C6 cells express a sodium-calcium exchanger/GM1 complex in the nuclear envelope but have no exchanger in the plasma membrane: comparison to astrocytes.
Previous work demonstrated the presence of an isoform of Na(+)/Ca(2+) exchanger in the nuclear envelope of neurons and NG108-15 cells that is tightly associated with GM1 ganglioside and potentiated by the latter. This contrasted with the Na(+)/Ca(2+) exchanger(s) in the plasma membrane, which were suggested to associate more loosely with GM1. To study these aspects of Na(+)/Ca(2+) exchanger expression in nonneuronal neural cells, we have examined nuclear and plasma membrane exchanger patterns in astrocytes and C6 cells, a glia-derived line. We find both cell types contain the tightly associated exchanger/GM1 complex in the nuclear envelope but, surprisingly, only astrocytes possess Na(+)/Ca(2+) exchanger activity in the plasma membrane. This is the first reported example of a cell (C6) with Na(+)/Ca(2+) exchangers in the nuclear envelope but not in the plasma membrane. RT-PCR established the presence of the NCX1 subtype in C6 cells and both NCX1 and NCX2 in astrocytes. Comparison was made with NG108-15 cells, which have Na(+)/Ca(2+) exchangers in both nuclear and plasma membranes, and Jurkat cells, which have no Na(+)/Ca(2+) exchanger in either membrane. Culturing of C6 cells in the presence dibutyryl-cAMP caused upregulation of a high molecular weight isoform of the exchanger together with GM1 in the nuclear envelope, resulting in significant elevation of Na(+)/Ca(2+) exchanger activity in the latter. Application of exogenous GM1 to nuclei from non-treated cells also potentiated exchanger activity, although to a lesser degree. The Na(+)/Ca(2+) exchanger/GM1 complex occurs in the inner membrane of the nuclear envelope, suggesting a functional role in transferring Ca(2+) between nucleoplasm and the envelope lumen.
Xie
Xin
X
Department of Neurology and Neurosciences, New Jersey Medical School, UMDNJ, Newark, NJ 07103, USA.
Wu
Gusheng
G
Ledeen
Robert W
RW
D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D016543:Central Nervous System Neoplasms / Q000378:metabolism; D005677:G(M1) Ganglioside / Q000378:metabolism*; D005910:Glioma / Q000378:metabolism*; D009457:Neuroglia / Q000145:classification / Q000378:metabolism; D009685:Nuclear Envelope / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D014018:Tissue Distribution
D020033:Protein Isoforms; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D005677:G(M1) Ganglioside