A Rapid, Nongenomic, Signaling Pathway Regulates the Actin Reorganization Induced by Activation of Membrane Testosterone Receptors

The human prostate cancer cell line LNCaP bears functional membrane testosterone receptors, which modify the actin cytoskeleton and increase the secretion of prostate-specific antigen (PSA) within minutes. Membrane steroid receptors are, indeed, a newly identified element of steroid action that is different from the classical intracellular sites. In the present work, using a nonpermeable analog of testosterone (testosterone-BSA), we investigated the signaling pathway that is triggered by the membrane testosterone receptors' activation and leads to actin cytoskeleton reorganization. We report that exposure of cells to testosterone-BSA resulted in phosphorylation of focal adhesion kinase (FAK), the association of FAK with the phosphatidylinositol-3 (PI-3) kinase, and the subsequent activation of the latter as well as the activation of the small guanosine triphosphatases Cdc42/Rac1. Pretreatment of cells with the specific PI-3 kinase inhibitor wortmannin abolished both the activation of the small guanosine triphosphatases and the alterations of actin cytoskeleton, whereas it did not affect the phosphorylation of FAK. These findings indicate that PI-3 kinase is activated downstream of FAK and upstream of Cdc42/Rac1, which subsequently regulate the actin organization. Moreover, wortmannin diminished the secretion of PSA, implying that the signaling events described above are responsible for the testosterone-BSA-induced PSA secretion. Our results are discussed under the prism of a possible implication of these membrane receptors in prostate cancer chemotherapy.