Abstract 18194: Mst1 Stimulates Cell Protective Mechanisms of FoxO1 Through Phophorylation in Cardiomyocytes
The FoxO family transcription factors control survival and death in cardiomyocytes (CMs). The function of FoxOs is regulated by posttranslational modifications, including phosphorylation. Mst1 (mammalian sterile 20-like kinase 1), a stress-activated and proapoptotic kinase, phosphorylates FoxO1. We investigated how the function of FoxO1 is modulated by Mst1 and the role of FoxO1 in regulating the cell death promoting effect of Mst1 in the heart. Co-immunoprecipitation assay and in vitro kinase assay showed that Mst1 physically interacts with and phosphorylates FoxO1. Mst1 induced nuclear translocation of FoxO1 in CMs. However, Mst1 fails to induce nuclear translocation of a FoxO1 mutant in which Mst1 phosphorylation sites are mutated (S209/216/231/232A). Overexpression of FoxO1 significantly inhibited, whereas knock-down of FoxO1 exacerbated, Mst1-induced apoptosis. FoxO1 upregulated cell survival genes but inhibited proapoptotic genes in the presence of Mst1. In order to examine the functional significance of the Mst1 and FoxO1 interaction in vivo, we generated cardiac-specific FoxO1 knockout mice (FoxO1-CKO), and then crossbred cardiac-specific Mst1 transgenic (Tg) mice (Mst1-Tg) with the FoxO1-CKO mice (Mst1-Tg × FoxO1-CKO, bigenic). Ablation of FoxO1 in Mst1-Tg significantly exacerbated the left ventricular (LV) dysfunction observed in Mst1-Tg (LV ejection fraction: Wild type (WT) =73±2%, Mst1-Tg=57±2%*, FoxO1-CKO=65±2%*, bigenic=51±3%*#, *p<0.05 vs WT, #p<0.05 vs Mst1-Tg). LV dP/dt was decreased in bigenic mice compared to Mst1-Tg (WT=7733±961, Mst1-Tg=5400±200*, FoxO1-CKO=7733±961, bigenic=4000±327*#, *p<0.05 vs WT, #p<0.05 vs Mst1-Tg). TUNEL-positive CMs were significantly increased in bigenic mice compared to Mst1-Tg (WT=0.04±0.002%, Mst1-Tg=0.32±0.02%*, FoxO1-CKO=0.04±0.001%, bigenic=0.45±0.43%*#, *p<0.05 vs WT, #p<0.05 vs Mst1-Tg) as was the level of interstitial fibrosis (WT=1.9±0.4%, Mst1-Tg=6.6±0.8%*, FoxO1-CKO=2.1±0.2%, bigenic=8.1±1.1%*#, *p<0.05 vs WT, #p<0.05 vs Mst1-Tg). In summary, Mst1 plays an important role in mediating phosphorylation and nuclear localization of FoxO1 during stress. Mst1 stimulates cell protective mechanism of FoxO1 as a negative feedback mechanism.
- © 2010 by American Heart Association, Inc.