Regulation of transglutaminase activity in Chinese hamster ovary cells

We have investigated the regulation of transglutaminase activity (epsilon-(gamma-glutamyl)lysine crosslinking enzyme) in Chinese hamster ovary cells in culture. We report that transglutaminase activity increases several-fold in CHO cells at maximum density in suspension culture. This increase cannot be explained by the presence of soluble regulators of the enzyme activity or the appearance of a new enzyme activity with a different affinity for substrate, but appears to be due to an increase in total enzyme activity. Treatment of CHO cells at low cell density with 8-bromo cyclic AMP results in a small increase (20--70%) in transglutaminase activity. By studying CHO mutants which have altered or absent cyclic-AMP-dependent protein kinases, we have demonstrated that the effect of cyclic AMP on transglutaminase activity at low cell density is mediated by cyclic-AMP-dependent protein kinase. However, the protein kinase mutants show normal increases in transglutaminase activity at high cell density, indicating that cyclic AMP-dependent protein kinase does not mediate density-dependent changes in transglutaminase activity.