Biosynthesis of the precursor of a soluble human insulin receptor ectodomain in insect Sf9 cells infected with a recombinant baculovirus

Chaperone and foldase coexpression in the baculovirus-insect cell expression system

CONCLUSIONS

The BEVS has become widely utilized for production of recombinant proteins. However, protein aggregation and inefficient processing often limit yields, especially for secreted and membrane proteins. Since many proteins of pharmaceutical interest require similar posttranslational processing steps, engineering the folding, assembly, and secretion pathway may enhance the production of a wide variety of valuable complex proteins. Efforts should be undertaken to coexpress the relevant chaperones or foldases at low levels in concert with the final product to ensure the ideal folding and assembly environment. In the future, expression of oligosaccharide modifying enzymes and secretion factors may further improve secretion rates of assembled proteins and provide heterologous proteins with altered glycoforms. Also significant is the use of BEVS as an in vivo eucaryotic laboratory to study the fundamental roles of differnt chaperones, foldases, and secretion factors. The coexpression of chaperones and foldases will complement other approaches such as the development of alternative insect cell lines, promoters, and signal peptides to optimize the baculovirus-insect cell expression system for generating high yields of valuable proteins.

Injection of the insulin receptor alpha subunit increases blood glucose levels in mice

Using the expression vector of the truncated human insulin receptor (hIR), we have constructed a stable Chinese hamster ovary (CHO) cell line which secretes the His-tagged alpha subunit (insulin-binding domain) of hIR into medium. To examine characteristics of the His-tagged hIRalpha, we purified the protein secreted from the CHO cells. The His-tagged hIRalpha was glycosylated and processed a dimer. The molecule bound insulin with an affinity similar to that of the intact hIR. The His-tagged full length of hIR was autophosphorylated by insulin stimulation in CHO cells. Injection of the purified His-tagged hIRalpha into veins of mice increased in the concentration of blood glucose within 30 min. The intraperitoneal glucose tolerance test (ipGTT) done after injection of the purified His-tagged hIRalpha showed evidence of a marked hyperglycemia. These findings provide direct evidence that the presence of hIRalpha in the blood stream inhibits insulin actions by binding with plasma insulin.

A bacterial signal peptidase enhances processing of a recombinant single chain antibody fragment in insect cells

The production of an antibody single chain fragment (scFv) in insect cells was accompanied by the formation of an insoluble intracellular precursor even with the inclusion of the bee melittin signal peptide. The presence of the precursor polypeptide suggests a limitation in the processing of the signal peptide so a baculovirus containing a signal peptidase from Bacillus subtilis (SipS) was constructed for expression studies. When the wild type SipS was coexpressed with scFv, preprocessed scFv fragments were no longer detected in insect cell lysates. Conversely, coexpression of scFv alone or with an inactive mutant SipS resulted in at least 30% of the intracellular polypeptide in an unprocessed form at 3 days post infection. Production of scFv in the medium was also enhanced in the presence of SipS; however, low secretion levels indicate the presence of a post-processing bottleneck.

Antibody Production in Silkworm Cells and Silkworm Larvae Infected with a Dual Recombinant Bombyx Mori Nuclear Polyhedrosis Virus

We have examined the efficiency of coexpression of two heterologous genes from a recombinant Bombyx mori nuclear polyhedrosis virus for the production of antibodies in silkworm larvae. The cDNAs encoding the light and the heavy chains of a murine immunoglobulin, directed against lipoprotein I of Pseudomonas aeruginosa, were brought under the control of two separate copies of the viral polyhedrin promotor. Infection of silkworm cells with the recombinant baculovirus yielded a maximum of 6.4 micrograms/ml IgG2A in the culture supernatant 72 hours post infection, while 800 micrograms/ml IgG2A was found in the hemolymph of infected fifth instar silkworm larvae seven days after infection with the same construct. The recombinant antibody exhibited a similar antigen specificity and avidity to that of the monoclonal antibody derived from ascites fluid.