Akt/protein kinase B is constitutively active in non-small cell lung cancer cells and promotes cellular survival and resistance to chemotherapy and radiation

To evaluate the role of Akt/PKB in non-small cell lung cancer (NSCLC) survi val, we analyzed NSCLC cell lines that differed in tumor histology as well as p53, Rb, and K-ras status. Constitutive Akt/protein kinase B (PI(B) acti vity was demonstrated in 16 of 17 cell lines by maintenance of S473 phospho rylation with serum deprivation, Additional analysis of five of these NSCLC lines revealed that phosphorylation of S473 and T308 correlated with ill v itro kinase activity. Akt/PKB activation was phosphatidylinositol 3-kinase- dependent and promoted survival because the phosphatidylinositol 3 inhibito rs LY294002 and wortmannin inhibited Akt/PKB phosphorylation, Akt/PKB activ ity, and increased apoptosis only in cells with active Akt/PKB. To test whe ther Akt/PKB activity promoted therapeutic resistance, LY294002 was added w ith individual chemotherapeutic agents or irradiation. LY294002 greatly pot entiated chemotherapy-induced apoptosis in cells with high Akt/PKB levels, but did not significantly increase chemotherapy-induced apoptosis in cells with low Akt/PKB levels, Combined with radiation in cells with active Akt/P KB, LY294002 additively increased apoptosis and inhibited clonogenic growth , These results mere extended with transiently transfected Akt/PKB mutants. Transfecting dominant negative Akt/PKB decreased Akt/PKB activity and incr eased basal apoptosis as well as chemotherapy- and irradiation-induced apop tosis only in cells with high Akt/PKB activity, Conversely, transfecting co nstitutively active Akt/PKB into cells with low Akt/PKB activity increased Akt/PKB activity and attenuated chemotherapy- and radiation-induced apoptos is, We therefore identify Akt/PKB as a constitutively active kinase that pr omotes survival of NSCLC cells and demonstrate that modulation of Akt/PKB a ctivity by pharmacological or genetic approaches alters the cellular respon siveness to therapeutic modalities typically used to treat patients with NS CLC.