Intracellular Dynamics of σ-1 Receptors (σ₁Binding Sites) in NG108-15 Cells

Abstract

The -1 receptors bind diverse kinds of psychoactive compounds, including cocaine, and translocate upon stimulation by these compounds. However, the exact intracellular localization and dynamics of -1 receptors have been unclear. We recently found that -1 receptors specifically localize on cholesterolenriched loci on the endoplasmic reticulum (ER) membrane that function as neutral lipid storage sites (i.e., ER lipid droplets or ER-LDs) from which neutral lipids bud out to form cytosolic lipid droplets. By combining immunocytochemistry and real-time monitoring of enhanced yellow fluorescent protein (EYFP)-tagged -1 receptors (Sig-1R-EYFP) in living cells, we characterized the -1 receptor translocation in this study. (ϩ)-Pentazocine, a selective -1 receptor agonist, causes a significant decrease of -1 receptors in ER-LDs and a diffused distribution of -1 receptors over the entire endoplasmic reticulum reticular network in NG108-15 cells. In the presence of -1 receptor agonists, Sig-1R-EYFP move out from ER-LDs and slide along the endoplasmic reticulum network toward nuclear envelope and the tip of neurites. Fluorescence recovery after photobleaching analysis demonstrates that Sig-1R-EYFP on endoplasmic reticulum reticular network are highly mobile compared with those in ER-LDs. A sucrose gradient fractionation study shows that (ϩ)-pentazocine shifts -1 receptors from ER-LD membranes to higher density membranes. These results indicate that -1 receptors localize on ER-LDs and upon stimulation translocate on continuous endoplasmic reticulum reticular network toward peripheries of cells. Because -1 receptors specifically target ER lipid storage sites and compartmentalize neutral lipids therein, these results suggest that -1 receptors' dynamic translocation might affect lipid transport and distribution in neuronal cells.

Sigma-1 receptor mediates cocaine-induced transcriptional regulation by recruiting chromatin-remodeling factors at the nuclear envelope

“…In this report, we first used NG108 cells (16) and Neuro2A (32) as model cellular systems to provide critical information.…”

“…Cocaine also causes the translocation of Sig-1Rs from the ER to the nucleus (16), where Sig-1Rs are shown to be present at the nuclear envelope (NE) (17). However, the functional role of Sig1Rs at the nucleus remains unknown.…”

Differential Effect on Two Immobility Responses by Chronic Administration of 1,3-di-o-Tolyl-Guanidine (Sigma Receptor Agonist) in Rats with Neonatal Ventral Hippocampal Lesion

“…The σ-1 receptor gene encodes 25 kDa membrane proteins that have no homology to any mammalian protein [37]. Sigma-1 receptors are intracellular receptors mainly localized on the endoplasmic reticulum, and they dynamically translocate inside cells [38] [39]. Sigma-1 receptors are expressed in specific regions of the brain such as layers of the cortex, hippocampus, hypothalamic nuclei, substantia nigra and Purkinje cells in the cerebellum [28] [40].…”

“…Sigma-1 receptors are expressed in specific regions of the brain such as layers of the cortex, hippocampus, hypothalamic nuclei, substantia nigra and Purkinje cells in the cerebellum [28] [40]. Occupancy of sigma-1 receptors by agonists causes translocation of the receptor protein from the endoplasmatic reticulum to the cell membrane where the receptor can regulate ion channels and neurotransmitter release [38] [41]. The sigma-1 receptor is implicated in cellular differentiation [42] [43], neuroplasticity [44] [45], neuroprotection [46] [47], and cognitive functioning of the brain [48].…”

Long-Term Haloperidol Treatment Prolongs QT Interval and Increases Expression of Sigma 1 and IP₃ Receptors in Guinea Pig Hearts

“…In 2001, Hayashi and Su (2001) reported the existence of the trimeric structure consisting of sigma 1 receptor, inositol 1,4,5-trisphosphate (IP 3 ) receptor and ankyrin isomer 220 on the membrane of endoplasmic reticulum in cultured rodent cells. Dissociation of this triplet and translocation of either a dimer sigma 1 receptor/ankyrin (in case of sigma receptor agonist binding) or sigma 1 receptor alone (after antagonist binding) has been described in the same model (Hayashi and Su 2003). Due to the effect on calcium current in cardiomyocytes (Tarabova et al 2009) and an impact on the regulation of intracellular calcium store, sigma receptors are suggested to play a role in modulation of cardiac functions.…”