Abstract 274: Expression and Phosphorylation States of Eukaryotic Elongation Factor 2 (EEF2) and EEF2 Kinase in Cardiomyocytes From Hypertrophy Models
Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K, also known as calmodulin (CaM)-dependent protein kinase III) is regulated by both CaM-dependent and -independent mechanisms. Activated eEF2K phosphorylates and inactivates a specific substrate, eEF2. eEF2 activation facilitates protein translation. It is recognized that increased protein synthesis is one of the primary factors for cardiomyocyte hypertrophy. In fact, angiotensin II, which induces cardiomyocyte hypertrophy, was reported to facilitate eEF2 dephosphorylation (activation) and protein synthesis in rat isolated cardiomyocytes. We have previously demonstrated that protein expression of eEF2K was increased specifically in left ventricles (LV) of spontaneously hypertensive rats (SHR). However, expression and phosphorylation states of eEF2K and eEF2 in LV of other cardiac hypertrophy models are unknown. The aim of this study was to explore it. Male C57BL/6NJcl mice and Wistar rats received transverse aortic constriction (TAC) and isoproterenol (5 mg/kg; ISO) injection, respectively, which induced cardiac hypertrophy. After 3 and 28 days from TAC operation and 7 days from ISO injection, LV were isolated and used for Western blotting (WB) and immunohistochemistry (IHC). Echocardiography was done in TAC mice before LV isolation. In TAC-induced hypertrophied LV (3 days), eEF2K expression was significantly increased (p<0.01 vs. SHAM) and its phosphorylation at Ser366 was significantly decreased (p<0.05 vs. SHAM). Consistently, eEF2 phosphorylation was significantly increased (p<0.01 vs. SHAM). In LV from ISO rats, eEF2K phosphorylation at Ser366 was significantly decreased as determined by WB (p<0.01 vs. control). In addition, eEF2K- and phosphorylated eEF2-positive cardiomyocytes were increased as determined by IHC. These changes were also confirmed in LV from SHR. At 28 days after TAC, fractional shortening was significantly decreased (from 56.6±1.6% to 44.4±2.3%, p<0.01). Interestingly, eEF2 phosphorylation in LV was significantly decreased (p<0.05 vs. SHAM). The present results suggest the potential role of eEF2K/eEF2 signals in the pathogenesis of cardiac hypertrophy/failure.