Inositol 1,4,5-Trisphosphate Receptor Is Located to the Inner Nuclear Membrane Vindicating Regulation of Nuclear Calcium Signaling by Inositol 1,4,5-Trisphosphate

Abstract

Transient rise in nuclear calcium concentration is implicated in the regulation of events controlling gene expression. Mechanism by which calcium is transported to the nucleus is vehemently debated. Inositol 1,4,5-trisphosphate (InsP3) and inositol-1,3,4,5-tetrakisphosphate (InsP4) receptors have been located to the nucleus and their role in nuclear calcium signaling has been proposed. Outer nuclear membrane was separated from the inner membrane. The two membrane preparations were, as best as possible, devoid of cross contamination as attested by marker enzyme activity, Western blotting with antilamin antibody, and electron microscopy. InsP4 receptor and Ca(2+)-ATPase were located to the outer nuclear membrane. InsP3 receptor was located to the inner nuclear membrane. ATP or InsP4 induced nuclear calcium uptake. External free calcium concentration, in the medium bathing the nuclei, determined the choice for ATP or InsP4-mediated calcium transport. We present a mechanistic model for nuclear calcium transport. According to this model, calcium can reach the nucleus envelope either by the action of ATP or InsP4. However, the calcium release from the nucleus envelope to the nucleoplasm is mediated by InsP3 through the activation of InsP3 receptor, which is located to the inner nuclear membrane. The action of InsP3 in this process was instantaneous and transient and was sensitive to heparin.

An update on nuclear calcium signalling

“…Evidence in support of a role for nuclear InsP 3 Rs in regulating nuclear Ca 2+ release has been obtained by using InsP 3 -binding assays (Humbert et al, 1996), InsP 3 R-specific antibodies Malviya, 1994;Stehno-Bittel et al, 1995), electrophysiological recordings from nuclear envelope (NE) patches or from whole nuclei (Bustamante et (Thomas et al, 1997), and can occur globally or as subcellular events (Bootman et al, 2001). To generate such a diverse spectrum of signals, cells employ a range of messengers and mechanisms to evoke Ca 2+ fluxes between various cellular compartments.…”

“…Evidence in support of a role for nuclear InsP 3 Rs in regulating nuclear Ca 2+ release has been obtained by using InsP 3 -binding assays (Humbert et al, 1996), InsP 3 R-specific antibodies Malviya, 1994;Stehno-Bittel et al, 1995), electrophysiological recordings from nuclear envelope (NE) patches or from whole nuclei (Bustamante et al, 2000; Stehno-Bittel …”

“…The reason for this is the lack of Ca 2+ ATPases on the inner NE (Humbert et al, 1996). Because of the slow dissipation of nuclear Ca 2+ , it is plausible that rapid cellular stimulation could cause a progressive accumulation of Ca 2+ in the nucleoplasm.…”

Gangliosides of the nuclear membrane: A crucial locus of cytoprotective modulation

“…Efforts to more specifically localize GM1 utilized a procedure involving mild treatment with sodium citrate solution to selectively remove and isolate the outer membrane of the NE [Gilchrist and Pierce, 1993;Humbert et al, 1996]. The inner membrane was obtained from the resulting nucleus remnant, and shown to contain GM1 and GD1a .…”

“…The NE lumen is continuous with the ER intermembrane space and thus provides a luminal storage site for a significant portion of nuclear Ca 2þ [Petersen et al, 1998;Strubing and Clapham, 1999]. The INM contains a number of Ca 2þ -release mechanisms regulated by Ins(1,4,5)P 3 , cADPribose, and NAADP; activation of these results in Ca 2þ transfer from NE to nucleoplasm [Stehno-Bittel et al, 1995;Humbert et al, 1996;Gerasimenko et al, 2003]. The apparent ability of Ca 2þ to freely diffuse through the nuclear pore complexes under many (perhaps all) conditions has raised doubts concerning the possible existence of nuclear-cytosolic Ca 2þ gradients (for review: Gerasimenko and Gerasimenko, 2004).…”