Expression of Streptococcus mutans wall-associated protein A gene in Chinese hamster ovary cells: prospect for a dental caries DNA vaccine.

The Streptococcus mutans strain GS-5 wall-associated protein A (Wap-A) is a precursor to the extracellular antigen A (AgA), a recognized candidate dental caries vaccine. The full-length wapA gene (wapA-E) and a C-terminal truncated version (wapA-G) encoding the AgA were cloned into the mammalian expression vector pcDNA 3.1/V5/His-TOPO. The resulting constructs were propagated in the Escherichia coli Top10. To investigate the expression of the S. mutans genes in mammalian cells, the above constructs were used to transfect Chinese hamster ovary (CHO) cells in the presence of the cationic lipid pfx-8. Transient expression of the wapA-E and wapA-G genes was observed at 24 h post-transfection, as shown by Western immunoblot analysis using a rabbit antiserum to S. mutans cell wall. Immunochemical staining of the transfected CHO cells showed expression of WapA mainly in the cells and budding vesicles, whereas AgA was found mainly in the transfected cells and extracellular medium. The expression of S. mutans proteins in CHO cells, in either vesicles or soluble form, suggested an antibody response to the above DNA constructs. Work is under way to test the efficacy of these as DNA vaccines against S. mutans.

High-level expression of a truncated wall-associated protein A from the dental cariogenic Streptococcus mutans.

Streptococcus mutans plays a primary role in the formation of dental caries. Previously, in our laboratory, an S. mutans genomic library was prepared, and the wapA gene was cloned into the shuttle vector, pSA4/4B2. To generate overexpression of wapA and to facilitate efficient purification of the WapA protein for use as an immunogen, an expression vector with the strong tac promoter was used. In order to answer questions regarding the optimization of solubility and expression based on gene size or the hydrophobicity of the protein product, 12 truncated constructs of the wapA gene were prepared using PCR. The truncated products were subcloned into the pGEX-6P-1 glutathione S-transferase (GST) fusion vector and expressed in E. coli BL21. The fusion proteins were analyzed by SDS-PAGE and confirmed by analysis with anti-GST and anti-WapA antibodies. Our study suggests that abrogation of the wapA promoter is necessary for expression of this gene in this expression system. Deletion of the signal peptide and the hydrophobic C terminus of WapA increased expression compared with the full-length construct, and truncation at the protease cleavage site of the C-terminal region greatly increased the stability of the protein without a loss in reactivity with the anti-WapA antibody. Western immunoblot analysis with anti-WapA antiserum clearly showed that the majority of the epitopes of the GST-WapA fusions are located in the N-terminal region of WapA. The immunogenicity of the various WapA fusion products is being examined in mice and rats to further map the immunologically dominant regions of the protein. This method effectively increased the expression of WapA and should contribute to the further understanding of gene expression of E. coli, as well as aid in the characterization of this protein for future immunologic evaluation.

Identification and analysis of a collagenolytic activity in Streptococcus mutans.

Streptococcus mutans is an important pathogen in coronal caries and is implicated in dental root decay by its ability to bind collagen from various sources. In the present study, electron microscopic analysis demonstrated the ability of S. mutans to bind and to disrupt collagen fibrils of the amniotic membrane. The synthetic peptide FALGPA, which is similar in structure to collagen, was degraded by S. mutans, with a lower level of FALGPA hydrolytic activity observed in sucrose-grown cells compared with cells grown in the absence of sucrose. Inhibition studies of FALGPA hydrolytic activity showed a pattern characteristic of collagenase activity, with inhibition by 1,10-phenanthroline and EDTA, but not by phenylmethylsulfonyl fluoride (PMSF). Additionally, immunological cross-reactivity was observed between proteins from disrupted cells of S. mutans and antiserum to collagenase from Clostridium histolyticum. Gelatinolytic activity was demonstrated by gelatin zymogram analysis. These findings suggest that collagenolytic activity by S. mutans may be an important virulence factor in dental root decay.

Nucleotide sequence analysis of a complementary DNA coding for a Blomia tropicalis allergen.

Blomia tropicalis is a mite of allergenic importance in tropical and subtropical areas. A clone (Bt11a) from a B. tropicalis complementary DNA library was expressed in lambda phage and analyzed by plaque radioimmunoassay. The recombinant allergen produced by this clone was bound by IgE in 16 of 32 sera from individuals with asthma with a positive RAST response and none of 3 control sera from healthy individuals with negative RAST response to B. tropicalis. The cDNA insert was amplified by polymerase chain reaction with use of universal primers. A 582-base-pair (bp) fragment was cloned into a pCR II vector. The complete sequence of both strands was determined by using T7, SP6, and internal primers. The sequence shows a 432 bp reading frame with a 34 bp 5' untranslated region and a 116 bp 3' untranslated region with a poly A tail. Analysis of the sequence suggests that it encodes a putative signal peptide of 20 residues and a 124-residue mature protein allergen of 14,206 Da. The nucleotide and the inferred amino acid sequences did not show homology to any known sequence. No potential N-linked glycosylation site was found. The recombinant protein appears to represent a major allergen of the mite B. tropicalis.

Cell-associated collagenolytic activity by group B streptococci.

Group B streptococci (GBS) are important pathogens in neonatal sepsis, pneumonia, and meningitis. The ability of GBS to invade the collagen-rich amniotic membrane of the placenta has been shown in vitro. In the presence of GBS, the collagen fibrils of the amnion appear disordered, suggesting a role for GBS in premature rupture of membranes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Sephadex G-200 column chromatography, and gelatin zymograms were used in this study to characterize cell-associated collagenolytic activities of GBS. The synthetic peptide 2-furanacryloyl-Leu-Gly-Pro-Ala (FALGPA), which mimics the primary structure of collagen, was degraded by GBS USF704, a clinical isolate from the placenta of a septic newborn. Cells of GBS USF704 (9 x 10(7) CFU/ml) hydrolyzed 902 nmol of FALGPA over a 24-h period. As reported for zinc metalloenzymes such as collagenase, the hydrolysis of FALGPA by GBS was inhibited by addition of EDTA or 1,10-phenanthroline. Boiling of the cells resulted in loss of activity, while higher activity was observed with crude GBS cell lysates (hydrolysis of 970 nmol of FALGPA in 1.5 h). Antiserum raised against collagenase from Clostridium histolyticum was found to cross-react with cell-associated proteins produced by GBS and to inhibit GBS FALGPA hydrolysis. Twenty-five additional GBS clinical isolates were screened and found to have various levels of FALGPA hydrolytic activity. These observations suggest a cell-associated collagenolytic activity by GBS which may be involved in premature rupture of membranes and neonatal disease.

Inactivation of the Streptococcus mutans wall-associated protein A gene (wapA) results in a decrease in sucrose-dependent adherence and aggregation.

A 0.8-kb HindIII-BamHI internal fragment of the Streptococcus mutans wall-associated protein A gene (wapA) was ligated to the 5.1-kb HindIII-BamHI fragment of the chimeric Streptococcus-Escherichia coli plasmid pVA891 (Emr Cmr). The resulting construct was used to transform S. mutans GS-5, and erythromycin-resistant mutants were isolated and analyzed. Directed mutagenesis of the wapA gene by plasmid insertion through homologous recombination was demonstrated by Southern blot hybridization with the wapA and pVA891 probes. Stable mutants were obtained, and the alteration of the wapA gene by insertional inactivation was associated with a significant decrease in S. mutans sucrose-dependent aggregation and binding to smooth surfaces. Thus, WapA may play an important role in the colonization of the tooth surface by S. mutans and in the buildup of dental plaque. These findings provided an explanation for previous studies which indicated that WapA was effective in the prevention of dental caries in animal models. Thus, the use of recombinant WapA in the preparation of a safe and effective human dental vaccine should be investigated further.

Decreased expression of protein kinase-C alpha, beta, and epsilon in soleus muscle of Zucker obese (fa/fa) rats.

Skeletal muscle is one of the first tissues to become insulin resistant in genetically obese rodents. The activation of protein kinase-C (PKC) in rat skeletal muscle is mediated by insulin stimulation of diacylglycerol (DAG) levels. Defects in the activation of PKC in the heart and liver of obese Zucker rats indicate that an abnormality in either stimulation of DAG or PKC occurs in obese tissues. DAG levels were significantly increased in soleus muscle from 15- to 19-week-old obese (fa/fa) Zucker rats. PKC activity was diminished in soleus muscle from fa/fa rats. Decreased levels of PKC alpha and -beta activity wer enoted after resolution of common PKC isozymes (Ca2+ and phospholipid dependent) by hydroxyapatite chromatography. Immunoreactivity of PKC-alpha, -beta, and -epsilon also indicated that their levels are diminished in fa/fa soleus muscle by 70-90%. To determine at which level down-regulation occurs (i.e. gene expression or protein turnover), mRNA levels were examined by Northern blot analysis of total RNA. PKC alpha and -beta levels were diminished in Zucker obese soleus muscle compared to soleus from Zucker lean control (fa/-) animals, and PKC epsilon mRNA was not detected on the same blots. The transcript size for PKC beta mRNA in Zucker soleus muscle was unique. Both lean and obese Zucker muscle tissues expressed three transcripts that hybridized with the full-length PKC beta cDNA probes, with sizes ranging between 2.5-1.7 kilobases. Levels of all PKC beta transcripts were significantly decreased in obese Zucker tissues. Thus, levels of common PKC isozyme mRNA, protein, and enzyme activity in soleus muscle of the obese Zucker rat are decreased even though levels of the endogenous PKC activator DAG are elevated. The decreased levels of PKC may be related to the etiology of insulin resistance in skeletal muscle.

Dietary manipulation of mammary tumor development in adult C3H/Bi mice.

Chronic energy intake restriction (CEIR) in virgin female mice is one of the most effective ways of reducing significantly mammary adenocarcinoma in C3H/Bi mice, a strain which develops mammary adenocarcinoma associated with the murine mammary tumor virus spontaneously and at high incidence. In this study, the influence of chronic energy intake restriction imposed on fully mature (4- to 5-month-old), breeding female C3H/Bi mice was addressed, and the influence of energy intake where energy was derived largely from fat versus diets in which energy was derived largely from carbohydrates on tumor development and survival rate was investigated. The results show that chronic energy intake restriction can be delayed until full maturation and successful reproduction and still reduce significantly the incidence of mammary tumor development in this relatively short-lived strain of mice. Our findings demonstrate that the overriding dietary factor controlling mammary tumor development in these experiments in C3H/Bi mice was the level of energy intake, regardless of the primary source of energy (fat or carbohydrates).

Calorie consumption level influences development of C3H/Ou breast adenocarcinoma with indifference to calorie source.

To analyze simultaneously the influence attributable to calorie consumption level and percentage of dietary fat on the spontaneous development of mammary adenocarcinoma, virgin female C3H/Ou mice were separated into five dietary groups. Four groups of mice were fed purified diets either ad libitum (16-18 kcal/mouse/day) or restricted 40% in calorie consumption (10-11 kcal/mouse/day), and diets contained either 4.5%, 7.5%, 67%, or 68% calories from fat. Mice that consumed isocaloric diets developed breast malignancy at a comparable pace. Consuming a diet in which fats were present only at levels sufficient to satisfy the threshold requirement of essential fatty acids, 4.5-7.5% of the total calories, or alternatively where dietary fat represented greater than 67% of the total calories consumed, did not significantly alter the tendency for breast tumor development. The pace and frequency with which tumors occurred reflected the host's level of calorie consumption. Mice consuming a high caloric diet, low or high in fat, tended to have a shortened latency to breast tumor formation, an increased incidence of breast tumors, elevated serum prolactin levels, elevated levels of antibodies to mouse mammary tumor virus, and elevated circulating immune complex levels.

Influence of chronic energy intake restriction on intestinal alkaline phosphatase in C3H/Bi mice and autoimmune-prone MRL/lpr,lpr mice.

The influence of chronic energy intake restriction (CEIR) on the level and activity of intestinal alkaline phosphatase was investigated in mice of the autoimmune-prone MRL/lpr,lpr strain and in mice of the autoimmune-resistant C3H/Bi strain. In both strains of mice, CEIR of 40% resulted in a significant increase in intestinal alkaline phosphatase (IAP) specific activity in MRL/lpr,lpr mice after 10 wk of feeding, and in C3H/Bi mice after 6 wk of feeding. An increase in the amount of immunoreactive alkaline phosphatase antigen was also found to be associated with the increased enzyme activity in CEIR mice. These results suggest that a specific induction of an intestinal enzyme occurs or, alternatively, that there is a specific relative decrease in synthesis of intestinal proteins other than IAP as a function of CEIR. Thus, CEIR appears to regulate the expression of proteins in the small intestine in a specific manner.

Molecular cloning of the Streptococcus mutans gene specifying antigen A.

A gene encoding a Streptococcus mutans surface protein antigen has been isolated from a strain GS-5 gene bank constructed via the Streptococcus-Escherichia coli shuttle vector pSA3. This E. coli recombinant clone, designated 4B2, expressed S. mutans proteins, as shown by Western immunoblot analysis with a specific rabbit antibody to S. mutans surface antigens. Three bands were observed, including a 52-kilodalton (kDa) protein (pI 5.7), a 29-kDa protein (pI 4.2), and a 20-kDa protein usually present in lower amounts. The 52- and 29-kDa proteins both reacted with a monoclonal antibody to S. mutans antigen A, a 29-kDa protein which has been characterized and used as a vaccine for the prevention of induced caries in rodents and monkeys. The 52-kDa protein, but not the 29-kDa protein, showed a capacity to bind to a broad number of carbohydrate polymers. The results from this study suggest that the recombinant 4B2 clone specifies a 52-kDa protein which is a precursor to the 29-kDa antigen A.

Decrease by chronic energy intake restriction of cellular proliferation in the intestinal epithelium and lymphoid organs in autoimmunity-prone mice.

In previous studies we demonstrated that chronic energy intake restriction (CEIR) by a diet relatively low in fat, relatively high in carbohydrate, and reduced 40% in total calories extends life span and delays development of autoimmune disease in autoimmunity-prone mice. To investigate a possible cellular basis for this dramatic action of CEIR, we analyzed the rate of incorporation of [3H]thymidine by cells of the intestinal epithelium, thymus, spleen, and mesenteric lymph nodes in ad libitum-fed mice vs. CEIR mice of three autoimmunity-prone strains. In New Zealand Black (NZB), MRL/MP-lpr/lpr (MRL/lpr), and BXSB mice, CEIR slowed the rate of uptake of [3H]thymidine and, by inference, the rate of cellular proliferation among epithelial cells along the entire length of the gastrointestinal tract. Furthermore, CEIR decreased the apparent proliferative rate of lymphoid cells of the thymus, spleen, and mesenteric lymph nodes. This action by CEIR on the proliferative rate of cells of these rapidly replicating cell populations may point to an important mechanism by which calorie restriction inhibits the development of autoimmune disease and extends longevity in autoimmunity-prone mice.

Sequence analysis of the wall-associated protein precursor of Streptococcus mutans antigen A.

The nucleotide sequence has been determined for the Streptococcus mutans wall-associated protein A (wapA) gene from serotype c strains Ingbritt and GS5. The nucleotide sequence for each wapA gene was virtually identical, although the gene from strain GS5 contained a 24 base pair deletion. A 29 amino acid signal peptide was specified by each wapA gene with a mature protein of 424 amino acids (Mr, 45,276) for strain Ingbritt and 416 amino acids (Mr, 44,846) for strain GS5. In the C-terminal region of the wall-associated protein A, considerable sequence similarity was found with the membrane anchor region of proteins from other Gram-positive organisms such as the group A streptococcal M protein and the group G streptococcal IgG binding protein. Adjacent to the proposed membrane anchor is a highly hydrophilic region which may span the cell wall; both sequence data and experimental evidence indicate the existence of a region immediately outside the wall at which proteolytic cleavage occurs to release antigen A of Mr 29,000 into the culture supernatant. Thus, the wall-associated protein A is a precursor of the 29,000 Mr antigen A.

An improved method of antigen detection on nitrocellulose: in situ staining of alkaline phosphatase conjugated antibody.

A biological stain for alkaline phosphatase was applied to detect immune complexes immobilized on nitrocellulose. This method was sensitive and useful for in situ staining of antigens, in dot-immunobinding assays and immunoblots. In addition to its sensitivity, the staining of alkaline phosphatase conjugated antibody was also highly stable, and allowed a permanent record of original immunochemical data. A rapid and simple method is also described using this technique for screening translation products of recombinant clones.

Streptococcus-Escherichia coli shuttle vector pSA3 and its use in the cloning of streptococcal genes.

A shuttle vector that can replicate in both Streptococcus spp. and Escherichia coli has been constructed by joining the E. coli plasmid pACYC184 (chloramphenicol and tetracycline resistance) to the streptococcal plasmid pGB305 (erythromycin resistance). The resulting chimeric plasmid is designated pSA3 (chloramphenicol, erythromycin, and tetracycline resistance) and has seven unique restriction sites: EcoRI, EcoRV, BamHI, SalI, XbaI, NruI, and SphI. Molecular cloning into the EcoRI or EcoRV site results in inactivation of chloramphenicol resistance, and cloning into the BamHI, SalI, or SphI site results in inactivation of tetracycline resistance in E. coli. pSA3 was transformed and was stable in Streptococcus sanguis and Streptococcus mutans in the presence of erythromycin. We have used pSA3 to construct a library of the S. mutans GS5 genome in E. coli, and expression of surface antigens in this heterologous host has been confirmed with S. mutans antiserum. A previously cloned determinant that specifies streptokinase was subcloned into pSA3, and this recombinant plasmid was stable in the presence of a selective pressure and expressed streptokinase activity in E. coli, S. sanguis (Challis), and S. mutans.

Cross-reacting material to monoclonal anti-G6PD in the absence of catalytic activity.

Monoclonal antibody prepared against highly purified rat liver G6PD was used to probe the mode of regulation of this enzyme in a mammalian model system. Material cross-reacting with antibody against liver G6PD was found in similar amounts in extracts of two genetically related rat hepatoma cell lines, only one of which exhibits detectable enzymatic activity when both are cultured under identical conditions in vitro. The data suggest a post-translational event is necessary for the expression of catalytic activity for G6PD in this model system.

Preparation of a monoclonal antibody to rat liver glucose-6-phosphate dehydrogenase and the study of its immunoreactivity with native and inactivated enzyme.

A monoclonal antibody of the IgG class was prepared against rat liver glucose-6-phosphate dehydrogenase (G6PD; D-glucose-6-phosphate:NADP+ 1-oxidoreductase, EC 1.1.1.49) by the hybridoma technique. This antibody does not affect the catalytic activity of the enzyme and shows crossreactivity with the palmitoyl CoA-inactivated G6PD. By solid phase radioimmunoassay, the presence of crossreacting materials in comparable amounts was determined in liver homogenate supernatants from rats that had been starved and refed a high-sucrose diet (containing a high level of G6PD activity) and from rats that had been starved and refed a high-fat diet (containing a low level of G6PD activity). These findings indicate that G6PD is present in an inactive form in rats fed a high-fat diet. The monoclonal antibody will facilitate isolation and characterization of the inactive variant G6PD.

Purification of a new high activity form of glucose-6-phosphate dehydrogenase from rat liver and the effect of enzyme inactivation on its immunochemical reactivity.

A new form of cytoplasmic glucose-6-phosphate dehydrogenase (E.C.1.1.1.49) was purified from rat liver by protamine sulfate precipitation, ammonium sulfate fractionation, ion exchange chromatography with diethylaminoethyl cellulose, and affinity chromatography with Cibacron blue agarose and NADP agarose. This form of the enzyme has a specific activity of over 600 units/mg of protein and gives essentially a single band by polyacrylamide gel electrophoresis. The form of the enzyme isolated by this purification method is 3 times more active than the form purified from liver by previously reported procedures. The relative mass of this pure glucose-6-phosphate dehydrogenase enzyme was determined by disc gel electrophoresis to be 269,000. This high activity glucose-6-phosphate dehydrogenase enzyme, after inactivation by reaction with palmityl-CoA, was no longer precipitated by specific rabbit and goat antisera to this purified enzyme. Thus, the possibility still exists that starved fat-refed animals contain glucose-6-phosphate dehydrogenase (G6PD) enzyme protein in an inactivated form no longer detectable by either enzyme activity or immunoprecipitation.