Presence of Sodium–Calcium Exchanger/GM1 Complex in the Nuclear Envelope of Non-neural Cells: Nature of Exchanger-GM1 Interaction

Abstract

Previous studies have revealed the presence of Na⁺Ca²⁺ exchanger (NCX) activity associated with GM1 ganglioside in the nuclear envelope (NE) of neurons and glia as well as various neural cell lines. The nuclear NCX1 exchanger, unlike that in the plasma membrane, was shown to be tightly associated with GM1 and potentiated by the latter. One non-neural cell line, Jurkat, was found to contain no Na⁺Ca²⁺ exchanger of the NCX1, NCX2, or NCX3 types in either nuclear or plasma membrane. To determine whether such absence in the NE is generally characteristic of non-neural cells we have examined two more such cell lines in addition to human lymphocytes. RT-PCR showed NCX1 expression in both HeLa and NCTC cell lines and also NCX2 in the latter; NCX3, a subtype previously observed in NG108-15 cells, was not expressed in either. Immunocytochemical and immunoblot studies indicated NCX1 on the cell surface and nuclear envelope of both cell types. Some alternatively spliced isoforms of NCX1 in the nuclear envelope of both cell types were tightly associated with ganglioside GM1. Human lymphocytes, a mixed population of T and B cells, showed similar evidence for plasma membrane and nuclear expression in some but not all cells. The high affinity association between NCX1 and GM1, explored by reaction with base, acid, and proteases, was found to involve charge–charge interaction with a requirement for a positively charged moiety in NCX.