Growth arrest-specific protein 6
positive regulation of protein export from nucleus
GAS6-induced signaling in human endothelial cells is mediated by FOXO1a.
<h4>Background</h4>Growth Arrest Specific gene product 6 (gas6) is a gamma-carboxylated protein that protects endothelial cells against apoptosis. Gas6 has previously been shown to induce phospatidyl-3-inositol-kinase (PI3K)/Akt signaling. Other studies have demonstrated a link between PI3K/Akt signaling and forkhead transcription factors in endothelial cells.<h4>Objective</h4>To test the hypothesis that gas6 promotes cell survival via a forkhead-dependent pathway.<h4>Results and conclusions</h4>Treatment of serum-starved human umbilical vein endothelial cells (HUVECs) with gas6 induced time-dependent phosphorylation and nuclear exclusion of FOXO1a. This effect was suppressed by the PI3K inhibitor wortmannin, demonstrating that FOXO1a phosphorylation is PI3-kinase dependent. Transduction of HUVECs with a phosphorylation-resistant form of FOXO1a [triple mutant (TM)-FOXO1a] abrogated the pro-survival effect of gas6 on serum-starved endothelial cells. Finally, treatment of serum-starved HUVECs with gas6 resulted in a reduction of FOXO1a transcriptional activity and downregulation of the pro-apoptotic gene, p27(kip1). Taken together, these findings suggest that gas6 protects endothelial cells from apoptosis by a mechanism that involves PI3K-Akt-dependent inactivation of FOXO1a.