capabilities of HIV-1Vpr in vivo. Viral particles pseudotyped with VSV-G or N2c envelopes were generated from spleen necrosis virus (SNV) and HIV-1-based vectors to transduce CNS cells. The in vitro studies have demonstrated that Vpr generated by SNV vectors had less apoptotic effects on CNS cells compared with Vpr expressed by HIV-1 vectors. The in vivo study has suggested that viral particles, expressing Vpr generated by HIV-1-based vectors, when delivered through the ventricle, caused loss of neurons and dendritic processes in the cortical region. The apoptotic effect was extended beyond the cortical region and affected the hippocampus neurons, the lining of the choroids plexus, and the cerebellum. However, the effect of Vpr, when delivered through the cortex, showed neuronal damage only around the site of injection. Interestingly, the number of apoptotic neurons were significantly higher with HIV-1 vectors expressing Vpr than by the SNV vectors. This may be due to the differences in the proteins expressed by these viral vectors. These results suggest that Vpr induces apoptosis in CNS cells in vitro and in vivo. To our knowledge, this is the first study to investigate the apoptosis-inducing capabilities of HIV-1Vpr in vivo in neonatal mice. We propose that this, in expensive animal model, may be of value to design-targeted neuroprotective therapeutics.

Molecular characterization of the HIV-1 gag nucleocapsid gene associated with vertical transmission

BACKGROUND

The human immunodeficiency virus type 1 (HIV-1) nucleocapsid (NC) plays a pivotal role in the viral lifecycle: including encapsulating the viral genome, aiding in strand transfer during reverse transcription, and packaging two copies of the viral genome into progeny virions. Another gag gene product, p6, plays an integral role in successful viral budding from the plasma membrane and inclusion of the accessory protein Vpr within newly budding virions. In this study, we have characterized the gag NC and p6 genes from six mother-infant pairs following vertical transmission by performing phylogenetic analysis and by analyzing the degree of genetic diversity, evolutionary dynamics, and conservation of functional domains.

RESULTS

Phylogenetic analysis of 168 gag NC and p6 genes sequences revealed six separate subtrees that corresponded to each mother-infant pair, suggesting that epidemiologically linked individuals were closer to each other than epidemiologically unlinked individuals. A high frequency (92.8%) of intact open reading frames of NC and p6 with patient and pair specific sequence motifs were conserved in mother-infant pairs' sequences. Nucleotide and amino acid distances showed a lower degree of viral heterogeneity, and a low degree of estimates of genetic diversity was also found in NC and p6 sequences. The NC and p6 sequences from both mothers and infants were found to be under positive selection pressure. The two important functional motifs within NC, the zinc-finger motifs, were highly conserved in most of the sequences, as were the gag p6 Vpr binding, AIP1 and late binding domains. Several CTL recognition epitopes identified within the NC and p6 genes were found to be mostly conserved in 6 mother-infant pairs' sequences.

CONCLUSION

These data suggest that the gag NC and p6 open reading frames and functional domains were conserved in mother-infant pairs' sequences following vertical transmission, which confirms the critical role of these gene products in the viral lifecycle.

A trans-lentiviral packaging cell line for high-titer conditional self-inactivating HIV-1 vectors

Lentiviral vector safety has been the impetus underlying the progress in packaging cell line development. The prospects of generating replication-competent lentiviruses (RCLs) and the potential for vector mobilization continue to be the driving force for the advancement of packaging cell lines. We have exploited the trans-lentiviral packaging system to develop the SODk3 packaging cell line for the generation of conditional self-inactivating (cSIN) vectors. Separating the gag-pol genome into two distinct expression cassettes (gag-pro and vpr-RT-IN) may reduce the potential for RCL formation, while concurrently employing cSIN vectors supports retention of the SIN phenotype in target cells and alleviates technical constraints associated with generating producer cell lines. Through development of the SODk3 packaging cell line we determined that the ratio of Gag/Pol in vector particles may be used as an indicator for packaging cell clones that yield high vector titers. Conditional SIN vector titers (1 x 10(7) TU/ml) were augmented through clonal selection. Distinct producer cell clones revealed a parallel between vector titer and transgene expression levels. We exploited this observation to demonstrate that incorporation of an internal ribosome entry site between the GFP marker and a relevant transgene affords efficient selection of high-titer producer cell lines. Furthermore, cSIN vectors generated from SODk3 packaging cells imparted efficient transduction of primary human fibroblasts, an indication of the future applicability of the SODk3 packaging cell line.