A variety of culture conditions which perturb the cellular phyisiology have been shown to increase specific productivity in cultured mammalian cells. Examples include hyperosmotic stress, sodium butyrate and temperature and pH shifts. However, the majority of these perturbations adversely affect growth and viability reducing their overall utility. We have undertaken a series of experiments to determine the mechanisms by which these changes increase specific productivity as well as the mechanisms for the deleterious effects on growth. We have focused primarily on hyperosmotic stress.

In murine hybridoma cells, changes in specific productivity occurred primarily at the level of overall protein translation with no specific effects on monoclonal antibody production. Post-translational processing did not exert any regulatory effects. Changes in transcriptional rates did not appear to have a significant effect. To further understand the global changes in cellular physiology, a DNA microarray study was performed. We identified 215 genes which were signficantly (p<0.05) differentially expressed. Within the 215 characterized, differentially expressed genes, many are involved in metabolism/catabolism (19 induced, 12 repressed), cell-cycle regulation (10 induced, 5 repressed) and apoptosis (8 induced, 2 repressed), regulation of transcription (18 induced, 13 repressed) and translation (2 induced, 2 repressed), transport and signaling pathways (24 induced, 12 repressed). Surprisingly, there were very few changes within the stress-response genes. Currently, we are exploring the signal transduction pathways to learn how the hyperosmotic stress signal is transduced to the nucleus. Through these studies, we hope to identify regulatory bottlenecks as well as strategies for cellular engineering to improve overall productivity.