The RER-localized rotavirus intracellular receptor: a truncated purified soluble form is multivalent and binds virus particles

A budding event transfers the immature, single-shelled rotavirus particle (SSP) across the RER membrane prior to assembly of mature virions in the ER lumen. Budding is triggered by the interaction of the SSP with a viral receptor glycoprotein (NS28) which is located in the RER membrane. We have expressed the cytoplasmic domain of the NS28 receptor as a glutathione S-transferase fusion protein to generate a soluble polypeptide that in turn can be cleaved to yield a carboxy-terminal receptor domain. The soluble terminal domain (delta 1-85 NS28) has been purified to homogeneity and retains SSP-binding activity when immobilized on a solid matrix. Integral membrane status therefore is not an essential prerequisite for ligand binding. The Kd for the interaction between immobilized delta 1-85 NS28 and purified particles is 4.6 x 10(-11) M, a value indistinguishable from the value obtained for the full-length and membrane-anchored receptor. Cross-linking with the bifunctional reagent dimethylsuberimidate indicates that delta 1-85 NS28 is a tetramer. When delta 1-85 NS28 is added to a monodisperse suspension of purified virus, the particles aggregate, indicating that the receptor is multivalent. The rotavirus intracellular receptor therefore provides a model for the detailed analysis of the early events that trigger the budding of cytoplasmically located particles across cell membranes.

A nonnucleoside reverse transcriptase inhibitor active on human immunodeficiency virus type 1 isolates resistant to related inhibitors

Pyridinone derivatives are potent and specific inhibitors of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) and HIV-1 replication in cell culture. However, the potential clinical usefulness of these compounds as monotherapeutic agents may be limited by the selection of inhibitor-resistant viral variants. Resistance in cell culture is due primarily to mutational alterations at RT amino acid residues 103 and 181. A recombinant HIV-1 RT containing both of these mutations was used to screen a panel of pyridinone analogs for inhibitory activity. L-696,229 and L-697,661, pyridinones currently undergoing clinical evaluation, were more than 4,000-fold weaker against the mutant enzyme than against the wild-type enzyme. In contrast, one derivative of L-696,229, L-702,019 (3-[2-(4,7-dichlorobenzoxazol-2-yl)ethyl]-5-ethyl-6-methylpyrid in-2(1H)-thione), showed only three-fold different potencies against the two enzymes. L-702,019 was also a potent inhibitor of the replication of mutant HIV-1 containing the individual mutations at amino acid 103 or 181 as well as of clinical isolates resistant to L-697,661 and L-696,229. Isolation and analysis of resistant viral variants in cell culture showed that significant resistance to L-702,019 could be engendered only by multiple amino acid substitutions in RT. Accordingly, these studies demonstrated the potential of identifying second-generation specific HIV-1 RT inhibitors that can overcome the viral resistance selected by the first generation of inhibitors.

Regulatory volume increase after hypertonicity- or vasoactive-intestinal-peptide-induced cell-volume decrease in small-intestinal crypts is dependent on Na(+)-K(+)-2Cl- cotransport

The volume of intact crypts isolated from guinea-pig small intestine has been measured to assess the capacity of the cells to regulate their volume after hypertonic shock or vasoactive-intestinal-peptide (VIP)-induced shrinkage. Crypts exposed to anisotonic medium initially behave as perfect osmometers. Continued exposure to a hypertonic (400 mosmol/l) medium was followed by regulatory volume increase (RVI), which led to complete volume recovery in about 20 min. VIP produced a volume reduction, attributed to KCl loss through channels activated by the secretagogue, without any recovery during exposure to the polypeptide. Removal of VIP led to an increase of cellular volume towards control levels. This volume recovery after secretagogue-induced shrinkage is termed SVI. Both RVI and SVI were abolished by removal of Na+ or Cl- from the bathing solution, by addition of the loop diuretic bumetanide (1 microM), but not by addition of ethylisopropylamiloride (10 microM) or amiloride (1 mM). Cell shrinkage was also observed when tonicity was increased by addition of 100 mM NaCl or 200 mM D-mannitol, but RVI was seen only when NaCl was the added osmolyte. The ion dependence, pharmacological sensitivity and thermodynamic considerations of these effects are consistent with the operation of a Na(+)-K(+)-2Cl- cotransport mechanism activated by cell shrinkage and the secretagogue action of VIP.

Calbindin D28K expression in transfected mouse NIH3T3 cells

Calbindin D28K (formerly known as vitamin D-dependent calcium binding protein and referred to here as calbindin) is found in a wide variety of tissues, but only in certain cells within those tissues. Apart from its ability to bind calcium, nothing is known about its function in these cells. To investigate its role we have transfected the chick calbindin cDNA into mouse NIH3T3 fibroblasts and established a new cell line where calbindin is permanently expressed. Immunofluorescence studies show that calbindin is distributed throughout the cytoplasm, and treatment of the cells with cycloheximide shows that it has a relatively long half-life within the cell. Measurements of intracellular calcium concentration using Fura-2 suggest that the presence of calbindin within the cells does not affect the increase in intracellular calcium levels which occurs in response to serum stimulation or the rate at which these return to the basal level, but that it may act as a buffer for the entry of extracellular calcium.

A rapid bioassay for the determination of non-nucleoside HIV-1 reverse transcriptase inhibitor plasma levels

A rapid method for measuring pyridinone HIV-1 reverse transcriptase inhibitor plasma levels was necessary for identifying potential clinical candidates and for choosing a clinical formulation. Due to its sensitivity to the pyridinones, ability to tolerate extraneous material, and its capability for rapid, high through-put screening, the HIV-1 RT assay was developed into a bioassay for determining plasma levels of the pyridinones in Rhesus monkey plasma. With this assay, dose proportionality of L-697, 639 was established. Formulation studies using L-697, 639 indicated that the plasma levels achieved in Rhesus monkeys with the clinical formulation (peak levels = 3.9 microM at 30 min) fall between the levels achieved with polyethylene glycol 300 and hydroxypropyl methyl cellulose formulations (peak levels = 8.9 microM and 0.4 microM respectively, at 60 min). Two other pyridinones, L-696, 229 and L-697, 661, administered as the clinical formulation, had peak plasma levels of 1.6 microM (30 min) and 0.3 microM (60 min), respectively. In Rhesus monkeys, the bioavailabilities of these compounds (administered as the clinical formulation) ranged from 11 to 24% and their half-life values ranged from 24 to 120 min. The results of oral studies in Rhesus monkeys with these compounds were very similar to initial results of studies in humans.

Metabolism of a new HIV-1 reverse transcriptase inhibitor, 3-[2-(benzoxazol-2-yl)ethyl]-5-ethyl-6-methylpyridin-2(1H)-one (L-696,229), in rat and liver slices

L-696,229 is a potent and specific inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase and is currently undergoing clinical evaluation. In vivo metabolism in rats was investigated using an intravenous bolus dose of 5 mg/kg [3H]L-696,229. The amount of radioactivity eliminated in bile and urine over a period of 6 hr was 60 and 22%, respectively. Radiochromatographic analysis of the bile and urine showed that L-696,229 was metabolized rapidly and completely to several common metabolites. Sequential oxidation at the alpha-position of the 5-ethyl group to an acetyl moiety, aromatic hydroxylation of the benzoxazole group (position C4', C6', or C7'), and subsequent sulfate conjugation were the major metabolic pathways as determined by the application of enzymatic hydrolysis, FAB-MS, and 1H- and 13C-NMR spectroscopies. The in vitro metabolism of this 2-pyridinone derivative with rat liver slices resulted primarily in hydroxylation at the 6-methyl and 5-ethyl groups. The 6-hydroxymethyl- and 5-alpha-hydroxyethyl analogs were also inhibitors of HIV-1 reverse transcriptase.

Synthesis and evaluation of 2-pyridinone derivatives as HIV-1 specific reverse transcriptase inhibitors. 1. Phthalimidoalkyl and -alkylamino analogues

A potent (IC50 = 30 nM), specific nonnucleoside HIV-1 reverse transcriptase (RT) inhibitor 3-[N-(phthalimidomethyl)amino]-5-ethyl-6-methylpyridin-2(1H) -one (1), was discovered through an in vitro screening program. This compound did not inhibit (IC50 > 300 microns) other DNA and RNA polymerases, including HIV-2 RT and SIV-RT. Unfortunately, hydrolytic instability of this (aminomethyl)phthalimide precluded use as an antiviral agent. In the first paper of this series, preliminary development efforts are described which produced ethylphthalimide 20, a hydrolytically stable compound with reduced (100-fold) HIV-1 RT inhibitory activity and weak (CIC95 = 40 microM) antiviral activity in H9 cells. Structure-activity studies demonstrated the importance of the 5-ethyl, 6-methyl substituent pattern on the pyridinone ring and the need for a flexible two-atom linker between the pyridinone and phthalimide heterocycles. These leads, 1 and 20, provided a basis for the further development of this structural class of inhibitors from which several compounds, the subject of accompanying reports, were selected for clinical evaluation.

Membrane conductance and cell volume changes evoked by vasoactive intestinal polypeptide and carbachol in small intestinal crypts

We have used the perforated-patch whole-cell recording mode of the patch-clamp technique to monitor membrane potential and measured cell volume changes by image analysis, to determine the nature of the response to secretagogues of isolated whole guinea-pig small-intestinal crypts. Vasoactive intestinal polypeptide (VIP) produced a dose-dependent depolarisation (EC50 = 30 nM) and an increase in membrane conductance that could be potentiated by carbachol. Similar depolarisations were observed with forskolin. The depolarisation induced by 100 nM VIP was smaller when pipette [Cl-] was 60 mM than when it was 145 mM, suggesting an effect through Cl- conductance activation. Carbachol alone produced a hyperpolarisation (EC50 = 2 microM). The Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) produced a small hyperpolarization. When VIP was added in the presence of NPPB, the depolarisation was observed instead, consistent with the parallel activation of a K+ conductance. Both carbachol (100 microM) and VIP (100 nM) induced a 25%-30% shrinkage of crypts, which was maximal 8 min after addition of the secretagogue. The induced shrinkage was sustained in the continued presence of agonist and was reversed upon washout. Shrinkage induced by the agonists was abolished by increasing extracellular K+ from 6 mM to 20 mM and was inhibited partially in the presence of 100 microM anthracene-9-carboxylic acid in the bath. The decrease in volume induced by 100 nM VIP was totally abolished in the presence of 100 microM NPPB. The results are consistent with the view that both VIP and carbachol induce secretion in small-intestinal crypts.

Transient expression and mutational analysis of the rotavirus intracellular receptor: the C-terminal methionine residue is essential for ligand binding

Maturation of rotavirus involves an intracellular membrane budding event in which the single-shelled icosahedral particle interacts with a virus-encoded receptor glycoprotein, NS28, that is located in the rough endoplasmic reticulum membrane. The receptor is a tetramer and is oriented with the C-terminal 131 amino acids on the cytoplasmic side of the membrane (A.R. Bellamy and G.W. Both, Adv. Virus Res. 38:1-48, 1990). We have used the T7-vaccinia virus transient expression system to deliver mutant variants of the NS28 gene to CV1 cells in order to assess the effects of site-specific modifications on receptor function. Three types of mutant proteins have been constructed by altering the extreme C-terminal methionine, cysteine residues within the third hydrophobic domain, and internal residues located within the cytoplasmic portion of the receptor, respectively. Deletion or conservative substitution of the C-terminal methionine completely abolishes receptor activity. Substitution of cysteine residues has no effect on receptor activity or on the ability of the receptor to adopt its native oligomeric state. Internal deletions result only in a reduction in the level of binding. An N-terminally truncated form of the receptor, containing only the cytoplasmic domain, retains full receptor activity and can form membrane-associated tetramers.

L-696,229 specifically inhibits human immunodeficiency virus type 1 reverse transcriptase and possesses antiviral activity in vitro

L-696,229 (3-[2-(benzoxazol-2-yl)ethyl]-5-ethyl-6-methyl-pyridin-2 (1H)-one) is a specific inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) activity that possesses antiviral activity in cell culture (W.S. Saari, J.M. Hoffman, J.S. Wai, T.E. Fisher, C.S. Rooney, A.M. Smith, C.M. Thomas, M. E. Goldman, J. A. O'Brien, J. H. Nunberg, J. C. Quintero, W. A. Schleif, E. A. Emini, and P. S. Anderson, J. Med. Chem. 34:2922-2925, 1991). In the present study, the RT-inhibitory activity and antiviral properties were characterized in detail. The inhibition of RT activity was template-primer dependent with 50% inhibitory concentrations of 0.018 to 0.50 microM and was noncompetitive with respect to deoxynucleoside triphosphates. L-696,229 inhibited RT activity in a mutually exclusive manner with respect to either phosphonoformate or azidothymidine triphosphate and was a weak partial inhibitor of the RNase H activity associated with HIV-1 RT. The compound did not significantly inhibit other retroviral or cellular polymerases at 300 microM.L-696,229 inhibited the spread of HIV-1 infection in cell cultures with all cell types and viral isolates tested, including human peripheral blood mononuclear cells and a virus isolate resistant to azidothymidine.

Glucocorticoid effects on rabbit fetal lung maturation in vivo: an ultrastructural morphometric study

Maternal administration of glucocorticoids is known to stimulate fetal lung maturation. In the present study, we used microscopy and stereology to evaluate the morphological effects of maternal glucocorticoid treatment on rabbit fetal lung tissue. Betamethasone was administered to pregnant rabbits on days 25 and 26 of gestation at a dose of 0.2 mg/kg body weight. The animals were sacrificed on day 27 of gestation. Glucocorticoid treatment significantly increased the presumptive airspace in the fetal lung tissue but did not alter the relative proportion of epithelium, connective tissue, or vasculature in the tissue. In addition, glucocorticoid treatment significantly increased the proportion of type II cells in the prealveolar epithelium, increased the rate of phosphatidylcholine synthesis, and increased the content of the major surfactant-associated protein, SP-A, in the fetal lung tissue. We could detect no effect of betamethasone on lamellar body cross-sectional area, numerical density, or volume density within fetal lung type II cells. Glucocorticoid treatment of the pregnant doe caused a decrease in the volume density of intracellular glycogen and an increase in the volume density of mitochondria in fetal lung type II cells. Betamethasone treatment did not alter the distance between fetal lung epithelial cells and subadjacent connective tissue cells. However, glucocorticoid treatment increased the number of connective tissue foot processes that pierced the epithelial basal lamina. Thus, glucocorticoid treatment of the pregnant doe results in structural changes in the fetal lung tissue, an acceleration of some aspects of type II cell differentiation, and a concomitant increase in epithelial-mesenchymal interactions.

Regulatory volume decrease in small intestinal crypts is inhibited by K+ and Cl- channel blockers

Total crypt volume has been estimated by analysis of photographic images of intact viable crypts isolated from guinea-pig small intestine. Exposing these crypts to a hypotonic medium, led to transient swelling followed by regulatory volume decrease (RVD) in 12-20 min. RVD was blocked by inhibitors of K+ and Cl- conductance, suggesting that it occurs by activation of K+ and Cl- permeability pathways and loss of these ions.

Viral resistance to human immunodeficiency virus type 1-specific pyridinone reverse transcriptase inhibitors

Human immunodeficiency virus type 1 (HIV-1)-specific pyridinone reverse transcriptase (RT) inhibitors prevent HIV-1 replication in cell culture (M. E. Goldman, J. H. Nunberg, J. A. O'Brien, J.C. Quintero, W. A. Schleif, K. F. Freund, S. L. Gaul, W. S. Saari, J. S. Wai, J. M. Hoffman, P. S. Anderson, D. J. Hupe, E. A. Emini, and A. M. Stern, Proc. Natl. Acad. Sci. USA 88:6863-6867, 1991). In contrast to nucleoside analog inhibitors, such as AZT, which need to be converted to triphosphates by host cells, these compounds act directly to inhibit RT via a mechanism which is noncompetitive with respect to deoxynucleoside triphosphates. As one approach to define the mechanism of action of pyridinone inhibitors, we isolated resistant mutants of HIV-1 in cell culture. Serial passage in the presence of inhibitor yielded virus which was 1,000-fold resistant to compounds of this class. Bacterially expressed RTs molecularly cloned from resistant viruses were also resistant. The resistant RT genes encoded two amino acid changes, K-103 to N and Y-181 to C, each of which contributed partial resistance. The mutation at amino acid 181 lies adjacent to the conserved YG/MDD motif found in most DNA and RNA polymerases. The mutation at amino acid 103 lies within a region of RT which may be involved in PPi binding. The resistant viruses, although sensitive to nucleoside analogs, were cross-resistant to the structurally unrelated RT inhibitors TIBO R82150 (R. Pauwels, K. Andries, J. Desmyter, D. Schols, M. J. Kukla, H. J. Breslin, A. Raeymaeckers, J. Van Gelder, R. Woestenborghs, J. Heykanti, K. Schellekens, M. A. C. Janssen, E. De Clercq, and P. A. J. Janssen, Nature [London] 343:470-474, 1990) and BI-RG-587 (V. J. Merluzzi, K. D. Hargrave, M. Labadia, K. Grozinger, M. Skoog, J. C. Wu, C.-K. Shih, K. Eckner, S. Hattox, J. Adams, A. S. Rosenthal, R. Faanes, R. J. Eckner, R. A. Koup, and J. L. Sullivan, Science 250:1411-1413, 1990). Thus, these nonnucleoside analog inhibitors may share a common binding site on RT and may all make up a single pharmacologic class of RT inhibitor. This observation may have important implications for the clinical development of these compounds.

An ectopic pregnancy in the upper retroperitoneum following in vitro fertilization and embryo transfer

Thirty-seven days after successful embryo transfer, a chorionic vesicle was recovered from the upper abdominal retroperitoneal space in a patient presenting with an acute life-threatening hemorrhage. This is the first case report of a retroperitoneal ectopic pregnancy which, although uncommon, is a potentially fatal complication of in vitro fertilization-embryo transfer.

Primary cultures of guinea-pig gall-bladder epithelial cells suitable for patch-clamp studies

Cells derived from explants of guinea-pig gall-bladder maintained in culture for up to 14 days, exhibit a network of cytoskeletal filaments that are labelled by an anti-cytokeratin antibody, but not by an anti-desmin antibody, suggesting that they are of epithelial origin. These cells proved suitable for patch-clamp studies and by using this method channels selective for K+ and Cl- were observed.

Pyridinone derivatives: specific human immunodeficiency virus type 1 reverse transcriptase inhibitors with antiviral activity

Derivatives of pyridinones were found to inhibit human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) activity and prevent the spread of HIV-1 infection in cell culture without an appreciable effect on other retroviral or cellular polymerases. 3-[( (4,7-Dimethyl-1,3-benzoxazol-2-yl) methyl]amino ]-5-ethyl-6-methylpyridin-2(1H)-one (L-697,639) and 3-[[ (4,7-dichloro-1,3-benzoxazol-2-yl) methyl]amino]-5-ethyl-6-methylpyridin-2(1H)-one (L-697,661), two compounds within this series, had HIV-1 RT IC50 values in the range of 20-800 nM, depending upon the template-primer used. The most potent inhibition was obtained with rC.dG and dA.dT as template--primers. With rC.dG, reversible slow-binding non-competitive inhibition was observed. [3H]L-697,639 bound preferentially to enzyme-template-primer complexes. This binding was magnesium-dependent and saturable with a stoichiometry of 1 mol of [3H]L-697,639 per mol of RT heterodimer. Displacement of [3H]L-697,639 was seen with phosphonoformate. In human T-lymphoid-cell culture, L-697,639 and L-697,661 inhibited the spread of HIV-1 infection by at least 95% at concentrations of 12-200 nM. Synergism between 3'-azido-3'-deoxythymidine or dideoxyinosine and either of these compounds was also demonstrated in cell culture. Based upon their specificity for HIV-1 RT activity, template-primer dependence on potency and ability to displace [3H]L-697,639; a tetrahydroimidazo [4,5,1-jk] [1,4]-benzodiazepin-2(1H)-thione derivative R82150 and the dipyridodiazepinone BI-RG-587 appear to inhibit RT activity by the same mechanism as the pyridinones.

Lung cancer at Groote Schuur Hospital--a local perspective

Over a 1-year period (1 January 1987-31 December 1987) 401 patients at Groote Schuur Hospital with newly diagnosed lung cancer were evaluated prospectively. The mean age of the patients was 59 years (range 31-87 years); 251 were coloured (62%), 100 white (25%), 47 black (12%) and 3 Asian (1%), and 280 were men (70%). Smokers numbered 378 (95%). The median delay between the onset of symptoms and presentation was 13 weeks (range 0-65 weeks). The commonest cell type was squamous--127 patients (34%), followed by adenocarcinoma 84 (23%), undifferentiated 78 (21%), small-cell 48 (13%), large-cell 29 (8%) and other types in 5 (1%). At the time of diagnosis 228 patients (57%) had evidence of metastases. Forty-six patients (11%) underwent surgery, 46 (11%) received chemotherapy, 141 (35%) radiotherapy and 168 (42%) symptomatic treatment as initial management. The overall 1- and 2-year survival rates were 18% and 8% respectively.

Uptake of the 35 kDa major surfactant apoprotein (SP-A) by neonatal rabbit lung tissue

Secreted surfactant is made up of both phospholipid and protein components. Therefore, we investigated the possibility that surfactant apoproteins might be taken up by the alveolar type II cell in a manner similar to the uptake of surfactant phosphatidylcholines. Day 2 neonatal rabbits were infused via the trachea with a solution of carrier surfactant and 125I-labelled surfactant apoprotein (SP-A, Mr approx. 35,000). Most of the 125I-SP-A remained within the alveolus; however, a fraction of the 125I-SP-A was taken up by the lung tissue from the alveolus in a time-dependent manner. The small amount of radiolabeled material detected in blood, liver or kidney tissues of 125I-SP-A-infused animals was not trichloroacetic acid (TCA) precipitable, i.e., probably represented degradation products. In contrast, the proportion of TCA-precipitable 125I-SP-A in lung tissue or lavage samples did not change as function of time after tracheal administration. Two-dimensional gel electrophoresis of the 125I-SP-A present in the lavage samples or associated with lung tissue was used to show that a small proportion of the 125I-SP-A was partially degraded in the lung tissue and alveolus. These data are suggestive that the SP-A is taken up by lung tissue, perhaps in a manner similar to the uptake of surfactant phospholipid by the alveolar type II cell.

The concentration of the 35-kDa surfactant apoprotein in amniotic fluid from normal and diabetic pregnancies

A specific, enzyme-linked immunoabsorbent assay was used to determine the concentration of the 35,000 mol wt surfactant apoprotein (SP-A) in samples of amniotic fluid obtained from nondiabetic (n = 358) and diabetic (n = 29) women. The enzyme-linked immunoabsorbent assay was performed with rabbit antibodies directed against SP-A present in lavage fluid from a patient with alveolar proteinosis. Amniotic fluid SP-A concentrations increased as a function of gestational age, from less than 3 micrograms/ml at 30-31 wk to 24 micrograms/ml at 40-41 wk, and were positively correlated with the lecithin to sphingomyelin ratio (p less than 0.01). SP-A concentrations also increased as a function of gestational age in shake test positive samples (p less than 0.05), but were unchanged in shake test-negative samples. There was no difference in the surfactant apoprotein concentration of male compared with female fetuses at any gestational age. In amniotic fluid obtained from 20 diabetic women, SP-A levels were significantly less than in nondiabetic pregnancies that were matched for gestational age and sex of the fetus (p less than 0.05). The SP-A concentrations in amniotic fluids obtained from nine women who were diabetic and hypertensive and from 10 hypertensive women were not different from matched controls. The relationships described above were valid whether the SP-A concentration was expressed per mg protein or per ml amniotic fluid. These data are suggestive that the concentration of amniotic fluid SP-A is decreased in diabetic pregnancies.