The cultural divide: exponential growth in classical 2D and metabolic equilibrium in 3D environments

Cellular metabolism can be considered to have two extremes: one is characterized by exponential growth (in 2D cultures) and the other by a dynamic equilibrium (in 3D cultures). We have analysed the proteome and cellular architecture at these two extremes and found that they are dramatically different. Ultrastructurally, actin organization is changed, microtubules are increased and keratins 8 and 18 decreased. Metabolically, glycolysis, fatty acid metabolism and the pentose phosphate cycle are increased while Krebs cycle and oxidative phosphorylation is unchanged. Enzymes involved in cholesterol and urea synthesis are increased underpinning the attainment of cholesterol and urea production rates seen in vivo. DNA repair enzymes are increased even though cells are predominantly in G0. Transport around the cell – along the microtubules, through the nuclear pore and in various types of vesicle has been prioritized. There are numerous coherent changes in transcription, splicing, translation, protein folding and degradation. The amount of individual proteins within complexes is shown to be highly coordinated. Typically subunits which initiate a particular function are present in increased amounts compared to other subunits of the same complex.
We have previously demonstrated that cells at dynamic equilibrium can match the physiological performance of cells in tissues in vivo (Wrzesinski and Fey 2013, Wrzesinski et al 2013, Fey and Wrzesinski 2012). Here we describe the multitude of protein changes necessary to achieve this performance.