Changes in Rabbit Brain Cytosolic and Membrane Bound Gangliosides During Prenatal Life

136

Calcium is recognized as an important intracellular messenger with a pivotal role in the regulation of many cytosolic and nuclear processes. Gangliosides of various types, especially GM1, are known to have a role in some aspects of Ca 2+ regulation, operating through a variety of mechanisms that are gradually coming to light. The present study provides evidence for a sodium-calcium exchanger in the nuclear envelope of NG108-15 neuroblastoma cells that is potently and specifically activated by GM1. Immunoblot analysis revealed an unusually tight association of GM1 with the exchanger in the nuclear envelope but not with that in the plasma membrane. Exchanger and associated GM1 were located in the inner membrane of the nuclear envelope, suggesting this system could function to transfer Ca 2+ between nucleoplasm and the envelope lumen. The GM1-enhanced exchange was blocked by cholera toxin B subunit while C2-ceramide, a recently discovered inhibitor of the exchanger, blocked all transfer. Exchanger activity was significantly elevated in nuclei isolated from cells that were induced to differentiate by KCl + dibutyryl-cAMP, a treatment previously shown to promote up-regulation of nuclear GM1 in conjunction with axonogenesis. Similar enhancement was achieved by addition of exogenous GM1 to nuclei from undifferentiated cells. These results suggest a prominent role for nuclear GM1 in regulation of nuclear Ca 2+ homeostasis. et al. 1991;Kocsis et al. 1994).The present study was undertaken to determine the specific role of GM1, which was suggested to contribute to this altered regulation of nuclear Ca 2+ (Wu et al. 1995b;Ledeen et al. 1998). We have obtained evidence for the presence of a sodium-calcium (Na-Ca) exchanger in the NE that is strongly associated with and potentiated by GM1. This exchanger was detected by immunocytochemistry in the NE of cortical neurons and NG108-15 cells, and its function demonstrated in isolated nuclei from the latter. ] i , intracellular calcium content; Ctx B, cholera toxin B subunit; Ctx B-FITC, cholera toxin B linked to fluoroisothiocyanate; Ctx B-HRP, cholera toxin B linked to horseradish peroxidase; db-cAMP, dibutyryl cyclic AMP; DMEM, Dulbecco's modified Eagle's medium; DTT, dithiothreitol; HPTLC, high-performance thin-layer chromatography; Membr. Mix, mixture of non-nuclear membranes; NE, nuclear envelope; NPP, nuclear pore protein; PBS, phosphate-buffered saline; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis.

mentioning

confidence: 99%

Potentiation of a sodium–calcium exchanger in the nuclear envelope by nuclear GM1 ganglioside

Xie

et al. 2002

136

“…1996), but very little is known about the mechanisms of escape from the lysosome and the transfer of these intermediates to the Golgi or other cellular districts, nor on the regulation of these processes. The presence of soluble ganglioside/protein complexes in the cytosol reported by some Authors (Sonnino et al. 1979, 1981, 1984; Chigorno et al.…”

Section: Glycosphingolipid Intracellular Traffic and Metabolismmentioning

confidence: 90%

Modulation of cell functions by glycosphingolipid metabolic remodeling in the plasma membrane

Prinetti

Chigorno

Mauri

et al. 2007

The endoplasmic reticulum and the Golgi apparatus are the subcellular sites for glycosphingolipid neobiosynthesis. In addition to this very well-established knowledge, it is now emerging that post-Golgi changes in glycosphingolipid structures occurring at the plasma membrane are an important opportunity to modulate cell glycosphingolipid composition and to affect consequently a number of signaling processes. In fact, it is possible to modify very rapidly the membrane organization by the modulation of plasma membrane-associated enzymes through external stimuli, thus affecting the membrane environment and the functional properties of plasma membrane proteins involved in cell signaling. The number of enzymes for glycosphingolipid metabolism that have been shown to be associated with the plasma membrane and the information on their features are growing very rapidly, and today some of these enzymes have been deeply characterized. In this review, we focus on the possible role and on the involvement of these plasma membrane-associated enzymes in modulating cell functions.

“…There are, however, several indications of intracellular pools as well which, while quantitatively minor, may subserve important signaling, transport, and metabolic functions (Keenan et al. 1972; Sonnino et al. 1981; Ledeen et al.…”

Section: Gangliosides Of the Nuclear Membranementioning

confidence: 99%

GM1 in the nuclear envelope regulates nuclear calcium through association with a nuclear sodium‐calcium exchanger

Ledeen

2007

The inner membrane of the nuclear envelope (NE) of neurons and other cells has been shown to contain GM1 tightly associated with a Na + /Ca 2+ exchanger (NCX) whose activity it potentiates in mediating transfer of Ca 2+ from nucleoplasm to the NE lumen. This is consistent with localization of the NCX/GM1 complex in the inner membrane of the NE. NCXs of the plasma membrane, in contrast, appear to bind GM1 much less avidly. This is believed due to different isoforms of NCX in the two membranes, and a difference in topology of NCX relative to GM1. A cytoprotective function for nuclear NCX/GM1 was suggested in the observation that cultured neurons from mice lacking GM1 (GM2/GD2 synthase knockout) were vulnerable to Ca 2+ -induced apoptosis. These neurons in culture were rescued to some extent by GM1 but more effectively by LIGA-20, a membrane-permeant derivative of GM1 that entered the NE. Further indication came from a study of the mutant mice, which were highly susceptible to kainate-induced seizures and could be rescued by LIGA-20. This correlated with the ability of LIGA-20 to cross the blood-brain barrier, enter brain cells, insert into the NE, and potentiate nuclear NCX.