Foreign protein production and cellular protein expression in recombinant CHO cells subjected to osmotic and low culture temperature stress

Abstract

Hyperosmotic pressure has been suggested as an economical solution to increase the specific protein productivity (q). When we investigated the response of antibody-expressing rCHO cells ($CS13^*$ -1.00) subjected to hyperosmotic pressure, the positive relationship between immunoglobulin (Ig) mRNA level per cell and antibody productivity ($q_{Ab}$). It represented that transcriptional regulation was involved in the response of rCHO cells to hyperosmotic pressure. While much work has been performed on the response of rCHO cells to hyperosmotic pressure, there are few reported studies on the response to hypoosmotic pressure. Considering the importance of rCHO cells as a mammalian host, we also investigated the effect of hypoosmotic pressure on rCHO cells ($CS13^*$ -1.00). At hypoosmotic pressure, $CS13^*$ -1.00 cells displayed decreased specific growth rate (μ) and $q_{Ab}$. When the medium osmolality was decreased from 300 mOsm/kg to 150 mOsm/kg, μ was decreased by 68% and qAb was increased by 128%. To understand the mechanism of enhanced $q_{Ab}$ resulting from hypoosmotic pressure, cellular responses of cells in the exponential phase of growth were observed at the transcription level. Total cytoplasmic RNA content per cell at 150 mOsm/kg was increased by 140%, compared with that at 300 mOsm/kg. On a per μ g RNA basis, Ig mRNA levels at 150 mOsm/kg were comparable to those at 300 mOsm/kg, indicating that hypoosmotic pressure did not lead to the preferential transcription of Ig mRNAs. Taken together, the data obtained here suggest that the increase in total RNA pool is primarily responsible for the enhanced $q_{Ab}$ of $CS13^*$-1.00 cells subjected to hypoosmotic pressure. To better understand intracellular responses to osmotic pressure of rCHO cells expressing an antibody, we have taken a proteomics approach. Using two-dimensional electrophoresis and mass spectrometry, a proteome profile of $CS13^*$-1.00 cells comprising 23 identified proteins was established...