Activation of phosphatidylinositol 3-kinase/Akt pathway by androgen through interaction of p85alpha, androgen receptor, and Src.

Recent studies have demonstrated that the cell growth and antiapoptotic actions of androgen could be dissociated from the transcriptional activity of the receptor and were, instead, mediated by activation of a mitogen-activated protein kinase pathway. This finding suggests an important cellular function of androgen receptor (AR) outside the nucleus. In this report, we demonstrate that androgen activates phosphatidylinositol 3-kinase (PI3K) and Akt, including AKT1 and AKT2, in AR-positive cells. Androgen-induced cell growth and survival were inhibited by PI3K inhibitor and dominant-negative Akt. AR interacts with the p85alpha regulatory subunit of PI3K, and its binding affinity is increased after androgen stimulation. The sites of interaction on the two proteins were mapped to the C-terminal Src-homology 2 domain of p85alpha and N terminus of AR. Activation of PI3K/Akt by androgen was inhibited by dominant-negative Src. Neither N-terminal truncated nor proline-rich region-deleted AR mutants, which are unable to bind to p85alpha and Src, respectively, was able to mediate androgen-induced PI3K/Akt activation. AR with deletion of C-terminal region including ligand binding domain, however, retains the ability to activate PI3K/Akt upon androgen stimulation, which supports the notion that nongenomic function of androgen is mediated by its interaction with membrane receptors (1, 3, 4). These findings indicate that a triple complex between AR, p85alpha, and Src is required for androgen-stimulated PI3K/Akt activation, and that the PI3K/Akt pathway, in addition to mitogen-activated protein kinase, mediates androgen-induced cell growth and cell survival.