Abstract 2958: Novel Role of Protein Inhibitor of Activated Stat1 (PIAS1) as a Substrate of P90rsk in Diabetic (DM) Cardiomyopathy via Small Ubiquitin-related Modification of ERK5 Kinase (ERK5-sumoylation)
Post-myocardial infarction (MI) left ventricular (LV) function is worse in DM patients, but the exact mechanism remains unclear. After extensive survey of activated kinases in DM, we reported the significant increase of p90RSK activation, and inhibition of p90RSK by dominant negative form of p90RSK (DN-RSK) was cardio-protective. Recently, we found the critical role of ERK5-SUMOylation, which decreased ERK5 transactivation, in DM-mediated exaggeration of apoptosis and LV dysfunction after MI (DM + MI) in vivo. However, the relationship between p90RSK and ERK5-SUMOylation remains unclear. First we found that overexpression of p90RSK increased ERK5-SUMOylation and subsequent apoptosis. PIAS1, as a SUMO E3 ligase, has a key role for H2O2-mediated ERK5-SUMOylation and apoptosis shown by depletion study using siRNA in cardiomyocytes. Based on mass spectrometry analysis and in vitro kinase assay, we found that PIAS1 Ser 510, 517, and 522 were p90RSK phosphorylation sites, and mutation of Ser 510, 517 and 522 to Ala decreased PIAS1 sumoylation activity on ERK5, suggesting the critical role of p90RSK-mediated PIAS1 phosporylation on ERK5-SUMOylation and apoptosis in vitro. Next we investigated the role of p90RSK on ERK5-SUMOylation in vivo. Cardiac-specific wild type p90RSK transgenic mice (WT-RSK-Tg) increased ERK5-SUMOylation and accelerated mortality one week after MI without inducing DM compared with non-Tg littermate control mice (NLC) (% of fraction shortening (FS) of WT-RSK-Tg vs NLC: 13.0±1.2 vs 22.7±2.8, p<0.05), suggesting that p90RSK activation can mimic LV dysfunction in DM cardiomyopathy. While DN-RSK-Tg showed the inhibition of ERK5-SUMOylation and LV dysfunction in DM after MI (% of FS of DN-RSK-Tg vs NLC: 22.8±2.1 vs 15.5±1.9, p<0.05). Double transgenic mice (D-Tg) of WT-RSK and active form of MEK5α (specific ERK5 activator), inhibited LV dysfunction and significantly improved survival rate after MI compared with single WT-RSK-Tg (survival rate of D-Tg vs WT-RSK-Tg: 71 % vs 51 %, log rank test: p<0.05). These data suggest the critical role of p90RSK-mediated increase of PIAS1 sumoylation activity and ERK5-SUMOylation in accelerated LV dysfunction in DM after MI. We believe that p90RSK is a novel therapeutic target for DM cardiomyopathy.