Differential Response of Akt to Cyclic AMP Modulates Drug Sensitivity

Abstract

Although Akt is known to be associated with drug resistance, its role in cyclic AMP (cAMP)-related inhibition of cell proliferation is not clear. Here, we report that Akt modulates the sensitivity of hepatocellular carcinoma cells to cAMP. Treatment of hepatocellular carcinoma cell lines (HepG₂ and Bel-7402) with cAMP inhibited proliferation, with HepG₂ cells showing lower sensitivity to cAMP. Biochemical studies showed that cAMP increased FBS-stimulated Akt phosphorylation in HepG₂ cells, but completely inhibited FBS-stimulated Akt phosphorylation in Bel-7402 cells, suggesting that the differential response of Akt to cAMP in these two cell lines might contribute to their differential sensitivity. LY294002, a phosphatidylinositol 3-kinase inhibitor that inhibits FBS-stimulated Akt phosphorylation, restored the sensitivity of HepG₂ cells to cAMP and API-2 (Akt/protein kinase B signaling inhibitor-2) also showed similar effect. These results collectively indicate that the response level of Akt to cAMP may play a critical role in determining drug sensitivity.