Expression of Type 2a Protein Phosphatases in Cardiac Health and Disease

Abstract

Cardiac physiology and hypertrophy are regulated by the phosphorylation status of many proteins, which is partly controlled by a poorly defined type 2A protein phosphatase-alpha4 intracellular signalling axis. Quantitative PCR analysis revealed that mRNA levels of the type 2A catalytic subunits were differentially expressed in H9c2 cardiomyocytes (PP2ACb [ PP2ACa [ PP4C [ PP6C), NRVM (PP2ACb [ PP2ACa = PP4C = PP6C), and adult rat ventricular myocytes (PP2ACa [ PP2ACb [ PP6C [ PP4C). Western analysis confirmed that all type 2A catalytic subunits were expressed in H9c2 cardiomyocytes; however, PP4C protein was absent in adult myocytes and only detectable following 26S protea-some inhibition. Short-term knockdown of alpha4 protein expression attenuated expression of all type 2A catalytic subunits. Pressure overload-induced left ventricular (LV) hypertrophy was associated with an increase in both PP2AC and alpha4 protein expression. Although PP6C expression was unchanged, expression of PP6C regulatory subunits (1) Sit4-associated protein 1 (SAP1) and (2) ankyrin repeat domain (ANKRD) 28 and 44 proteins was elevated, whereas SAP2 expression was reduced in hypertrophied LV tissue. Co-immunoprecipitation studies demonstrated that the interaction between alpha4 and PP2AC or PP6C subunits was either unchanged or reduced in hypertrophied LV tissue, respectively. Phosphorylation status of phospholemman (Ser63 and Ser68) was significantly increased by knockdown of PP2ACa, PP2ACb, or PP4C protein expression. DNA damage assessed by histone H2A.X phosphorylation (cH2A.X) in hypertrophied tissue remained unchanged. However, exposure of cardiomy-ocytes to H 2 O 2 increased levels of cH2A.X which was unaffected by knockdown of PP6C expression, but was abolished by the short-term knockdown of alpha4 expression. This study illustrates the significance and altered activity of the type 2A protein phosphatase-alpha4 complex in healthy and hypertrophied myocardium. Keywords Type 2A protein phosphatase Á Alpha4 Á Cardiac hypertrophy Á Hydrogen peroxide Á H2A.X

Integrative analysis of promising molecular biomarkers and pathways for coronary artery disease using WGCNA and MetaDE methods

“…Nonetheless, the role of IMPDH2 in CAD has been poorly defined. The PPP4C gene encodes the PP4C protein, which is a member of the type 2 serine/threonine protein phosphatase family ( 46 ), and partly regulates the phosphorylation of numerous proteins implicated in cardiac physiology and hypertrophy ( 47 , 48 ). The present study indicated that IMPDH2 and PPP4C may be important genes in CAD.…”