Human B cell lines can be triggered to secrete an interleukin 2-like molecule

To determine whether human B cells can be triggered to secrete interleukin 2 (IL-2), 19 tumor cell lines derived from patients with undifferentiated lymphomas of Burkitt's and non-Burkitt's types and 6 normal lymphoblastoid cell lines were tested. Cells were grown in the presence or absence of the new tumor promoter teleocidin, and culture supernatants were assayed for IL-2 activity using the standard CTLL-2 assay. Teleocidin (10 ng/ml) triggered IL-2 secretion in 7/8 (87%) EBV-negative lymphoma cell lines of American origin and in 6/6 (100%) normal lymphoblastoid cell lines, but in only 1/6 (16%) EBV-positive tumor cell lines of American origin. Teleocidin had no effect on 5/5 (0%) African Burkitt's cell lines. IL-2 secretion was not detected in control supernatants. IL-2 secretion correlated with the induction of IgM secretion and was linked to both EBV status and karyotype. The following similarities in the functional biological characteristics of T cell and B cell IL-2 suggest that B cell IL-2 is not a factor which mimics IL-2 activity in the CTLL-2 assay: (i) neutralization of IL-2 by anti-IL-2 monoclonal antibody (DMS-1); (ii) elution of IL-2 following its adsorption to CTLL-2 cells; (iii) determination of the MW of IL-2 by SDS-PAGE and Western blot analysis; and (iv) ability of B cell IL-2 to support T cell proliferation and blocking of this activity by anti-tac monoclonal antibody. cDNA probes for T cell IL-2, however, did not detect IL-2 mRNA in B cells. The cell lines were also found to constitutively express IL-2 receptors detected by anti-tac monoclonal antibody, and to secrete soluble IL-2 receptors measured by ELISA. Our results imply that under certain circumstances, B cells can be triggered to secrete IL-2 or an IL-2-like molecule and thus influence T cell activation and proliferation.     

An endogenous 'hypertensive factor' enhances the voltage-dependent calcium current

The effects of an immunoaffinity-purified putative endogenous hypertensive factor (HF) on voltage-dependent calcium current in frog cardiac myocytes were assessed. In 9 out of 10 cells, HF reversibly increased the peak amplitude of the calcium current. HF increased peak calcium current density at -5 mV from a control level of 1.8 +/- 1.3 pA/pF (mean +/- SD) to 4.4 +/- 2.0 pA/pF. HF shifted the peak of the calcium current-voltage relationship in the hyperpolarizing direction. HF shifted the voltage dependence of the inactivation of the calcium current to more negative potentials with prepulses from -80 to 0 mV, but the inactivation was not affected with prepulses more positive than 0 mV. Modulation of the voltage-dependent calcium current by HF may be the mechanism underlying its pressor effects.     

The surface potential on the purple membrane measured using a modified bacteriorhodopsin chromophore as the spectroscopic probe

The surface potential of the purple membrane was measured by a novel method by using an artificial bacteriorhodopsin whose chromophore was 13-CF₃ retinal instead of retinal. When attached to the apoprotein by a Schiff base, the intrinsic pK of the 13-CF₃ chromophore is around 7.3. The apparent p_K of this pigment depends on the surface potential and thus on the electrolyte concentration. This allowed us to determine the surface charge density using the Gouy-Chapman equation. The surface charge density was found to be −1.65 ± 0.15 × 10⁻³ electronic charges per Ų or about 2 negative charges/bacteriorhodopsin. This large value for the surface potential probably explains both part of the strong apparent association of divalent cations with the membrane and the effect of low salt concentrations on light-induced proton release from the purple membrane.     

Characterization of third chromosome dominant alpha-methyl dopa resistant mutants (Tcr) and their interactions with l(2)amd alpha-methyl dopa hypersensitive alleles in Drosophila melanogaster

In Drosophila melanogaster two alleles at the Third chromosome resistance locus (Tcr; 3-39-6) were isolated in a screen of EMS mutagenized third chromosomes for dominant resistance to dietary alpha-methyl dopa, alpha-MD, a structural analogue of DOPA. Both alleles of Tcr are recessive lethals exhibiting partial complementation. Almost half (48.3%) of the Tcr40/Tcr45 heterozygotes die as embryos but some survive past adult eclosion. Both the embryonic lethal phenotype and the adult phenotype suggest that Tcr is involved in cuticle synthesis. Tcr mutants suppress the lethality of partially complementing alleles at the alpha-MD hypersensitive locus, l(2)amd. The viability of Tcr40/Tcr45, however, is not increased by the presence of a l(2)amd allele. The possibility that the Tcr and l(2)amd mutations reveal a catecholamine metabolic pathway involved in cuticle structure is discussed.     

The order of loci in the pericentric region of chromosome 17, based on evidence from physical and genetic breakpoints.

Previous genetic analyses of chromosome 17 markers and NF1 (Fain et al. 1987) were extended in an attempt to order marker loci that map physically to 17cen----17q12. Three additional markers (HHH202, CRI-L581, and CRI-L946) were included in the analyses. Recombinants within the cluster of seven unordered marker loci were identified by pairwise analyses for each family and by examining the within-sibship segregation patterns for different markers. Changes in the segregation pattern for different loci define genetic breakpoints. Given that interference is complete in the region, markers with the same segregation pattern lie on one side of the breakpoint, while markers with different segregation patterns lie on opposite sides of the breakpoint. If the order of boundary markers is known, markers on each side of a breakpoint can be oriented in relation to the centromere. The order cen-(HHH202/NF1)-(EW207)-(EW203/CRI-L581)- (CRI-L946)-(HOX-2/NGFR)-qter was inferred by combining information from physical breakpoints in a panel of mouse/human hybrids and information from genetic breakpoints found in 16 NF1 families.     

Generation of nitric oxide by human neutrophils

Human neutrophils were evaluated for their ability to generate nitric oxide. Neutrophils incubated with superoxide dismutase at 37 degrees C produce nitrite anion at a rate of 1.8 nmols/2 x 10(6) cells/30 min, providing indirect evidence of nitric oxide production. Incubation of the neutrophils with concentrations of serum-opsonized zymosan, N-formyl-methionyl-leucyl-phenylalanine, or phorbol myristate acetate sufficient to stimulate the respiratory burst and lysosomal enzyme release caused no additional nitrite anion production. Glass wool-adherent neutrophils exhibited a similar dissociation of nitrite anion production from the respiratory burst and lysosomal enzyme release. Direct evidence for nitric oxide production was also obtained using nitric oxide-specific chemiluminescence. These results demonstrate that human neutrophils are capable of generating nitric oxide.     

Lysophosphatidylcholine metabolism to 1,2-diacylglycerol in lymphoblasts: involvement of a phosphatidylcholine-hydrolyzing phospholipase C

We have previously described the chemoattraction of lymphoblasts by lysophosphatidylcholine [Hoffman, R. D., et al. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 3285-3289]. In studying the mechanism of chemoattraction it was found that lysophosphatidylcholine was metabolized to 1,2-diacylglycerol by the lymphoblastic cell line 6C3HED. One route of metabolism involves the acylation of lysophosphatidylcholine to phosphatidylcholine with subsequent hydrolysis to 1,2-diacylglycerol and phosphocholine by the action of phospholipase C. The increase in cellular 1,2-diacylglycerol was established by metabolic experiments using [14C]glycerol-labeled lysophosphatidylcholine and by mass measurements of 1,2-diacylglycerol. The presence of a phosphatidylcholine-hydrolyzing phospholipase C was confirmed in 6C3HED cell homogenates. In intact cells, lysophosphatidylcholine induced a pattern of protein phosphorylation similar to those of 1,2-dioctanoylglycerol and phorbol 12-myristate 13-acetate, two known activators of protein kinase C. This pathway of lysophosphatidylcholine metabolism, which involves a phosphatidylcholine-hydrolyzing phospholipase C, may be important in the activation of protein kinase C independent of inositol phospholipid hydrolysis.     

Carbonyldiphosphonate, a selective inhibitor of mammalian DNA polymerase delta

Twenty-three pyrophosphate analogues were screened as inhibitors of proliferating cell nuclear antigen independent DNA polymerase delta (pol delta) derived from calf thymus. Carbonyldiphosphonate (COMDP), also known as alpha-oxomethylenediphosphonate, inhibited pol delta with a potency (Ki = 1.8 microM) 20 times greater than that displayed for DNA polymerase alpha (pol alpha) derived from the same tissue. Characterization of the mechanism of inhibition of pol delta indicated that COMDP competed with the dNTP specified by the template and was not competitive with the template-primer. In the case of pol alpha, COMDP did not compete with either the dNTP or the polynucleotide substrate. COMDP inhibited the 3'----5' exonuclease activity of pol delta weakly, displaying an IC50 greater than 1 mM.     

Assignment of the proton NMR spectrum of reduced and oxidized thioredoxin: sequence-specific assignments, secondary structure, and global fold

Complete proton assignments are reported for the 1H nuclear magnetic resonance (NMR) spectrum of Escherichia coli thioredoxin in the oxidized (with active-site disulfide bridge) and reduced (with two sulfhydryl groups) states. The assignments were obtained by using an integrated assignment strategy in which spin systems were identified from a combination of relayed and multiple quantum NMR techniques prior to sequential assignment. Elements of secondary structure were identified in each protein from characteristic nuclear Overhauser effects (NOE), coupling constants, and slowly exchanging amide protons. In both oxidized and reduced thioredoxin, approximately 33% of the 108 amino acid residues participate in a beta-sheet containing four major strands (three antiparallel and one parallel). A further short beta-strand is connected in a parallel fashion at the N-terminal end of the sheet. Two of the antiparallel beta-strands are connected by a 7-residue beta-bulge loop. Three helical segments, also containing approximately 33% of the amino acid residues, are well-defined in both oxidized and reduced thioredoxin. The remaining third of the molecule apparently consists of reverse turns and loops with little defined secondary structure. The global folds of oxidized and reduced thioredoxin are shown to be essentially identical. Both NOE connectivities and chemical shift values for the two proteins are very similar, except in the immediate vicinity of the active site where significant variations in the chemical shift indicate subtle conformational changes. While the overall fold of oxidized thioredoxin is the same in solution and in the crystalline state, some small differences in local conformation are apparent.