Human T cell lymphotropic virus type I Tax activates IL-15R alpha gene expression through an NF-kappa B site.

IL-15 mRNA levels are increased in diseases caused by human T cell lymphotropic virus type I (HTLV-I). In this study, we demonstrated that IL-15Ralpha, the IL-15-specific binding receptor, mRNA and protein levels were also elevated in HTLV-I-infected cells. We showed that transient HTLV-I Tax expression lead to increased IL-15Ralpha mRNA levels. In addition, by using a reporter construct that bears the human IL-15Ralpha promoter, we demonstrated that Tax expression increased promoter activity by at least 4-fold. Furthermore, using promoter deletion constructs and gel shift analysis, we defined a functional NF-kappaB-binding motif in the human IL-15Ralpha promoter, suggesting that Tax activation of IL-15Ralpha is due, in part, to the induction of NF-kappaB. These data indicate that IL-15Ralpha is transcriptionally regulated by the HTLV-I Tax protein through the action of NF-kappaB. These findings suggest a role for IL-15Ralpha in aberrant T cell proliferation observed in HTLV-I-associated diseases.

The HIV-inactivating protein, cyanovirin-N, does not block gp120-mediated virus-to-cell binding.

Concentrations of the potent, HIV(human immunodeficiency virus) inactivating protein, cyanovirin-N (CV-N), which completely inhibit HIV-1 infectivity, do not block the binding of soluble CD4-receptor (sCD4) to HIV-1 lysates nor the attachment of intact HIV-1 virions to several target T-cell lines. Furthermore, in contrast to the known disassociative effects of sCD4 on viral envelope glycoproteins, treatment of HIVRF with high concentrations of CV-N results in complete viral inactivation but without apparent shedding of gp120 or other ultrastructural changes. These results are consistent with the view that the virucidal effects of CV-N result from interference with step(s) in the fusion process subsequent to the initial binding of the virus to target cells.

Antiviral activity and mechanism of action of calanolide A against the human immunodeficiency virus type-1.

Calanolide A, recently discovered in extracts from the tropical rainforest tree, Calophyllum lanigerum, is a novel inhibitor of the human immunodeficiency virus (HIV) type 1. The compound is essentially inactive against strains of the less common HIV type 2. The present study focused on the further characterization of the selective antiviral activity and mechanism of action of calanolide A. The compound inhibited a wide variety of laboratory strains of HIV type 1, with EC50 values ranging from 0.10 to 0.17 microM. The compound similarly inhibited promonocytotropic and lymphocytotropic isolates from patients in various stages of HIV disease, as well as drug-resistant strains. Viral life-cycle studies indicated that calanolide A acted early in the infection process, similar to the known HIV reverse transcriptase (RT) inhibitor 2', 3'-dideoxycytidine. In enzyme inhibition assays, calanolide A potently and selectively inhibited recombinant HIV type 1 RT but not cellular DNA polymerases or HIV type 2 RT within the concentration range tested. Serial passage of the virus in host cells exposed to increasing concentrations of calanolide A yielded a calanolide A resistant virus strain. RT from the resistant virus was not inhibited by calanolide A but retained sensitivity to other nonnucleoside as well as nucleoside RT inhibitors, including 3'-azido-2',3'-dideoxythymidine triphosphate and nevirapine. The study substantially supports the conclusion that calanolide A represents a novel subclass of nonnucleoside RT inhibitor which merits consideration for anti-HIV drug development.

Kinetic analysis of inhibition of human immunodeficiency virus type-1 reverse transcriptase by calanolide A.

Calanolide A, first isolated from the tropical rain forest tree Calophyllum lanigerum, is a potent human immunodeficiency virus type-1 (HIV-1) specific reverse transcriptase (RT) inhibitor, broadly active against diverse HIV-1 strains, including nucleoside and nonnucleoside-resistant variants. We examined the biochemical mechanism of inhibition of HIV-1 RT by calanolide A. Two template/primer systems were examined: ribosomal RNA and homopolymeric rA-dT 12-18. Calanolide A inhibited HIV-1 RT by a complex mechanism involving two calanolide A binding sites. With respect to either deoxynucleotide triphosphate (dNTP) or template/primer binding, one site was competitive and the other was uncompetitive. The data indicated that calanolide A bound near the active site of the enzyme and interfered with dNTP binding. Calanolide A inhibited HIV-1 RT in a synergistic fashion with nevirapine, further distinguishing it from the general class of nonnucleoside RT inhibitors. At certain concentrations, calanolide A bound HIV-1 RT in a mutually exclusive fashion with respect to both the pyrophosphate analog, phosphonoformic acid and the acyclic nucleoside analog 1-ethoxymethyl-5-ethyl-6-phenylthio-2-thiouracil. This indicates that calanolide A shares some binding domains with both phosphonoformic acid and 1-ethoxymethyl-5-ethyl-6-phenylthio-2-thiouracil, presumably reflecting that it interacts with RT near both the pyrophosphate binding site and the active site of the enzyme.