Stimulation of cardiac sarcoplasmic reticulum calcium pump by acylphosphatase. Relationship to phospholamban phosphorylation

Dipartimento di Scienze Biochimiche, Università di Firenze, Viale Morgagni 50, 50134 Firenze, Italy.
Journal of Biological Chemistry (Impact Factor: 4.57). 09/1996; 271(32):19066-73. DOI: 10.1074/jbc.271.32.19066
Source: PubMed


Ca2+ transport by cardiac sarcoplasmic reticulum is tightly coupled with the enzymatic activity of Ca2+-dependent ATPase, which forms and decomposes an intermediate phosphoenzyme. Heart sarcoplasmic reticulum Ca2+ pump is regulated by cAMP-dependent protein kinase (PKA) phospholamban phosphorylation, which results in a stimulation of the initial rates of Ca2+ transport and Ca2+ ATPase activity. In the present studies we found that acylphosphatase from heart muscle, used at concentrations within the physiological range, actively hydrolyzes the phosphoenzyme of cardiac sarcoplasmic reticulum Ca2+ pump, with an apparent Km on the order of 10(-7) M, suggesting an high affinity of the enzyme for this special substrate. In unphosphorylated vesicles acylphosphatase enhanced the rate of ATP hydrolysis and Ca2+ uptake with a concomitant significant decrease in apparent Km for Ca2+ and ATP. In vesicles whose phospholamban was PKA-phosphorylated, acylphosphatase also stimulated the rate of Ca2+ uptake and ATP hydrolysis but to a lesser extent, and the Km values for Ca2+ and ATP were not significantly different with respect to those found in the absence of acylphosphatase. These findings suggest that acylphosphatase, owing to its hydrolytic effect, accelerates the turnover of the phosphoenzyme intermediate with the consequence of an enhanced activity of Ca2+ pump. It is known that phosphorylation of phospholamban results in an increase of the rate at which the phosphoenzyme is decomposed. Thus, as discussed, a competition between phospholamban and acylphosphatase effect on the phosphoenzyme might be proposed to explain why the stimulation induced by this enzyme is less marked in PKA-phosphorylated than in unphosphorylated heart vesicles.

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Available from: Chiara Nediani, Apr 03, 2015
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    • "The true physiological function of AcP has not been fully revealed. Studies have shown that AcP is involved in the control of the ionic states of the cells by hydrolyzing the b-aspartyl phosphate intermediates formed during ATPases action [2] [3] [4]. It was also shown that AcP associates with male hybrid sterility in Drosophila [5]. "
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    FEBS letters 07/2010; 584(13):2852-6. DOI:10.1016/j.febslet.2010.04.069 · 3.17 Impact Factor
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    • "a cytosolic enzyme, well represented in cardiac muscle, that catalyzes the hydrolysis of acylphosphates [5– 7]. In previous studies, we have shown that ACPase can interact with SERCA2a and actively hydrolyze the EP intermediate of this transport system, an effect that results in an enhanced activity of the SR Ca 2 + pump [8] [9]. Besides their consequences on cardiomyocyte contractile functioning, intracellular Ca 2 + homeostasis alterations have been consistently related to apoptosis. "
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    ABSTRACT: To identify early adaptive processes of cardiac remodeling (CR) in response to volume overload, we investigated the molecular events that may link intracellular Ca(2+) homeostasis alterations and cardiomyocyte apoptosis. In swine heart subjected to aorto-cava shunt for 6, 12, 24, 48 and 96 h sarcoplasmic reticulum (SR) Ca(2+) pump activity was reduced until 48 h (-30%), but a recovery of control values was found at 96 h. The decrease in SR Ca(2+)-ATPase (SERCA2a) expression at 48 h, was more marked (-60%) and not relieved by a subsequent recovery, while phospholamban (PLB) concentration and phosphorylation were unchanged at all the considered times. Conversely, acylphosphatase activity and expression significantly increased from 48 to 96 h (+40%). Bcl-2 expression increased significantly from 6 to 24 h, but at 48 h, returned to control values. At 48 h, microscopic observations showed that overloaded myocardium underwent substantial damage and apoptotic cell death in concomitance with an enhanced Fas/Fas-L expression. At 96 h, apoptosis appeared attenuated, while Fas/Fas-L expression was still higher than control values and cardiomyocyte hypertrophy became to develop. These data suggest that in our experimental model, acylphosphatase could be involved in the recovery of SERCA2a activity, while cardiomyocyte apoptosis might be triggered by a decline in Bcl-2 expression and a concomitant activation of Fas.
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    • "a cytosolic 11 kDa enzyme well represented in cardiac muscle that catalyzes the hydrolysis of acylphosphates [4] [5] [6]. In previous studies we have shown that acylphosphatase actively hydrolyzes the EP intermediate of this transport system, an effect that results in an enhanced activity of the SR Ca 2þ pump [7] [8]. We have also demonstrated that acylphosphatase, in addition to its hydrolytic activity on EP, stimulated SER- CA2a activity through another mechanism, probably due to its conformational properties. "
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    ABSTRACT: We previously reported that acylphosphatase, a cytosolic enzyme present in skeletal and heart muscle, actively hydrolyzes the phosphoenzyme (EP) of cardiac sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a), inducing an increased activity of this pump. We hypothesized that acylphosphatase-induced stimulation of SERCA2a, in addition to enhanced EP hydrolysis, may be due to a displacement of phospholamban (PLN), removing its inhibitory effect. To verify this hypothesis co-immunoprecipitation experiments were performed by adding recombinant muscle acylphosphatase to solubilized heart SR vesicles, used as a source of SERCA2a and PLN. With anti-acylphosphatase antibodies only SERCA2a was co-immunoprecipitated in an amount which increased in parallel to the concentrations of our enzyme. Conversely, using anti-SERCA2a antibody, both PLN and acylphosphatase were co-immunoprecipitated with SERCA2a, and the PLN amount in the precipitate decreased with increasing acylphosphatase concentrations. SERCA2a and PLN were co-immunoprecipitated by anti-phospholamban antibodies, but while the amount of precipitated phospholamban increased in the presence of acylphosphatase, the level of SERCA2a decreased. These preliminary results strengthen the supposed displacement of phospholamban by acylphosphatase.
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