Abstract
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‐α and ‐β localize in the cytoplasm, whereas magphinin‐γ lacking the peptide encoded by exon‐3 is nuclear. Following Triton X‐100 extraction, DNA digestion, and high salt extraction magphinin‐γ remained nuclear, suggesting strong association with the nuclear matrix. A series of magphinin‐γ 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‐γ was expressed in NIH3T3 cells, cells underwent G1 arrest. These results suggest that human magphinin‐γ inhibits cell cycle progression through nuclear activity. J. Cell. Biochem. 103: 765–777, 2008. © 2007 Wiley‐Liss, Inc.