Formation of HIV-1 envelope-hepatitis B core antigen hybrids with high affinity for CD4.

We have identified an acceptor site on HIV gp120, where foreign protein sequences can be inserted while retaining the native conformation of gp120. The resulting hybrids showed dual antigenicity, normal glycosylation, and high affinity binding of the CD4 receptor. This site allows insertion of highly immunogenic proteins such as core antigen of hepatitis B virus. By combining the immunogenicity of the carrier protein with the antigenicity of gp120, these hybrids may lead to modified HIV-1 antigens with enhanced immunogenicity.     

Differential induction of PPAR-gamma by luminal glutamine and iNOS by luminal arginine in the rodent postischemic small bowel

Using a rodent model of gut ischemia-reperfusion (I/R), we have previously shown that the induction of inducible nitric oxide synthase (iNOS) is harmful, whereas the induction of heme oxygenase 1 (HO-1) and peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is protective. In the present study, we hypothesized that the luminal nutrients arginine and glutamine differentially modulate these molecular events in the postischemic gut. Jejunal sacs were created in rats at laparotomy, filled with either 60 mM glutamine, arginine, or magnesium sulfate (osmotic control) followed by 60 min of superior mesenteric artery occlusion and 6 h of reperfusion, and compared with shams. The jejunum was harvested for histology or myeloperoxidase (MPO) activity (inflammation). Heat shock proteins and iNOS were quantitated by Western blot analysis and PPAR-gamma by DNA binding activity. In some experiments, rats were pretreated with the PPAR-gamma inhibitor G9662 or with the iNOS inhibitor N-[3(aminomethyl)benzyl]acetamidine (1400W). iNOS was significantly increased by arginine but not by glutamine following gut I/R and was associated with increased MPO activity and mucosal injury. On the other hand, PPAR-gamma was significantly increased by glutamine but decreased by arginine, whereas heat shock proteins were similarly increased in all experimental groups. The PPAR-gamma inhibitor G9662 abrogated the protective effects of glutamine, whereas the iNOS inhibitor 1400W attenuated the injurious effects of arginine. We concluded that luminal arginine and glutamine differentially modulate the molecular events that regulate injurious I/R-mediated gut inflammation and injury. The induction of PPAR-gamma by luminal glutamine is a novel protective mechanism, whereas luminal arginine appears harmful to the postischemic gut due to enhanced expression of iNOS.     

In situ release of coral mucus by <Emphasis Type="Italic">Acropora</Emphasis> and its influence on the heterotrophic bacteria

In situ mucus release by Acropora nobilis and degradation of mucus from A. nobilis and Acropora formosa, by heterotrophic bacteria were investigated at Bidong and Tioman Island, Malaysia. Mucus release rate for A. nobilis was on average 38.7 ± 35.2 mg C m⁻² h⁻¹, of which ca. 70% consisted of dissolved organic carbon (DOC) and 30% particulate organic carbon (POC). In the mucus degradation experiment, seawater-mucus mixtures were incubated and compared with control runs for 24 h. Bacterial abundance in the seawater-mucus mixture increased significantly and coincided with a decline in DOC concentration. In controls, bacteria and DOC did not significantly change. The coral mucus had a high content of inorganic phosphate. It is suggested that the coral mucus rich in DOC and phosphate can induce the high bacterial growth.     

Plio-Pleistocene history of West African Sudanian savanna and the phylogeography of the Praomys daltoni complex (Rodentia): the environment/geography/genetic interplay

Rodents of the Praomys daltoni complex are typical inhabitants of the Sudanian savanna ecosystem in western Africa and represent a suitable model for testing the effects of Quaternary climatic oscillations on extant genetic variation patterns. Phylogeographical analyses of mitochondrial DNA sequences (cytochrome b) across the distribution range of the complex revealed several well‐defined clades that do not support the division of the clade into the two species currently recognized on the basis of morphology, i.e. P. daltoni (Thomas, 1892) and Praomys derooi ( Van der Straeten & Verheyen 1978 ). The observed genetic structure fits the refuge hypothesis, suggesting that only a small number of populations repeatedly survived in distinct forest‐savanna mosaic blocks during the arid phases of the Pleistocene, and then expanded again during moister periods. West African rivers may also have contributed to genetic differentiation, especially by forming barriers after secondary contact of expanding populations. The combination of three types of genetic markers (mtDNA sequences, microsatellite loci, cytogenetic data) provides evidence for the presence of up to three lineages, which most probably represent distinct biological species. Furthermore, incongruence between nuclear and mtDNA markers in some individuals unambiguously points towards a past introgression event. Our results highlight the importance of combining different molecular markers for an accurate interpretation of genetic data.     

Testing metabolic ecology theory for allometric scaling of tree size, growth and mortality in tropical forests

The theory of metabolic ecology predicts specific relationships among tree stem diameter, biomass, height, growth and mortality. As demographic rates are important to estimates of carbon fluxes in forests, this theory might offer important insights into the global carbon budget, and deserves careful assessment. We assembled data from 10 old-growth tropical forests encompassing censuses of 367 ha and > 1.7 million trees to test the theory's predictions. We also developed a set of alternative predictions that retained some assumptions of metabolic ecology while also considering how availability of a key limiting resource, light, changes with tree size. Our results show that there are no universal scaling relationships of growth or mortality with size among trees in tropical forests. Observed patterns were consistent with our alternative model in the one site where we had the data necessary to evaluate it, and were inconsistent with the predictions of metabolic ecology in all forests.     

Correlation between EBV DNA and rearrangement and expression of Bcl-2 gene in aggressive non-Hodgkin's lymphoma

Previous in vitro studies have shown that bcl-2 expression can be induced by transfection of Epstein-Barr virus (EBV)-negative non-Hodgkin's lymphoma (NHL) cell lines with EBV. This induced expression of bcl-2 is important for the long survival of EBV-positive cells and might be a first step in tumorigenesis. The purpose of the present study was to investigate the possibility of similar correlation between bcl-2 expression and EBV infection in vivo in a cohort of patients with aggressive NHL, who were uniformly evaluated and treated with effective chemotherapy. The 42 patients included were 25-65 years old. None had prior treatment, discordant lymphoma, or human immunodeficiency virus seropositivity. Fresh biopsied samples were obtained and stored frozen for analysis of bcl-2 gene rearrangement major break point and of EBV DNA by PCR. Bcl-2 protein expression was estimated by Western blot, and enzyme immunoassay. With a median follow-up of 30 months, overall survival (OS) and disease-free survival (DFS) were measured to determine the prognostic significance of these variables. Analyzable DNA was present in all samples, 24% demonstrating bcl-2 rearrangement and 33% showing EBV DNA. Patients with bcl-2 gene rearrangement tended to have shorter DFS, and OS than patients without translocation. Bcl-2 protein expression was not correlated to gene rearrangement and had no significant influence on survival. The presence of EBV DNA in NHL had no prognostic significance but was correlated to bcl-2 expression. EBV-positive tumors showed higher bcl-2 expression than EBV-negative tumors did. Our results suggest a role of EBV infection in inducing bcl-2 expression as a survival factor for EBV-positive cells.     

NADPH oxidase restrains the matrix metalloproteinase activity of macrophages

Matrix metalloproteinases (MMPs) regulate numerous functions in normal and disease processes; thus, irreversibly blocking their activity is a key step in regulating MMP catalysis. We previously showed in vitro that oxidizing intermediates generated by phagocytes inactivate MMPs by modifying specific amino acids. To assess whether this mechanism operates in vivo, we focused on MMP-12, a macrophage-specific MMP known to mediate emphysema in mouse models. We found that mice lacking gp91(phox), a phagocyte-specific component of the NADPH oxidase, developed extensive, spontaneous emphysematous destruction of their peripheral air spaces, whereas mice deficient in both NADPH oxidase and MMP-12 were protected from spontaneous emphysema. Although gp91(phox)-null and wild-type macrophages produced equivalent levels of MMP-12 protein, the oxidant-deficient cells had greater MMP-12 activity than wild-type macrophages. These findings indicate that reactive intermediates provide a physiological mechanism to protect tissues from excessive macrophage-mediated damage during inflammation.     

Sulfhydryl-reactive heavy metals increase cell membrane K+ and Ca2+ transport in renal proximal tubule

Summary The cellular mechanisms by which nephrotoxic heavy metals injure the proximal tubule are incompletely defined. We used extracellular electrodes to measure the early effects of heavy metals and other sulfhydryl reagents on net K⁺ and Ca²⁺ transport and respiration (QO₂) of proximal tubule suspensions. Hg²⁺, Cu²⁺, and Au³⁺ (10^–4 m) each caused a rapid net K⁺ efflux and a delayed inhibition of QO₂. The Hg²⁺-induced net K⁺ release represented passive K⁺ transport and was not inhibited by barium, tetraethylammonium, or furosemide. Both Hg²⁺ and Ag⁺ promoted a net Ca²⁺ uptake that was nearly coincident with the onset of the net K⁺ efflux. A delayed inhibition of ouabainsensitive QO₂ and nystatin-stimulated QO₂, indicative of Na⁺, K⁺-ATPase inhibition, was observed after 30 sec of exposure to Hg²⁺. More prolonged treatment (2 min) of the tubules with Hg²⁺ resulted in a 40% reduction in the CCCP-uncoupled QO₂, indicating delayed injury to the mitochondria. The net K⁺ efflux was mimicked by the sulfhydryl reagents pCMBS and N-ethylmaleimide (10^–4 m) and prevented by dithiothreitol (DTT) or reduced glutathione (GSH) (10^–4 m). In addition, both DTT and GSH immediately reversed the Ag⁺-induced net Ca²⁺ uptake. Thus, sulfhydryl-reactive heavy metals cause rapid, dramatic changes in the membrane ionic permeability of the proximal tubule before disrupting Na⁺, K⁺-ATPase activity or mitochondrial function. These alterations appear to be the result of an interaction of the metal ions with sulfhydryl groups of cell membrane proteins responsible for the modulation of cation permeability.