Involvement of the Golgi region in the intracellular trafficking of cholera toxin

The intracellular pathway following receptor-mediated endocytosis of cholera toxin was studied using brefeldin A (BFA), which inhibited protein secretion and induced dramatic morphological changes in the Golgi region. In both mouse Y1 adrenal cells and CHO cells, BFA at 1 μg/ml caused a 80–90% inhibition of the cholera toxin (CT)-elevation of intracellular cAMP. The inhibition of the cytotoxicity of CT by BFA was also observed in a rounding assay of Y1 adrenal cells. The inhibition of CT cytotoxicity by BFA was dose dependent, with the ID₅₀ value similar to the LD₅₀ of BFA in Y1 adrenal cells. Binding and internalization of [¹²⁵I]-cholera toxin in Y1 adrenal cells was not affected by BFA. Unlike the BFA-sensitive cell lines such as Y1 adrenal and CHO cells, BFA at 1 μg/ml did not inhibit the cytotoxicity of CT in PtK₁ cells, of which the Golgi structure was BFA-resistant. These results strongly suggest that a BFA-sensitive Golgi is required for the protection of CT cytotoxicity by BFA. In contrast, elevation of the intracellular cAMP by forskolin, which acts directly on the plasma membrane adenylate cyclase, was not affected by BFA. These observations indicate that the intoxication of target cells by CT requires an intact Golgi region for its intracellular trafficking and/or processing. In this respect, CT shares a common intracellular pathway with ricin, Pseudomonas toxin, and modeccin, even though their structures and modes of action are very different. © 1993 Wiley-Liss, Inc.     

Analysis of common antigen of flagella in Bacillus cereus and Bacillus thuringiensis

Abstract Flagellar antigen of Bacillus cereus H.1 was purified and tested for serodiagnostic antigen by ELISA. The antibody against the flagellar antigen of B. cereus H.1 reacted not only with the homologous specific antigen but also reacted with the flagellar antigens of 23 strains of B. cereus . This common flagellar antigen of B. cereus was found to be due to 61-kDa protein by SDS-PAGE and immunoblot assay. Monoclonal antibody H15A5 against common antigenic epitope of B. cereus also reacted with flagellar antigens of 21 strains of Bacillus thuringiensis by ELISA. This monoclonal antibody reacted with the 61-kDa protein of the flagella of B. cereus H.1 and H.2 and B. thuringiensis Kurstaki HD1, Alesti and Aizawai juroi by immunoblot analysis. These results indicated that the common antigenic epitope of the 61-kDa protein existed in the flagella both of B. cereus and B. thuringiensis .     

An immunoelectron-microscopical observation of mouse juxtaglomerular cells in the case of experimental hydronephrosis.

Changes in juxtaglomerular (JG; renin-containing) cells in experimental hydronephrosis 1 month after ureteral ligation were investigated with immunoelectron-microscopical techniques. Two types of granules, electron dense (D) and lucent (L), were observed. D type granules were labeled more intensely with gold particles than those of L type. Granules intermediate between D and L types and exocytosis of D types were observed. In the cells containing D types exclusively, gold particles were restricted to the granules, whereas in the cells containing both D and L type granules, the particles were scattered throughout the cytoplasmic cytosol. The authors discuss the mechanisms of renin release in JG cells.     

Changes of erythrocyte deformability induced by calcium accumulation and calmodulin inhibitors

The deformability of human erythrocytes was investigated with a rheoscope to study the role of intracellular calcium in the dynamic cytoskeletal structure. Calcium was loaded to or depleted from erythrocytes with a calcium ionophore (A 23187) in a Na- or a K-HEPES buffer. (1) After calcium loading in the Na-HEPES buffer, the cell volume of erythrocytes was greatly reduced due to dehydration. On the contrary, upon calcium-loading or -depletion in the K-HEPES buffer, the intracellular calcium content could be varied in the range of 1/4 to 3 times as much as that of control cells without the reduction of mean cell volume. Further incubation without A 23187 and calcium in the K-HEPES buffer enabled the calcium-loaded erythrocytes to restore the cell shape and the ATP concentration. (2) When intracellular calcium content was increased to above 1.5 times of the normal value, the deformability was distinctly decreased. On the other hand, the deformability was unchanged when the intracellular calcium content was reduced below the normal level. (3) The deformability, once decreased due to the calcium accumulation, was recovered by the treatment with a calmodulin inhibitor, W-7 or trifluoperazine, while these drugs were not effective on the deformability of control or calcium-depleted erythrocytes. We conclude that the membrane stiffness which influence the deformability of erythrocytes, is modulated by the intracellular calcium content through the interaction between the calcium-calmodulin complex and the cytoskeletal proteins.     

Chromatic Regulation of Photosystem Composition in the Cyanobacterial Photosynthetic System: Kinetic Relationship between Change of Photosystem Composition and Cell Proliferation

Kinetics of the change of photosystem (PS) composition in cyanobacteriainduced by chromatic light were studied in relation to cellproliferation. The study was made for two unicellular strains,Synechococcus NIBB 1059 and Synechocystis (Aphanocapsa) PCC6714. We found that (1) the change to a higher or lower PS I/IIratio was due to acceleration or suppression of apparent PSI formation, and (2) it progressed on a similar time scale tothat of the cell proliferation. The apparent rate constant ofthe change in the PS I/II ratio was proportional to that ofcell proliferation, µ, when this was low, but at highvalues of µ the increase in the rate constant of the changein the PS I/II ratio became smaller, causing a deviation fromthe linear relationship. Results indicate that under autotrophicconditions, the photoregulated composition change occurs asa result of thylakoid development, which accompanies cell proliferation. (Received June 23, 1986; Accepted December 5, 1986)     

Characterization of revertants derived from a mouse DNA temperature-sensitive mutant strain, tsFT20, which contains heat-labile DNA polymerase alpha activity

One spontaneous and four N-methyl-N'-nitro-N-nitrosoguanidine-induced revertants of a mouse FM3A mutant, tsTF20, which has heat-labile DNA polymerase alpha activity and cannot grow at 39 degrees C, were isolated and characterized with respect to the thermolability of their DNA polymerase alpha activity, the intracellular level of enzyme activity, growth rate, cell cycle progression, and frequency of initiation of DNA replication at the origin of replicons. DNA polymerase alpha activity in the extracts from the revertant cells showed partial recovery of heat stability. The intracellular level of enzyme activity of the revertant cells was lower than that of wild-type cells even at 33 degrees C. The level of enzyme activity in the revertant cells decreased considerably after a temperature upshift to 39 degrees C, but the DNA synthesizing ability of these cells did not decrease as much as the level of enzyme activity. The growth rates of the wild-type and revertant lines were almost the same at 33 degrees C. At 39 degrees C, the rate for the wild-type increased considerably compared to that at 33 degrees C, while little difference in the growth rates of the revertant lines was observed at the two temperatures. Therefore, the doubling times of the revertant cells were relatively increased compared to those of wild-type cells cultured at the restrictive temperature. Flow microfluorometric analysis and cell cycle analysis to measure labeled mitosis revealed that the increase in the doubling time was due mainly to the increase in the duration of the S phase. Analysis of the center-to-center distance between replicons by DNA fiber autoradiography indicated that the frequency of replicon initiation per unit length DNA at a given time was reduced in the revertant cells growing at 39 degrees C.     

Requirement of the Escherichia coli dnaA gene function for ori-2-dependent mini-F plasmid replication.

The mini-F plasmids pSC138, pKP1013, and pKV513 were unable to transform Escherichia coli cells with a dnaA-defective mutation under nonpermissive conditions. The dnaA defect was suppressed for host chromosome replication either by the simultaneous presence of the rnh-199 (amber) mutation or by prophage P2 sig5 integrated at the attP2II locus on the chromosome, both providing new origins for replication independent of dnaA function. The dnaA mutations tested were dnaA17, dnaA5, and dnaA46. dnaA5 and dnaA46 are missense mutations. dnaA17 is an amber mutation whose activity is controlled by the temperature-sensitive amber suppressor supF6. Under permissive conditions in which active DnaA protein was available, the mini-F plasmids efficiently transformed the cells. However, the transformants lost the plasmid as the cells multiplied under conditions in which DnaA protein was inactivated or its synthesis was arrested. As controls, plasmids pSC101 and pBR322 were examined along with mini-F; pSC101 behaved in the same manner as mini-F, showing complete dependence on dnaA for stable maintenance, whereas pBR322 was indifferent to the dnaA defect. Thus, ori-2-dependent mini-F plasmid replication seems to require active dnaA gene function. This notion was strengthened by the results of deletion analysis which revealed that integrity of at least one of the two DnaA boxes present as a tandem repeat in ori-2 was required for the origin activity of mini-F replication.     

Purification and characterization of human salivary carbonic anhydrase

A novel carbonic anhydrase was purified from human saliva with inhibitor affinity chromatography followed by ion-exchange chromatography. The molecular weight was determined to be 42,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis, indicating that the human salivary enzyme is larger than the cytosolic isoenzymes CA I, CA II, and CA III (Mr 29,000) from human tissue sources. Each molecule of the salivary enzyme had two N-linked oligosaccharide chains which were cleaved by endo-beta-N-acetylglucosaminidase F but not by endo-beta-N-acetylglucosaminidase H, indicating that the oligosaccharides are complex type. The isoelectric point was determined to be 6.4, but significant charge heterogeneity was found in different preparations. The human salivary isozyme has lower specific activity than the rat salivary isozyme and the human red blood cell isozyme II in the CO2 hydratase reaction. The inhibitory properties of the salivary isozyme resemble those of CA II with iodide, sulfanilamide, and bromopyruvic acid, but the salivary enzyme is less sensitive to acetazolamide and methazolamide than CA II. Antiserum raised in a rabbit against the salivary enzyme cross-reacted with CA II from human erythrocytes, indicating that human salivary carbonic anhydrase and CA II must share at least one antigenic site. CA I and CA III did not crossreact with this antiserum. The amount of salivary carbonic anhydrase in the saliva of the CA II-deficient patients was greatly reduced, indicating that the CA II deficiency mutation directly or indirectly affects the expression of the salivary carbonic anhydrase isozyme. From these results we conclude that the salivary carbonic anhydrase is immunologically and genetically related to CA II, but that it is a novel and distinct isozyme which we tentatively designate CA VI.     

In vitro replication of DNA containing either the SV40 or the polyoma origin

The replication of DNA containing either the polyoma or SV40 origin has been done in vitro. Each system requires its cognate large-tumour antigen (T antigen) and extracts from cells that support its replication in vivo. The host-cell source of DNA polymerase alpha - primase complex plays an important role in discriminating between polyoma T antigen and SV40 T antigen-dependent replication of their homologous DNA. The SV40 origin- and T antigen-dependent DNA replication has been reconstituted in vitro with purified protein components isolated from HeLa cells. In addition to SV40 T antigen, HeLa DNA polymerase alpha - primase complex, eukaryotic topoisomerase I and a single-strand DNA binding protein from HeLa cells are required. The latter activity, isolated solely by its ability to support SV40 DNA replication, sediments and copurifies with two major protein species of 72 and 76 kDa. Although crude fractions yielded closed circular monomer products, the purified system does not. However, the addition of crude fractions to the purified system resulted in the formation of replicative form I (RFI) products. We have separated the replication reaction with purified components into multiple steps. In an early step, T antigen in conjunction with a eukaryotic topoisomerase (or DNA gyrase) and a DNA binding protein, catalyses the conversion of a circular duplex DNA molecule containing the SV40 origin to a highly underwound covalently closed circle. This reaction requires the action of a helicase activity and the SV40 T antigen preparation contains such an activity. The T antigen associated ability to unwind DNA copurified with other activities intrinsic to T antigen (ability to support replication of SV40 DNA containing the SV40 origin, poly dT-stimulated ATPase activity and DNA helicase).