Silkworm as a host of baculovirus expression.

While the Baculovirus Expression Vector System (BEVS) mainly uses insect cell lines, such as Sf9 cells, the robust high expression system using silkworm has also been developed. We have further improved technologies for enhancement of virus recombination, reduction of proteolytic degradation and aggregation, and more reliable promoters. These developments made it possible to achieve high and soluble expression of recombinant proteins. We review here such technology developments, advantage of using silkworm and some example applications. There are areas where this technology can be further improved as implicated in the end.

Production of recombinant Japanese eel gonadotropins by baculovirus in silkworm larvae.

Recombinant follicle-stimulating hormone (reFSH) and luteinizing hormone (reLH) of the Japanese eel Anguilla japonica were produced by baculovirus in silkworm Bombyx mori larvae. cDNAs encoding Japanese eel gonadotropin subunits (i.e., FSH beta, LH beta, and common alpha) were introduced into the baculovirus, which was infected into silkworm larvae after propagation of the recombinant virus in B. mori culture cells. A 100ml solution of pooled hemolymph from silkworm larvae containing reFSH or reLH were obtained from approximately 250 infected larvae. Ten milliliters of hemolymph were applied to Ni-affinity choromatography, and 5.6 and 3.5mg of partially purified reFSH and reLH were obtained, respectively. Using Western blot analysis concentrations of reFSH and reLH in the original hemolymph was estimated to be 2.2 and 1.1mg/ml, respectively. Biological activities of reFSH and reLH were assessed in vitro and in vivo. Purified reFSH and reLH induced eel oocyte maturation in vitro, and administration of hemolymph containing reFSH or reLH induced spermatogenesis in vivo in sexually immature Japanese eel. The present study indicates that a baculovirus-silkworm system could produce large amounts of biologically active recombinant fish gonadotropins for use in investigations in reproductive endocrinology and/or aquaculture of fish.

Establishment of a large-scale purification procedure for purified recombinant bovine interferon-tau produced by a silkworm-baculovirus gene expression system.

We developed a procedure for the large-scale purification of bovine interferon-tau (boIFN-tau) by means of a silkworm-baculovirus gene expression system. Recombinant boIFN-tau (rboIFN-tau) was efficiently produced in the silkworm infected with boIFN-tau cDNA recombinant baculovirus and accumulated in the haemolymph. To establish a purification method suitable for mass production, we tried three crude purification methods, namely, an acidification and neutralization treatment (ANT), silica gel column chromatography (SGCC), and Blue sepharose column chromatography (BSCC) with a combination of Q-sepharose (QSC) and chelating sepharose column chromatographies (CSCC). As a result, the acidification and neutralization treatment was found to be the most efficient and cost effective. With this combination, we obtained 91% pure products. To confirm the applicability of the procedure for mass production, we inoculated 100 silkworms with the recombinant virus, and recovered about 4.55 mg (1.26 x 10(8)U/mg) of 91% pure rboIFN-tau by means of a combination of the ANT, followed by QSC and CSCC.

Recombinant human chymase produced by silkworm-baculovirus expression system: its application for a chymase detection kit.

Human chymase is a mast cell-derived serine proteinase, which is a non-angiotensin converting enzyme angiotensin II-generating enzyme. It appears to participate in various diseases, but it is unclear whether chymase plays major roles in physiological and pathophysiological functions in vivo. To obtain information on the physiological and pathophysiological functions of chymase and to search for diseases in which chymase participates, in the present study, we aimed at producing recombinant human chymase in large quantities and at developing an ELISA system using anti-human chymase antibodies. A recombinant human chymase was produced by a silkworm-baculovirus expression system. The recombinant chymase in active form was efficiently purified from larval hemolymph using cation-exchange and heparin column chromatography. This recombinant enzyme was enzymatically identical with native human chymase. On the other hand, the stability of the recombinant enzyme in cultured medium for mammalian cells at 37 degrees C was very high as compared with the stability of the native enzyme; 20% of the activity was maintained 120 h after addition of medium. These results indicated that the recombinant enzyme could also utilize in vitro and in vivo assay systems. We obtained several anti-chymase monoclonal antibodies by using the recombinant human chymase as antigen. These antibodies were used to construct an ELISA system for measuring the chymase concentration in blood. As a result of preliminary examination using this ELISA system, it was shown that the chymase concentration in each serum from hypertensive patients is significantly higher than in normal serum. The ELISA system will be applicable for clinical diagnosis and in vivo evaluation systems for chymase-targeting drugs.