Analysis of the interactions of HIV1 replication primer tRNA(Lys,3) with nucleocapsid protein and reverse transcriptase.

Packaging of the genomic RNA dimer and replication primer tRNA(Lys,3) into HIV virions are required for the production of infectious virus. The initiation of reverse transcription necessitates the annealing of tRNA(Lys,3) to the primer binding site (PBS) of HIV RNA by nucleocapsid (NC) protein. In this report the interactions of replication primer tRNA(Lys,3) with various forms of reverse transcriptase (RT) and nucleocapsid protein have been analyzed by ultraviolet light (UV) cross-linking and gel retardation assays. We show that of the three forms of RT studied, p66/p51, p66 and p51, only the heterodimer p66/p51 can tightly and stably interact with tRNA(Lys,3). Tight interactions between tRNA(Lys,3) and nucleocapsid protein, either NCp15 or NCp7, were found to take place within the anticodon domain. Interestingly enough, primer tRNA(Lys,3) can interact with RTp66/p51 and NCp15 to form a high molecular weight complex in which RTp66/p51 appears to enhance the binding of NCp15 to tRNA(Lys,3). These findings favor the notion that the RT enzyme and NC protein co-operate to select and package primer tRNA.

Kaposi's sarcoma: is the hunt for the culprit over now?

Patients suffering from the acquired immune deficiency syndrome (AIDS) have a 20000-fold increased risk of developing a severe form of Kaposi's sarcoma (KS), a previously rare malignancy involving sharply defined nodular lesions of the skin and/or oral mucosa. Epidemiological evidence has long suggested that an infectious agent is the probable cause of KS. Recently sequences from a putative new herpesvirus have been found to be associated with KS in virtually 100% of the cases analyzed. The suspected etiological agent, a new human herpesvirus termed Kaposi's sarcoma associated herpes virus (human herpes virus 8) has now been propagated in cell culture. This significant advance should form the basis for a detailed analysis of the pathogenetic mechanisms involved in the development of KS.

Detection of antibodies against viral capsid proteins of human herpesvirus 8 in AIDS-associated Kaposi's sarcoma.

Sequences of a new herpesvirus with homology to gammaherpesvirinae were recently identified in AIDS-associated Kaposi's sarcoma (KS). Subsequently this novel virus, called KS-associated virus (KSHV) or human herpesvirus (HHV) 8 was detected in classical KS and AIDS-associated body cavity based lymphomas by polymerase chain reaction. In this report major and minor capsid proteins of HHV-8 were molecularly cloned and produced as recombinant proteins in Escherichia coli. Sera from 69 HIV-1 infected patients with KS, 30 HIV-1 infected patients without KS and 106 control individuals were tested by enzyme-linked immunosorbent assay for anti-HHV-8 capsid IgM and IgG antibodies. Sera from four patients were tested over periods ranging from 18 months to 6 years. IgG antibodies directed against HHV-8 capsid antigens were detected in patients with AIDS-associated KS and in some AIDS patients without KS. Seroconversion with IgM and IgG antibodies directed against HHV-8 capsid proteins occurred more than 1 year prior to diagnosis of KS. In a considerable portion of KS patients no IgM or IgG antibodies against HHV-8 capsid proteins were detected. In these patients there was an inverse relationship between antibodies against HHV-8orf26 and the CD4/CD8 ratio, suggesting that the inconsistency of anti-HHV-8orf26 antibodies is due at least partly to an impaired immune response. No reactivity against HHV-8 capsid antigens was detected in the vast majority of sera from HIV-negative control individuals. Our findings indicate that a specific humoral immune response against capsid proteins is raised in HHV-8 infected individuals, and that anti-capsid antibodies can be used to diagnose HHV-8 infection. The correlation between occurrence of anti-HHV-8 antibodies and KS supports the hypothesis of a causative role of HHV-8.

Point mutations in conserved amino acid residues within the C-terminal domain of HIV-1 reverse transcriptase specifically repress RNase H function.

Two single site substitutions (E478----Q and H539----F) were introduced into the C-terminal RNase H domain of HIV-1 reverse transcriptase. These mutant proteins were expressed in Escherichia coli and purified by Ni2+-nitrilotriacetic acid affinity chromatography. Both enzymes are clearly defective in RNase H function, but exhibit wild type reverse transcriptase activity.

Serum concentrations of fibroblast growth factor 2 are increased in HIV type 1-infected patients and inversely related to survival probability.

HIV-1-infected patients develop a generalized vasculopathy that is clinically most evident as Kaposi's sarcoma (KS), a multifocally appearing endothelial cell-derived tumor. Fibroblast growth factor 2 (FGF-2) is a potent autocrine and paracrine mitogen of endothelial cells and has been implicated in the cell proliferation and angiogenesis observed in KS. Here we determined by ELISA the FGF-2 serum concentrations in different clinical groups of HIV-1-infected patients. AIDS-KS patients (n = 53) and HIV-1-infected patients without KS (n = 39) revealed significantly increased FGF-2 serum concentrations (median, 4.5 and 4.6 pg/ml, respectively), as compared with the healthy control group (n = 22; median, 2.2 pg/ml; p < 0.01). FGF-2 concentrations were highest in untreated HIV-1-infected patients (median, 8.6 pg/ml) and were significantly decreased in patients undergoing antiretroviral therapy (AZT-median, 4.5 pg/ml; HAART-median, 2.5 pg/ml; p < 0.01). In addition, FGF-2 serum concentrations above 5.2 pg/ml were associated with a statistically significant higher risk of death in HIV-1-infected patients. Multivariate analysis showed that this effect is independent of CD4 levels, localization of KS (cutaneous or visceral), AIDS-defining opportunistic diseases, and therapy. Circulating FGF-2 may contribute to AIDS-associated vasculopathy and may be a sensitive and easily accessible surrogate marker to determine the survival time of HIV-1-infected patients and the efficacy of antiretroviral therapy.

HIV-1 RT-associated ribonuclease H displays both endonuclease and 3'----5' exonuclease activity.

We have analysed the mechanism of ribonuclease H (RNaseH) induced cleavage of a defined RNA-DNA hybrid by human immuno-deficiency virus (HIV-1) reverse transcriptase (RT). An in vitro transcribed RNA labelled at the 3' end was hybridized to a pentadecameric DNA oligonucleotide complementary to an internal region of the RNA. Upon incubation of this RNA-DNA hybrid with recombinant p66 or p66/p51 HIV-1 reverse transcriptase, RT-RNaseH mediated cleavage is observed at most nucleotides within the short hybridized stretch, resulting in a spectrum of RNA fragments extending from the 3' label to this region and differing in length by one nucleotide. The same RNA, this time labelled at the 5' end, yields only one or two major cleavage products corresponding to RNA species extending from the 5' label to the middle of the hybridized region. Such a result can be explained by the action of both endonuclease and 3'----5' exonuclease activities inherent to the C-terminal domain of p66 RT. To investigate how RNaseH cleavage is coupled to reverse transcription, a combination of deoxynucleoside triphosphates was used which allowed controlled extension of the primer DNA. Concomitantly with the elongation of the oligonucleotide primer, RNaseH cleavage proceeds towards the 5' end of the RNA with identical increments, suggesting a simultaneous action of both activities.

Subunit-selective mutagenesis indicates minimal polymerase activity in heterodimer-associated p51 HIV-1 reverse transcriptase.

We have purified and determined functional parameters of reconstituted, recombinant HIV-1 reverse transcriptase (RT) heterodimers within which either the p66 or p51 polypeptide was selectively mutated in one or both aspartic acid residues constituting the proposed polymerase active site (-Y-M-D-D-). Heterodimers containing a mutated p51 polypeptide retain almost wild type levels of both RNA-dependent DNA polymerase and ribonuclease H (RNaseH) activity. In contrast, heterodimers whose p66 polypeptide was likewise mutated exhibit wild type RNaseH activity but are deficient in RNA-dependent DNA polymerase activity. These results indicate that in heterodimer RT, the p51 component cannot compensate for active site mutations eliminating the activity of p66, indirectly implying that solely the p66 aspartic acid residues of heterodimer are crucial for catalysis.

Hydroxyl radical footprint analysis of human immunodeficiency virus reverse transcriptase-template.primer complexes.

Human immunodeficiency virus type 1 reverse transcriptase protects sugar moieties of a model template.primer DNA in a region from positions +3 to -15 from hydroxyl radical attack. A protected region of equivalent size migrates in concert with the translocating enzyme, as shown by hydroxyl radical footprints of replication complexes after primer extension by 4, 10, and 19 nt. The pattern of these footprints suggests that the DNA template.primer is in the A conformation when complexed with reverse transcriptase. Enhanced accessibility of the DNA template strand around position -15 to hydroxyl radicals indicates a conformational change in the template induced by the C-terminal RNase H-containing domain of p66 reverse transcriptase.

Domain structure of the human immunodeficiency virus reverse transcriptase.

The spatial arrangement of subunits p51 and p66 of the HIV-1 reverse transcriptase and the position of the RNase H containing domain, p15, have been determined by means of neutron small-angle scattering. The reverse transcriptase (p66/p51) is a flat molecule, which can be approximated by an ellipsoid with the half axes of 5.2 nm, 4.8 nm and 1.4 nm. The two subunits p51 and p66 having a centre-to-centre distance of 3.3 +/- 0.3 nm are attached at their flat sides, slightly shifted sideways. The p15 domain is located at the long axis of the ellipsoidal reverse transcriptase having a distance of 5.0 +/- 0.5 nm to the centre of the p51d domain, which is part of the p66 subunit, and a distance of 5.3 +/- 1.2 nm to the centre of the neighbouring p51s subunit.

Interaction of the HIV-1 rev cofactor eukaryotic initiation factor 5A with ribosomal protein L5.

It has previously been shown that interaction of eukaryotic initiation factor 5A (eIF-5A) with the Rev trans-activator protein of HIV-1 mediates the transport of unspliced or incompletely spliced viral mRNAs across the nuclear envelope. Consequently, mutants of eIF-5A block Rev function and thereby replication of HIV-1 in trans, indicating that eIF-5A is a crucial protein that connects the viral Rev regulator with cellular RNA transport systems. Here we show that the ribosomal protein L5, which is the central protein component of the 5S rRNA export system, is a cellular interaction partner of eIF-5A. Functional studies demonstrate that overexpression of L5 protein significantly enhances Rev activity. Furthermore, Rev nuclear export activity is inhibited in human somatic cells by antibodies that recognize eIF-5A or L5. Our data suggest that the Rev export pathway shares components of a cellular transport system involved in the intracellular trafficking of polymerase III (5S rRNA) transcripts.

Infection with human immunodeficiency virus-1 increases expression of vascular endothelial cell growth factor in T cells: implications for acquired immunodeficiency syndrome-associated vasculopathy.

Alterations in the vascular system and the onset of angioproliferative lesions such as Kaposi's sarcoma (KS) are common traits of human immunodeficiency virus-1 (HIV-1)-infected patients. To investigate possible factors involved in acquired immunodeficiency syndrome (AIDS)-associated vasculopathy and vascular malfunction, expression of vascular endothelial cell growth factor-A (VEGF-A) was analyzed in HUT 78 T lymphocytes upon infection with HIV-1. VEGF-A was found to be increased in supernatants from infected cells as compared with uninfected cells. In addition, VEGF-A mRNA expression and protein secretion were significantly increased in HUT 78 cells incubated with conditioned medium (CM) derived from HIV-1 chronically infected HUT 78 cells (HIV-TCM) as compared with CM from uninfected cells (TCM). Increase of VEGF-A production in T cells was promoted by inflammatory cytokines (IC) present in HIV-TCM, including tumor necrosis factor alpha (TNFalpha), interferon gamma (IFNgamma), interleukin-1beta (IL-1beta), and IL-6. These IC that have been shown to be increased in sera of HIV-1-infected patients and to be increased by HIV-1 infection or cell activation in these individuals as well as HIV-TCM also increased VEGF-A expression in primary T lymphocytes. Consistent with this, VEGF-A concentrations were found to be higher in sera of HIV-1-infected patients with (mean, 357.1 +/- 197.9 pg/mL) and without KS (mean, 256.7 +/- 137.5 pg/mL) as compared with uninfected individuals (mean, 188.6 +/- 91.7 pg/mL). These data suggest that increased secretion of VEGF-A by T lymphocytes of HIV-1-infected individuals may induce vascular leakage and stimulate proliferation of vascular endothelial cells, which are hallmarks of AIDS-associated vasculopathy and especially of KS development.

HIV-1 reverse transcriptase specifically interacts with the anticodon domain of its cognate primer tRNA.

The virion cores of the replication competent type 1 human immunodeficiency virus (HIV-1), a retrovirus, contain and RNA genome associated with nucleocapsid (NC) and reverse transcriptase (RT p66/p51) molecules. In vitro reconstructions of these complexes with purified components show that NC is required for efficient annealing of the primer tRNALys,3. In the absence of NC, HIV-1 RT is unable to retrotranscribe the viral RNA template from the tRNA primer. We demonstrate that the HIV-1 RT p66/p51 specifically binds to its cognate primer tRNALys,3 even in the presence of a 100-fold molar excess of other tRNAs. Cross-linking analysis of this interaction locates the contact site to a region within the heavily modified anti-codon domain of tRNALys,3.

Kaposi's sarcoma-associated herpesvirus serology in Europe and Uganda: multicentre study with multiple and novel assays.

A multicentre study was undertaken to define novel assays with increased inter-assay concordance, sensitivity, specificity and predictive value for serological diagnosis of human herpesvirus type 8 (HHV-8) infection. A total of 562 sera from European and Ugandan human immunodeficiency virus (HIV)-infected or uninfected individuals with or without Kaposi's sarcoma (KS) and blood donors were examined under code by 18 different assays in seven European laboratories. Sera from KS patients and all non-KS sera found positive by at least 70%, 80%, or 90% of the assays were considered "true positive." The validity of the assays was then evaluated by univariate logistic regression analysis. Two immunofluorescence assays (IFA) for detection of antibodies against HHV-8 lytic (Rlyt) or latent (LLANA) antigens and two enzyme-linked-immunosorbent assays (ELISA) (M2, EK8.1) for detection of antibodies against HHV-8 structural proteins were found to be highly concordant, specific, and sensitive, with odds ratios that indicated a high predictive value. When used together, the two IFA (Rlyt-LLANA) showed the best combination of sensitivity (89.1%) and specificity (94.9%). The performance of these assays indicate that they may be used for the clinical management of individuals at risk of developing HHV-8 associated tumours such as allograft recipients.