Abstract 13606: Mst1 Plays a Protective Role in Response to Ischemia in the Heart by Promoting C/EBP-β Activation
Persistent activation of mammalian sterile 20-like kinase 1 (Mst1) plays a critical role in mediating cardiac dysfunction in response to stress. On the other hand, we have also shown that Mst1-mediated phosphorylation of both FoxO1 and C/EBP-β stimulates a cell-protective mechanism by enhancing FoxO1-C/EBP-β interaction and C/EBP-β-mediated transcription in the heart. We here examined how Mst1 mediates this cell-protective mechanism in the heart. After 3 hours of prolonged ischemia, both transgenic mice with cardiac-specific overexpression of dominant-negative Mst1 (Tg-DN-Mst1) and mice with C/EBP-β knockout (C/EBP-β[[Unable to Display Character: –]]/+) exhibited a significantly greater infarct size/area at risk, as determined by alcian blue and tetrazolium chloride staining, than non-transgenic (NTg) mice (Tg-DN-Mst1: 60.2 ± 2.1 %*, C/EBP-β[[Unable to Display Character: –]]/+: 58.2 ± 1.6 %*, NTg: 51.2 ± 3.4 %, *p < 0.05). Conversely, transgenic mice with cardiac-specific Mst1 overexpression (Tg-Mst1) exhibited smaller infarcts than NTg mice after prolonged ischemia (40.3 ± 3.4 %*). The beneficial effects of Mst1 were reversed in C/EBP-β[[Unable to Display Character: –]]/+-Tg-Mst1 mice (52.4 ± 8.4 %). Consistently, we observed that shRNA-mediated knockdown of Mst1 in CMs significantly exacerbated CM death after 4 hours of hypoxia in vitro (28.8 ± 2.3 % vs. 44.3 ± 2.5 %, p < 0.05). Mst1 activity was significantly higher (2.3-fold), and phosphorylated C/EBP-β at Thr299, a phosphorylation site of C/EBP-β by Mst1, was significantly accumulated (3.6-fold) in CMs in response to hypoxia compared to those in normoxia. Hypoxic conditions induced nuclear translocation of C/EBP-β in CMs as determined by immunostaining. However, knockdown of Mst1 failed to induce nuclear translocation of C/EBP-β. Pull-down assays revealed that phosphorylation of C/EBP-β at Thr299 by Mst1 facilitated homodimerization of C/EBP-β by promoting leucine zipper formation, thereby facilitating binding of C/EBP-β to DNA. Thus, hypoxia induces nuclear translocation and transcriptional activation of C/EBP-β through Mst1-mediated phosphorylation. Collectively, these results suggest that the beneficial effects of Mst1 during hypoxia are mediated through facilitation of C/EBP-β transcriptional activity, thereby stimulating a cell-protective mechanism.
Author Disclosures: Y. Maejima: None. N. Nagarajan: None. P. Zhai: None. M. Isobe: None. J. Sadoshima: None.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.