CaMKII negatively regulates calcineurin-NFAT signaling in cardiac myocytes.
BACKGROUND
Pathological cardiac myocyte hypertrophy is thought to be induced by the persistent increases in intracellular Ca(2+) needed to maintain cardiac function when systolic wall stress is increased. Hypertrophic Ca(2+) binds to calmodulin (CaM) and activates the phosphatase calcineurin (Cn) and CaM kinase (CaMK)II. Cn dephosphorylates cytoplasmic NFAT (nuclear factor of activated T cells), inducing its translocation to the nucleus where it activates antiapoptotic and hypertrophic target genes. Cytoplasmic CaMKII regulates Ca(2+) handling proteins but whether or not it is directly involved in hypertrophic and survival signaling is not known.


OBJECTIVE
This study explored the hypothesis that cytoplasmic CaMKII reduces NFAT nuclear translocation by inhibiting the phosphatase activity of Cn.


RESULTS
Green fluorescent protein-tagged NFATc3 was used to determine the cellular location of NFAT in cultured neonatal rat ventricular myocytes (NRVMs) and adult feline ventricular myocytes. Constitutively active (CaMKII-CA) or dominant negative (CaMKII-DN) mutants of cytoplasmic targeted CaMKII(deltac) were used to activate and inhibit cytoplasmic CaMKII activity. In NRVM CaMKII-DN (48.5+/-3%, P<0.01 versus control) increased, whereas CaMKII-CA decreased (5.9+/-1%, P<0.01 versus control) NFAT nuclear translocation (Control: 12.3+/-1%). Cn inhibitors were used to show that these effects were caused by modulation of Cn activity. Increasing Ca(2+) increased Cn-dependent NFAT translocation (to 71.7+/-7%, P<0.01) and CaMKII-CA reduced this effect (to 17.6+/-4%). CaMKII-CA increased TUNEL and caspase-3 activity (P<0.05). CaMKII directly phosphorylated Cn at Ser197 in CaMKII-CA infected NRVMs and in hypertrophied feline hearts.


CONCLUSIONS
These data show that activation of cytoplasmic CaMKII inhibits NFAT nuclear translocation by phosphorylation and subsequent inhibition of Cn.
MacDonnell
Scott M
SM
Department of Physiology, Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Weisser-Thomas
Jutta
J
Kubo
Hajime
H
Hanscome
Marie
M
Liu
Qinghang
Q
Jaleel
Naser
N
Berretta
Remus
R
Chen
Xiongwen
X
Brown
Joan H
JH
Sabri
Abdel-Karim
AK
Molkentin
Jeffery D
JD
Houser
Steven R
SR
D021581:Active Transport, Cell Nucleus / Q000235:genetics; D000818:Animals; D019703:Calcineurin / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000235:genetics / Q000378:metabolism; D006332:Cardiomegaly / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D002415:Cats; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism; D006352:Heart Ventricles / Q000378:metabolism / Q000473:pathology; D006801:Humans; D020014:K562 Cells; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D050778:NFATC Transcription Factors / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley
D002147:Calmodulin; D009124:Muscle Proteins; D050778:NFATC Transcription Factors; C494008:NFATC3 protein, human; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D019703:Calcineurin; C505407:CASP3 protein, human; C505410:Casp3 protein, rat; D053148:Caspase 3; D002118:Calcium