Inhibition of HIV-1 Gag-membrane interactions by specific RNAs

HIV-1 particle assembly, which occurs at the plasma membrane (PM) of cells, is driven by the viral polyprotein Gag. Gag recognizes phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2], a PM-specific phospholipid, via the highly basic region (HBR) in its N-terminal matrix (MA) domain. The HBR is also known to bind to RNA. We have previously shown, using an in vitro liposome binding assay, that RNA inhibits Gag binding to membranes that lack PI(4,5)P2 If this RNA block is removed by RNase treatment, Gag can bind nonspecifically to other negatively charged membranes. In an effort to identify the RNA species that confer this inhibition of Gag membrane binding, we have tested the impact of purified RNAs on Gag interactions with negatively charged liposomes lacking PI(4,5)P2 We found that some tRNA species and RNAs containing stem-loop 1 of the psi region in the 5' untranslated region of the HIV-1 genome impose inhibition of Gag binding to membranes lacking PI(4,5)P2 In contrast, a specific subset of tRNAs, as well as an RNA sequence previously selected in vitro for MA binding, failed to suppress Gag-membrane interactions. Furthermore, switching the identity of charged residues in the HBR did not diminish the susceptibility of Gag-liposome binding for each of the RNAs tested, while deletion of most of the NC domain abrogates the inhibition of membrane binding mediated by the RNAs that are inhibitory to WT Gag-liposome binding. These results support a model in which NC facilitates binding of RNA to MA and thereby promotes RNA-based inhibition of Gag-membrane binding.

Triazole-polyene antagonism in experimental invasive pulmonary aspergillosis: in vitro and in vivo correlation

Combination antifungal therapy is increasingly used in the treatment of invasive aspergillosis. Whether the interaction between amphotericin B and triazoles is antagonistic against invasive aspergillosis is a controversial issue that is not likely to be resolved through a randomized clinical trial. Here, we found both in vitro and in vivo antagonism between liposomal amphotericin B and ravuconazole in simultaneous treatment of experimental invasive pulmonary aspergillosis in persistently neutropenic rabbits. Bliss independence-based drug-interaction modeling showed significant antagonism in vitro and in vivo, with the observed drug effects being 20%-69% lower than would be expected if the drugs were acting independently. These in vitro and in vivo findings of antagonism were consistent with the findings from Loewe additivity-based drug-interaction modeling. No pharmacokinetic interaction was found. The combination of a triazole and polyene may be antagonistic in the treatment of invasive pulmonary aspergillosis.

Regulation of the water channel aquaporin-1: isolation and reconstitution of the regulatory complex

Aquaporins (AQP) are involved in rapid and active gating of water across biological membranes. The molecular regulation of AQP is unknown. Here we report the isolation, identification and reconstitution of the regulatory complex of AQP-1. AQP-1 and Galphai3 have been implicated in GTP-induced gating of water in zymogen granules (ZG), the secretory vesicles in exocrine pancreas. In the present study, detergent-solubilized ZGs immunoprecipitated with monoclonal AQP-1 antibody, co-isolates AQP-1, PLA2, Galphai3, potassium channel IRK-8, and the chloride channel ClC-2. Exposure of ZGs to either the potassium channel blocker glyburide, or the PLA2 inhibitor ONO-RS-082, blocked GTP-induced ZG swelling. RBC known to possess AQP-1 at the plasma membrane, swell on exposure to the Galphai-agonist mastoparan, and respond similarly to ONO-RS-082 and glyburide, as ZGs. Liposomes reconstituted with the AQP-1 immunoisolated complex from solubilized ZG, also swell in response to GTP. Glyburide or ONO-RS-082 abolished the GTP effect. Immunoisolate-reconstituted planar lipid bilayers demonstrate conductance, which is sensitive to glyburide and an AQP-1 specific antibody. Our results demonstrate a Galphai3-PLA2 mediated pathway and potassium channel involvement in AQP-1 regulation.

Deoxyribonuclease I-like III is an inducible macrophage barrier to liposomal transfection

Extra- and intracellular nucleases are predicted to decrease the in vivo efficiency of liposomal transfection. DNASE1 (D1) has been proposed as the main nuclease barrier, yet liposome-complexed DNA and in vitro lipofection are generally immune to D1. In contrast, medium conditioned by the macrophage enzyme DNASE1-like 3 (DNASE1L3 or D3) erects a potent in vitro barrier to liposomal transfection. Although homologous to D1 over its amino-terminal sequence, D3 has a distinct, highly basic carboxy terminus, which resembles polylysine stretches often found in polycationic liposomal reagents. If this domain is truncated from D3, the resulting enzyme has more nuclease activity against naked DNA ("free DNA"-nuclease activity), yet does not block transfection. C-terminal fusion of this domain to D1 forms a chimeric protein able to block transfection. D3 can be immunodetected in both serum and macrophage lysates. Macrophage-conditioned medium contains both "free DNA"-nuclease activity and the ability to block transfection, and by zymogram only a 28-kDa DNASE, consistent by size with D3, is present. Thus, medium containing D3 confers to cells an in vivo shield to the nuclear acquisition of exogenous DNA. Modulation and further elucidation of this activity are likely to have importance for both gene therapy and autoimmune disorders.

Fucoidan-dependent conformational changes in annexin II tetramer

Fucoidan, a sulfated fucopolysaccharide, mimics the fucosylated glycans of glycoproteins and has therefore been used as a probe for investigating the role of membrane polysaccharides in cell-cell adhesion. In the present report we have characterized the interaction of fucoidan with the Ca(2+)- and phospholipid-binding protein annexin II tetramer (AIIt). AIIt bound to fucoidan with an apparent K(d) of 1.24 +/- 0.69 nM (mean +/- SD, n = 3) with a stoichiometry of 0.010 +/- 0.001 mol of fucoidan/mol of AIIt (mean +/- SD, n = 3). The binding of fucoidan to AIIt was Ca(2+)-independent. Furthermore, in the presence but not the absence of Ca(2+), the binding of fucoidan to AIIt caused a decrease in the alpha-helical content from 32% to 7%. A peptide corresponding to a region of the p36 subunit of AIIt, F(306)-S(313), which contains a Cardin-Weintraub consensus sequence for heparin binding, was shown to undergo a conformational change upon fucoidan binding. This suggests that heparin and fucoidan bound to this region of AIIt. The binding of fucoidan but not heparin by AIIt also inhibited the ability of AIIt to bind to and aggregate phospholipid liposomes. These results suggest that the binding of AIIt to the carbohydrate conjugates of certain membrane glycoproteins may have profound effects on the structure and biological activity of AIIt.

Semliki Forest virus mRNA capping enzyme requires association with anionic membrane phospholipids for activity

The replication complexes of all positive strand RNA viruses of eukaryotes are associated with membranes. In the case of Semliki Forest virus (SFV), the main determinant of membrane attachment seems to be the virus-encoded non-structural protein NSP1, the capping enzyme of the viral mRNAs, which has guanine-7-methyltransferase and guanylyltransferase activities. We show here that both enzymatic activities of SFV NSP1 are inactivated by detergents and reactivated by anionic phospholipids, especially phosphatidylserine. The region of NSP1 responsible for binding to membranes as well as to liposomes was mapped to a short segment, which is conserved in the large alphavirus-like superfamily of viruses. A synthetic peptide of 20 amino acids from the putative binding site competed with in vitro synthesized NSP1 for binding to liposomes containing phosphatidylserine. These findings suggest a molecular mechanism by which RNA virus replicases attach to intracellular membranes and why they depend on the membranous environment.