Human magphinin proteins are translation products of differentially spliced transcripts from the 5' region of the human trophinin gene (TRO), whose 3' region encodes trophinin, a unique cell adhesion molecule involved in human embryo implantation. Magphinins belong to the MAGE (melanoma-associated antigen) family, and a previous study of mouse magphinins showed their expression in male and female germ cells, suggesting a role in germ cell development. Here, we characterized the structure and subcellular localization of human magphinins. Confocal microscopy analysis of ectopically expressed magphinins revealed that magphinin-alpha and -beta localize in the cytoplasm, whereas magphinin-gamma lacking the peptide encoded by exon-3 is nuclear. Following Triton X-100 extraction, DNA digestion, and high salt extraction magphinin-gamma remained nuclear, suggesting strong association with the nuclear matrix. A series of magphinin-gamma deletion mutants were generated and assayed for localization, which showed that the N-terminal region of the MAGE homology domain is necessary for nuclear localization. When magphinin-gamma was expressed in NIH3T3 cells, cells underwent G1 arrest. These results suggest that human magphinin-gamma inhibits cell cycle progression through nuclear activity.
Copyright 2007 Wiley-Liss, Inc.