Control of protein turnover by the cellular hydratation state.

The hydratation state of the hepatocyte, i.e. liver cell volume can change physiologically within minutes under the influence of hormones and substrates and can also experimentally be modulated by anisoosmotic exposure. Recent studies suggest that the degree of cellular hydratation is a major determinant of cellular protein and RNA turnover. Apparently, hormones and amino acids modify protein turnover at least in part by altering the hydratation state of the cell, i.e. cell volume. Accordingly, cell volume changes are not yet recognized signals linking hormone and amino acid effects to the control of protein turnover. Cell swelling inhibits proteolysis and RNA degradation and stimulates protein, DNA and RNA synthesis, whereas cell shrinkage results in opposite alterations of RNA, DNA and protein turnover. Thus, cell swelling triggers an anabolic, proliferative pattern of metabolism, whereas cell shrinkage is a catabolic and antiproliferative signal.