ACTIVATION OF PROTEIN-KINASE B AKT IS SUFFICIENT TO REPRESS THE GLUCOCORTICOID AND CAMP INDUCTION OF PHOSPHOENOLPYRUVATE CARBOXYKINASE GENE/

A rat hepatoma cell line, H4IIE, was stably transfected with a tamoxif en regulatable Akt-1 construct. Treatment of these cells with tamoxife n caused a rapid stimulation of Akt enzymatic activity that was compar able with the activity observed with the endogenous Akt after insulin stimulation. Prior studies have extensively documented that insulin ca n repress the glucocorticoid and cAMP-stimulated increase in phosphoen olpyruvate carboxykinase (PEPCK) gene transcription. Activation of thi s regulatable Akt with tamoxifen was found to mimic the dominant inhib itory effect of insulin on PEPCK gene transcription. Dose response cur ves to insulin and tamoxifen demonstrated that this response was very sensitive to Akt activation although the maximal response observed wit h tamoxifen activation was slightly less than that observed with insul in, indicating that the response to insulin mag also involve other sig naling cascades. The regulation of PEPCK transcription via Akt was, l ike that previously described for insulin, not dependent upon 70 kDa S 6 kinase activity in that it was not inhibited by rapamycin, Finally, the expression of a kinase dead Akt was able to partially inhibit the ability of insulin to stimulate this response. in summary, the present results indicate that activation of Akt alone is sufficient to repres s the glucocorticoid and cAMP-stimulated increase in PEPCK gene transc ription.