CaMKIIδ Isoforms Differentially Affect Calcium Handling but Similarly Regulate HDAC/MEF2 Transcriptional Responses

Abstract

The ␦ B and ␦ C splice variants of Ca 2؉ /calmodulin-dependent protein kinase II (CaMKII), which differ by the presence of a nuclear localization sequence, are both expressed in cardiomyocytes. We used transgenic (TG) mice and CaMKII expression in cardiomyocytes to test the hypothesis that the CaMKII␦ C isoform regulates cytosolic Ca 2؉ handling and the ␦ B isoform, which localizes to the nucleus, regulates gene transcription. Phosphorylation of CaMKII sites on the ryanodine receptor (RyR) and on phospholamban (PLB) were increased in CaMKII␦ C TG. This was associated with markedly enhanced sarcoplasmic reticulum (SR) Ca 2؉ spark frequency and decreased SR Ca 2؉ content in cardiomyocytes. None of these parameters were altered in TG mice expressing the nuclear-targeted CaMKII␦ B . In contrast, cardiac expression of either CaMKII␦ B or ␦ C induced transactivation of myocyte enhancer factor 2 (MEF2) gene expression and up-regulated hypertrophic marker genes. Studies using rat ventricular cardiomyocytes confirmed that CaMKII␦ B and ␦ C both regulate MEF2-luciferase gene expression, increase histone deacetylase 4 (HDAC4) association with 14-3-3, and induce HDAC4 translocation from nucleus to cytoplasm, indicating that either isoform can stimulate HDAC4 phosphorylation. Finally, HDAC4 kinase activity was shown to be increased in cardiac homogenates from either CaMKII␦ B or ␦ C TG mice. Thus CaMKII␦ isoforms have similar effects on hypertrophic gene expression but disparate effects on Ca 2؉ handling, suggesting distinct roles for CaMKII␦ isoform activation in the pathogenesis of cardiac hypertrophy versus heart failure.is the predominant isoform of CaMKII in the heart. Splice variants differing in the presence of a nuclear localization sequence (NLS) show distinct subcellular targeting to either cytoplasmic or nuclear compartments (1-3). The CaMKII␦ B isoform contains an 11 amino acid NLS that is absent from ␦ C . Thus CaMKII heteromers comprised predominantly of ␦ B subunits localize to the nucleus while those with predominantly ␦ C localize to the cytoplasm (1-3). We recently demonstrated that both ␦ B and ␦ C CaMKII are activated in response to pressure overload induced by thoracic aortic banding but that expression of these isoforms is differentially regulated (4). The possibility that there are discrete roles for these two isoforms in regulating Ca 2ϩ homeostasis and gene transcription has not yet been explored.CaMKII has long been implicated as a regulator of Ca 2ϩ homeostasis and excitation-contraction (E-C) coupling in ventricular myocytes. This enzyme has been shown to phosphorylate proteins involved in sarcoplasmic reticulum (SR) Ca 2ϩ handling including the cardiac ryanodine receptors (RyR2) and phospholamban (PLB) (4 -10). Phosphorylation of the RyR2 appears to alter its channel open probability (9 -11) while phosphorylation of PLB by CaMKII can regulate SR Ca 2ϩ uptake (10, 12). Altered intracellular Ca 2ϩ handling plays an important role in the pathogenesis of heart failure with changes in Ca 2ϩ cycling pr...

Nuclear Calcium/Calmodulin-dependent Protein Kinase II Signaling Enhances Cardiac Progenitor Cell Survival and Cardiac Lineage Commitment

“…Mef2c cardiac transcription factor expression in CPCs supports progression of myocyte progenitor precursor cells in to cells of the cardiomyogenic lineage (36). Additionally, CaMKII␦B overexpression is known to enhance the up-regulation of Mef2c to promote growth and maturation of cardiomyocytes (18). As expected, Mef2c gene expression in CPCe␦B was increased and is consistent with elevated protein expression during basal cell culture conditions compared with CPCe (Fig.…”

“…G, quantitation of ␣-smooth muscle actin represented as a fold change relative to CPC sh-Ctrl in GM and after normalizing to GAPDH. MEF2 and serum response factor elements (18,19). Inactivation of Class IIa HDACs by CaMKII and protein kinase D promotes shuttling of HDAC4 from the nuclear compartment by the chaperone 14-3-3 (28,42).…”

“…CaMKII␦B localization remains differentiated from CaMKII␦C because of a nuclear-localized sequence. Yet CaMKII␦B expression is not exclusive to the nucleus as the CaMKII holoenzyme is formed by a majority of ␦ subunits (17,18). Nuclear CaMKII␦ (B isoform) regulates cellular growth through indirect de-repression of myocyte enhancer factor 2 (MEF2) after phosphorylation and inactivation of the histone deacetylase 4 (HDAC4) (18 -20).…”

Protein Kinase D3 Is a Pivotal Activator of Pathological Cardiac Hypertrophy by Selectively Increasing the Expression of Hypertrophic Transcription Factors

“…Therefore, the initiation of cardiac hypertrophy in adult hearts requires at least nuclear export of the HDACs and/or nuclear import of NFAT-like TFs. Studies in the past two decades have established that nuclear export of class II HADCs (HDAC-4, -5, -7, -9) is primarily mediated by phosphorylation catalyzed by the HDAC kinases including Ca 2ϩ / calmodulin-activated kinase II (CaMKII␦) (18) and protein kinase D1 (PKD1, known as PKC) (19). In comparison, activation of NFATs is achieved by CaN-catalyzed dephosphorylation (20).…”

α-Kinase Anchoring Protein αKAP Interacts with SERCA2A to Spatially Position Ca2+/Calmodulin-dependent Protein Kinase II and Modulate Phospholamban Phosphorylation

“…Although the intracellular targeting of protein kinase A to the effectors is being unraveled, little is known about the targeting of CaMKII activity, which is ubiquitously expressed and serves important roles in calcium signaling to guide synaptic transmission (2,5,6), gene transcription (7), cell growth (8), and excitation-contraction coupling (9 -11). Although four different isoforms of CaMKII (␣, ␤, ␦, and ␥) are expressed in a tissuespecific manner, cardiac tissue is shown to have predominance of CaMKII␦ C (cytosolic) and CaMKII␦ B (nuclear) isoforms, which serve roles in excitation-contraction coupling and cell growth, respectively (7,12). Studies have also revealed a significant level of a muscle-specific CaMKII ␤ isoform (CaMKII␤ 4 ) in skeletal and cardiac muscle (11,(13)(14)(15).…”