Regulation of Transferrin Receptor and IGF-I Receptor Numbers at the Cell Surface Drives Growth and Productivity of Hybridoma Cells

Abstract

Supplementation of serum-free medium with a combination of LONG®R3IGF-I, an IGF-I analogue, and rTransferrin results in synergistic effects on CHO and SP2/0 growth and productivity. Although the mechanisms underlying the synergy are unknown, cell surface availability of the transferrin receptor may play a key role. Both IGF-I and insulin can stimulate translocation of transferrin receptor to the cell surface of human and rat adipocytes and human fibroblasts. Therefore, the purpose of this study was to determine the effects of LONG®R3IGF-I and rTransferrin on the cell surface localisation of transferrin receptor and IGF-I receptor in hybridoma cells. SP2/0 hybridoma cells were grown in the presence or absence of LONG®R3IGF-I and/or rTransferrin in a 50 ml spin tube mini-bioreactor model. Cells were harvested for total and cell surface protein isolation at various time points to study acute and long-term responses to these supplements. Samples were analysed by immunoblotting and the ratios of cell surface to total levels of transferrin receptor and IGF-I receptor were determined. At 10 min, LONG®R3IGF-I treatment was found to significantly increase cell surface transferrin receptor and decrease cell surface IGF-I receptor. At 6 days, rTransferrin was found to have stimulated recruitment of the transferrin receptor but not the IGF-I receptor to the cell surface. Changes to both transferrin receptor and IGF-I receptor populations may therefore play a key role in the observed synergy with LONG®R3IGF-I and rTransferrin on growth and productivity of hybridoma cells.