Intracellular dynamics of sigma-1 receptors (sigma(1) binding sites) in NG108-15 cells.
The sigma-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 sigma-1 receptors have been unclear. We recently found that sigma-1 receptors specifically localize on cholesterol-enriched 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 sigma-1 receptors (Sig-1R-EYFP) in living cells, we characterized the sigma-1 receptor translocation in this study. (+)-Pentazocine, a selective sigma-1 receptor agonist, causes a significant decrease of sigma-1 receptors in ER-LDs and a diffused distribution of sigma-1 receptors over the entire endoplasmic reticulum reticular network in NG108-15 cells. In the presence of sigma-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 (+)-pentazocine shifts sigma-1 receptors from ER-LD membranes to higher density membranes. These results indicate that sigma-1 receptors localize on ER-LDs and upon stimulation translocate on continuous endoplasmic reticulum reticular network toward peripheries of cells. Because sigma-1 receptors specifically target ER lipid storage sites and compartmentalize neutral lipids therein, these results suggest that sigma-1 receptors' dynamic translocation might affect lipid transport and distribution in neuronal cells.
Cellular Pathobiology Unit, Cellular Neurobiology Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, MD 21224, USA.
Teruo
T
Hayashi
Tsung-Ping
TP
Su
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002499:Centrifugation, Density Gradient; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006825:Hybridomas; D051379:Mice; D010423:Pentazocine / Q000494:pharmacology; D051381:Rats; D017480:Receptors, sigma / Q000378:metabolism*; D000097605:Sigma-1 Receptor
D000701:Analgesics, Opioid; D010423:Pentazocine; D017480:Receptors, sigma; D000097605:Sigma-1 Receptor