title: Sodium-calcium exchanger complexed with GM1 ganglioside in nuclear membrane transfers calcium from nucleoplasm to endoplasmic reticulum.
abstract: The inner membrane of the nuclear envelope (NE) was previously shown to contain a Na/Ca exchanger (NCX) tightly linked to GM1 ganglioside that mediates transfer of nucleoplasmic Ca(2+) to the NE lumen and constitutes a cytoprotective mechanism. This transfer was initially observed with isolated nuclei and is now demonstrated in living cells in relation to subcellular Ca(2+) dynamics. Four cell lines with varying expression of NCX and GM1 in the NE were transfected with cameleon-fluorescent Ca(2+) indicators genetically targeted to NE/endoplasmic reticulum (ER) and nucleoplasm to monitor [Ca(2+)](ne/er) and [Ca(2+)](n) respectively. Cytosolic Ca(2+) ([Ca(2+)](cyt)) was indicated with fura-2. Thapsigargin caused progressive loss of [Ca(2+)](ne/er), which was rapidly replaced on addition of extrinsic Ca(2+) to those cells containing fully functional NCX/GM1: differentiated NG108-15 and C6 cells. Reduced elevation of [Ca(2+)](ne/er) following thapsigargin depletion occurred in cells containing little or no GM1 in the NE: undifferentiated NG108-15 and NG-CR72 cells. No change in [Ca(2+)](ne/er) due to applied Ca(2+) was seen in Jurkat cells, which entirely lack NCX. Ca(2+) entry to NE/ER was also blocked by KB-R7943, inhibitor of NCX. [Ca(2+)](n) and [Ca(2+)](cyt) were elevated independent of [Ca(2+)](ne/er) and remained in approximate equilibrium with each other. Ca(2+) rise in the ER originated in the NE region and extended to the entire ER network. These results indicate the nuclear NCX/GM1 complex acts to gate Ca(2+) transfer from cytosol to ER, an alternate route to the sarcoplasmic/endoplasmic reticulum calcium ATPase pump. They also suggest a possible contributory mechanism for independent regulation of nuclear Ca(2+).
authors.affiliation: Department of Neurology and Neurosciences, New Jersey Medical School-University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
authors.forename: Gusheng
authors.initials: G
authors.lastname: Wu
authors.forename: Xin
authors.initials: X
authors.lastname: Xie
authors.forename: Zi-Hua
authors.initials: ZH
authors.lastname: Lu
authors.forename: Robert W
authors.initials: RW
authors.lastname: Ledeen
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005677:G(M1) Ganglioside / Q000378:metabolism*; D006801:Humans; D006822:Hybrid Cells; D015151:Immunoblotting; D007150:Immunohistochemistry; D017136:Ion Transport; D019169:Jurkat Cells; D008856:Microscopy, Fluorescence; D009685:Nuclear Envelope / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D019831:Sodium-Calcium Exchanger; D005677:G(M1) Ganglioside; D013890:Thiourea; D002118:Calcium