Investigating the trade-offs between resource allocation and growth rates in mammalian cells

Understanding how mammalian cells allocate intracellular resources between growth and protein production has been a critical area for optimising biotherapeutic production. While bacterial growth laws have established links between growth rates, ribosome content, and macromolecular composition, the equivalent principles remain largely uncharacterised in mammalian cells. This thesis systematically investigates how Chinese Hamster Ovary (CHO-S) cells modulate RNA and protein levels under different extrinsic conditions, including altered nutrient availability, temperature shifts, and selective inhibition of key biosynthetic pathways. By culturing CHO-S cells in different carbon sources, distinct growth profiles were observed. Quantitative analyses of RNA, protein, and rRNA revealed negative correlations with growth rate over time and no consistent correlation between the RNA/protein ratio and growth rate. This challenges the trends commonly observed in bacterial cells. Using a GFP reporter to assess recombinant protein production under varied growth conditions revealed that slower-growing cells in weaker nutrient environments exhibited significantly higher protein expression. Furthermore, lower temperatures under standard culture conditions also led to increased protein production, which was linked to elevated RNA levels. Transcriptomic profiling using RNA sequencing identified coordinated temporal shifts in the expression of genes related to transcriptional and translational machinery, including altered RNA polymerase expression and stable ribosomal gene expression. Functional enrichment analyses revealed nutrient-specific activation of stress response and metabolic adaptation pathways. These findings advance the understanding of growth–productivity trade-offs in mammalian cells and offer strategies to optimise bioproduction through resource reallocation.