Nuclear inositol 1,4,5-trisphosphate receptors regulate local Ca2+ transients and modulate cAMP response element binding protein phosphorylation

Abstract

Several lines of evidence indicate that increases in nuclear Ca2+ have specific biological effects that differ from those of cytosolic Ca2+, suggesting that they occur independently. The mechanisms involved in controlling nuclear Ca2+ signaling are both controversial and still poorly understood. Using hypotonic shock combined with mechanical disruption, we obtained and characterized a fraction of purified nuclei from cultured rat skeletal myotubes. Both immunoblot studies and radiolabeled inositol 1,4,5-trisphosphate [IP3] binding revealed an important concentration of IP3 receptors in the nuclear fraction. Immunofluorescence and immunoelectron microscopy studies localized type-1 and type-3 IP3 receptors in the nucleus with type-1 receptors preferentially localized in the inner nuclear membrane. Type-2 IP3 receptor was confined to the sarcoplasmic reticulum. Isolated nuclei responded to IP3 with rapid and transient Ca2+ concentration elevations, which were inhibited by known blockers of IP3 signals. Similar results were obtained with isolated nuclei from the 1B5 cell line, which does not express ryanodine receptors but releases nuclear Ca2+ in an IP3-dependent manner. Nuclear Ca2+ increases triggered by IP3 evoked phosphorylation of cAMP response element binding protein with kinetics compatible with sequential activation. These results support the idea that Ca2+ signals, mediated by nuclear IP3 receptors in muscle cells, are part of a distinct Ca2+ release component that originates in the nucleus and probably participates in gene regulation mediated by cAMP response element binding protein.

Visualization, characterization and modulation of calcium signaling during the development of slow muscle cells in intact zebrafish embryos

“…We tried several commercially available (as well as one custom-made zebrafish) anti-IP 3 R antibodies without success. However, we suspect that the IP 3 Rs responsible for generating the nuclear Ca 2+ signal are most likely to be localized preferentially in the inner nuclear membrane, as has been reported in cultured rat skeletal muscle cells (Cárdenas et al, 2005). We found that this region of the nucleus is difficult to access successfully and thus label via immunohistochemistry in intact embryos, and we suggest that this might be why we do not see any IP 3 R labeling of the nuclear envelope in SMCs that would correspond to the IP 3 -mediated nuclear Ca 2+ signaling during the early SP1.…”

“…Furthermore, this slow IP 3 R-mediated Ca 2+ transient was reported to be linked to developmental gene expression, where K + -induced depolarization of mouse myotubes resulted in the rapid (i.e., within 30 sec -10 min) phosphorylation of the mitogen activated kinases, ERK 1/2 and the transcription factor, CREB, as well as the expression (within 5 -15 min) of various early genes (Powell et al, 2001;Jaimovich and Carrasco, 2002;Cárdenas et al, 2005). Thus, we suggest that our early Ca 2+ oscillations located in and around the nucleus of SMCs at 17.5 hpf (Fig.…”

Endothelin-1 enhances nuclear Ca2+ transients in atrial myocytes through Ins(1,4,5)P3-dependent Ca2+ release from perinuclear Ca2+ stores

“…Thus, it is likely that ET increased the [Ins(1,4,5)P 3 ] in the cytoplasm and nucleus and augmented CaTs in the two compartments through Ca 2+ release from Ins(1,4,5)P 3 receptors located in the SR and the nuclear envelope, respectively. Ins(1,4,5)P 3 -dependent Ca 2+ release from perinuclear stores into the nucleoplasm has been observed before in rat neonatal myocytes (Ibarra et al, 2004;Luo et al, 2007), in cat atrial myocytes (Zima et al, 2007) and in nuclei isolated from rat skeletal myotubes (Cardenas et al, 2005) or rat heart (Zima et al, 2007). The most elegant and direct evidence for independent Ins(1,4,5)P 3 -mediated nuclear Ca 2+ signalling comes from a recent study on permeabilised atrial myocytes and isolated cardiac nuclei (Zima et al, 2007).…”

“…There is clear experimental evidence for the functional relevance of Ins(1,4,5)P 3 -dependent Ca 2+ release for gene expression in striated muscle. In isolated nuclei of skeletal myotubes, Ins(1,4,5)P 3 -dependent Ca 2+ release into the nucleoplasm causes phosphorylation of the transcription factor cAMP response element binding protein (Cardenas et al, 2005). Moreover, in cardiac myocytes, Ins(1,4,5)P 3 receptors and CaMKII colocalise in the nucleus (Bare et al, 2005), and Ins(1,4,5)P 3 -dependent Ca 2+ release into the nucleoplasm has been implicated in CaMKII-mediated phosphorylation of histone deacetylases and de-repression of gene expression .…”

Altered Gene Expression Pathways in Duchenne Muscular Dystrophy

“…We have previously described that membrane depolarization of skeletal myotubes evokes a fast Ca 2+ transient during the stimuli, that promotes a contractile response through "E-C coupling", and a slow Ca 2+ transient peaking 60-100 seconds later, mostly associated to cell nuclei (Jaimovich et al 2000;Estrada et al 2001;Powell et al 2001;Araya et al 2003;Cardenas et al 2005). Slow Ca 2+ transients are involved in the "E-T coupling" mechanism, which relates membrane depolarization with gene expression (Powell et al 2001;Araya et al 2003;Carrasco et al 2003;Juretic et al 2006;Juretic et al 2007).…”