Immediate early gene X1 (IEX-1) is organized in subnuclear structures and partially co-localizes with promyelocytic leukemia protein in HeLa cells.

Laboratory of Molecular Gastroenterology and Hepatology, First Department of Medicine, Christian-Albrechts-University of Kiel, Schittenhelmstrasse 12, D-24105 Kiel, Germany.
Immediate early gene X1 (IEX-1) represents a stress response gene involved in growth control and modulation of apoptosis. Here, we report a detailed analysis of IEX-1 with respect to its intracellular localization. By means of confocal laser scanning microscopy, a green fluorescent protein-IEX-1 fusion protein transfected into HeLa cells, as well as endogenous IEX-1, could be detected in distinct subnuclear structures. This particular subnuclear localization of IEX-1 was not observed with a green fluorescent protein-IEX-1 fusion protein lacking a putative nuclear localization sequence, along with a decreased effect on apoptosis. Double immunofluorescence staining revealed a partial co-localization of endogenous promyelocytic leukemia protein (PML) and IEX-1 in these subnuclear structures. Nuclear localization of IEX-1 is also enhanced upon treatment of cells with leptomycin B, an inhibitor of the nuclear exporter CRM1. These observations indicate that IEX-1 is specifically shuttled to and from the nucleus. Overexpression experiments using PML isoforms III and IV revealed distinct intranuclear interaction of IEX-1 and PML. Coprecipitation experiments showed physical interaction between IEX-1 and PML. The close structural relation of IEX-1-containing nuclear subdomains and PML nuclear bodies suggests a function of IEX-1 related to the multiple functions of these unique subnuclear regions, particularly during stress response and growth control.
Mesh Terms:
Active Transport, Cell Nucleus, Apoptosis, Apoptosis Regulatory Proteins, Blotting, Western, Caspases, Cell Nucleus, Fatty Acids, Unsaturated, Genes, Immediate-Early, Glutathione Transferase, Green Fluorescent Proteins, HeLa Cells, Humans, Immediate-Early Proteins, Immunoprecipitation, Membrane Proteins, Microscopy, Confocal, Microscopy, Fluorescence, Neoplasm Proteins, Nuclear Proteins, Protein Binding, Protein Isoforms, Recombinant Fusion Proteins, Transcription Factors, Transfection, Tumor Suppressor Proteins
J. Biol. Chem. Jul. 01, 2005; 280(26);24849-56 [PUBMED:15855159]
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