A Novel Atypical PKC-Iota Inhibitor, Echinochrome A, Enhances Cardiomyocyte Differentiation from Mouse Embryonic Stem Cells

Echinochrome A (EchA) is a marine bioproduct extracted from sea urchins having antioxidant, antimicrobial, anti-inflammatory, and chelating effects, and is the active component of the clinical drug histochrome. We investigated the potential use of Ech A for inducing cardiomyocyte differentiation from mouse embryonic stem cells (mESCs). We also assessed the effects of Ech A on mitochondrial mass, inner membrane potential (Delta psi m), reactive oxygen species generation, and levels of Ca2+. To identify the direct target of Ech A, we performed in vitro kinase activity and surface plasmon resonance binding assays. Ech A dose-dependently enhanced cardiomyocyte differentiation with higher beating rates. Ech A (50 mu M) increased the mitochondrial mass and membrane potential but did not alter the mitochondrial superoxide and Ca2+ levels. The in vitro kinase activity of the atypical protein kinase C-iota (PKC iota) was significantly decreased by 50 mu M of Ech A with an IC50 for PKC activity of 107 M. Computational protein-ligand docking simulation results suggested the direct binding of Ech A to PKC, and surface plasmon resonance confirmed the direct binding with a low K-D of 6.3 nM. Therefore, Ech A is a potential drug for enhancing cardiomyocyte differentiation from mESCs through direct binding to PKC and inhibition of its activity.