Molecular cloning and characterization of the human AKT1 promoter uncovers its up-regulation by the Src/Stat3 pathway

Akt1, also known as protein kinase B (PKB) alpha, is frequently activated in human cancers and has been implicated in many cell processes by phosphorylation of downstream molecules. However, transcriptional regulation of Akt1 has not been documented. Here, we report the isolation and characterization of the human AKT1 promoter and demonstrate transcriptional up-regulation of AKT1 by the Src/Stat3 pathway. Protein and mRNA levels of AKT1 are elevated in cells expressing constitutively active Stat3 as well as in v-Src-transformed NIH3T3 cells. Knockdown of Stat3 reduces AKT1 expression induced by v-Src. Although the 4.2-kb region upstream of the transcription start site of the AKT1 promoter contains five putative Stat3-binding motifs, the promoter failed to be induced by Stat3 and/or Src. Further analysis reveals that major Stat3 response elements are located within exon 1 and intron 1 regions of the AKT1 gene, which is upstream of the AKT1 translation initiation site. In addition, ectopic expression of wild type AKT1 in Stat3(-/-) MEF cells largely rescues serum starvation-induced cell death. These findings indicate that the AKT1 promoter comprises exon 1 and intron 1, in addition to the sequence upstream of transcriptional start site. Our data further show that AKT1 is a direct target gene of Stat3 and contributes to Stat3 anti-apoptotic function.