The glucocorticoid dexamethasone and the tumor-promoting artificial sweetener saccharin stimulate protein kinase C from T51B rat liver cells

Abstract

Diacylglycerols, such as 1,2-diolein, and tumor-promoting phorbol comoounds, such as TPA (12-O-tetradecanoyl phorbol-13-acetate), stimulate the Ca 2+ phospholipid -dependent protein kinase C from T51B rat liver cells, probably by sensitizing it to activation by Ca 2+, and they reduce the liver cells' content of EDTA-extractable (i.e., soluble) protein kinase C activity. Evidence is presented that indicates that the glucocorticoid, dexamethasone, and the tumor-promoting artificial sweetener, saccharin, also trigger a Ca 2+-dependent increase in the activity of the protein kinase C from T51B liver cells and reduce the cells' content of EDTA-extractable protein kinase C activity. However, these novel stimulators do not activate the enzyme by binding to the same site as diacylglycerols and TPA, although they do alter this site as indicated by an increase in the binding of the TPA analogue PDBu (phorbol 12,13-dibutyrate).