Local InsP3-dependent perinuclear Ca$^2+$ signaling in cardiac myocyte excitation-transcription coupling.
X. Wu, T. Zhang, J. Bossuyt, X. Li, T. McKinsey, J. Dedman, E. Olson, J. Chen, J. Brown, and D. Bers.
J. Clin. Invest. 116 (3): 675--682 (March 2006)

Previous work showed that calmodulin (CaM) and Ca$^2+$-CaM-dependent protein kinase II (CaMKII) are somehow involved in cardiac hypertrophic signaling, that inositol 1,4,5-trisphosphate receptors (InsP3Rs) 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 Ca$^2+$ release via InsP3R. This local Ca$^2+$ release activates nuclear CaMKII, which triggers HDAC5 phosphorylation and nuclear export (derepressing transcription). Remarkably, this Ca$^2+$-dependent pathway cannot be activated by the global Ca$^2+$ transients that cause contraction at each heartbeat. This novel local Ca$^2+$ 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 Ca$^2+$ signals involved in contractile activation from those targeting gene expression.
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