OBJECTIVETo clone the LTB gene of E.coli and the CTB gene of V.cholerae, and to construct expression vectors of these genes.

METHODSThe LTB gene from E.coli strain 44815 and the CTB gene from V.cholerae strain eastern 74 were amplified by high fidelity PCR. The nucleotide sequences of the two target DNA amplification fragments were sequenced after T-A cloning. pET32a expression vectors with inserted LTB and CTB genes were constructed. The LTB and CTB fusion proteins were expressed in E.coli strain BL21DE3 inducted by IPTG at different dosages. The two expression products were identified by SDS-PAGE and G(M1)-ELISA.

RESULTSIn comparison with the reported LTB and CTB sequences, the nucleotide sequence homologies of the cloned LTB gene and CTB gene were from 99.12% approximate, equals 99.71% and 98.54% approximate, equals 99.42%, while their putative amino acid sequence homologies were as high as 97.58% approximate, equals 99.19% and 96.77% approximate, equals 99.19%. The expression outputs of LTB and CTB fusion proteins in pET32a LTB BL21DE3 and pET32a-CTB-BL21DE3 systems were approximately 30% and 10% of the total bacterial proteins, respectively. The LTB and CTB fusion proteins were able to combine with bovine G(M1) confirmed by ELISA.

CONCLUSIONThe expression systems of LTB and CTB genes have been successfully established. Both the expressed LTB and CTB fusion proteins possess mucosal adjuvant immunoactivity.

Adjuvants, Immunologic ; pharmacology ; Animals ; Bacterial Toxins ; genetics ; pharmacology ; Base Sequence ; Cholera Toxin ; genetics ; pharmacology ; Cloning, Molecular ; Enterotoxins ; genetics ; pharmacology ; Escherichia coli ; genetics ; Escherichia coli Proteins ; Immunity, Mucosal ; Rabbits ; Vibrio cholerae ; genetics

BACKGROUNDCholera toxin B subunit (CTB) was shown to be a potent adjuvant for protein immunogen, especially when inoculated through mucosal route. We aimed to optimize the expression approach for CTB and thereafter to determine the adjuvant effect on DNA vaccine.

METHODSWild type CTB coding gene was amplified and cloned into prokaryotic expression vector pET-30a, and the recombinant CTB was expressed in the presence of different concentration of chloramphenicol and isopropyl β-D-thiogalactoside. Purified recombinant CTB was mixed with HIV-1 AE2f tat-rev-integrase-vif-nef fusion gene DNA vaccine and female BALB/c mice were vaccinated with a DNA priming-recombinant vaccinia vectored vaccine boosting regimen through intramuscular injection. Interferon γ (IFN-γ) enzyme-linked immunospot (Elispot) assay was used to read out the specific T-cell immunity.

RESULTSChloramphenicol was essential for the efficient expression of recombinant CTB (rCTB) in pET-30a/BL21 (DE3) system and could be optimized at the concentration of 0.625 µg/ml in the presence of chloramphenicol. The purified rCTB could bind with GM1 efficiently. INF-γ Elispot data showed the T-cell response induced in CTB adjuvanted group ((734 ± 240) spot forming cells/10(6) splenocytes) was higher than that induced by non-adjuvanted ((520 ± 150) spot forming cells/10(6) splenocytes), all responses against different antigens were enhanced in parallel.

CONCLUSIONCTB could be efficiently expressed in the presence of chloramphenicol and purified CTB is functional and capable of enhancing the specific T cell responses elicited by DNA vaccine, the mechanism needs to be explored in the future.

Adjuvants, Immunologic ; pharmacology ; Animals ; Blotting, Western ; Chloramphenicol ; pharmacology ; Cholera Toxin ; metabolism ; Electrophoresis, Polyacrylamide Gel ; Escherichia coli ; drug effects ; metabolism ; Female ; Mice ; Mice, Inbred BALB C ; Recombinant Fusion Proteins ; genetics ; immunology ; metabolism ; Vaccines, DNA ; genetics ; immunology ; metabolism

Hydrophilic low molecular drugs, peptides and proteins, which are always poor in bioavailability, are mainly absorbed through the paracellular way in which the tight junction is the elementary framework. The tight junctions are a multiple unit structure composed of multiprotein complex that affiliates with the underlying apical actomyosin ring. Tight junction proteins are identified including transmembrane proteins (occludin, claudin and JAM) , cytoplasmic plaque proteins (ZO-1, ZO-2, ZO-3 and cingulin) and cytoskeleton. Traditional absorption enhancers can usually impair mucous membranes which constraint the utilization of these enhancers. Recently, with the increasing knowledge of the structure and function of tight junctions, many new absorption enhancers have been developed such as NO donor, CPE, Zot, and so on. In vivo and in vitro studies have shown that these enhancers could be effectively used to increase the absorption of paracellular markers and low bioavailable drug across intestinal epithelium with lower side effect. In short, the transient opening of the tight junctions by these enhancers provides new ideas that could help in novel drug delivery of therapeutic agents.
Animals ; Biological Availability ; Cell Adhesion Molecules ; metabolism ; Cholera Toxin ; pharmacology ; Claudin-1 ; Cytoskeleton ; metabolism ; Decanoic Acids ; pharmacology ; Drug Delivery Systems ; Enterotoxins ; pharmacology ; Humans ; Intestinal Absorption ; drug effects ; Membrane Proteins ; metabolism ; Nitric Oxide Donors ; pharmacology ; Occludin ; Phosphoproteins ; metabolism ; Receptors, Cell Surface ; metabolism ; Tight Junctions ; metabolism ; physiology ; Zonula Occludens-1 Protein

Previously it has been shown that persistent activation of the stimulatory adenylyl cyclase pathway with cholera toxin (CT) downregulates the Gs alpha polypeptide (80%) in a cAMP-independent manner in C6 glioma cells (Shah, 1997). This study was conducted to examine the short and long term effects of CT on the regulation of pertussis toxin-sensitive and -insensitive G proteins and their transcripts in C6 glioma cells. Treatment of C6 cells with CT (100 ng/ml) up to 16 h had no effect on either Gi or Gq/11 alpha proteins. However, prolonged exposure (24-48 h) caused increased expression of Gi (20-30%) and Gq/11 alpha proteins (40%). Urea gradient gels, which can separate Gq alpha and G11 alpha proteins, revealed that prolonged CT treatment increased the expression of both of these G proteins. The CT-mediated enhanced expression of Gq alpha and G11 alpha proteins was accompanied by increased mRNA levels of these proteins as determined by RT/PCR. Cyclic-AMP elevating agents like forskolin (10 microM) and db-cAMP (1 mM) mimicked the effect of CT on Gi but not Gq/11 alpha proteins. These studies show long term cAMP-dependent regulation of Gi and cAMP-independent expression of Gq/11 alpha proteins in C6 glioma cells.
Animal ; Blotting, Western ; Bucladesine/pharmacology ; Cholera Toxin/pharmacology* ; Cyclic AMP-Dependent Protein Kinases/metabolism ; Forskolin/pharmacology ; GTP-Binding Proteins/genetics* ; GTP-Binding Proteins/biosynthesis ; Gene Expression Regulation* ; Glioma ; Membrane Proteins/analysis ; RNA, Messenger/metabolism ; RNA, Messenger/genetics ; Rats ; Reverse Transcriptase Polymerase Chain Reaction