Activation of the CaR-CSE/H2S pathway confers cardioprotection against ischemia-reperfusion injury.

Ischemia-reperfusion (I/R) injury is a multifactorial process triggered when an organ is subjected to transiently reduced blood supply. The result is a cascade of pathological complications and organ damage due to the production of reactive oxygen species following reperfusion. The present study aims to evaluate the role of activated calcium-sensing receptor (CaR)-cystathionine γ-lyase (CSE)/hydrogen sulfide (H2S) pathway in I/R injury. Firstly, an I/R rat model with CSE knockout was constructed. Transthoracic echocardiography, TTC and HE staining were performed to determine the cardiac function of rats following I/R Injury, followed by TUNEL staining observation on apoptosis. Besides, with the attempt to better elucidate how CaR-CSE/H2S affects I/R, in-vitro culture of human coronary artery endothelial cells (HCAECs) was conducted with gadolinium chloride (GdCl3, a CaR agonist), H2O2, siRNA against CSE (siCSE), or W7 (a CaM inhibitor). The interaction between CSE and CaM was subsequently detected. Plasma oxidative stress indexes, H2S and CSE, and apoptosis-related proteins were all analyzed following cell apoptosis. We found that H2S elevation led to the improvement whereas CSE knockdown decreased cardiac function in rats with I/R injury. Moreover, oxidative stress injury in I/R rats with CSE knockout was aggravated, while the increased expression of H2S and CSE in the aortic tissues resulted in alleviated the oxidative stress injury. Moreover, increased H2S and CSE levels were found to inhibit cell apoptotic ability in the aortic tissues after I/R injury, thus attenuating oxidative stress injury, accompanied by inhibited expression of apoptosis-related proteins. In HCAECs following oxidative stress treatment, siCSE and CaM inhibitor were observed to reverse the protection of CaR agonist. Coimmunoprecipitation assay revealed the interaction between CSE and CaM. Taken together, all above-mentioned data provides evidence that activation of the CaR-CSE/H2S pathway may confer a potent protective effect in cardiac I/R injury.

Acquired substrate preference for GAB1 protein bestows transforming activity to ERBB2 kinase lung cancer mutants.

Activating mutations in the αC-ß4 loop of the ERBB2 kinase domain, such as ERBB2(YVMA) and ERBB2(G776VC), have been identified in human lung cancers and found to drive tumor formation. Here we observe that the docking protein GAB1 is hyper-phosphorylated in carcinomas from transgenic mice and in cell lines expressing these ERBB2 cancer mutants. Using dominant negative GAB1 mutants lacking canonical tyrosine residues for SHP2 and PI3K interactions or lentiviral shRNA that targets GAB1, we demonstrate that GAB1 phosphorylation is required for ERBB2 mutant-induced cell signaling, cell transformation, and tumorigenesis. An enzyme kinetic analysis comparing ERBB2(YVMA) to wild type using physiologically relevant peptide substrates reveals that ERBB2(YVMA) kinase adopts a striking preference for GAB1 phosphorylation sites as evidenced by ∼150-fold increases in the specificity constants (kcat/Km) for several GAB1 peptides, and this change in substrate selectivity was predominantly attributed to the peptide binding affinities as reflected by the apparent Km values. Furthermore, we demonstrate that ERBB2(YVMA) phosphorylates GAB1 protein ∼70-fold faster than wild type ERBB2 in vitro. Notably, the mutation does not significantly alter the Km for ATP or sensitivity to lapatinib, suggesting that, unlike EGFR lung cancer mutants, the ATP binding cleft of the kinase is not significantly changed. Taken together, our results indicate that the acquired substrate preference for GAB1 is critical for the ERBB2 mutant-induced oncogenesis.

Induction of ebolavirus cross-species immunity using retrovirus-like particles bearing the Ebola virus glycoprotein lacking the mucin-like domain.

BACKGROUND: The genus Ebolavirus includes five distinct viruses. Four of these viruses cause hemorrhagic fever in humans. Currently there are no licensed vaccines for any of them; however, several vaccines are under development. Ebola virus envelope glycoprotein (GP1,2) is highly immunogenic, but antibodies frequently arise against its least conserved mucin-like domain (MLD). We hypothesized that immunization with MLD-deleted GP1,2 (GPΔMLD) would induce cross-species immunity by making more conserved regions accessible to the immune system. METHODS: To test this hypothesis, mice were immunized with retrovirus-like particles (retroVLPs) bearing Ebola virus GPΔMLD, DNA plasmids (plasmo-retroVLP) that can produce such retroVLPs in vivo, or plasmo-retroVLP followed by retroVLPs. RESULTS: Cross-species neutralizing antibody and GP1,2-specific cellular immune responses were successfully induced. CONCLUSION: Our findings suggest that GPΔMLD presented through retroVLPs may provide a strategy for development of a vaccine against multiple ebolaviruses. Similar vaccination strategies may be adopted for other viruses whose envelope proteins contain highly variable regions that may mask more conserved domains from the immune system.

In vivo targeting of lentiviral vectors pseudotyped with the Tupaia paramyxovirus H glycoprotein bearing a cell-specific ligand.

Despite their exceptional capacity for transgene delivery ex vivo, lentiviral (LV) vectors have been slow to demonstrate clinical utility in the context of in vivo applications. Unresolved safety concerns related to broad LV vector tropism have limited LV vectors to ex vivo applications. Here, we report on a novel LV vector-pseudotyping strategy involving envelope glycoproteins of Tupaia paramyxovirus (TPMV) engineered to specifically target human cell-surface receptors. LV vectors pseudotyped with the TPMV hemagglutinin (H) protein bearing the interleukin (IL)-13 ligand in concert with the TPMV fusion (F) protein allowed efficient transduction of cells expressing the human IL-13 receptor alpha 2 (IL-13Rα2). Immunodeficient mice bearing orthotopically implanted human IL-13Rα2 expressing NCI-H1299 non-small cell lung cancer cells were injected intravenously with a single dose of LV vector pseudotyped with the TPMV H-IL-13 glycoprotein. Vector biodistribution was monitored using bioluminescence imaging of firefly luciferase transgene expression, revealing specific transduction of tumor tissue. A quantitative droplet digital PCR (ddPCR) analysis of lung tissue samples revealed a >15-fold increase in the tumor transduction in mice treated with LV vectors displaying IL-13 relative to those without IL-13. Our results show that TPMV envelope glycoproteins can be equipped with ligands to develop targeted LV vectors for in vivo applications.

Efficient trapping of HIV-1 envelope protein by hetero-oligomerization with an N-helix chimera.

BACKGROUND: The N-heptad repeat region of the HIV-1 Transmembrane Envelope protein is a trimerization domain that forms part of a "six helix bundle" crucial to Envelope-mediated membrane fusion. N-heptad repeat peptides have been used as extracellular reagents to inhibit virus fusion. RESULTS: When expressed intracellularly with wild-type HIV-1 Envelope protein, the N-heptad repeat domain efficiently hetero-oligomerized with Envelope and trapped it in the endoplasmic reticulum or early Golgi, as indicated by lack of transport to the cell surface, absent proteolytic processing, and aberrant glycosylation. CONCLUSION: Post-translational processing of HIV Envelope is very sensitive to an agent that binds to the N-heptad repeat during synthesis, suggesting that it might be possible to modify drugs that bind to this region to have transport-blocking properties.

Intravenous flurbiprofen axetil enhances analgesic effect of opioids in patients with refractory cancer pain by increasing plasma ß-endorphin.

BACKGROUND: The study aimed to investigate the analgesic effect of a combination of intravenous flurbiprofen axetil and opioids, and evaluate the relationship between refractory pain relief and plasma ß-endorphin levels in cancer patients. MATERIALS AND METHODS: A total of 120 cancer patients was randomly divided into two groups, 60 patients took orally morphine sulfate sustained-release tablets in group A, and another 60 patients receiving the combination treatment of intravenous flurbiprofen axetil and opioid drugs in group B. After 7 days, pain relief, quality of life improvement and side effects were evaluated. Furthermore, plasma ß-endorphin levels were measured by radioimmunoassay. RESULTS: With the combination treatment of intravenous intravenous flurbiprofen axetil and opioids, the total effective rate of pain relief rose to 91.4%, as compared to 82.1% when morphine sulfate sustained-release tablet was used alone. Compared with that of group A, the analgesic effect increased in group B (p=0.031). Moreover, satisfactory pain relief was associated with a significant increase in plasma ß-endorphin levels. After the treatment, plasma ß-endorphin level in group B was 62.4±13.5 pg/ml, which was higher than that in group A (45.8±11.2 pg/ml) (p<0.05). CONCLUSIONS: Our results suggest the combination of intravenous flurbiprofen axetil and opioids can enhance the analgesic effect of opioid drugs by increasing plasma ß-endorphin levels, which would offer a selected and reliable strategy for refractory cancer pain treatment.

Targeting of herpes simplex virus 1 thymidine kinase gene sequences into the OCT4 locus of human induced pluripotent stem cells.

The in vitro differentiation of human induced pluripotent stem cells (hiPSC) to generate specific types of cells is inefficient, and the remaining undifferentiated cells may form teratomas. This raises safety concerns for clinical applications of hiPSC-derived cellular products. To improve the safety of hiPSC, we attempted to site-specifically insert a herpes simplex virus 1 thymidine kinase (HSV1-TK) suicide gene at the endogenous OCT4 (POU5F1) locus of hiPSC. Since the endogenous OCT4 promoter is active in undifferentiated cells only, we speculated that the HSV1-TK suicide gene will be transcribed in undifferentiated cells only and that the remaining undifferentiated cells can be depleted by treating them with the prodrug ganciclovir (GCV) prior to transplantation. To insert the HSV1-TK gene at the OCT4 locus, we cotransfected hiPSC with a pair of plasmids encoding an OCT4-specific zinc finger nuclease (ZFN) and a donor plasmid harboring a promoter-less transgene cassette consisting of HSV1-TK and puromycin resistance gene sequences, flanked by OCT4 gene sequences. Puromycin resistant clones were established and characterized regarding their sensitivity to GCV and the site of integration of the HSV1-TK/puromycin resistance gene cassette. Of the nine puromycin-resistant iPSC clones analyzed, three contained the HSV1-TK transgene at the OCT4 locus, but they were not sensitive to GCV. The other six clones were GCV-sensitive, but the TK gene was located at off-target sites. These TK-expressing hiPSC clones remained GCV sensitive for up to 90 days, indicating that TK transgene expression was stable. Possible reasons for our failed attempt to selectively target the OCT4 locus are discussed.

Specific targeting of human interleukin (IL)-13 receptor α2-positive cells with lentiviral vectors displaying IL-13.

The ability to selectively and efficiently target transgene delivery to specific cell types in vitro and in vivo remains one of the formidable challenges in gene therapy. Lentiviral vectors have several advantages that make them attractive as gene delivery vehicles and their tropism can be altered through pseudotyping, allowing transgene delivery to specific populations of cells. The human interleukin-13 receptor α2 (IL-13Rα2) is uniquely overexpressed in many different human tumors, making it an attractive target for cancer therapy. In this study, we examined whether IL-13Rα2-positive tumor cells can be specifically targeted with lentiviral vector pseudotypes containing a truncated fusion (F) protein derived from measles virus (MV) and a tail-truncated and receptor-blind MV hemagglutinin (H) protein bearing IL-13 at the C terminus. The retargeted lentiviral vector efficiently transduced cells that express high levels of IL-13Rα2, but not cells expressing low levels of IL-13Rα2 in vitro. In vivo, it specifically targeted IL-13Rα2-positive glioma cell xenografts in immunodeficient mice in the context of subcutaneous and intracranial glioma models. Similar lentiviral vectors may be developed for targeting other tumors expressing specific cell surface receptors.

Development and characterization of rabbit and mouse antibodies against ebolavirus envelope glycoproteins.

Ebolaviruses are the etiologic agents of severe viral hemorrhagic fevers in primates, including humans, and could be misused for the development of biological weapons. The ability to rapidly detect and differentiate these viruses is therefore crucial. Antibodies that can detect reliably the ebolavirus surface envelope glycoprotein GP1,2 or a truncated variant that is secreted from infected cells (sGP) are required for advanced development of diagnostic assays such as sandwich ELISAs or Western blots (WB). We used a GP1,2 peptide conserved among Bundibugyo, Ebola, Reston, Sudan, and Taï Forest viruses and a mucin-like domain-deleted Sudan virus GP1,2 (SudanGPΔMuc) to immunize mice or rabbits, and developed a panel of antibodies that either cross-react or are virus-specific. These antibodies detected full-length GP1,2 and sGP in different assays such as ELISA, FACS, or WB. In addition, some of the antibodies were shown to have potential clinical relevance, as they detected ebolavirus-infected cells by immunofluorescence assay and gave a specific increase in signal by sandwich ELISA against sera from mouse-adapted Ebola virus-infected mice over uninfected mouse sera. Rabbit anti-SudanGPΔMuc polyclonal antibody neutralized gammaretroviral particles pseudotyped with Sudan virus GP1,2, but not particles pseudotyped with other ebolavirusGP1,2. Together, our results suggest that this panel of antibodies may prove useful for both in vitro analyses of ebolavirus GP1,2, as well as analysis of clinically relevant samples.

Phenylalanines at positions 88 and 159 of Ebolavirus envelope glycoprotein differentially impact envelope function.

The envelope glycoprotein (GP) of Ebolavirus (EBOV) mediates viral entry into host cells. Through mutagenesis, we and other groups reported that two phenylalanines at positions 88 and 159 of GP are critical for viral entry. However, it remains elusive which steps of viral entry are impaired by F88 or F159 mutations and how. In this study, we further characterized these two phenylalanines through mutagenesis and examined the impact on GP expression, function, and structure. Our data suggest that F159 plays an indirect role in viral entry by maintaining EBOV GP's overall structure. In contrast, we did not detect any evidence for conformational differences in GP with F88 mutations. The data suggest that F88 influences viral entry during a step after cathepsin processing, presumably impacting viral fusion.

Role of protein disulfide isomerase and other thiol-reactive proteins in HIV-1 envelope protein-mediated fusion.

Cell-surface protein disulfide isomerase (PDI) has been proposed to promote disulfide bond rearrangements in HIV-1 envelope protein (Env) that accompany Env-mediated fusion. We evaluated the role of PDI in ways that have not been previously tested by downregulating PDI with siRNA and by overexpressing wild-type or variant forms of PDI in transiently and stably transfected cells. These manipulations, as well as treatment with anti-PDI antibodies, had only small effects on infection or cell fusion mediated by NL4-3 or AD8 strains of HIV-1. However, the cell-surface thiol-reactive reagent 5, 5'-dithiobis(2-nitrobenzoic acid) (DTNB) had a much stronger inhibitory effect in our system, suggesting that cell-surface thiol-containing molecules other than PDI, acting alone or in concert, have a greater effect than PDI on HIV-1 Env-mediated fusion. We evaluated one such candidate, thioredoxin, a PDI family member reported to reduce a labile disulfide bond in CD4. We found that the ability of thioredoxin to reduce the disulfide bond in CD4 is enhanced in the presence of HIV-1 Env gp120 and that thioredoxin also reduces disulfide bonds in gp120 directly in the absence of CD4. We discuss the implications of these observations for identification of molecules involved in disulfide rearrangements in Env during fusion.

Stoichiometry of murine leukemia virus envelope protein-mediated fusion and its neutralization.

Envelope glycoproteins (Envs) of retroviruses form trimers that mediate fusion between viral and cellular membranes and are the targets for neutralizing antibodies. Understanding in detail how Env trimers mediate membrane fusion, and how antibodies interfere with this process, is a fundamental problem in biology with practical implications for the development of antiviral drugs and vaccines. We investigated the stoichiometry of Env-mediated fusion and its inhibition by antibody by inserting an epitope from human immunodeficiency virus for a neutralizing antibody (2F5) into the surface (SU) or transmembrane (TM) protein of murine leukemia virus Env, along with point mutations that abrogate SU and TM function but complement one another. We transfected various combinations of these Env genes and investigated Env-mediated cell fusion and its inhibition by 2F5 antibody. Our results showed that heterotrimers with one functional SU molecule were fusion competent in complementation experiments and that one antibody molecule was sufficient to inactivate the fusion function of a trimer when its epitope was in functional SU or TM. 2F5 antibody could also neutralize trimers with the 2F5 epitope in nonfunctional SU or TM, but less efficiently.

Effect of epitope position on neutralization by anti-human immunodeficiency virus monoclonal antibody 2F5.

The membrane-proximal region of the human immunodeficiency virus type 1 (HIV-1) transmembrane protein (TM) is critical for envelope (Env)-mediated membrane fusion and contains the target for broadly reactive neutralizing antibody 2F5. It has been proposed that 2F5 neutralization might involve interaction of its long, hydrophobic, complementarity-determining region (CDR) H3, with adjacent viral membrane. Using Moloney murine leukemia virus (MLV) as a tool, we examined the effect of epitope position on 2F5 neutralization. When the 2F5 epitope was inserted in the proline-rich region of MLV Env surface protein (SU), 2F5 blocked cell fusion and virus infection, whereas MLV with a hemagglutinin (HA) epitope at the same position was not neutralized by anti-HA, even though the antibodies bound their respective Envs on the surface of infected cells and viruses equally well. When the 2F5 epitope was inserted in the MLV Env TM at a position comparable to its natural position in HIV-1 TM, 2F5 antibody blocked Env-mediated cell fusion. Epitope position had subtle effects on neutralization by 2F5: the antibody concentration for 50% inhibition of cell fusion was more than 10-fold lower when the 2F5 epitope was in SU than in TM, and inhibition was less complete at high concentrations of antibody; we discuss possible explanations for these effects of epitope position. Since membrane proximity was not required for neutralization by 2F5 antibody, we speculate that the CDR H3 of 2F5 contributes to neutralization by destabilizing an adjacent protein rather than by inserting into an adjacent membrane.

Downregulation of protein disulfide isomerase inhibits infection by the mouse polyomavirus.

Early stages of infection by the mouse polyomavirus have been studied using HeLa cells stably expressing small interfering RNA to protein disulfide isomerase (PDI). Infectibility measured by nuclear T antigen expression was reduced commensurately with the degree of PDI downregulation. Infectibility was restored by transfection with a plasmid expressing PDI but not with a control expressing catalytically inactive enzyme. Deconvolution microscopy using fluorescently labeled virus and cellular markers showed that virus reaches the endoplasmic reticulum (ER) normally in cells with reduced PDI but subsequently fails to exit the ER. Simian virus 40 infection was not inhibited in PDI-downregulated cells. The results are discussed in terms of structural differences between the two viruses and current knowledge of virus disassembly in the ER.

Inhibition of murine leukemia virus envelope protein (env) processing by intracellular expression of the env N-terminal heptad repeat region.

A conserved structural motif in the envelope proteins of several viruses consists of an N-terminal, alpha-helical, trimerization domain and a C-terminal region that refolds during fusion to bind the N-helix trimer. Interaction between the N and C regions is believed to pull viral and target membranes together in a crucial step during membrane fusion. For several viruses with type I fusion proteins, C regions pack as alpha-helices in the grooves between N-helix monomers, and exogenously added N- and C-region peptides block fusion by inhibiting the formation of the six-helix bundle. For other viruses, including influenza virus and murine leukemia virus (MLV), there is no evidence for comparably extended C-region alpha-helices, although a short, non-alpha-helical interaction structure has been reported for influenza virus. We tested candidate N-helix and C-region peptides from MLV for their ability to inhibit cell fusion but found no inhibitory activity. In contrast, intracellular expression of the MLV N-helix inhibited fusion by efficiently blocking proteolytic processing and intracellular transport of the envelope protein. The results highlight another mechanism by which the N-helix peptides can inhibit fusion.

Photoactivation of quantum dot fluorescence following endocytosis.

We studied the fluorescence of quantum dots in cells. Coating quantum dots with cationic peptides caused them to be endocytosed and transported to lysosomes. After overnight incubation, their fluorescence apparently dimmed but became markedly "photoactivatable", increasing more than 3-fold within minutes on exposure to bright light, and decaying over hours in the dark. Photoactivation was greater in the presence of water than ethanol, and UV illumination compensated for lack of water during photoactivation. Dimming and photoactivation could affect the use of quantum dots as quantitative probes in vivo and lead to new uses, such as tracking molecular movement.

[Efficacy of NO regimen and NP regimen on advanced non-small cell lung cancer: a prospective randomized trial].

BACKGROUND & OBJECTIVE: Oxaliplatin (LOHP) is an effective drug in treatment of non-small cell lung cancer (NSCLC) with mild toxicities to gastrointestinal tract, kidney, and bone marrow. Cisplatin (DDP) plus vinorelbine (NVB) constitute the first-line regimen (NP regimen) for NSCLC. This study was to compare the short-term response, long-term outcome, and adverse events between advanced NSCLC patients received NO regimen (LOHP plus NVB) and NP regimen. METHODS: A total of 90 patients with advanced NSCLC were randomized into NO group (58 patients, 25 mg/m(2) of NVB, day 1 and day 8; 130 mg/m(2) of LOHP, day 1) and NP group (32 patients, 25 mg/m(2) of NVB, day 1 and day 8; 50 mg/m(2) of DDP, day 2 and day 3). The short-term response, long-term outcome, adverse events, and survival status of the 2 groups were observed. RESULTS: The response rates were 33.33% in NO group, and 35.48% in NP group, but no significant difference was detected between the 2 groups (P > 0.05). The clinical benefit response rate was significantly higher in NO group than in NP group (80.70% vs. 64.52%, P < 0.05). The median time to progression (TTP) was 17 weeks in NO group, and 15 weeks in NP group; the median time of remission was 21 weeks in NO group, and 19 weeks in NP group; the median survival time was 39 weeks in NO group, and 37 weeks in NP group; the 1-year survival rate was 37.93% in NO group, and 31.25% in NP group. No significant differences were detected between the 2 groups. The incidence rates of phlebitis and grade I-II peripheral neuritis were significantly higher in NO group than in NP group (77.59% vs. 50.00%, P<0.01; 43.10% vs. 15.63%, P<0.01). The incidence rate of grade III-IV nausea/vomiting was significantly higher in NP group than in NO group (31.25% vs. 3.45%, P<0.05). CONCLUSIONS: The efficacy of NO regimen on advanced NSCLC is similar to that of NP regimen, but the clinical benefit response rate is higher in NO group than in NP group. In short, NO regimen may be recommended as the first-line chemotherapy regimen for advanced NSCLC.

Role of a conserved amino-terminal sequence in the ecotropic MLV receptor mCAT1.

The amino-terminus of mCAT1 and homologous proteins is predicted to form a positively charged, amphipathic alpha helix on the cytoplasmic side of the plasma membrane. Peptides with similar sequence motifs often provide membrane anchors, protein-protein interaction domains, or intracellular transport-targeting signals. Deleting most of the cytoplasmic N-terminal sequence of mCAT1 led to reduced expression on the cell surface and accumulation in the endoplasmic reticulum but did not abrogate receptor function. Surprisingly, when the N-terminal 36 or 18 amino acids of mCAT1 were fused to green fluorescent protein (gfp), gfp accumulated almost exclusively in mitochondria. Mitochondrial targeting depended on arginines at positions 15 and 16 and was inhibitable by downstream transmembrane sequences. Although the full-length mCAT1 was not detected in mitochondria, the mitochondrial-targeting property of the N-terminal sequence fused to gfp is conserved in orthologous and paralogous proteins that diverged approximately 80 million years ago, suggesting a conserved biological function. We propose that the conserved N-terminal motif of CAT proteins provides a regulatable signal for transport to, or retention in, different cell membrane compartments.

Quantification of virus-envelope-mediated cell fusion using a tetracycline transcriptional transactivator: fusion does not correlate with syncytium formation.

Cell fusion occurs in many cellular processes and viral infections. We developed a new, quantitative cell fusion assay based on the tetracycline-controlled transactivator (tTA)-induced expression of a luciferase reporter gene. The assay is objective, sensitive, linear over 2-3 orders of magnitude, amenable to microtiter-plate format, and generalizable to study fusion mediated by a variety of genes. Applied to HIV and MLV, cell fusion paralleled virus entry in terms of co-receptor requirements, need for post-translational processing of envelope, and complementation of SU mutations by soluble receptor-binding domain. However, biochemically measured fusion did not correlate with syncytia detected by standard light microscopy. When the assay indicated cell fusion occurred but overt syncytia were not observed, confocal microscopy using fluorescent protein markers showed that fusion was limited mainly to pairs of cells. Such nonprogressive cell fusion suggests that post-translational processing of envelope may be altered in heterokaryons co-expressing envelope and receptor.

Inhibition of certain strains of HIV-1 by cell surface polyanions in the form of cholesterol-labeled oligonucleotides.

Cholesterol-labeled oligonucleotides were found several years ago to inhibit HIV-1 in tissue culture at nanomolar concentrations. We present evidence that this is mainly due to an electrostatic interaction between polyanionic oligonucleotide concentrated at the cell surface and a positively charged region in the V3 loop of the HIV-1 envelope protein. When added to tissue culture, cholesterol-labeled oligonucleotides became concentrated at the plasma membrane and potently inhibited virus entry and cell fusion mediated by the envelope protein of some X4 strains of HIV-1, but had little effect on fusion mediated by R5 strains of HIV-1, amphotropic MLV envelope protein, or VSV-G protein. Noncholesterol-labeled oligonucleotides did not bind to the cell surface or inhibit fusion. The pattern of susceptibility to cholesterol-labeled oligonucleotides among HIV-1 strains was the same as reported for nonmembrane-associating polyanions such as dextran sulfate, but the cholesterol-labeled oligonucleotides were effective at lower concentrations. Substitution of a basic 33 amino acid V3 loop sequence from the envelope protein of a resistant strain into a susceptible strain made the envelope protein resistant to inhibition. Inhibition by cholesterol-labeled oligonucleotides was abrogated by the polycation DEAE-dextran. Cholesterol-labeled oligonucleotides bound to nonraft regions of the plasma membrane and did not inhibit HIV virus binding to cells. Many infectious agents first associate with target cells via relatively nonspecific charge interactions; our data suggest that molecules that combine a membrane-targeting motif with multiple negative charges might be useful to modify these interactions.