OVEREXPRESSION OF A CYTOSOLIC CHAPERONE TO IMPROVE SOLUBILITY AND SECRETION OF A RECOMBINANT IGG PROTEIN IN INSECT CELLS

The secretion of heterologous IgG proteins in the baculovirus-insect c ell expression system is accompanied by substantial insoluble immunogl obulin in the infected cells. The accumulation of these insoluble form s suggests a limitation in the processing and secretory pathway of the infected cells. As a result, cytosolic hsp70 chaperones, which are kn own to associate and prevent aggregation of polypeptides in vitro, hav e been coexpressed in the infected cells. The hsp70 protein coprecipit ated with the immunoglobulin to indicate the formation of a specific h sp70-immunoglobulin complex in vivo, Immunoblot and pulse chase studie s indicated that coexpression of hsp70 increased intracellular immunog lobulin solubility. Metabolic labeling experiments revealed that hsp70 increased secreted immunoglobulin levels after several days infection as compared to infection with control baculoviruses. Pulse chase stud ies indicated that hsp70 increases the solubility of immunoglobulin pr ecursors that are then processed and assembled into the complete antib ody oligomer. A comparison of the action of cytosolic hsp70 chaperone to the endoplasmic reticulum chaperone BiP suggests sequential action in which hsp70 increases the solubility of preprocessed immunoglobulin , while BiP enhances the solubility of processed immunoglobulin chains . (C) 1998 John Wiley & Sons, Inc.