TY - JOUR
T1 - The antiapoptotic protein HAX-1 mediates half of phospholamban's inhibitory activity on calcium cycling and contractility in the heart
AU - Bidwell, Philip A.
AU - Haghighi, Kobra
AU - Kranias, Evangelia G.
N1 - Publisher Copyright:
© 2018 by The American Society for Biochemistry and Molecular Biology, Inc.
PY - 2018/1/5
Y1 - 2018/1/5
N2 - The antiapoptotic protein HAX-1 (HS-associated protein X-1) localizes to sarcoplasmic reticulum (SR) in the heart and interacts with the small membrane protein phospholamban (PLN), inhibiting the cardiac sarco/endoplasmic reticulum calcium ATPase 2a (SERCA2a) in the regulation of overall calcium handling and heart muscle contractility. However, because global HAX-1 deletion causes early lethality, how much endogenous HAX-1 contributes to PLN's inhibitory activity on calcium cycling is unknown. We therefore generated a cardiacspecific and inducible knock-out mouse model. HAX-1 ablation in the adult heart significantly increased contractile parameters and calcium kinetics, associated with increased SR calcium load. These changes occurred without any changes in the protein expression of SERCA2a, PLN, and ryanodine receptor or in the PLN phosphorylation status. The enhanced calcium cycling in the HAX-1-depleted heart was mediated through increases in the calcium affinity of SERCA2a and reduced PLN-SERCA2a binding. Comparison of the HAX-1 deletion-induced stimulatory effects with those elicited by PLN ablation indicated that HAX-1 mediates∼50% of the PLN-associated inhibitory effects in the heart. Stimulation with the inotropic and lusitropic agent isoproterenol eliminated the differences among wild-type, HAX-1-deficient, and PLN-deficient hearts, and maximally stimulated contractile and calcium kinetic parameters were similar among these three groups. Furthermore, PLN overexpression in the HAX-1-null cardiomyocytes did not elicit any inhibitory effects, indicating thatHAX-1may limitPLNactivity. These findings suggest that HAX-1 is a major mediator of PLN's inhibitory activity and a critical gatekeeper of SR calcium cycling and contractility in the heart.
AB - The antiapoptotic protein HAX-1 (HS-associated protein X-1) localizes to sarcoplasmic reticulum (SR) in the heart and interacts with the small membrane protein phospholamban (PLN), inhibiting the cardiac sarco/endoplasmic reticulum calcium ATPase 2a (SERCA2a) in the regulation of overall calcium handling and heart muscle contractility. However, because global HAX-1 deletion causes early lethality, how much endogenous HAX-1 contributes to PLN's inhibitory activity on calcium cycling is unknown. We therefore generated a cardiacspecific and inducible knock-out mouse model. HAX-1 ablation in the adult heart significantly increased contractile parameters and calcium kinetics, associated with increased SR calcium load. These changes occurred without any changes in the protein expression of SERCA2a, PLN, and ryanodine receptor or in the PLN phosphorylation status. The enhanced calcium cycling in the HAX-1-depleted heart was mediated through increases in the calcium affinity of SERCA2a and reduced PLN-SERCA2a binding. Comparison of the HAX-1 deletion-induced stimulatory effects with those elicited by PLN ablation indicated that HAX-1 mediates∼50% of the PLN-associated inhibitory effects in the heart. Stimulation with the inotropic and lusitropic agent isoproterenol eliminated the differences among wild-type, HAX-1-deficient, and PLN-deficient hearts, and maximally stimulated contractile and calcium kinetic parameters were similar among these three groups. Furthermore, PLN overexpression in the HAX-1-null cardiomyocytes did not elicit any inhibitory effects, indicating thatHAX-1may limitPLNactivity. These findings suggest that HAX-1 is a major mediator of PLN's inhibitory activity and a critical gatekeeper of SR calcium cycling and contractility in the heart.
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U2 - 10.1074/jbc.RA117.000128
DO - 10.1074/jbc.RA117.000128
M3 - Article
C2 - 29150445
AN - SCOPUS:85040125772
SN - 0021-9258
VL - 293
SP - 359
EP - 367
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 1
ER -