Pediatric HIV-1-specific cytotoxic T-lymphocyte responses suggesting ongoing viral replication despite combination antiretroviral therapy

Human immunodeficiency virus-1 (HIV-1)-specific cytotoxic T-lymphocyte (CTL) responses are common in infected adults and usually exhibit rapid decay after combination antiretroviral therapy (ART). CTLs develop later in the first year of life, and the fate of HIV-1-specific responses in perinatally infected children after ART is less well described. HIV-1-specific CTL responses were measured in 17 perinatally infected children and adolescents (ages 3-20 y) receiving combination ART. Seven had prolonged viral suppression (<400 copies/mL) for 2.5-5.3 y and 10 had persistent viremia (median, 77,550 copies/mL). HIV-1-specific CTL responses were tested by interferon (IFN)-gamma enzyme-linked immunospot (ELIS-pot) assays using 53 overlapping peptide pools spanning the entire HIV-1 proteome. HIV-1-specific CTL responses were detected in 14 of 17 individuals. Responses to one to four viral proteins were found in eight of 10 individuals with persistent viremia and six of seven with prolonged viral suppression. The magnitude and breadth of CTL responses were similar between groups. HIV-1-specific CTL responses were present in the majority of perinatally infected subjects, irrespective of viremia at evaluation. Because ART-treated infected adults usually have rapid decay of responses, these data suggest viral replication below the limits of detection is more persistent in combination ART-treated perinatally infected pediatric subjects. The long-term clinical implications of these findings remain to be determined.

HIV protease cleaves poly(A)-binding protein

The PABP [poly(A)-binding protein] is able to interact with the 3' poly(A) tail of eukaryotic mRNA, promoting its translation. Cleavage of PABP by viral proteases encoded by several picornaviruses and caliciviruses plays a role in the abrogation of cellular protein synthesis. We report that infection of MT-2 cells with HIV-1 leads to efficient proteolysis of PABP. Analysis of PABP integrity was carried out in BHK-21 (baby-hamster kidney) and COS-7 cells upon individual expression of the protease from several members of the Retroviridae family, e.g. MoMLV (Moloney murine leukaemia virus), MMTV (mouse mammary tumour virus), HTLV-I (human T-cell leukaemia virus type I), SIV (simian immunodeficiency virus), HIV-1 and HIV-2. Moreover, protease activity against PABP was tested in a HeLa-cell-free system. Only MMTV, HIV-1 and HIV-2 proteases were able to cleave PABP in the absence of other viral proteins. Purified HIV-1 and HIV-2 proteases cleave PABP1 directly at positions 237 and 477, separating the two first RNA-recognition motifs from the C-terminal domain of PABP. An additional cleavage site located at position 410 was detected for HIV-2 protease. These findings indicate that some retroviruses may share with picornaviruses and caliciviruses the capacity to proteolyse PABP.

The phosphorylation of phospholipase C-gamma1, Raf-1, MEK, and ERK1/2 induced by a conserved retroviral peptide

A synthetic 17-amino acid peptide (CKS-17) homologous to a highly conserved region of human and animal retroviral transmembrane proteins has been found to exhibit suppressive properties for numerous immune functions. It has been shown that CKS-17 causes an imbalance of human types 1 and 2 cytokines and inhibition of the immune responses of lymphocytes, monocytes, and macrophages. CKS-17 induced increased intracellular levels of cAMP, which plays an important role in regulation of cytokine biosynthesis. In this study, using a Jurkat T-cell line and Western blot analysis, CKS-17 induced phosphorylation of PLC-gamma1, Raf-1, MEK and ERK1/2. Using a PLC selective inhibitor U73122 or PLC-gamma1-deficient Jurkat cell line, phosphorylation induced by CKS-17 of ERK1/2, PLC-gamma1, or Raf-1, respectively, were undetectable or significantly reduced. Reintroduction of PLC-gamma1 into the PLC-gamma1-deficient Jurkat cells restored the phosphorylation of ERK1/2 and PLC-gamma1 induced by CKS-17. Further, pretreatment of Jurkat cells with PKC inhibitors blocks the phosphorylation of Raf-1, MEK, and ERK1/2 induced by CKS-17. These results indicate that CKS-17 induces the PLC-gamma1-PKC-Raf-1-MEK-ERK1/2 signaling pathway.

The human T-cell leukemia virus type 1 p13II protein: effects on mitochondrial function and cell growth

p13(II) of human T-cell leukemia virus type 1 (HTLV-1) is an 87-amino-acid protein that is targeted to the inner mitochondrial membrane. p13(II) alters mitochondrial membrane permeability, producing a rapid, membrane potential-dependent influx of K(+). These changes result in increased mitochondrial matrix volume and fragmentation and may lead to depolarization and alterations in mitochondrial Ca(2+) uptake/retention capacity. At the cellular level, p13(II) has been found to interfere with cell proliferation and transformation and to promote apoptosis induced by ceramide and Fas ligand. Assays carried out in T cells (the major targets of HTLV-1 infection in vivo) demonstrate that p13(II)-mediated sensitization to Fas ligand-induced apoptosis can be blocked by an inhibitor of Ras farnesylation, thus implicating Ras signaling as a downstream target of p13(II) function.

C-terminal octylation rescues an inactive T20 mutant: implications for the mechanism of HIV/SIMIAN immunodeficiency virus-induced membrane fusion

T20, a synthetic peptide corresponding to a C-terminal segment of the envelope glycoprotein (gp41) of human and simian immunodeficiency viruses, is a potent inhibitor of viral infection. We report here that C-terminal octylation of simian immunodeficiency virus gp41-derived T20 induces a significant increase in its inhibitory potency. Furthermore, when C-terminally octylated, an otherwise inactive mutant in which the C-terminal residues GNWF were replaced by ANAA has potency similar to that of the wild type T20. This effect cannot be explained by a trivial inhibitory effect of the octyl group added to the peptides, because the N-terminally octylated peptides have the same activity as the non-octylated parent peptides. The effects caused by octylation on the oligomerization, secondary structure, and membrane-interaction properties of the peptides were investigated. Our results shed light on the mechanism of inhibition by T20 and provide experimental support for the existence of a pre-hairpin intermediate.

Retroviral proteases

SUMMARY

The proteases of retroviruses, such as leukemia viruses, immunodeficiency viruses (including the human immunodeficiency virus, HIV), infectious anemia viruses, and mammary tumor viruses, form a family with the proteases encoded by several retrotransposons in Drosophila and yeast and endogenous viral sequences in primates. Retroviral proteases are key enzymes in viral propagation and are initially synthesized with other viral proteins as polyprotein precursors that are subsequently cleaved by the viral protease activity at specific sites to produce mature, functional units. Active retroviral proteases are homodimers, with each dimer structurally related to the larger class of single-chain aspartic peptidases. Each monomer has four structural elements: two distinct hairpin loops, a wide loop containing the catalytic aspartic acid and an alpha helix. Retroviral gene sequences can vary between infected individuals, and mutations affecting the binding cleft of the protease or the substrate cleavage sites can alter the response of the virus to therapeutic drugs. The need to develop new drugs against HIV will continue to be, to a large extent, the driving force behind further characterization of retroviral proteases.

Monomer-trimer equilibrium of the ectodomain of SIV gp41: insight into the mechanism of peptide inhibition of HIV infection

The monomer-trimer equilibrium of the ectodomain of SIV gp41 (residues 27-149, e-gp41) has been characterized by analytical ultracentrifugation, circular dichroism (CD), and NMR spectroscopy. Based on analytical ultracentrifugation experiments performed at different rotor speeds and protein concentrations, the equilibrium association constant for the SIV e-gp41 trimer is 3.1 x 10(11) M(-2). The presence of intermolecular nuclear Overhauser effects in a mixture of 12C and 13C-labeled e-gp41 prepared under nondenaturing conditions unambiguously demonstrates that there is a dynamic equilibrium between the monomer and trimer. The CD spectra taken as a function of SIV e-gp41 concentration suggest that the helical content of the monomeric state does not change significantly relative to that of the trimeric state. The relevance of the monomer-trimer equilibrium is discussed with respect to gp41 function and the inhibitory properties of gp41 peptides.

Differential modulation of Th1- and Th2-related cytokine mRNA expression by a synthetic peptide homologous to a conserved domain within retroviral envelope protein

The influence of a synthetic retroviral peptide, CKS-17, on T helper type 1 (Th1)- or Th2-related cytokines was investigated in human blood mononuclear cells. Cells were stimulated with staphylococcal enterotoxin A, anti-CD3 plus anti-CD28 monoclonal antibodies, or lipopolysaccharide to induce cytokine mRNA. mRNA was detected by a reverse transcription-polymerase chain reaction or Northern blot analysis. CKS-17 down-regulated stimulant-induced mRNA accumulation for interferon gamma (IFN-gamma), interleukin (IL)-2, and p40 heavy and p35 light chains of IL-12, a cytokine that mediates development of Th1 response. CKS-17 up-regulated stimulant-induced mRNA accumulation of IL-10 and did not suppress Th2-related cytokine (IL-4, IL-5, IL-6, or IL-13) mRNA expression. A reverse sequence of CKS-17 peptide, used as a control, showed no such action. Anti-human IL-10 monoclonal antibody blocked ability of CKS-17 to inhibit mRNA accumulation for IFN-gamma but not the CKS-17 suppressive activity of IL-12 p40 heavy chain mRNA. Thus, CKS-17-mediated suppression of IFN-gamma mRNA expression is dependent upon augmentation of IL-10 production by CKS-17. This conserved component of several retroviral envelope proteins, CKS-17, may act as an immunomodulatory epitope responsible for cytokine dysregulation that leads to suppression of cellular immunity.

Human immunodeficiency virus-infected adherent cell-derived inhibitory factor (p29) inhibits normal T cell proliferation through decreased expression of high affinity interleukin-2 receptors and production of interleukin-2

Adherent cells from HIV-infected subjects as well as in vitro HIV-infected normal adherent cells produce spontaneously a 29-kD (p29) factor that inhibits mitogen-induced proliferation of normal T cells. p29 mediates a partial dose-dependent inhibition of total protein synthesis in both nonstimulated and PHA-activated cells that is associated with impaired PHA-induced expression of IL-2 receptor (IL-2R)alpha chain, HLA-class II molecules, and production of IL-2 by these cells; conversely, p29 does not modify the expression of IL-2R beta chain, 4F2, CD9, or transferrin receptor, or the production of IL-1 and TNF alpha by the cells. 1 h preincubation of the cells with p29 is sufficient to detect its biologic activity and added rIL-2 abrogates p29-induced inhibition of IL-2R alpha chain expression; however, p29 does not display any biologic effect on already expressed IL-2R alpha chains. The impaired expression of IL-2R alpha chain mediated by p29 is not due to a decreased accumulation of the corresponding mRNA transcripts, but is associated with a two-fold increase of intracellular cAMP. Binding experiments with 125I-rIL-2 reveals that p29 induces a 50% decrease in the number of both high and low affinity IL-2R per cell. p29 also inhibits alloantigen-induced proliferation of PBMC, whereas it does not modify IL-2-dependent proliferation of 48-h PHA-blasts that already express high affinity IL-2R. These findings indicate that p29 mediates its biologic activity during early stages of T cell activation affecting the expression of high affinity IL-2R and production of IL-2, through a nontranscriptional mechanism involving an increase of intracellular cAMP.

Transactivation of human immunodeficiency virus type 1 long terminal repeat-directed gene expression by the human foamy virus bel1 protein requires a specific DNA sequence

Human foamy virus (HFV) encodes the transcriptional transactivator bel1. The bel1 protein transactivates HFV long terminal repeat (LTR)-directed gene expression by recognizing a region in U3. It also transactivates human immunodeficiency virus type 1 (HIV-1) LTR-directed gene expression in transient transfection assays. To identify the specific region in HIV-1 LTR responsible for bel1 action, we examined the effect of bel1 on chloramphenicol acetyltransferase (CAT) gene expression in transfected cells with a series of mutant HIV-1 LTR/CAT plasmids. The region between -158 and -118 from the transcription initiation site, immediately upstream of the core enhancer element, was identified as responsible for the transactivation by bel1. In addition, bel1 transactivated a heterologous promoter when this region was positioned upstream of it in the sense and antisense orientations. Optimal transactivation of the HIV-1 LTR by bel1 did not require an intact TAR sequence, suggesting that the binding of tat to the TAR sequence is not a prerequisite for bel1 function in HIV-1 LTR-directed gene expression. In the region of the HIV-1 LTR that is necessary for the bel1-mediated transactivation, we have found a sequence which is conserved between HIV-1 and HFV. Our results suggest that the bel1 action on HIV-1 seems to be mediated by a specific DNA sequence which is shared by both the HIV-1 LTR and HFV LTR.

Inhibitory effect of HIV-1 envelope glycoproteins gp120 and gp160 on the in vitro growth of enriched (CD34+) hematopoietic progenitor cells

The effect of increasing concentrations (from 0.01 to 10 micrograms/ml) of HIV-1 envelope glycoproteins gp160, gp120, gp41 and core protein p24 was evaluated on the in vitro growth of enriched hematopoietic progenitors (CD34+ cells). Both gp120 and gp160, at concentrations from 0.01 to 10 micrograms/ml, caused a progressive and significant (p less than 0.05) decrease in viable CD34+ cell count in liquid cultures supplemented with 2 ng/ml of human recombinant (r) interleukin-3 (IL-3), evaluated by means of Trypan-blue exclusion and [3H]thymidine ([3H]TdR) incorporation. In the absence of rIL-3, no inhibitory effects were observed even at the highest gp160 and gp120 concentrations explored (10 micrograms/ml). On the contrary, gp41 and p24 did not affect the number of viable CD34+ cells, either in the presence or in the absence of rIL-3. Moreover, gp160 and gp120, but not gp41 and p24, significantly (p less than 0.05) inhibited the in vitro growth of granulomacrophage progenitors (CFU-GM) in a dose-dependent fashion. These data clearly demonstrate that HIV-1 envelope glycoproteins inhibit the growth of purified hematopoietic progenitors. We propose that HIV-1 can impair hematopoiesis through the interaction of gp120/gp160 with CD34+ cell surface, independently of an infectious process.

Biological and biochemical characterization of a factor produced spontaneously by adherent cells of human immunodeficiency virus-infected patients inhibiting interleukin-2 receptor alpha chain (Tac) expression on normal T cells

Adherent cells from human immunodeficiency virus (HIV)-infected subjects but not from normal blood donors, patients with Gram-positive or -negative bacteremia, active tuberculosis, toxoplasmosis, pulmonary aspergillosis, and cytomegalovirus infection produce spontaneously an activity which inhibits alpha chain of interleukin-2 (Tac) expression and interleukin 2 (IL-2) production by normal activated T cells and IL-2 production by these cells. A similar biologic activity was detected in culture supernatants of in vitro HIV-I-infected normal adherent and leukemic U937 cells. Tac-inhibitory activity is not cytotoxic and it could be detected in serum-free conditioned media. Recombinant granulocyte/macrophage colony-stimulating factor and phorbol myristate acetate stimulation of patients' and normal adherent cells did not enhance specifically the production of the Tac inhibitor. Biologically active conditioned media did not contain infectious virus as well as secreted p24, gp120 viral proteins; the biologic activity could not be abolished by anti-p24, anti-gp120, and anti-nef monoclonal antibodies or human purified polyclonal anti-HIV IgG. Gel filtration of conditioned media followed by anion exchange chromatography resulted in a 1,200-fold degree of purification and revealed that the biologically active molecule was cationic. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of this fraction and gel elution of the proteins showed that the biologic activity was associated with a 29-kD protein which was distinct from alpha- or gamma-interferon, tumor necrosis factor-alpha, and prostaglandin E2. The above findings demonstrate the production of inhibitory factor(s) during HIV infection, which might be involved in the pathogenesis of the patients' immune defect.

Biological activities of a synthetic peptide composed of two unlinked domains from a retroviral transmembrane protein sequence

We report several biological activities of a synthetic peptide whose sequence contains the highly conserved region of feline leukemia virus transmembrane protein (TM) synthetically linked to another short TM-derived sequence particularly rich in polar positive residues. This 29-amino-acid peptide blocked [3H]thymidine uptake 30 to 50% by concanavalin A-stimulated CD4(+)--but not CD8(+)-enriched murine splenocytes. Maximal suppression was detected at 12.5 micrograms (3 microM) to 75 micrograms (19 microM) per ml of growth medium; stimulation of [3H]thymidine uptake was observed at higher peptide concentrations. The synthetic peptide inhibited but did not stimulate [3H]thymidine uptake by mitogen-activated thymocytes and antibody production by splenocytes as determined in a liquid hemolytic plaque assay. Similarities are reported between a consensus sequence of diverse retroviral TMs and a region of alpha interferons shown by others to be important for antiviral and cytostatic properties. The TM sequence-derived synthetic peptide blocked in a nontoxic and sequence-specific manner the release of murine leukemia virus from two chronically infected cell lines. We suggest that some of the biological effects of retroviral TM are mediated through a common pathway shared with alpha interferons.

Repression of transcription mediated at a thyroid hormone response element by the v-erb-A oncogene product

Several recent observations, such as the identification of the cellular homologue of the v-erb-A oncogene as a thyroid-hormone receptor, have strongly implicated nuclear oncogenes in transcriptional control mechanisms. The v-erb-A oncogene blocks the differentiation of erythroid cells, and changes the growth requirements of fibroblasts and erythroblasts. Mutations in v-erb-A protein have led to the loss of its affinity for thyroid hormones but do not affect its DNA-binding ability, a property required for biological activity. We report here the identification of a novel thyroid-hormone response element (TRE) in the long terminal repeat of Moloney murine leukaemia virus that binds the c-erb-A-alpha protein. The v-erb-A protein abolishes the responsiveness of this TRE to thyroid hormone, although it has a lower affinity than the normal receptor for the TRE. The data indicate that overexpressed v-erb-A protein negatively interferes with normal transcriptional-control mechanisms, and that amino-acid substitutions have altered its DNA-binding properties.

Expression and purification of biologically active v-sis/platelet-derived growth factor B protein by using a baculovirus vector system

Malignant transformation induced by simian sarcoma virus is mediated by its v-sis protein, the monkey homolog of the platelet-derived growth factor (PDGF) B chain. By use of an appropriately engineered baculovirus expression vector, the v-sis protein was expressed in the insect cell line Spodoptera frugiperda (Sf9) at a level 50- to 100-fold higher than that observed with overexpression in mammalian-cell transfectants. The sis protein produced by Sf9 cells underwent processing similar to that observed in mammalian cells, including efficient disulfide-linked dimer formation. Moreover, the recombinant sis protein was capable of binding PDGF receptors and inducing DNA synthesis as efficiently as PDGF-B synthesized by mammalian cells. A significant fraction of sis protein was released from Sf9 cells, which made possible a one-step immunoaffinity purification to near homogeneity with a 40% recovery of biological activity. These results demonstrate that a protein whose normal processing requires both intrachain and interchain disulfide-bridge formation can be efficiently expressed in a biologically active form in insect cells by using a baculovirus vector system.

Synthetic peptide corresponding to a conserved domain of the retroviral protein p15E blocks IL-1-mediated signal transduction

We studied the mode of action of the synthetic peptide CKS-17, which is a heptadecapeptide homologous to a highly conserved region of the immunosuppressive retroviral envelope protein p15E, as well as to envelope proteins of the human T cell leukemia virus I and II. Previous studies have established that CKS-17 conjugated to BSA (CKS-17-BSA) inhibited IL-1-mediated tumor toxicity in melanoma cells and proliferation in murine Th clones. We examined the effects of CKS-17-BSA on IL-1 action. CKS-17-BSA did not bind to IL-1, nor did it affect the number of IL-1 receptors, their binding affinity, or their ability to internalize IL-1. However, CKS-17-BSA inhibited production of IL-2 by murine thymoma cells treated with IL-1 or with 12-O-tetradecanoyl phorbol-13 acetate. The potent protein kinase C inhibitor, H7, also inhibited IL-1-mediated responses, while HA1004, a weak inhibitor of protein kinase C, did not. Protein kinase C activity in the cytosolic fraction prepared from thymoma cells was found to be inhibited by CKS-17-BSA in a dose-dependent manner. All of these findings are consistent with the idea that CKS-17-BSA inhibits IL-1-mediated responses by interfering with signal transduction through a protein kinase C pathway.

Neurotrophic activity of monomeric glucophosphoisomerase was blocked by human immunodeficiency virus (HIV-1) and peptides from HIV-1 envelope glycoprotein

Glucophosphoisomerase (GPI), a glycolytic enzyme, was recently described to share 90% sequence homology with neuroleukin, a recently discovered growth factor which promotes motor neuron regeneration in vivo, survival of peripheral and central neurons in vitro, and affects B cell immunoglobulin synthesis. Interestingly, neuroleukin activity was described to be antagonized by the human immunodeficiency virus (HIV-1) envelope glycoprotein (gp120), with which neuroleukin was found to share partial sequence homology. In this study, reduced GPI demonstrated similar activity to neuroleukin in a novel bioassay using human and rat neuroblastoma cell lines. In the presence of reduced GPI, these cells were found to differentiate, in terms of enhanced neurite extension at a reduced proliferation rate. These results demonstrate the existence of a novel growth factor activity of an evolutionary ancient enzyme. The nonreduced commercial form of GPI, probably the dimer, was found to be inactive in this bioassay. Using the neuroblastoma cells model system, we further investigated the significance of the region of homology to HIV-1 envelope glycoprotein (gp120) as the putative binding site of GPI to its receptor on neuronal cells.

Identification of the fusion peptide of primate immunodeficiency viruses

Membrane fusion induced by the envelope glycoproteins of human and simian immunodeficiency viruses (HIV and SIVmac) is a necessary step for the infection of CD4 cells and for the formation of syncytia after infection. Identification of the region in these molecules that mediates the fusion events is important for understanding and possibly interfering with HIV/SIVmac infection and pathogenesis. Amino acid substitutions were made in the 15 NH2-terminal residues of the SIVmac gp32 transmembrane glycoprotein, and the mutants were expressed in recombinant vaccinia viruses, which were then used to infect CD4-expressing T cell lines. Mutations that increased the overall hydrophobicity of the gp32 NH2-terminus increased the ability of the viral envelope to induce syncytia formation, whereas introduction of polar or charged amino acids in the same region abolished the fusogenic function of the viral envelope. Hydrophobicity in the NH2-terminal region of gp32 may therefore be an important correlate of viral virulence in vivo and could perhaps be exploited to generate a more effective animal model for the study of acquired immunodeficiency syndrome.

HIV-1 GP120-mediated immune suppression and lymphocyte destruction in the absence of viral infection

The magnitude of immunologic defects observed in HIV-1-infected individuals before the development of overt AIDS is disproportionately high in comparison to the levels of infectious virus in these patients--suggesting that factors other than direct virus-induced cytopathology may be involved. With this in mind, we investigated the immunologic consequences of the interaction between purified HIV-1 gp120 and the CD4 molecules expressed by uncommitted as well as Ag-specific lymphocytes. HIV-1 gp120 exhibited a dose-dependent immunosuppressive effect on: 1) Ag-driven proliferation of cloned CD4+ lymphocytes, 2) OKT3-driven proliferation of cloned CD4+ lymphocytes, and 3) cytolytic activity of CD4+, EBV-specific CTL. Thus, HIV-1 gp120 can, in a manner similar to OKT4A antibodies, suppress T cell activation and the expression of cytolytic activities through its interaction with CD4. Additionally, activated CD4+ lymphoblasts can be rendered susceptible to immune cytolysis by virtue of their binding of purified gp120. This "targeting" of activated lymphoblasts can occur with levels of gp120 far below that which is needed to saturate all OKT4A-defined CD4 epitopes. Adsorbed gp120 could be demonstrated on the surface of these cells for up to 12 h, a sufficient time for interaction with host cytolytic elements. The data from these in vitro modeling experiments highlight one of many potential mechanisms of HIV-1 induced immunosuppression and lymphocyte destruction that can occur in the absence of infectious virus and that is based on the unique interaction between HIV-1 gp120 and its cellular receptor, CD4.

Human immunodeficiency virus-infected T cells and monocytes are killed by monoclonal human anti-gp41 antibodies coupled to ricin A chain

Two human monoclonal antibodies specific for the envelope glycoprotein (gp), gp41, of the human immunodeficiency virus were conjugated to deglycosylated ricin A chain. These immunotoxins killed human immunodeficiency virus-infected H9 (T cell) and U937 (monocyte) cell lines but were nontoxic to the uninfected cell lines or to class II-positive Daudi cells. Specific killing of infected H9 cells could be completely blocked by recombinant gp160 and partially blocked by unconjugated anti-gp41 antibody but was not blocked by recombinant gp120 or human IgG demonstrating specificity for gp41. The specific toxicity of the immunotoxins for infected U937 cells was markedly potentiated by chloroquine.

CD4+ lymphocyte function with early human immunodeficiency virus infection

The pathogenesis of cellular immune deficiency following human immunodeficiency virus (HIV) infection could result from quantitative and/or qualitative dysfunction of the CD4+ lymphocyte population. To better characterize the T-cell response to soluble antigen with HIV infection, we have isolated peripheral blood lymphocytes and purified populations of CD4+ lymphocytes from healthy HIV antibody-positive subjects, patients with acquired immunodeficiency syndrome (AIDS)-related complex (ARC), and healthy HIV antibody-negative controls. T-lymphocyte function was determined by proliferative response to lectin (phytohemagglutinin), phorbol 12-myristate 13-acetate (PMA), calcium ionophore, purified recombinant HIV envelope gp120, tetanus toxoid antigen, and tetanus toxoid antigen in the presence of recombinant gp120 or purified recombinant soluble CD4. PBLs and CD4+ lymphocytes from asymptomatic HIV-infected subjects responded equally well to lectin, PMA, and/or calcium ionophore and to tetanus toxoid as cells from uninfected control subjects. The cells that proliferated in response to a soluble antigenic stimulus did not respond to gp120. Cells from subjects with ARC had a selective antigen recognition defect independent of the number of CD4+ lymphocytes. Recombinant gp120 inhibited CD4+ lymphocyte proliferation to antigenic stimulus by 30-40%. Recombinant soluble CD4, a proposed therapeutic for HIV, had no effect on T-cell response to antigen. A selective antigen recognition response was not compromised early in HIV infection but was compromised in subjects with ARC. Inhibition of proliferation to tetanus toxoid by gp120 suggests that HIV may affect major histocompatibility complex II restricted antigen recognition independent of CD4+ cell loss.

Rapid repression of quiescence-specific gene expression by epidermal growth factor, insulin, and pp60v-src

We isolated a cDNA for p20K, a secreted protein preferentially synthesized in nonproliferating cells. p20K mRNA and protein levels declined rapidly following treatment with various mitogens. DNA sequence analysis of the p20K cDNA predicted a novel protein distantly related to alpha 2 mu-globulin and plasma retinol-binding protein.

Bovine leukemia virus trans-activator p38tax activates heterologous promoters with a common sequence known as a cAMP-responsive element or the binding site of a cellular transcription factor ATF

The genome of bovine leukemia virus (BLV) encodes a transcriptional trans-activator p38tax (also referred to as pXBL-I) which amplifies the virus gene expression driven by its long terminal repeat (LTR). It was proposed that activation of cellular gene expression by p38tax might be involved in the mechanism of B-cell transformation caused in vivo by BLV infection. Here, we report that the U3 region of BLV LTR contains multiple regulatory elements responsive to p38tax. A core element composing the p38tax-inducible U3 structure is suggested to be a heptanucleotide motif of 5'TGACGTCA3', the consensus sequence proposed for a cAMP-responsive element (CRE) and for the binding sites of a cellular transcription factor (ATF). Adenovirus-5 E3 and E4, c-fos and somatostatin regulatory regions containing CRE/ATF-element exhibited responsiveness to p38tax in a chloramphenicol acetyltransferase transient expression assay. These suggest that in BLV-infected cells, cellular gene expression might be induced abnormally by the virus trans-activator through ATF or ATF-like factors.

Human immunodeficiency virus glycoprotein (gp120) induction of monocyte arachidonic acid metabolites and interleukin 1

This study reports on the direct effect of the envelope glycoprotein (gp120) of the human immunodeficiency virus type 1 (HIV-1) on human monocyte function. Addition of preparations of purified gp120 from the HIV-1 to human monocytes resulted in the production of interleukin 1 (IL-1) and arachidonic acid metabolites from the cyclooxygenase and lipoxygenase pathways. Quantification of prostaglandin E2 (PGE2) and IL-1 revealed an increase in both mediators with 50 ng of gp120 per ml and an increase of 12- and 30- to 40-fold with 200-400 ng of gp120 per ml, respectively. Unlike native gp120, the recombinant nonglycosylated gp120 fragments PB1-RF and PB1-IIIB, as well as one of the core structural proteins of HIV-1, p24, did not increase arachidonic acid metabolism or IL-1 activity. Cytofluorometric analysis revealed that gp120 blocked the binding of OKT4A to the CD4 on monocytes, whereas OKT4 binding was unaffected. Involvement of the CD4 in signal transduction was further demonstrated by the ability of OKT4 and OKT4A monoclonal antibodies to increase monocyte PGE2, IL-1 activity, and nanogram amounts of IL-1 beta.

In vivo depression of lymphocyte traffic in sheep by VIP and HIV (AIDS)-related peptides

Core pentapeptides and an octapeptide (Peptide T) computer deduced from amino acid sequences from vasoactive intestinal peptide (VIP) and the 120 gp external envelope of the HIV (AIDS) virus and synthesized have been reported to have important in vitro and in vivo activity including inhibition of HIV binding to CD4 surface antigens of brain cells and lymphocytes and limitation of HIV infectivity. Two of these core pentapeptides, peptide TTNYT (Peptide T [4-8]) and peptide TDNYT (VIP [7-11]), are reported here, on acute infusion into cannulated afferent popliteal lymphatics of sheep, to produce prompt and marked depressions in the output of both small recirculating and blast lymphocytes into popliteal lymph node efferent lymph. As with a prior VIP infusion study, there appeared to be a selective effect on T4 (CD4) lymphocytes, with a marked predominance of T4 (CD4) lymphocytes in the lymphocyte depleted efferent lymph.

Functional replacement of the HIV-1 rev protein by the HTLV-1 rex protein

Two evolutionarily distinct families of human retroviruses, the human immunodeficiency viruses (HIV) and the human T-cell leukaemia viruses (HTLV), have been defined (reviewed in ref. 1). Although these virus groups share tropism for human CD4+ T cells, they differ markedly in primary sequence, genetic organization and disease association (AIDS versus adult T-cell leukaemia), but show similar general strategies for the regulation of viral gene expression. Each encodes a protein able to trans-activate transcription from the homologous viral long terminal repeat (tat in HIV, tax in HTLV), although these proteins act by different mechanisms and do not appear to be interchangeable. Each virus also produces a second trans-acting protein that induces the expression of the unspliced messenger RNAs encoding the viral structural proteins (rev in HIV and rex in HTLV). Here we show that the rex protein of HTLV-I can functionally replace the rev protein of HIV-1 in transient expression assays. This genetic complementation by rex is adequate for the rescue of a replication-defective rev mutant of HIV-1. This unexpected shared function between the structurally distinct rex and rev proteins emphasizes the importance of this highly conserved pathway for the regulation of human retrovirus gene expression.

Neuronal cell killing by the envelope protein of HIV and its prevention by vasoactive intestinal peptide

The clinical manifestations of AIDS (acquired immune deficiency syndrome) often include neuropsychiatric and neurological deficits, including early memory loss and progressive dementia. HIV (human immunodeficiency virus), the aetiological agent of AIDS, is probably carried by infected macrophages in the central nervous system. The virus enters cells by binding its envelope glycoprotein gp120 to the CD4 antigen present on brain and immune cells. From the data reported in this paper, we now suggest that the neuronal deficits associated with HIV may not be entirely a result of infectivity, but that gp120 shed from HIV could directly produce the neuropathology as a result of its interference with endogenous neurotrophic substances. It is known that an analogue of a sequence contained in vasoactive intestinal peptide (VIP) occurs in all known sequenced gp120 isolates and that VIP is important for neuronal survival in cell culture. Here we show that purified gp120 from two diverse HIV isolates and a recombinant gp120 from a third isolate were all potent in specifically producing significant neuronal cell death in dissociated hippocampal cultures derived from fetal mice, and that this could be reduced by monoclonal antibodies against the murine CD4 antigen and completely antagonized by VIP.

Rapid turnover of the platelet-derived growth factor receptor in sis-transformed cells and reversal by suramin. Implications for the mechanism of autocrine transformation

In cells transformed by either v-sis or c-sis, the majority of the newly synthesized platelet-derived growth factor (PDGF) receptors fail to reach the cell surface and are rapidly degraded. This rapid turnover (t1/2 less than 30 min) appears to result from interaction of the sis gene product with the PDGF receptor in the endoplasmic reticulum and/or Golgi apparatus during their intracellular routing from the endoplasmic reticulum to the plasma membrane or extracellular compartment. Several lines of evidence support this hypothesis. 1) Both the 160-kDa precursor and the intracellular 180-kDa mature form of the PDGF receptor possessed ligand binding activity for PDGF; 2) both the 160-kDa precursor and the 180-kDa mature form of the receptor in sis-transformed cells were found to be activated (phosphorylated); 3) protamine, a competitive inhibitor for PDGF or v-sis gene product binding to the cell-surface receptor, did not affect the rapid turnover of the PDGF receptor in sis-transformed cells; 4) suramin, an inhibitor for PDGF or v-sis gene product binding to the PDGF receptor, not only reversed the rapid turnover of the PDGF receptor in sis-transformed cells, but also increased the secretion of sis gene products; and 5) rapid turnover of the PDGF receptor was only observed in sis-transformed cells but not in cells transformed by other oncogenes. We suggest that the persistence of a mitogenic signal from cellular organelles, arising from the intracellular interaction of sis gene products with newly synthesized PDGF receptors, is the mechanism for autocrine transformation by sis.

HLA-DR is involved in the HIV-1 binding site on cells expressing MHC class II antigens

The primary interaction of HIV-1 with the target cell involves the viral large envelope protein (gp120) and the cellular CD4 molecule. mAb reacting with portions of CD4 have been shown to block HIV-1 attachment and infection. In one of the early reports describing HIV-1 cell interaction, some mAb reacting with MHC class II Ag were also found to block infection. To investigate further a possible role for MHC class II in HIV-1 binding, a cultured T lymphocyte cell line (H-9) that expresses MHC class II molecules and PHA-stimulated PBL was exposed for various time periods to concentrated viral particles and individual HIV-1 proteins. A decrease in the ability to detect the CD4a epitope and HLA-DR was observed after the cells were exposed to virus for 15, 30, and 60 min whereas HLA-DP and HLA-DQ Ag increased or remained unchanged. After 120 min of virus exposure, the CD4a epitope remained diminished whereas HLA-DR was detected at levels found on cells not exposed to virus. mAb detecting the CD4a epitope and HLA-DR, as well as alloantisera detecting the specific HLA-DR Ag on the target cell, blocked HIV-1 binding. When immunopurified gp120 was added to PHA-stimulated and unstimulated PBL, the CD4a epitope decreased in the same manner as was observed with whole virus preparations. In contrast to exposure to the intact virus, HLA-DR expression appeared to increase. Other viral proteins, p17, p24, and a portion of the small envelope protein, gp41, had no effect on the ability to detect cell surface Ag. Thus, although CD4 is the primary receptor for HIV-1 binding, HLA-DR appears to be involved in the binding site, probably by virtue of its close proximity to the CD4 molecule on the cell surface.

Inhibition of normal human natural killer cell activity by human immunodeficiency virus synthetic transmembrane peptides

The inhibitory effect on normal natural killer (NK) cell activity of two synthetic peptides corresponding to amino acid sequences 735-752 and 846-860, respectively, as deduced from the amino acid sequences of HTLV-IIIB gp160, was assessed. Sequences 735-752 and 846-860 correspond to regions located within the HIV transmembrane gp41, the carboxy terminus of HIV gp160. These two synthetic peptides have been shown previously to suppress the mitogen- and alloantigen-induced normal human lymphocyte blastogenic responses. Peptides 735-752 and 846-860 conjugated to protein carriers exerted a significant inhibition on the normal NK cell activity assayed against K562 tumor target cells in an in vitro 51Cr-release cytoltoxicity assay. At variance, control peptides similarly conjugated had no effect on NK activity. Addition of exogenous recombinant human interleukin-2 (IL-2) resulted in a partial restoration of the suppression of NK cell activity exerted by both peptides. Binding experiments indicated that peptides 735-752 and 846-860 did not affect the formation of effector cell-target cell conjugates, suggesting inhibitory effect(s) subsequent to the formation of the lytic complex as one potential mechanism of the observed NK suppression. These results suggest that peptides 735-752 and 846-860 homologous to sequences within the HIV transmembrane gp41 may play an important role in the pathogenesis of the defective NK cell activity observed in patients with acquired immunodeficiency syndrome (AIDS).

Human immunodeficiency virus-induced cytotoxicity for CD8 cells from some normal donors and virus-specific induction of a suppressor factor

Several aspects of human immunodeficiency virus (HIV)-induced pathology in vitro warrant close examination to ascertain their role in the development of disease in vivo. The ability of HIV to produce cytopathology of CD4 cells has been well documented, although the extent and mechanism(s) may be varied. Further, immune suppression by HIV envelope (env) is well documented in vitro, but its importance in vivo remains unknown and the role of other HIV components in immune suppression has not been examined. We have exposed peripheral blood mononuclear cells (PBMC) from normal donors to ultraviolet-irradiated HIV (uv-HIV) at concentrations similar to those found in AIDS patient serum and determined that in some normal donors (3/7) depletion of CD8 cells as well as CD4 cells is demonstrable. Abrogation of phytohemagglutinin (PHA)-induced proliferation by uv-HIV was also examined in the same normal donors. Immune suppression, unlike CD4 cell killing, does not require intact virus and occurs at physiologically relevant concentrations of HIV. Furthermore, PBMC exposed to uv-HIV in the presence of PHA produce a heat- and protease-labile suppressor factor(s) following removal of virus, whether or not they are reexposed to PHA. Our results suggest that cell killing may be a more broad event than previously described, including the killing of at least CD8 cells either directly or indirectly. In addition, suppressor factors produced following exposure of patient lymphocytes to agents that induce proliferation may exacerbate the development of opportunistic infection.

Effects of interleukin 2 and large envelope glycoprotein (gp 120) of human immunodeficiency virus (HIV) on lymphocyte proliferative responses to cytomegalovirus

Lymphocytes from many HIV-infected asymptomatic individuals or patients with AIDS-related conditions (ARC) and from all AIDS patients were unable to proliferate in vitro in response to UV-inactivated cytomegalovirus (CMV). The addition of recombinant IL2 (rIL2) restored proliferative responses of lymphocytes from most HIV-infected asymptomatic individuals and ARC patients to levels similar to those of HIV-seronegative (HIV-) CMV-seropositive (CMV+) individuals. In contrast, rIL2 augmented CMV-specific lymphocyte proliferation of only 33% (6/18) of AIDS patients. Proliferative responses to CMV with or without rIL2 did not correlate well with the levels of CD4+ lymphocytes, HIV antigen levels or ratios of CD4+ and CD8+ lymphocytes. Proliferative responses to CMV were inhibited by relatively high concentrations (greater than or equal to 10 micrograms/ml) of recombinant HIV envelope glycoprotein (rgp120) and this immunosuppression was completely overcome by rIL2. These results indicate that defects in antigen-driven lymphocyte responses of HIV-infected individuals are not simply the result of reduced numbers of CD4+ lymphocytes but are influenced by defects in IL2 pathways and by immunosuppressive effects of HIV gp120.

Effects of increasing cyclic AMP or calcium on feline erythroid progenitors in vitro: normal cells are stimulated while cells from retrovirus-infected cats are suppressed

Pharmacologic modulators of cyclic 3',5'-adenosine monophosphate (cAMP) and calcium were added to cultures of bone marrow cells from normal cats and cats with retrovirus-induced erythroid aplasia (EA). Treatment with the following reagents increased the number of erythroid progenitors (CFU-e and BFU-e) in cells from normal cats: isoproterenol, dibutyryl cAMP, forskolin, RO-20-1724 and A23187. However, treatment of cells collected from viremic cats not only failed to enhance CFU-e and BFU-e but inhibited their growth. These studies suggest that EA is related to a non-reversible block of primitive erythroid progenitors or to direct inhibition of BFU-e and CFU-e growth.

The JUN oncoprotein, a vertebrate transcription factor, activates transcription in yeast

Transcriptional activation of RNA polymerase II in eukaryotic organisms ranging from yeasts to mammals has many common features such as enhancer elements, TATA elements, and activator proteins that bind specifically to promoter DNA. The JUN oncoprotein, which causes sarcomas in chickens, shows significant homology to the DNA-binding domain of GCN4, a yeast protein that stimulates transcription of the amino acid biosynthetic genes. The GCN4 and JUN proteins bind the same DNA sequences, consensus ATGA(C/G)TCAT, even though the DNA-binding domains are only 45% identical in amino acid sequence. The JUN protein almost certainly represents the oncogenic version of the normal AP-1 transcription factor, suggesting an evolutionary relationship between yeast and vertebrate activator proteins. Here, I demonstrate that JUN efficiently activates transcription in yeast either through its own or a heterologous DNA-binding domain. As is the case for yeast activator proteins, transcriptional stimulation by JUN requires an acidic activation region distinct from the DNA-binding domain. The functional interchangeability between yeast and vertebrate transcription factors strongly suggests a basic similarity in the molecular mechanism of eukaryotic transcriptional activation.

The effects of human immunodeficiency virus recombinant envelope glycoprotein on immune cell functions in vitro

The effect of human immunodeficiency virus (HIV) recombinant envelope glycoprotein 120 (rgp 120) on the functions of peripheral blood mononuclear cells (PBMC) in vitro was investigated. The results demonstrate that rgp 120 used at concentrations less than 1 microgram/ml has no significant effects on PBMC function in vitro. However, the addition of 1-20 micrograms/ml of rgp 120 significantly inhibits the tetanus toxoid-induced PBMC proliferative response in a dose-related manner as determined by [3H]thymidine incorporation. The data also show that rgp 120 (5 micrograms/ml) causes up to 70% reduction in the number of immunoglobulin G-secreting cells in pokeweed mitogen-stimulated PBMC cultures. Further, rgp 120 can selectively interact with the CD4a epitope of the CD4 helper cell membrane receptor. These results indicate that microgram per milliliter levels of rgp 120 can depress certain immune functions in vitro. The significance of these findings to the pathogenesis of immunodeficiency in HIV infection remains to be determined.

Identification of protein phosphatases 1 and 2B as ribosomal protein S6 phosphatases in vitro and in vivo

Protein phosphatases 1 and 2B from rabbit skeletal muscle were found to catalyze the dephosphorylation of ribosomal protein S6 in vitro. Phosphorylation of protein phosphatase-1 by the transforming protein of Rous sarcoma virus, pp60v-src, abolished S6 dephosphorylation by the purified enzyme. Analysis of the dephosphorylation of phosphorylase a and phosphorylase kinase in Xenopus oocyte extracts and after microinjection indicated the presence of oocyte enzymes similar to protein phosphatases-1 and -2B. Studies with 32P-labeled 40 S ribosomal subunits suggested that these enzymes were functioning as S6 phosphatases in oocytes. These findings support the hypothesis that regulation of protein phosphatase activity may be involved in the increase in S6 phosphorylation observed after mitogenic stimulation.

Recombinant hydrophilic region of murine retroviral protein p15E inhibits stimulated T-lymphocyte proliferation

Retroviral envelope protein p15E and antigenically related proteins have been implicated as potential mediators of immune dysfunction associated with retroviral infections and with neoplasia. Due to its extreme hydrophobicity, purified p15E has not been available in a nondenatured form or in sufficient quantities for detailed studies on the mechanisms of its immunosuppressive effects. Therefore, a plasmid was constructed to direct the synthesis in Escherichia coli of the major hydrophilic region of murine p15E. The purified recombinant p15E derivative, soluble under physiological conditions, inhibited by up to 60% (EC50 = 7.5 nM) the anti-CD3-driven proliferation of human T lymphocytes but had no effect on the proliferation of the transformed T-cell line Jurkat. The recombinant protein also inhibited, by up to an average of 92% (EC50 = 2.1 microM), the proliferation of the murine T-cell line CTLL-2. These data (i) provide direct evidence that a retroviral envelope protein can itself inhibit lymphoproliferative function and (ii) map the inhibitory activity to a specific region of p15E. The availability of soluble, recombinant p15E should facilitate studies of the pathogenesis of the immunosuppression accompanying retroviral infections and neoplastic diseases.

Functional interaction and partial homology between human immunodeficiency virus and neuroleukin

Dementia is common in patients with AIDS, but the mechanism by which the human immunodeficiency virus type 1 (HIV-1) causes the neurological impairment is unknown. In this study the possibility that an antigen of HIV-1 suppresses neuronal responses to neurotrophic factors was examined. Both HIV-1 and a related retrovirus, simian immunodeficiency virus (SIV), inhibited the growth of sensory neurons from chick dorsal root ganglia in medium containing neuroleukin (NLK) but not in medium containing nerve growth factor. An unrelated type D retrovirus, simian acquired immunodeficiency syndrome virus, did not affect the growth of neurons in the presence of either neurotrophic factor. The inhibition by HIV-1 of neuron growth in the presence of NLK was found to be due to the gp120 envelope glycoprotein. Regions of sequence homology between gp120 and NLK may account for this inhibitory property of gp120 and functional interactions between gp120 and NLK may be important in the pathogenesis of the AIDS dementia complex.

HTLV-III large envelope protein (gp120) suppresses PHA-induced lymphocyte blastogenesis

The addition of inactivated preparations of purified human T cell lymphotropic virus (HTLV-III) was found to inhibit normal human lymphocyte phytohemagglutinin (PHA)-induced blastogenesis but had no effect on concanavalin A (Con A), pokeweek mitogen, or allogeneic stimulation. The inhibition was concentration-dependent and also dependent on adding the virus preparation before or at the same time as PHA. The CD4 molecule is the receptor for HTLV-III binding. Immunopurified large envelope protein (gp120) from HTLV-III was found to bind to the CD4 molecule and also inhibited PHA-induced lymphocyte blastogenesis. These results suggest that the gp120 viral protein may alter immune function by binding to the CD4 molecule, which in turn serves as an "off" signal to lymphocyte response to PHA stimulation. Alternatively, by binding to the CD4 molecule, gp120 may interfere with the interaction of this molecule with class II histocompatibility antigens on accessory cells, thus selectively suppressing PHA response.

Expression of pp60v-src alters the ionic permeability of the plasma membrane in rat cells

The transmembrane potential of Rous sarcoma virus (RSV)-infected Rat-1 cells, expressing the pp60v-src protein kinase, is markedly less negative (by approximately 30 mV) than that of their normal counterparts. By contrast, the membrane potential of Rat-1 cells infected with Kirsten sarcoma virus is virtually unaltered. The RSV-induced membrane depolarization is shown to be due to a severalfold increase in the cation permeability ratio (PNa/PK) of the plasma membrane. When cells infected with a temperature-sensitive mutant of RSV (ts LA29), encoding a src protein with heat-labile kinase activity, are shifted from the nonpermissive to the permissive temperature, a rapid and sustained membrane depolarization is observed. Conversely, thermal inactivation of the ts LA29 pp60v-src kinase activity rapidly restores the membrane potential to near normal levels. Addition of epidermal growth factor, platelet-derived growth factor, or insulin to uninfected cells fails to cause a detectable change in membrane potential. We conclude that, unlike growth factor receptor tyrosine kinases, pp60v-src can induce, either directly or indirectly, a major change in the membrane permeability to monovalent cations.

Inhibition of human natural killer cell activity by a synthetic peptide homologous to a conserved region in the retroviral protein, p15E

It has been shown previously that the retroviral envelope protein p15E suppresses certain monocyte and lymphocyte functions. In this paper, we describe the effects on natural killer (NK) activity of a synthetic peptide (CKS-17) with homology to a region of p15E conserved among numerous retroviruses. Enriched human NK cells were assayed against K562 tumor target cells in a 51Cr-release cytotoxicity assay. Pretreatment of NK cells with CKS-17 at concentrations as low as 1.5 microM, but not with equivalent concentrations of control materials, markedly and reproducibly suppressed NK lytic activity. Prior exposure of NK cells to interferon-alpha (IFN-alpha) at 1000 U/ml did not alter their sensitivity to CKS-17-induced inhibition. Pretreating NK cells with CKS-17 almost entirely diminished their responsiveness to IFN-alpha and IFN-gamma, but not to interleukin 2 (IL 2). Kinetics experiments demonstrated that CKS-17-mediated suppression of both endogenous and activated NK cells was reversible after 18 hr at 37 degrees C. Experiments designed to examine the CKS-17 mechanism of action revealed that the peptide bound to all Leu-11+ lymphocytes, as shown by two-color flow cytometry. CKS-17 did not, however, inhibit effector cell/target cell conjugate formation. These data suggest a new mechanism for immune suppression mediated by retroviruses; inhibition of NK function. They moreover imply that the CKS-17 peptide interferes with the lytic phase of NK cytolysis.

Suppression of human lymphocyte mitogen response by proteins of the type-D retrovirus PMFV

A type-D retrovirus, derived from a human cell line and designated PMFV, which is related to, but distinct from the Mason-Pfizer monkey virus (MPMV) suppressed the in vitro mitogen response of human lymphocytes. PMFV was suppressive either as intact virus or after disruption by ether or detergents. In kinetic studies, the time course of the interaction between suppressive virus components and lymphocytes was characterized. Neither cytotoxicity nor time shifts in optimum 3H-thymidine incorporation of responding lymphocytes were observed. The suppressive activity of the disrupted virus was diminished by heating, freeze-thawing or treatment with pronase or trypsin, indicating temperature-sensitive proteins as suppressive components. By Sephacryl S-200 gel chromatography, molecular weights of approximately 70 and 15 kDa were determined for the suppressive components which were isolated from disrupted virus or virus-producing cells but not from non-infected cells.

Phosphorylation and protein synthetic events in Xenopus laevis oocytes microinjected with pp60v-src

Microinjection of purified pp60v-src, the transforming protein of Rous sarcoma virus, into Xenopus laevis oocytes accelerated the rate of progesterone- or insulin-induced meiotic maturation. This acceleration was abolished by incubating the oocytes with cycloheximide or puromycin during a 2-h interval between pp60v-src microinjection and progesterone addition. In contrast, exposure to actinomycin D did not alter the acceleration of maturation by microinjected pp60v-src. Associated with progesterone treatment and pp60v-src microinjection were a number of qualitative changes in phosphoproteins; a few of these changes are common to both stimuli. These results indicate that the action of pp60v-src in oocytes involves both phosphorylation and protein synthetic events that affect oocyte maturation.

The selective induction of a small number of proteins during G1 transit results from the mitogenic action of pp60v-src in tsASV-infected rat cells

Since the mitogenic/oncogenic pp60v-src product of the avian sarcoma virus (ASV) mutant, tsLA23, is abnormally thermolabile, tsLA23-NRK cells were phenotypically nontransformed at 40 degrees C and were consequently rendered quiescent by serum deprivation at this temperature. These serum-deprived cells were stimulated to transit G1 either as transformed cells by simply dropping the temperature to a pp60v-src -activating 36 degrees C, or as nontransformed cells by adding serum at 40 degrees C. Serum stimulation rapidly increased total protein synthesis in these cells and over 100 changes in cellular proteins (resolved by two-dimensional gel electrophoresis) occurred during G1 transit. By contrast, pp60v-src-activation did not increase total protein synthesis and only six proteins (18.5-44 kD) were clearly seen to appear or increase when quiescent cells were stimulated to transit G1 by activating pp60v-src. Three of these six pp60v-src- induced proteins also appeared or accumulated during the G1 transit of serum-stimulated cells. The appearance and/or accumulation of the six proteins and the subsequent initiation of DNA replication may have resulted from pp60v-src stimulating only a small number of critical cellular genes because both the protein changes and DNA replication were completely suppressed by the transcription inhibitor actinomycin D.