Stimulation of FA and casein kinase II by insulin in 3T3-L1 cells.

Insulin stimulates protein phosphatase-1 and FA, assayed as phosphatase-1 activator, in 3T3-L1 cells. Since other kinases, such as casein kinase-II may also contribute to such FA activity, we assayed casein kinase-II and FA as peptide kinase on extracts from 3T3-L1 cells that had been exposed to insulin for various times. Under such conditions FA, assayed as phosphatase-1 activator, was stimulated 2-3-fold within 1-2 min. Casein kinase-II was stimulated about 2-fold but at a slightly later time (2-3 min) than FA, making it unlikely that casein kinase-II contributes to FA stimulation. Insulin slightly stimulated also the kinase activity of FA towards a synthetic peptide at 2 min, thus confirming the FA activation seen when FA was assayed as activator of phosphatase-1.