Epac enhances excitation–transcription coupling in cardiac myocytes

Abstract

Epac is a guanine nucleotide exchange protein that is directly activated by cAMP, but whose cardiac cellular functions remain unclear. It is important to understand cardiac Epac signaling, because it is activated in parallel to classical cAMP-dependent signaling via protein kinase A. In addition to activating contraction, Ca2+ is a key cardiac transcription regulator (excitation-transcription coupling). It is unknown how myocyte Ca2+ signals are decoded in cardiac myocytes to control nuclear transcription. We examine Epac actions on cytosolic ([Ca2+]i) and intranuclear ([Ca2+]n) Ca2+ homeostasis, focusing on whether Epac alters [Ca2+]n and activates a prohypertrophic program in cardiomyocytes. Adult rat cardiomyocytes, loaded with fluo-3 were viewed by confocal microscopy during electrical field stimulation at 1 Hz. Acute Epac activation by 8-pCPT increased Ca2+ sparks and diastolic [Ca2+]i, but decreased systolic [Ca2+]i. The effects on diastolic [Ca2+]i and Ca2+ spark frequency were dependent on phospholipase C (PLC), inositol 1,3,5 triphosphate receptor (IP3R) and CaMKII activation. Interestingly, Epac preferentially increased [Ca2+]n during both diastole and systole, correlating with the perinuclear expression pattern of Epac. Moreover, Epac activation induced histone deacetylase 5 (HDAC5) nuclear export, with consequent activation of the prohypertrophic transcription factor MEF2. These data provide the first evidence that the cAMP-binding protein Epac modulates cardiac nuclear Ca2+ signaling by increasing [Ca2+]n through PLC, IP3R and CaMKII activation, and initiates a prohypertrophic program via HDAC5 nuclear export and subsequent activation of the transcription factor MEF2.

Cyclic AMP Sensor EPAC Proteins and Their Role in Cardiovascular Function and Disease

“…105 This effect of EPAC activation correlates with the perinuclear expression of EPAC, 114 and requires PLC activation (probably via Rap2) and subsequent stimulation of inositol 1,4,5 trisphosphate receptor activation. 105 In line with this finding, EPAC1-dependent Rap activation stimulates PLCε but no other PLC isoforms. Also, EPAC1 is scaffolded at the nuclear envelope with PLCε and to muscle-specific A-kinase anchoring proteins in primary cardiomyocytes.…”

“…This RyR phosphorylation after EPAC activation is fully prevented in the presence of U73122, a specific phospholipase C (PLC) inhibitor, indicating that CaMKII acts downstream of PLC. 105 Importantly, the EPAC-induced CaMKII activation, RyR phosphorylation at Ser2814/15 and lack of L-type Ca 2+ current modulation have also been confirmed in mouse cardiomyocytes. [107][108][109][110] In contrast to rat ventricular myocytes, however, study using mouse cardiomyocytes showed that an acute stimulation of EPAC with 8-CPT induced a significant increase in the amplitude of electrically evoked [Ca 2+ ]i transients.…”

“…53 Likewise, mice lacking EPAC1 (and not EPAC2) are cardioprotected against other forms of stress such as pressure overload-and aging-induced cardiac dysfunction. 110 Taking into account that EPAC1 inhibition may prevent hyperphosphorylation of phospholamban and RyR2, 104,105,110 one could speculate that an EPAC1 inhibitor might represent a new means of normalizing Ca 2+ cycling in the setting of chronic β-ARinduced HF, and this may be an alternative strategy to current β-AR blocker therapy for the treatment of HF. Further investigation is needed to test this hypothesis.…”

Functional and cardioprotective effects of simultaneous and individual activation of protein kinase A and Epac

“…Although most of the biological effects of cAMP on the heart have been assigned to PKA (Bers, 2007), cAMP also activates Epac (a guanine nucleotide exchange protein directly activated by cAMP) (de Rooij et al, 1998). The cAMP/Epac pathway is independent of and parallel to the cAMP/PKA signalling pathway (Pereira et al, 2012; Okumura et al, 2014). Therefore, availability of cell‐permeable cAMP analogues allowing selective activation of either PKA or Epac represents a valuable tool to identify the involvement and the contribution of these cAMP sensors in cardioprotection (Dudley et al, 2014).…”

Les acteurs moléculaires du remodelage cardiaque pathologique

“…Cependant, des expériences montrent que ce facteur d'échange influence les mouvements calciques intracellulaires par le biais de la phospholipase C et des récepteurs à l'IP 3 (inositol triphosphate), pour activer les voies de signalisation dépen-dantes de la phosphatase CaN et de la CaMKII [23,26]. Ces événements moléculaires font intervenir la -arrestine, protéine d'échafaudage, et des régulations épigénétiques qui dépendent des HDAC ( Figure 3B) [26][27][28]. L'étude de souris invalidées pour les gènes Epac1 et Epac2 a permis de mieux comprendre le rôle de ces protéines dans le remodelage pathologique.…”