Glucocorticoid hormones increase the activity of plasma membrane alkaline phosphodiesterase I in rat hepatoma cells.

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Abstract
In rat hepatoma [HTC] cells the synthetic glucocorticoid dexamethasone caused a 3-fold increase in the activity of the plasma membrane enzyme alkaline phosphodiesterase I (oligonucleate 5''-nucleotidohydrolase). The data are consistent with an induction phenomenon mediated by the glucocorticoid receptor involved in tyrosine aminotransferase induction. The effect on alkaline phosphodiesterase I is not a reflection of a general membrane effect of dexamethasone, because the activity of three other enzymes of the plasma membrane is unaffected. Nucleoside diphosphatase (nucleoside diphosphate phosphohydrolase acting on ADP) activity is inhibited. Thus, 2 more enzymes sensitive to glucocorticoids have been identified in a cell line in which these hormones influence only very few gene products. Enzymatic changes in the plasma membrane of rat hepatoma cells are described in which glucocorticoids normalize a number of membrane-associated processes that are considered characteristic of transformed cells.