The protein X4 of severe acute respiratory syndrome-associated coronavirus is expressed on both virus-infected cells and lung tissue of severe acute respiratory syndrome patients and inhibits growth of Balb/c 3T3 cell line

BACKGROUND

The genome of the severe acute respiratory syndrome-associated coronavirus (SARS-CoV) includes sequences encoding the putative protein X4 (ORF8, ORF7a), consisting of 122 amino acids. The deduced sequence contains a probable cleaved signal peptide sequence and a C-terminal transmembrane helix, indicating that protein X4 is likely to be a type I membrane protein. This study was conducted to demonstrate whether the protein X4 was expressed and its essential function in the process of SARS-CoV infection.

METHODS

The prokaryotic and eukaryotic protein X4-expressing plasmids were constructed. Recombinant soluble protein X4 was purified from E. coli using ion exchange chromatography, and the preparation was injected into chicken for rising specific polyclonal antibodies. The expression of protein X4 in SARS-CoV-infected Vero E6 cells and lung tissues from patients with SARS was performed using immunofluorescence assay and immunohistochemistry technique. The preliminary function of protein X4 was evaluated by treatment with and over-expression of protein X4 in cell lines. Western blot was employed to evaluate the expression of protein X4 in SARS-CoV particles.

RESULTS

We expressed and purified soluble recombinant protein X4 from E.coli, and generated specific antibodies against protein X4. Western blot proved that the protein X4 was not assembled in the SARS-CoV particles. Indirect immunofluorescence assays revealed that the expression of protein X4 was detected at 8 hours after infection in SARS-CoV-infected Vero E6 cells. It was also detected in the lung tissues from patients with SARS. Treatment with and overexpression of protein X4 inhibited the growth of Balb/c 3T3 cells as determined by cell counting and MTT assays.

CONCLUSION

The results provide the evidence of protein X4 expression following SARS-CoV infection, and may facilitate further investigation of the immunopathological mechanism of SARS.

[Role of intron and 5' untranslated region in human thrombopoietin gene expression]

OBJECTIVE

To study the role of 5' untranslated region (UTR) and intron in the expression of human thrombopoietin (TPO) gene.

METHODS

A number of expression vectors containing TPO mini-gene fused to the regulatory elements of cytomegalovirus (CMV) were constructed and transfected via lipofectin into cultured cos-1 cells for transient expression of TPO gene. The cell culture media were analyzed with highly sensitive sandwich enzyme-linked immunosorbent assay (ELISA) 48 h after the transfection.

RESULTS

The expression levels of the TPO gene elements followed the order of TPO intron v> TPOcDNA> TPO intron I> TPO intron I> TPO gDNA in cos-1 cells.

CONCLUSION

The last intron of TPO gene obviously enhances the expression level of TPO gene, which can be inhibited by 5'UTR of TPO gene.

Identification of an HLA-A*0201-restricted CD8+ T-cell epitope SSp-1 of SARS-CoV spike protein

A novel coronavirus, severe acute respiratory syndrome (SARS)–associated coronavirus (SARS-CoV), has been identified as the causal agent of SARS. Spike (S) protein is a major structural glycoprotein of the SARS virus and a potential target for SARS-specific cell-mediated immune responses. A panel of S protein–derived peptides was tested for their binding affinity to HLA-A*0201 molecules. Peptides with high affinity for HLA-A*0201 were then assessed for their capacity to elicit specific immune responses mediated by cytotoxic T lymphocytes (CTLs) both in vivo, in HLA-A2.1/K^b transgenic mice, and in vitro, from peripheral blood lymphocytes (PBLs) sourced from healthy HLA-A2.1⁺ donors. SARS-CoV protein-derived peptide-1 (SSp-1 RLNEVAKNL), induced peptide-specific CTLs both in vivo (transgenic mice) and in vitro (human PBLs), which specifically released interferon-γ (IFN-γ) upon stimulation with SSp-1–pulsed autologous dendritic cells (DCs) or T2 cells. SSp-1–specific CTLs also lysed major histocompatibility complex (MHC)–matched tumor cell lines engineered to express S proteins. HLA-A*0201–SSp-1 tetramer staining revealed the presence of significant populations of SSp-1–specific CTLs in SSp-1–induced CD8⁺ T cells. We propose that the newly identified epitope SSp-1 will help in the characterization of virus control mechanisms and immunopathology in SARS-CoV infection, and may be relevant to the development of immunotherapeutic approaches for SARS.

Molecular evolution of the SARS coronavirus during the course of the SARS epidemic in China

Sixty-one SARS coronavirus genomic sequences derived from the early, middle, and late phases of the severe acute respiratory syndrome (SARS) epidemic were analyzed together with two viral sequences from palm civets. Genotypes characteristic of each phase were discovered, and the earliest genotypes were similar to the animal SARS-like coronaviruses. Major deletions were observed in the Orf8 region of the genome, both at the start and the end of the epidemic. The neutral mutation rate of the viral genome was constant but the amino acid substitution rate of the coding sequences slowed during the course of the epidemic. The spike protein showed the strongest initial responses to positive selection pressures, followed by subsequent purifying selection and eventual stabilization.

[Preparation and identification of egg yolk antibodies against HLA-A* 0201 heavy chain]

OBJECTIVE

To prepare a high-titer specific and efficient egg yolk immunoglobulin (IgY).

METHODS

The antigen of HLA-A* 0201 heavy chain was used to immunize the hens together with Freud's adjuvant and the eggs these hens laid were collected. IgY was purified from the egg yolk by water extraction, salt precipitation with ammonium sulfate and dialysis. The immunoactivity of the IgY was measured by enzyme-linked immunosorbent assay (ELISA) and its purity was determined by SDS-PAGE.

RESULTS

The titer of IgY was 1 10(6) as shown by ELISA, with protein concentration of 9.77 mg/ml. The purity of the resultant IgY was more than 90% as suggested by SDS-PAGE analysis.

CONCLUSIONS

The antigen of HLA-A* 0201 heavy chain along with complete Freund adjuvant is effective to elicit an immune response of hens for producing IgY antibodies in high yields.

[Preparation and preliminary characterization of soluble HLA-A2-peptide complex]

AIM

To express HLA-A2 heavy chain (HC) and light chain beta(2m) in bacteria and to prepare soluble HLA-A2-peptide complex.

METHODS

HC and beta(2m) expressing engineering bacteria was induced for 5 h with 0.5 mmol/L IPTG. After sonification of the bacteria,crude inclusion body was obtained which was then refined, renaturated, ultrafiltrated, and purified by DEAE Sepherose Fast Flow anion exchange chromatography. Then HC and beta(2m) were connected with two specific peptides, purified through Superdex 75 gel filtration, and identified with mAb W6/32 which can recognize native HLA-A2.

RESULTS

The expression rates of HC and beta(2m) in engineering bacteria was both about 50%. The purity of both expression products reached to 95%.Moreover, the two HLA-A2-peptide complexes could be recognized by mAb W6/32, even after being stored at 4 degrees Celsius for 2 months.

CONCLUSION

The two soluble HLA-A2-peptide complexes prepared by us are stable and lay the foundation for further research of CTL recognition and response.

[Purification and renaturation of recombinant human interleukin-2-pseudomonas exotoxin (IL2-PE66(4GLU)) fusion protein]

OBJECTIVE

To evaluate the effect of a novel approach for purification and renaturation of recombinant human interleukin-2-pseudomonas exotoxin (IL2-PE66(4Glu)) fusion protein.

METHODS

A novel purification method established in our laboratory was adopted for the purification of the inclusion body, and after renaturation, recombinant human IL2-PE66(4Glu) fusion protein was purified by DEAE-Sepharose FF ion-exchange chromatography.

RESULTS

The purity of the fusion protein that retain its biological activity was as high as 95%, and a recovery rate over 80% of the refolded IL2-PE66(4Glu) fusion protein was achieved.

CONCLUSION

The purification and refolding method for inclusion body adopted in this study is simple and practical, which lays the foundation for a large-scale production of the fusion protein.

Identification of the ligand-binding domain of human vascular-endothelial-growth-factor receptor Flt-1

The vascular-endothelial-growth-factor (VEGF) receptor Flt-1 has been shown to be involved in vasculogenesis and angiogenesis. The receptor is characterized by seven immunoglobulin-like loops within the extracellular domain and the first three N-terminal immunoglobulin-like loops are involved in high-affinity binding of VEGF. The minimal extracellular domains of Flt-1 to achieve VEGF binding were screened using the yeast two-hybrid system. The result showed that the binding capacity of loop2-3 was close to that of loop1-3. The two truncated mutants consisting of loop2-3 and loop1-3 were expressed in the methylotrophic yeast Pichia pastoris at high levels (0.3 g[corrected]/litre). The corresponding proteins, named soluble (s)Flt-1(2-3) and sFlt-1(1-3), were purified. An in vitro biological activity assay showed that the binding capacity of sFlt-1(2-3) to human VEGF(165) and the inhibiting effect of it on human umbilical-vein endothelial cell proliferation stimulated by human VEGF(165) were close to those of sFlt-1(1-3). Animal tests showed that sFlt-1(2-3) could significantly inhibit the formation of regenerated blood vessels stimulated by hVEGF(165).

Expression of human vascular endothelial growth factor (VEGF165) in Pichia pastoris and its biological activity

OBJECTIVE

To express human vascular endothelial growth factor (hVEGF165) cDNA in Pichia pastroris, purify the expressed product and detect the biological activity of it.

METHODS

By inserting hVEGF165 cDNA coding 165 amino acid residues into Pichia pastoris expression vector pPIC9K containing AOX1 promoter and the sequences of alpha secreting signal peptides, a recombinant expression plasmid pPIC9K/hVEGF165 was constructed and transformed to yeast host strain KM71, then multiple-copy insert transformants were screened out and cultured in flasks, and hVEGF165 was expressed under the induction of 1% methanol.

RESULTS

SDS-PAGE showed that after being induced with 1% methanol for 4 d, the expressed product existed in supernatant in the form of soluble molecule and contained 60% of total protein expressed. Western blot showed good antigenicity and specificity of expressed product. After being purified by Heparin-Sepharose CL6B affinity chromatography, the purity of expressed product reached above 90%. Biological assays proved that the expressed product could stimulate the proliferation of HUVEC.

CONCLUSION

hVEGF165 was successfully expressed. The study opened up a wide prospect for the application of VEGF165 in the prevention and treatment of ischemic heart disease and other tissue ischemic diseases such as secondary arterial occlusion in limbs.

Expression of human vascular endothelial growth factor receptor Flt-1 extracellular domain 1-3 loop cDNA in Pichia pastoris, purification of the expressed product and detection of its biological activity

OBJECTIVE

To express human vascular endothelial growth factor receptor Flt-1 extracellular domain 1-3 loop cDNA in Pichia. pastroris, and to purify the expressed product and detect its biological activity.

METHODS

By inserting human Flt-1 (1-3 loop) cDNA coding 316 amino acid residues into Pichia pastoris expression vector pPIC9K containing AOX1 promoter and the sequences of alpha secreting signal peptides, a recombinant expression plasmid pPIC9K/Flt-1 (1-3) was constructed and transformed to yeast host strain GS115, then His+ Muts phenotype transformant was screened out and cultured in flasks, and Flt-1 (1-3) was expressed under the induction of 1% methanol.

RESULTS

SDS-PAGE showed that after being induced with 1% methanol for 4d, the expressed product existed in supernatant in the form of soluble molecule and contained 60% of total protein expressed. Western blot showed good antigenicity and specificity of expressed product. After being purified by CM-Sepharose FF and Sephacryl S-100 chromatography, the purity of the expressed product reached above 90%. Biological assay proved that the expressed product could bind to hVEGF165 and inhibit the proliferation of HUVEC stimulated by hVEGF165.

CONCLUSION

Human vascular endothelial growth factor receptor Flt-1 extracellular domain 1-3 loop was successfully expressed. The study lays a foundation for further application of the expressed product in the treatment of vasoformation related diseases, such as tumor and diabetic retinopathy.

[Expression and characterization of human vascular endothelial growth factor receptor Flt-1 extracellular domain in Pichia pastoris]

By inserting VEGF receptor Flt-1(1-3 loop) cDNA into Pichia pastoris expression vector pPIC9K containing AOX1 promotor and the sequences of alpha secreting signal peptides, the expression plasmid pPIC9K/Flt-1(1-3) was constructed and transformed into GS115. The multi-copy insert transformants were selected and cultivated in flasks. After 4 days of 1% methanol induction, the expressed Flt-1(1-3) accumulated up to 30% of total proteins in supernatant. The expressed Flt-1(1-3) was further proved with good antigenicity and high specificity by ELISA and Western blot. They can bind to VEGF and inhibit HUVEC proliferation stimulated by VEGF.