Identification of AKT-regulated genes in inducible MERAkt cells

AKT/protein kinase B plays a critical role in the phosphoinositide 3-kinase (PI3-kinase) pathway regulating cell growth, differentiation, and oncogenic transformation. Akt1-regulated genes were identified by cDNA array hybridization analysis using an inducible AKT1 protein, MERAKT. Treatment of MERAkt cells with estrogen receptor ligands resulted in phosphorylative activation of MERAKT. Genes differentially expressed in MERAkt/NIH3T3 cells treated with tamoxifen, raloxifene, ICI-182780, and ZK955, were identified at 3 and 20 h. AKT activation resulted in the repression of c-myc, early growth response 1 (EGR1), transforming growth factor beta receptor III (TGF-betar III), and thrombospondin-1 (THBS1). Although c-myc induction is often associated with oncogenic transformation, the c-myc repression observed here is consistent with the anti-apoptotic function of AKT. Repression of THBS1 and EGR1 is consistent with the known pro-angiogenic functions of AKT. AKT-regulated genes were found to be largely distinct from platelet-derived growth factor-beta (PDGFbeta)-regulated genes; only T-cell death-associated gene 51 (TDAG51) was induced in both cases. In contrast to their repression by AKT, c-myc, THBS1, and EGR1 were induced by PDGFbeta, indicating negative interference between elements upstream and downstream of AKT1 in the PDGFbeta signal transduction pathway.