COEXPRESSION OF MOLECULAR CHAPERONE BIP IMPROVES IMMUNOGLOBULIN SOLUBILITY AND IGG SECRETION FROM TRICHOPLUSIA NI INSECT CELLS

Infection of Trichoplusia ni (BTI-TN5B1-4) insect cells with a baculov irus coding for immunoglobulin G resulted in significant intracellular insolubility of the immunoglobulin chains. In order to increase the I mmunoglobulin solubility, the chaperone BiP was coexpressed in the ins ect cells using a separate baculovirus vector. This heterologous BiP w as observed to associate with immunoglobulin chains in vivo and enhanc e the level of soluble intracellular and secreted IgG obtained from T. ni. Pulse chase studies indicated that the heterologous BiP increased the level of soluble nascent immunoglobulin chains and assembly inter mediates to suggest that BiP is acting as a true molecular chaperone. The effect of heterologous BiP became more significant with time post- infection as secreted IgG levels increased by 90% after 3.4 days of ba culovirus infection. Even following the treatment of cells with tunica mycin, BiP coexpression still enhanced immunoglobulin solubility and s ecretion to indicate that BiP does not function specifically to retain unglycosylated proteins in the endoplasmic reticulum. Thus, coexpress ion of a molecular chaperone may be used to enhance cellular productiv ity and protein secretion provided that the chaperone is involved with post-translational processing and significant protein aggregation is observed.