In vitroreconstitution of Sgk3 activation by phosphatidylinositol-3-phosphate

Summary Serum- and glucocorticoid-regulated kinase 3 (Sgk3) is activated by the phospholipid phosphatidylinositol-3-phosphate (PI3P) downstream of growth factor signaling and by Vps34-mediated PI3P production on endosomes. Upregulation of Sgk3 activity has recently been linked to a number of human cancers. Here, we show that Sgk3 is regulated by a combination of phosphorylation and allosteric activation by PI3P. We demonstrate that PI3P binding induces large conformational changes in Sgk3 associated with its activation, and that the PI3P binding pocket of the PX domain of Sgk3 is sequestered in its inactive conformation. Finally, we reconstituted Sgk3 activation via Vps34-mediated PI3P synthesis on phosphatidylinositol liposomes in vitro . In addition to defining the mechanism of Sgk3 activation by PI3P, our findings open up potential therapeutic avenues in allosteric inhibitor development to target Sgk3 in cancer.