Using silkworm Bombyx mori Bm5 cells, we established a stable cell line expressing the human granulocyte macrophage colony-stimulating factor (hGM-CSF), which gets its name from the Bm5-hGM-CSF cell in which the glycoprotein of the hGM-CSF is secreted in the cell culture supernatant (CCS). It was demonstrated that secreted hGM-CSF had in vivo biological activity and the white blood cell (WBC) value increased two times that of the control. We expect to produce useful human recombinant glycoproteins from silkworm cultured cells for a low price and a large quantity.

Using silkworm Bombyx mori Bm5 cells, we established a stable cell line expressing the human keratinocyte growth factor (hKGF), named by the Bm5-hKGF cell, in which the protein hKGF is synthesized in the cell and secreted in the cell culture supernatant (CCS) at approximately 15-20 ng/ml. When the Bm5-hKGF cell was co-expressed with B. mori protein disulfide isomerase (bPDI) cDNA, its secretion increased by about two times the original amount. Through wound healing migration assay, it was demonstrated that the secreted hKGF included in the CCS has a very powerful biological activity of keratinocyte proliferation. We expect to produce useful human recombinant proteins from silkworm cultured cells in large quantities at low prices.

Sericin is a type of high molecular weight water-soluble glycoprotein surrounding fibroin (silk protein) that has been used as a cell culture supplement and accelerates cell proliferation in various serum-free media. The purpose of this study was to investigate the enhancing effect of thyroglobulin (Tg) secretion by sericin in thyrocytes, FRTL-5 cells. While Tg-mRNA expression was not enhanced, a secreted form of Tg was obviously increased by sericin. In this status, expression of both endoplasmic reticulum (ER) molecular chaperones (Bip & calreticulin) and ER membrane proteins (IRE1, PERK & ATF6) was enhanced. The proximal step of IRE1, XBP1 mRNA splicing was slightly detected however, the proximal step of PERK, phosphorylation of eIF2α, was changeless. In addition, sericin enhanced cell viability by the MTT assay. The above results showing the ability of sericin to promote protein production demonstrated its potential usefulness as a new biomaterial.