Regulation of aromatase activity by Akt-mediated phosphorylation on Ser267 and Ser268

Abstract

In MCF-7 cells stably expressing aromatase, aromatase activity is reduced by serum starvation and rescued by EGF. Expression of a constitutive active Akt (CA-Akt) resulted in 4 fold increase in aromatase activity of MCF-7/CA cells. In Cos-7 cells, transient expression of aromatase and CA-Akt also increased aromatase acitivity upto 2 fold. By scansite analysis, we chose T268 as a possible Akt phosphorylation site in aromatase. However, T268A mutant showed only a modest reduction in aromatase activity and aromatase activity of phosphomimicking T268E mutant was still further stimulated by CA-Akt. So we generated double mutant S267AT268A and found that introduction of double alanine mutation could almost abrogate aromatase activity and double phosphomimicking mutant (S267ET267E) has a higher activity than T268E. We have found that phosphorylation status of aromatase is significantly reduced in S267AT268A mutant. Androtenedione-mediated luciferase activity was decreased in MCF-7 cells expressing S267AT268A mutant and increased in cells expressing S267ET268A mutant. The results suggest Akt-mediated phosphorylation on S267 and T268 may upregulate aromatase activity.