Trp-Lys-Tyr-Met-Val-D-Met stimulates superoxide generation and killing of Staphylococcus aureus via phospholipase D activation in human monocytes

Among the phagocytic leukocytes, monocytes have the important role of clearing out parasitic microorganisms. They accomplish this through production of toxic metabolites of oxygen. Trp-Lys-Tyr-Met-Val-D-Met (WKYMVm), a peptide that stimulates phosphoinositide (PI) hydrolysis in human leukocytes, including monocytes, binds to a unique cell surface receptor and stimulates superoxide generation, killing of Staphylococcus aureus, and activation of phospholipase D (PLD) in human monocytes. Preincubation of the cells with a PI-specific phospholipase C (PLC) inhibitor (U-73122), protein kinase C inhibitor (GF109203X), or intracellular Ca2+ chelator (BAPTA/AM) before the peptide stimulus totally inhibits the peptide-induced PLD activation and superoxide generation. On the other hand, tyrosine kinase inhibitor genistein only partially inhibits the peptide-induced processes. The peptide-induced bacteria killing activity shares regulatory mechanisms for PLD activation with the superoxide generation, which is inhibited in the presence of 1-butanol. We suggest that the peptide stimulates PLD downstream of PLC activation and PLD activation in turn is essential for the peptide-induced immunological functions such as the superoxide generation and killing of bacteria by human monocytes.

Distribution of the receptor for a novel peptide stimulating phosphoinositide hydrolysis in human leukocytes

OBJECTIVES

Previously we reported that a synthetic peptide, WKYMVm, stimulates phosphoinositide (PI) hydrolysis in several hematopoietic cell lines and human neutrophils. In addition, the peptide induces superoxide generation in human neutrophils. The biochemical stimulation appeared to be mediated by specific receptors on leukocytes. In this report we try to find whether the specific receptor(s) exists on specific types of cells in human leukocytes.

DESIGN AND METHODS

To study distribution of the peptide-specific receptors, we prepared a probe, biotin-labeled WKYMVm, and analyzed distribution of the peptide receptor using a biochemical study, cytochemical staining, and flow cytometric analysis.

RESULTS

The peptide-specific receptors are expressed in several human leukocytes including granulocytes, monocytes, and B-lymphocytes but not T-lymphocytes and erythrocytes.

CONCLUSIONS

These data suggest that the receptors for the peptide restricted to certain types of leukocytes and this specificity is probably related to the specific functions of the stimulated leukocytes.

Characterization of protein interaction among subunits of protein kinase CKII in vivo and in vitro

Protein kinase CKII (CKII) is a ubiquitous protein serine/threonine kinase. CKII usually exists in tetrameric complexes composed of two catalytic (CKII alpha and/or CKII alpha') and two regulatory (CKII beta) subunits. In the present study, using a combined in vivo and in vitro approach, we have investigated the role of CKII subunits in the formation of the tetrameric structure of CKII and the formation of the polymeric structure of CKII holoenzyme. Our in vivo experiments show that CKII beta interacts with either another CKII beta or CKII alpha and that CKII alpha does not interact with another CKII alpha (or CKII alpha'). Our in vitro experiments also show that CKII beta is able to associate with both CKII alpha and another CKII beta and that CKII alpha exists as a monomeric form in solution. These data indicate that CKII beta mediates the formation of a tetramer by both the dimerization of CKII beta and the interaction of CKII beta with CKII alpha. The results of this study also suggest that CKII beta may be involved in the formation of the polymeric structure of the CKII holoenzyme.

Activation of phospholipase C-gamma by phosphatidylinositol 3,4,5-trisphosphate

Signal transduction across cell membranes often involves the activation of both phosphatidylinositol (PI)-specific phospholipase C (PLC) and phosphoinositide 3-kinase (PI 3-kinase). Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), a substrate for both enzymes, is converted to phosphatidylinositol 3,4, 5-trisphosphate (PI(3,4,5)P3) by the action of PI 3-kinase. Here, we show that PI(3,4,5)P3 activates purified PLC-gamma isozymes by interacting with their Src homology 2 domains. Furthermore, the expression of an activated catalytic subunit of PI 3-kinase in COS-7 cells resulted in an increase in inositol phosphate formation, whereas platelet-derived growth factor-induced PLC activation in NIH 3T3 cells was markedly inhibited by the specific PI 3-kinase inhibitor LY294002. These results suggest that receptors coupled to PI 3-kinase may activate PLC-gamma isozymes indirectly, in the absence of PLC-gamma tyrosine phosphorylation, through the generation of PI(3,4,5)P3.

The highly basic ribosomal protein L41 interacts with the beta subunit of protein kinase CKII and stimulates phosphorylation of DNA topoisomerase IIalpha by CKII

Protein kinase CKII (CKII) is a heterotetramer composed of two catalytic (alpha or alpha') and two regulatory (beta) subunits. Using the yeast two-hybrid system, we have identified the highly basic, ribosomal protein L41 as a cellular protein capable of interacting with the beta subunit of CKII. We show, furthermore, using purified proteins, that L41 protein and CKIIbeta associate directly in vitro. L41 protein is not a substrate for CKII phosphorylation, and it does not stimulate CKII activity with either beta-casein or synthetic peptide substrate (RRREEETEEE). However, L41 protein stimulates the phosphorylation of DNA topoisomerase IIalpha by CKII by 2.5 times. Additionally, L41 protein enhances the autophosphorylation of CKIIalpha. The data indicate that L41 protein associates with CKII and can modulate its activity toward a specific substrate or substrates. The direct interaction of CKIIbeta with ribosomal proteins also suggests that CKIIbeta itself or CKII holoenzyme may be involved in ribosome assembly or translational control.

Molecular cloning and characterization of cDNAs for anionic and neutral peroxidases from suspension-cultured-cells of sweet potato and their differential expression in response to stress

Two peroxidase (POD) cDNAs, swpal and swpn1, were isolated and characterized from suspension-cultured cells of sweet potato in order to understand the physiological function of POD isozymes. Sequence analysis showed that swpa1 encoded an anionic POD and swpn1 encoded a neutral POD. The swpa1 and swpn1 genes were both highly expressed in suspension-cultured cells in accordance with the high POD activity of these cells. Although both gene transcripts were detected in the stems of intact plants, their transcription levels were much lower than in suspension-cultured cells. During cell growth the pattern of mRNA accumulation of swpa1 differed from that of swpn1, suggesting that expression of these genes is differentially regulated by cell growth stage. In addition, the swpa1 and swpn1 genes responded differently to oxidative stress induced by chilling. The expression of swpa1 was weakly induced by 15 degrees C acclimation and strongly induced by 4 degrees C chilling, whereas the mRNA level of swpn1 was increased by 15 degrees C acclimation and reduced by 4 degrees chilling. This indicates that the two isozymes encoded by swpa1 and swpn1 might contribute to protection against cold-induced oxidative stress through different signaling pathways. In leaves, both genes were induced by wounding with broadly similar expression. patterns. Genomic analysis suggests that the two isozymes are encoded by different loci in the sweet potato genome.

Synaptojanin inhibition of phospholipase D activity by hydrolysis of phosphatidylinositol 4,5-bisphosphate

A 150-kDa protein that inhibits phospholipase D (PLD) activity stimulated by ADP-ribosylation factor and phosphatidylinositol 4, 5-bisphosphate (PI(4,5)P2) was previously purified from rat brain. The sequences of peptides derived from the purified PLD inhibitor now identify it as synaptojanin, a nerve terminal protein that has been implicated in the endocytosis of fused synaptic vesicles and shown to be a member of the inositol polyphosphate 5-phosphatase family. Further characterization of the enzymatic properties of synaptojanin now shows that it hydrolyzes only the 5-phosphate from inositol 1,4,5-trisphosphate (I(1,4,5)P3) and that it does not catalyze the dephosphorylation of either I(1,3,4)P3 or inositol 1, 4-bisphosphate. However, synaptojanin hydrolyzes both the 4- and 5-phosphates of PI(4,5)P2 and the 4-phosphate of phosphatidylinositol 4-phosphate, converting both compounds to phosphatidylinositol. Magnesium is required for the hydrolysis of I(1,4,5)P3, but not for that of phosphoinositides, by synaptojanin. The inhibition of PLD by synaptojanin is attributable to its ability to hydrolyze PI(4,5)P2. Synaptojanin did not inhibit PLD in the absence of PI(4,5)P2, and the extent of PLD inhibition was related to the extent of PI(4,5)P2 hydrolysis in substrate vesicles. It has been proposed that the biosynthesis of PI(4,5)P2 and the activation of PLD by ADP-ribosylation factor constitute a positive loop to increase rapidly the concentrations of PI(4,5)P2 and phosphatidic acid (PA) during membrane vesiculation. The PA thus produced, probably together with PI(4,5)P2, facilitates vesicle coat assembly. The hydrolysis of PI(4,5)P2, and consequent inhibition of PLD, by synaptojanin might therefore constitute a mechanism to halt the positive loop connecting PI(4,5)P2 and PA during the endocytotic cycle of synaptic vesicles and serve as a signal for uncoating.

Inhibition of phospholipase D by clathrin assembly protein 3 (AP3)

In the accompanying paper (Chung, J.-K., Sekiya, F., Kang, H.-S., Lee, C., Han, J.-S., Kim, S. R., Bae, Y. S., Morris, A. J., and Rhee, S. G. (1997) J. Biol. Chem. 272, 15980-15985), synaptojanin is identified as a protein that inhibits phospholipase D (PLD) activity stimulated by ADP-ribosylation factor and phosphatidylinositol 4, 5-bisphosphate (PI(4,5)P2). Here, the purification from rat brain cytosol of another PLD-inhibitory protein that is immunologically distinct from synaptojanin is described, and this protein is identified as clathrin assembly protein 3 (AP3) by peptide sequencing and immunoblot analysis. AP3 binds both inositol hexakisphosphate and preassembled clathrin cages with high affinity. However, neither inositol hexakisphosphate binding nor clathrin cage binding affected the ability of AP3 to inhibit PLD. AP3 also binds to PI(4,5)P2 with low affinity. But the PI(4,5)P2 binding was not responsible for PLD inhibition, because the potency and efficacy of AP3 as an inhibitor of PLD were similar in the absence and presence of PI(4,5)P2. A bacterially expressed fusion protein, glutathione S-transferase-AP3 (GST-AP3), also inhibited PLD with a potency equal to that of brain AP3. The inhibitory effect of AP3 appeared to be the result of direct interaction between AP3 and PLD because PLD bound GST-AP3 in an in vitro binding assay. Using GST fusion proteins containing various AP3 sequences, we found that the sequence extending from residues Pro-290 to Lys-320 of AP3 is critical for both inhibition of and binding to PLD. The fact that AP3 is a synapse-specific protein indicates that the AP3-dependent inhibition of PLD might play a regulatory role that is restricted to the rapid cycling of synaptic vesicles.

Epidermal growth factor (EGF)-induced generation of hydrogen peroxide. Role in EGF receptor-mediated tyrosine phosphorylation

Recent evidence indicates that reactive oxygen species (ROS) may function as intracellular messengers in receptor signaling pathways. The possible role of ROS in epidermal growth factor (EGF) signaling was therefore investigated. Stimulation of A431 human epidermoid carcinoma cells with EGF resulted in a transient increase in the intracellular concentration of ROS, measured with the oxidation-sensitive fluorescent probe 2',7'-dichlorofluorescin diacetate and laser-scanning confocal microscopy. The predominant ROS produced appeared to be H2O2, because the EGF-induced increase in fluorescence was completely abolished by incorporation of catalase into the cells by electroporation. The elimination of H2O2 by catalase also inhibited the EGF-induced tyrosine phosphorylation of various cellular proteins including the EGF receptor and phospholipase C-gamma1. The dependence of H2O2 production on the intrinsic tyrosine kinase activity of the EGF receptor and the autophosphorylation sites located in its COOH-terminal tail was investigated. EGF failed to induce H2O2 generation in cells expressing a kinase-inactive EGF receptor. However, normal H2O2 generation was observed in cells expressing a mutant receptor from which the 126 COOH-terminal amino acids had been deleted to remove four (out of the total of five) autophosphorylation sites. These results suggest that EGF-induced H2O2 formation requires the kinase activity but probably not the autophosphorylation sites of the EGF receptor and that inhibition of protein tyrosine phosphatase activity by H2O2 may be required for EGF-induced protein tyrosine phosphorylation to be manifested.

Interaction of the beta subunit of casein kinase II with the ribosomal protein L5

Casein kinase II (CKII) usually exists as a heterotetramer with alpha 2 beta 2, alpha alpha'beta 2, or alpha'2 beta 2. The alpha or alpha' subunits catalyze protein phosphorylation, whereas the function of the beta subunit remains unclear. One of the possible functions of the beta subunit may be to mediate the interaction of the catalytic subunit with target proteins. To identify proteins capable of associating with the beta subunit in vivo, we have used a two-hybrid system. One protein identified is human ribosomal protein L5. The protein L5 does not interact with the alpha or alpha' subunits of CKII, supporting the idea that the beta subunit can determine a substrate specificity of CKII. These results furthermore suggest a novel role for CKII in ribosomal L5 phosphorylation, in ribosomal assembly, or ribosomal transport in the intact cells. The protein L5 may act as a regulator of the activity or subcellular localization of CKII.

Decreased expression of phospholipase C-beta 2 isozyme in human platelets with impaired function

Platelets from a patient with a mild inherited bleeding disorder and abnormal platelet aggregation and secretion show reduced generation of inositol 1,4,5-trisphosphate, mobilization of intracellular Ca2+, and phosphorylation of pleckstrin in response to several G protein mediated agonists, suggesting a possible defect at the level of phospholipase C (PLC) activation (see accompanying report). A procedure was developed that allows quantitation of platelet PLC isozymes. After fractionation of platelet extracts by high-performance liquid chromatography, 7 out of 10 known PLC isoforms were detected by immunoblot analysis. The amount of these isoforms in normal platelets decreased in the order PLC-gamma 2 > PLC-beta 2 > PLC-beta 3 > PLC-beta 1 > PLC-gamma 1 > PLC-delta 1 > PLC-beta 4. Compared with normal platelets, platelets from the patient contained approximately one-third the amount of PLC-beta 2, whereas PLC-beta 4 was increased threefold. These results suggest that the impaired platelet function in the patient in response to multiple G protein mediated agonists is attributable to a deficiency of PLC-beta 2. They document for the first time a specific PLC isozyme deficiency in human platelets and provide an unique opportunity to understand the role of different PLC isozymes in normal platelet function.

Activation of phospholipase C-gamma by the concerted action of tau proteins and arachidonic acid

Phospholipase C-gamma (PLC-gamma) isozymes are thought to be activated by receptor-induced tyrosine phosphorylation. Proteins that activate PLC-gamma1 have now been purified from bovine brain and identified as members of the tau family of microtubule-associated proteins. Activation of PLC-gamma by tau was enhanced in the presence of unsaturated fatty acids such as arachidonic acid, saturated fatty acids being ineffective. Maximal (15-20-fold) activation was apparent in the presence of 0.15 microM tau and 25 microM arachidonic acid (AA). The effect of tau and AA was specific to PLC-gamma isozymes in the presence of submicromolar concentrations of Ca2+ and was markedly inhibited by phosphatidylcholine. These results suggest that in cells that express tau, receptors coupled to cytosolic phospholipase A2 may activate PLC-gamma isozymes indirectly in the absence of tyrosine phosphorylation through the hydrolysis of phosphatidylcholine to generate AA.

Multiple forms of phospholipase D inhibitor from rat brain cytosol. Purification and characterization of heat-labile form

Rat brain cytosol contains proteins that markedly inhibit the activity of partially purified brain membrane phospholipase D (PLD) stimulated by ADP-ribosylation factor (Arf) and phosphatidylinositol 4,5-bisphosphate (PIP2). Sequential chromatography of the brain cytosol yielded four inhibitor fractions, which exhibited different kinetics to heat treatment at 70 degrees C. Purification of the most heat-labile inhibitor to homogeneity yielded two preparations, which displayed apparent molecular masses of 150 kDa and 135 kDa, respectively, on SDS-polyacrylamide gels. Tryptic digests of the 150- and 135-kDa proteins yielded similar elution profiles on a C18 reverse-phase column, suggesting that the 135-kDa form is a truncated form of the 150-kDa form. Sequences of two tryptic peptides were determined. A data base search revealed no proteins with these sequences. The purified 150-kDa inhibitor negated the PLD activity stimulated by Arf, RhoA, or Cdc42. The concentration required for half-maximal inhibition was 0.4 nM. Concentration dependence on the 150-kDa inhibitor was not affected by changes in the concentrations of Arf, PIP2, or phosphatidylcholine used in the assays, suggesting that the inhibition is not due to competition with the activators or substrate for PLD. The purified inhibitor did not affect the PIP2-hydrolyzing activity of a phospholipase C isozyme that was measured with substrate vesicles of lipid composition identical with that used for the PLD assay. Thus, the mechanism of inhibition appears to be a specific allosteric modification of PLD rather than disruption of substrate vesicles.

PLC gamma 1 Src homology domain induces mitogenesis in quiescent NIH 3T3 fibroblasts

Previously, we demonstrated that microinjection of phosphoinositide-specific phospholipase C gamma 1 (PLC gamma 1) and lipase-defective mutants of PLC gamma 1 induced G(0) growth arrested NIH 3T3 fibroblasts to enter S phase of the cell cycle. These experiments suggested that regions other than the catalytic domain of PLC gamma 1 may be responsible for inducing mitogenesis. To test other regions of PLC gamma 1 for DNA synthesis inducing activity, cDNA fragments encoding Src homology (SH) and pleckstrin homology (PH) domains were subcloned into the bacterial expression plasmid pGEX-2TK, and the GST fusion proteins were purified. The complete PLC gamma l SH domain peptide was found to induce DNA synthesis after microinjection into growth arrested fibroblasts. Peptides containing a single SH3 domain or two SH2 domains induced a partial response that was restored to full activity if they were co-injected. The PH domain peptide did not induce DNA synthesis. Thus, both SH3 and SH2 activity combine to give maximum DNA synthesis induction, demonstrating that non-catalytic structural domains of PLC gamma 1 have pronounced effects on mitogenic signaling pathways.

Homologous recombination of monkey alpha-satellite repeats in an in vitro simian virus 40 replication system: possible association of recombination with DNA replication

To study homologous recombination between repeated sequences in an in vitro simian virus 40 (SV40) replication system, we constructed a series of substrate DNAs that contain two identical fragments of monkey alpha-satellite repeats. Together with the SV40-pBR322 composite vector encoding Apr and Kmr, the DNAs also contain the Escherichia coli galactokinase gene (galK) positioned between two alpha-satellite fragments. The alpha-satellite sequence used consists of multiple units of tandem 172-bp sequences which differ by microheterogeneity. The substrate DNAs were incubated in an in vitro SV40 DNA replication system and used to transform the E. coli galK strain DH10B after digestion with DpnI. The number of E. coli galK Apr Kmr colonies which contain recombinant DNAs were determined, and their structures were analyzed. Products of equal and unequal crossovers between identical 172-bp sequences and between similar but not identical (homeologous) 172-bp sequences, respectively, were detected, although those of the equal crossover were predominant among all of the galK mutant recombinants. Similar products were also observed in the in vivo experiments with COS1 cells. The in vitro experiments showed that these recombinations were dependent on the presence of both the SV40 origin of DNA replication and SV40 large T antigen. Most of the recombinant DNAs were generated from newly synthesized DpnI-resistant DNAs. These results suggest that the homologous recombination observed in this SV40 system is associated with DNA replication and is suppressed by mismatches in heteroduplexes formed between similar but not identical sequences.

Flavan and procyanidin glycosides from the bark of blackjack oak

The bark of blackjack oak contains (+)-catechin, (-)-epicatechin, (+)-3-O-[beta-D-glucopyranosyl]-catechin, catechin-(4 alpha-->8)-catechin, epicatechin-(4 beta-->8)-catechin as well as the novel 3-O-[beta-D-glucopyranosyl]-catechin-(4 alpha-->8)-catechin and 3-O-[alpha-L-rhamnopyranosyl-(1-->6)-beta-D-glucopyranosyl]-catechin, as major components. The latter rutinoside of catechin is especially interesting because of the exceptionally small J2,3 C-ring coupling. The glucoside of catechin-(4 alpha-->8)-catechin is only the second proanthocyanidin found in nature in which a 3-O-glycoside is present in the upper 'extender unit' of a dimer.

Development of a recombinant RNA technique for the construction of chimeric RNA with a long poly(C) tract

The murine cardioviruses and bovine aphthoviruses are distinguished from other (+) strand RNA viruses by their long poly(C) tract in the 5'-noncoding region. The presence of this poly(C) tract has long hampered the construction of full-length cDNA with the complete poly(C) tract, because long poly(dC-dG) homopolymer-containing plasmids are difficult to amplify in bacterial systems. To overcome this problem, we constructed a chimeric RNA by joining the poly(C) region of the viral RNA to the 5'-truncated RNA transcript of the encephalomyocarditis (EMC) virus cDNA. The non-chimeric, recombinant EMC virus with a short poly(C) tract produces recombinant progeny virus, but this is not pathogenic in vivo. On the other hand, the EMC viral RNA chimera with the complete poly(C) tract produces recombinant progeny virus that is pathogenic in vivo. This method of viral RNA construction will be invaluable for functional studies of other cardioviruses and aphthoviruses, as well as for recombinant RNA manipulations.

Determination of diabetogenicity attributable to a single amino acid, Ala776, on the polyprotein of encephalomyocarditis virus

The best experimental evidence indicating that viruses have an etiological role in the pathogenesis of diabetes comes from studies of mice infected with EMC virus. For this study we generated mutant viruses from stocks of diabetogenic EMC-D and nondiabetogenic EMC-B viruses by serial passages of the viruses in L-cell cultures at high MOI. The genomic sequence information and the biological activities of three different plaque-purified diabetogenic variants of EMC virus (EMC-D, EMC-D1/6A, EMC-D2/4) and six different plaque-purified nondiabetogenic variants (EMC-B, EMC-BS, EMC-B1/G, EMC-DV1, EMC-D4/1B, EMC-D3/1) revealed that only one amino acid, Ala (776th amino acid on the polyprotein), is critical for the diabetogenicity of EMC virus. The G base at the nucleotide position 3155 (Ala[GCC]776 in the polyprotein) is unique to all diabetogenic variants, whereas the A base at the same position (Thr[ACC]776 in the polyprotein) is identical to all nondiabetogenic variants. A single-point mutation (G to A; Ala to Thr) results in the conversion of the diabetogenic variant into a nondiabetogenic variant of EMC virus. On the basis of these observations, we conclude that a single amino acid, Ala776, on the polyprotein of EMC virus appears responsible for the inducement of diabetes in susceptible mice. Conversion of Ala776 into Thr776 on the polyprotein by a point mutation, G to A at the nucleotide position 3155, results in the loss of diabetogenicity.

Casein kinase II phosphorylates p34cdc2 kinase in G1 phase of the HeLa cell division cycle

The activity of p34cdc2 kinase is regulated in the phases of vertebrate cell cycle by mechanisms of phosphorylation and dephosphorylation. In this paper, we demonstrate that casein kinase II (CKII) phosphorylates p34cdc2 in vivo and in vitro at Ser39 during the G1 phase of HeLa cell division cycle. Human p34cdc2 shows a typical phosphorylation sequence motif site for CKII at Ser39 (ES39EEE). In our experiments, either p34cdc2 expressed and purified from bacteria or p34cdc2 immunoprecipitated from HeLa cells enriched in G1 by elutriation were substrates for in vitro phosphorylation by CKII. Phosphoamino acid analysis, N-chlorosuccinimide mapping, and two-dimensional tryptic mapping of p34cdc2 phosphorylated in vitro were performed to determine the phosphorylation site. A synthetic peptide spanning residues 33-50 of human p34cdc2, including the CKII site, was used to map the site. In addition, phosphorylation at Ser39 also occurs in vivo, since p34cdc2 is phosphorylated during G1 on serine, and its two-dimensional tryptic map shows two phosphopeptides that comigrate exactly with the synthetic peptides used as standard.

A new type of insertion mutation in monkey cells: insertion accompanied by long target site duplication

We have developed a system for the detection of a new type of insertion mutation in mammalian cells. We have used a shuttle vector, plasmid pNK1, which contains the SV40 and pBR322 replication origins, and ApR, galK, and neoR genes. This plasmid was introduced into monkey COS1 cells, allowed to replicate, and then recovered plasmids were reintroduced into Escherichia coli HB101 to detect insertion mutations in the galK gene. We selected galK- KmR ApR mutants in order to eliminate galK- KmS deletion mutants. Insertion mutations in the plasmids recovered were then screened by agarose gel electrophoresis. Finally, insertion mutants that had the following characteristics were selected. First, they had the ability to produce gal+ revertants caused by the precise excision of inserted DNA in E. coli, implying that they had a target site duplication on both sides of the insertion. Second, they contained some repetitive sequence(s) as judged by hybridization with a bulk monkey DNA probe. Nucleotide sequence analysis of one of the mutants, 15K-1, showed that it contained alpha-satellite sequences within the coding region of the galK gene. It contained 13 1/2 tandem repeat units of alpha-satellite sequence and was flanked by a 64 bp target site duplication, indicating that the alpha-satellite sequence had been translocated from the monkey genome into the plasmid by illegitimate recombination. Another insertion mutant, N11-1, contained an 11 kb insert which included an unknown repetitive sequence that was also flanked by a target site duplication of 353 bp.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical localization of casein kinase II during interphase and mitosis

We have developed specific antibodies to synthetic peptide antigens that react with the individual subunits of casein kinase II (CKII). Using these antibodies, we studied the localization of CKII in asynchronous HeLa cells by immunofluorescence and immunoelectron microscopy. Further studies were done on HeLa cells arrested at the G1/S transition by hydroxyurea treatment. Our results indicate that the CKII alpha and beta subunits are localized in the cytoplasm during interphase and are distributed throughout the cell during mitosis. Further electron microscopic investigation revealed that CKII alpha subunit is associated with spindle fibers during metaphase and anaphase. In contrast, the CKII alpha' subunit is localized in the nucleus during G1 and in the cytoplasm during S. Taken together, our results suggest that CKII may play significant roles in cell division control by shifting its localization between the cytoplasm and nucleus.

A shuttle vector for analysis of illegitimate recombination in mammalian cells: effects of DNA topoisomerase inhibitors on deletion frequency

To study the mechanism of illegitimate recombination in mammalian cells, we have developed a shuttle vector, pNK1, that contains three bacterial markers, amp (ApR), galK, and neo (KmR). The frequency of deletions occurring in autonomously replicating pNK1 DNA during the growth of monkey COS1 cells was measured by transfecting the plasmid into Escherichia coli cells and counting the number of galK- ApS double mutants among total KmR cells. This method allowed us to test the effects of topoisomerase inhibitors on deletion formation in mammalian cells. The DNA topoisomerase II (TopII) inhibitor, 4'-dimethylepipodophyllotoxin thenylidene-beta-D-glucoside (VM26), stimulated deletions in pNK1 DNA in monkey cells. Since VM26 does not inhibit the strand-break activity of TopII, but rather stabilizes an enzyme-DNA complex in which DNA is cleaved upon treatment with sodium dodecyl sulfate, it is implicated that TopII participates in the deletion process in mammalian cells.

Characterization of synthetic peptide substrates for p34cdc2 protein kinase

Synthetic peptide substrates for the cell division cycle regulated protein kinase, p34cdc2, have been developed and characterized. These peptides are based on the sequences of two known substrates of the enzyme, Simian Virus 40 Large T antigen and the human cellular recessive oncogene product, p53. The peptide sequences are H-A-D-A-Q-H-A-T-P-P-K-K-K-R-K-V-E-D-P-K-D-F-OH (T antigen) and H-K-R-A-L-P-N-N-T-S-S-S-P-Q-P-K-K-K-P-L-D-G-E-Y-NH2 (p53), and they have been employed in a rapid assay of phosphorylation in vitro. Both peptides show linear kinetics and an apparent Km of 74 and 120 microM, respectively, for the purified human enzyme. The T antigen peptide is specifically phosphorylated by p34cdc2 and not by seven other protein serine/threonine kinases, chosen because they represent major classes of such enzymes. The peptides have been used in whole cell lysates to detect protein kinase activity, and the cell cycle variation of this activity is comparable to that measured with specific immune and affinity complexes of p34cdc2. In addition, the peptide phosphorylation detected in mitotic cells is depleted by affinity adsorption of p34cdc2 using either antibodies to p34cdc2 or by immobilized p13, a p34cdc2-binding protein. Purification of peptide kinase activity from mitotic HeLa cells yields an enzyme indistinguishable from p34cdc2. These peptides should be useful in the investigation of p34cdc2 protein kinase and their regulation throughout the cell division cycle.

Two amino acids, Phe 16 and Ala 776, on the polyprotein are most likely to be responsible for the diabetogenicity of encephalomyocarditis virus

The diabetogenic D variant of encephalomyocarditis virus (EMC-D) was previously shown to differ from the non-diabetogenic B variant (EMC-B) by 14 nucleotides out of 7829 bases. Similar approaches with a new nondiabetogenic variant, EMC-DV1, obtained by plaque purification of the EMC-D variant stock pool, enabled us to narrow down further the possible genomic area responsible for the diabetogenicity of EMC virus. EMC-DV1 does not induce interferon in vitro, differing from the highly interferon-inducing EMC-B. The complete nucleotide sequence of EMC-DV1 was determined by RNA-dependent DNA sequencing and cDNA sequencing. The genomic size and organization of EMC-DV1 are similar to those of EMC-D and EMC-B, with a long open reading frame encoding a polyprotein of 2292 amino acids. Comparative analyses of sequence information as well as biological activities of EMC-DV1 with EMC-D and EMC-B suggest that (i) the diabetogenicity is apparently distinct from the ability to induce interferon, which is probably due to the single U base insertion at position 765 in EMC-B, and (ii) the diabetogenicity of EMC virus is most probably controlled by one or both of two amino acids, Phe 16 (on the leader peptide) and Ala 776 (152nd amino acid on the VP1) on the polyprotein.

Interaction of human apolipoprotein A-I with dipalmitoylphosphatidylcholine in vesicular and micellar complexes

The interactions of human apolipoprotein A-I (apo A-I) with dipalmitoylphosphatidylcholine (DPPC) in vesicular complexes at low protein concentrations and in micellar complexes at high protein concentrations are compared. The C-terminal segment of this protein, with a relative molecular weight (Mr) of about 11,000, is protected on trypsin treatment of apo A-I-vesicle complexes. A segment within the sequence from Leu-189 to Arg-215 of apo A-I penetrates the hydrophobic interior of the membrane, as found in a hydrophobic labeling experiment involving 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)-diazirine ([125I]TID). No appreciable stretch of apo A-I in micellar complexes was found to be protected from the tryptic digestion. This indicates that the interactions of apo A-I with lipids in the vesicular and micellar complexes are different. The binding equilibrium of apo A-I as to DPPC vesicles at low protein concentrations, as studied by hydrophobic labeling of the bilayer-penetrating segment, is reached within about 1 h, while the formation of micellar complexes at high protein concentrations takes about 24 h at 42 degrees C. Time-dependent labeling studies involving photoreactive phosphatidylcholine (PC) with high apo A-I concentrations suggested an initial interaction with the head group region of the bilayer followed by interaction with the tail ends of the acyl chains of the lipid. A possible mechanism for the micellization process is discussed.

An efficient and site-specific gene trimming method

Trimming a DNA strand into a precisely determined fragment can be carried out efficiently by an improved method involving a site-specific trim-primer and a single-stranded DNA template which is generated from a multifunctional vector, pTZ18R, and linearized by using an Eco RI-pTZ18R splinter. A complementary DNA strand is synthesized by DNA polymerase I (Klenow), and the 3'-end of the template upstream from the annealed primer is trimmed by subsequent T4 DNA polymerase reaction. An ATG translation initiator codon or a termination codon can be incorporated into the trim-primer, providing versatility to this single-stranded DNA-initiated gene trimming method that can be applied to subcloning and expression of any DNA fragment with known terminal sequences.

Genomic differences between the diabetogenic and nondiabetogenic variants of encephalomyocarditis virus

Plaque purification of the M variant of encephalomyocarditis (EMC-M) virus resulted in the isolation of two stable variants. One is a highly diabetogenic D variant (EMC-D) and the other is a nondiabetogenic B variant (EMC-B). The cDNA of EMC-D and EMC-B genomes were cloned and seven overlapping cDNA clones were selected to cover the entire genome except the 5'-end 310 bases which were determined by RNA-dependent DNA sequencing and enzymatic RNA sequencing. Each clone was restriction-mapped, subcloned, and sequenced. The genomes of EMC-D and EMC-B are composed of 7829 and 7825 bases, respectively. Both genomes contain a long open reading frame of 6876 nucleotides starting at position 830 on the consensus sequence, which encodes a polyprotein of 2292 amino acids. The sequences of EMC-D and EMC-B differ by two deletions, one insertion, and eight point mutations. The first deletion of 3 nucleotides is located in the 5' poly(C) tract where EMC-B has 127 nucleotides compared with 130 nucleotides in EMC-D. The second deletion in EMC-B involves 2 nucleotides at the 3'-end polyadenylation site. A single base insertion of U occurs at the 5' noncoding region of EMC-B. The eight point mutations are located in the polyprotein coding region. Two are silent and are each located in the structural gene 1B and in the nonstructural gene 2B. The remaining six mutations, one on the L gene and the other five on the 1D gene, introduce respective amino acid changes. It is concluded that the diabetogenic EMC-D viral genome (7829 bases) differs from the nondiabetogenic EMC-B viral genome (7825 bases) by 14 nucleotides out of 7829.

Molecular identification of diabetogenic viral gene

The best evidence that viruses have a causative role in the pathogenesis of insulin-dependent diabetes mellitus comes from experiments in mice infected with encephalomyocarditis (EMC) virus. When SJL/J male mice were inoculated with a highly diabetogenic EMC-D virus, diabetes developed in 95% of the animals. In contrast, none of the mice inoculated with a nondiabetogenic EMC-B virus became diabetic. Tissue culture experiments showed that EMC-B induces considerable amounts of interferon, whereas EMC-D does not. Despite these differences, EMC-D and EMC-B could not be distinguished antigenically by a sensitive plaque-neutralization assay. Furthermore, the buoyant density in CsCl density gradients and the capsid proteins of these two variants on polyacrylamide gels could not be distinguished. Molecular-hybridization studies with radiolabeled DNA complementary to EMC-D and EMC-B RNAs failed to distinguish them. Determination of complete nucleotide sequences of EMC-D and EMC-B revealed that EMC-D (7829 bases) differs from EMC-B (7825 bases) by only 14 nucleotides. The differences consist of two deletions of five nucleotides, one base insertion, and eight point mutations. The first deletion of three nucleotides and the second deletion of two nucleotides are located in the 5'-poly(C) tract and the 3'-end polyadenylation site, respectively. One base insertion in EMC-B occurs in the 5'-noncoding region. The eight point mutations are located in the polyprotein-coding region. Two of them are silent, whereas the other six mutations, one located on the L gene and five on the VP1 gene, introduce amino acid changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of antigenic differences between the diabetogenic and non-diabetogenic variants of encephalomyocarditis virus using monoclonal antibodies

The M variant of encephalomyocarditis (EMC) virus consists of two biologically distinct variants: one, diabetogenic D variant (EMC-D) and the other, non-diabetogenic B variant (EMC-B). These two variants cannot be distinguished by hyperimmune sera. Monoclonal antibodies were generated against EMC-D or EMC-B to identify antigenic differences between these two variants. Fourteen independent hybrid cell lines, selected from seven separate fusions of mouse myeloma cells to spleen cells isolated from mice immunized with EMC-D, consisted of 12 hybrids which produced monoclonal antibodies that neutralized both EMC-D and EMC-B, and two hybrids (ED-HJ-23 and ED-HJ-31) which produced monoclonal antibodies that neutralized EMC-D but not EMC-B. Similarly, 16 independent hybrid cell lines, selected from eight separate fusions using spleen cells prepared from mice immunized with EMC-B, consisted of 15 hybrids which produced monoclonal antibodies neutralizing both EMC-D and EMC-B, and one hybrid (EB-48A-F1) which produced antibody that neutralized EMC-B, but not EMC-D. The specificities of these monoclonal antibodies (ED-HJ-23, ED-HJ-31, EB-48A-F1) were further confirmed using an immunofluorescent technique. The D variant-specific monoclonal antibodies reacted with cells infected with EMC-D but not EMC-B. In contrast, the B variant-specific monoclonal antibody reacted with the cells infected with EMC-B but not EMC-D. It is concluded that the EMC-D- and EMC-B-specific monoclonal antibodies are able to identify antigenic differences between diabetogenic and non-diabetogenic variants of EMC virus which cannot be distinguished by hyperimmune sera.

Amino acid differences in capsid protein, VP1, between diabetogenic and nondiabetogenic variants of encephalomyocarditis virus

The genes for the major capsid protein, VP1(1D), of both diabetogenic D variant (EMC-D) and nondiabetogenic B variant (EMC-B) of encephalomyocarditis virus were cloned by using two synthetic primers which are common to both EMC-D and EMC-B. The cloned genes were mapped for major restriction enzyme sites including AccI, BamHI, EcoRI, HincII, KpnI, PvuII, SstI, TaqI, and XbaI. Among those nine restriction enzyme sites, only the TaqI site distinguished EMC-D genome from the counterpart of EMC-B genome. The complete nucleotide sequences (831 bases) of the VP1 genes revealed five amino acid differences between the two variants. Three of the changes, at positions 41, 58, and 152, were Thr (EMC-B) to Ala (EMC-D). The additional two changes occurred at positions 63 [Gln (EMC-B) to Glu (EMC-D)] and 181 [Thr (EMC-B) to Ser (EMC-D)]. All of these amino acid changes were due to point mutations at the first base of each codon.

Illegitimate recombination mediated by calf thymus DNA topoisomerase II in vitro

We have found that purified calf thymus DNA topoisomerase II mediates recombination between two phage lambda DNA molecules in an in vitro system. The enzyme mainly produced a linear monomer recombinant DNA that can be packaged in vitro. Novobiocin and anti-calf thymus DNA topoisomerase II antibody inhibit this ATP-dependent recombination. The recombinant molecules contain duplications or deletions, and most crossovers take place between nonhomologous sequences of lambda DNA, as judged by the sequences of recombination junctions. Therefore, the recombination mediated by the calf thymus DNA topoisomerase II is an illegitimate recombination that is similar to recombination mediated by Escherichia coli DNA gyrase or phage T4 DNA topoisomerase. The subunit exchange model, which has been suggested for the DNA gyrase-mediated recombination, is now generalized as follows: DNA topoisomerase II molecules bind to DNAs, associate with each other, and lead to the exchange of DNA strands through the exchange of topoisomerase II subunits. Illegitimate recombination might be carried out by a general mechanism in organisms ranging from prokaryotes to higher eukaryotes.

An apparent deletion of an oligonucleotide detected by RNA fingerprint in the nondiabetogenic B variant of encephalomyocarditis virus is caused by a point mutation

The diabetogenic D variant of encephalomyocarditis virus (EMC-D) was previously shown to be different from the nondiabetogenic B variant of encephalomyocarditis virus (EMC-B) by a single spot in an oligonucleotide fingerprint after RNase T1 digestion of their genomic RNAs. An oligoribonucleotide was missing from EMC-B but was present in EMC-D. The oligoribonucleotide specific to EMC-D was isolated from a two-dimensional polyacrylamide gel and sequenced as 5'-ACAAUCUCACUUUUCCAACAACAG-3'. Molecular hybridizations of EMC-D and EMC-B genomic RNAs with a DNA primer complementary to the EMC-D-specific oligoribonucleotide revealed that the absence of a corresponding spot in EMC-B was due to a point mutation rather than a deletion. By sequencing a cloned cDNA of EMC-B corresponding to the EMC-D-specific oligoribonucleotide, the point mutation was identified as a G for EMC-B and an A for EMC-D transversion at base 9 of the oligonucleotide. Comparative sequence analysis of eight randomly picked RNA segments around the EMC-D-specific oligoribonucleotide revealed that there were no base changes between EMC-D and EMC-B. It is concluded that the diabetogenic EMC-D viral genome differs from the nondiabetogenic EMC-B viral genome by at least a point mutation.