Local InsP₃-dependent perinuclear Ca²⁺ signaling in cardiac myocyte excitation-transcription coupling

Previous work showed that calmodulin (CaM) and Ca²⁺-CaM- dependent protein kinase II (CaMKII) are somehow involved in cardiac hypertrophic signaling, that inositol 1,4,5-trisphosphate receptors (InsP ₃Rs) in ventricular myocytes are mainly in the nuclear envelope, where they associate with CaMKII, and that class II histone deacetylases (e.g., HDAC5) suppress hypertrophic gene transcription. Furthermore, HDAC phosphorylation in response to neurohumoral stimuli that induce hypertrophy, such as endothelin-1 (ET-1), activates HDAC nuclear export, thereby regulating cardiac myocyte transcription. Here we demonstrate a detailed mechanistic convergence of these 3 issues in adult ventricular myocytes. We show that ET-1, which activates plasmalemmal G protein-coupled receptors and InsP₃ production, elicits local nuclear envelope Ca²⁺ release via InsP ₃R. This local Ca²⁺ release activates nuclear CaMKII, which triggers HDAC5 phosphorylation and nuclear export (derepressing transcription). Remarkably, this Ca²⁺-dependent pathway cannot be activated by the global Ca²⁺ transients that cause contraction at each heartbeat. This novel local Ca²⁺ signaling in excitation-transcription coupling is analogous to but separate (and insulated) from that involved in excitation-contraction coupling. Thus, myocytes can distinguish simultaneous local and global Ca²⁺ signals involved in contractile activation from those targeting gene expression.