Abstract 29: Inhibition of Mst1 Kinase by Protein-l-Isoaspartate (d-aspartate) O-Methyltransferase Protects Cardiomyocytes from Hypoxia-Induced Apoptosis

Abstract

Background: Mammalian sterile 20-like kinase 1 (Mst1) is a mammalian homolog of Hippo kinase from Drosophila and it is a critical component of the Hippo signaling pathway, which regulates a variety of biological processes ranging from cell contact inhibition, organ size control, apoptosis and tumor suppression in mammals. Activation of Mst1 causes cardiomyocyte apoptosis and dilated cardiomyopathy. However, the mechanism underlying Mst1 activation in the heart is not known. Method and result: In a yeast two-hybrid screen of a human heart cDNA library with a dominant-negative Mst1 (K59R) mutant used as bait, protein-L-isoaspartate (D-aspartate) O-methyltransferase (PCMT1) was identified as an Mst1-interacting protein. The interaction of PCMT1 with Mst1 was confirmed by co-immunoprecipitation in both co-transfected HEK-293 cells and native cardiomyocytes, in which PCMT1 interacted with the kinase domain of Mst1, but not with its C-terminal regulatory domain. Knockdown of PCMT1 augments hypoxia/reoxygenation induced Mst1 activation and apoptosis. Overexpression of PCMT1 did not affect the Mst1 expression, but significantly attenuated the Mst1 activation and its apoptotic effects in response to the hypoxia/reoxygenation induced injury in cardiomyocytes. Moreover, upregulation of PCMT1 by CGP3466B, a compound related to the anti-Parkinson’s drug R-(-)-deprenyl with potent antiapoptotic effects, inhibited the hypoxia/reoxygenation induced Mst1 activation and cardiomyocyte apoptosis. Conclusion: PCMT1 is a novel inhibitor of Mst1 activation in cardiomyocytes and suggest that targeting PCMT1 may prevent myocardial apoptosis through inhibition of Mst1.