Water as a reactant in the differential expression of proteins in cancer

Introduction. How proteomes differ between normal tissue and tumor microenvironments is an important question for cancer biochemistry. Methods. More than 250 datasets for differentially expressed (up- and downregulated) proteins compiled from the literature were analyzed to calculate the stoichiometric hydration state, which represents the number of water molecules in theoretical mass-balance reactions to form the proteins from a set of basis species. Results. The analysis shows increased stoichiometric hydration state of differentially expressed proteins in cancer compared to normal tissue. In contrast, experiments with different cell types grown in 3D compared to monolayer culture, or exposed to hyperosmotic conditions under high salt or high glucose, cause proteomes to “dry out” as measured by decreased stoichiometric hydration state of the differentially expressed proteins. Conclusion. These findings reveal a basic physicochemical link between proteome composition and water content, which is elevated in many tumors and proliferating cells.