Abstract 1379: Proapoptotic Serine/Threonine Kinase Mst1 Prevents Cardiac Hypertrophy through Phosphorylation of PERK
Mammalian sterile 20-like kinase1 (Mst1) is a serine/threonine kinase, which plays an important role in mediating apoptosis. Mst1 is activated by pressure overload and ischemia/ reperfusion in the heart. Persistent activation of Mst1 leads to dilated cardiomyopathy (DCM) without compensatory hypertrophy. The lack of compensatory hypertrophy despite cardiac dilation increases wall stress and may be detrimental. We examined the molecular mechanism by which this proapoptotic kinase inhibits cardiac hypertrophy. Overexpression of Mst1 significantly inhibited increases in cell size by phenylephrine (PE), (PE 2.2 fold, PE+Mst1 1.1 fold, p<0.05) in cultured cardiac myocytes. Mst1 induced phosphorylation of eukaryotic translation initiation factor 2- α (Ser51, eIF2- α, 3.2 fold, p<0.05), a negative regulator of protein translation, and protein kinase R-like endoplasmic reticulum (ER) kinase (Thr980, PERK, 6.7 fold, p<0.05), a kinase phosphorylating eIF2- α. Activation of PERK and phosphorylation of eIF2- α are observed in the presence of ER stress. In fact, other markers of ER stress, such as CHOP (2.7 fold) and caspase12 (3.0 fold), were also stimulated by Mst1 in cardiac myocytes. Overexpression of dominant-negative PERK (DN-PERK) abolished Mst1-induced increases in Ser51 phosphorylation of eIF2- α. Furthermore, inhibition of PE-induced cardiac hypertrophy by Mst1 was alleviated by the presence of DN-PERK, suggesting that PERK plays an essential role in mediating Mst1-induced inhibition of cardiac hypertrophy. GST-PERK-C terminal fusion protein was able to bind Mst1 in vitro. Moreover, Mst1 co-stained with protein disulfide isomerase, an ER protein, indicating that Mst1 is localized at the ER. Mst1 phosphorylates GST-PERK-C terminal, including Thr980 in the activation loop of PERK, in vitro. These results suggest that Mst1 directly interacts with PERK at the ER, thereby phosphorylating it. Activation of PERK by Mst1 mimics ER stress responses, thereby mediating inhibition of cardiac hypertrophy, through Ser51 phosphorylation of eIF2- α. These results suggest that Mst1 not only stimulates apoptosis but also initiates cross talk with the ER stress pathway through activation of PERK, thereby inhibiting compensatory cardiac hypertrophy.