title: Subcellular localisation of human inositol 1,4,5-trisphosphate 3-kinase C: species-specific use of alternative export sites for nucleo-cytoplasmic shuttling indicates divergent roles of the catalytic and N-terminal domains.
abstract: The three isoforms of human Ins(1,4,5)P3 3-kinase (IP3K) show remarkable differences in their intracellular targeting. Whereas predominant targeting to the cytoskeleton and endoplasmic reticulum has been shown for IP3K-A and IP3K-B, rat IP3K-C shuttles actively between the nucleus and cytoplasm. In the present study we examined the expression and intracellular localisation of endogenous IP3K-C in different mammalian cell lines using an isoform-specific antibody. In addition, human IP3K-C, showing remarkable differences to its rat homologue in the N-terminal targeting domain, was tagged with EGFP and used to examine active transport mechanisms into and out of the nucleus. We found both a nuclear import activity residing in its N-terminal domain and a nuclear export activity sensitive to treatment with leptomycin B. Different from the rat isoform, an exportin 1-dependent nuclear export site of the human enzyme resides outside the N-terminal targeting domain in the catalytic enzyme domain. A phylogenetic survey of vertebrate IP3K sequences indicates that in each of the three isoforms a nuclear export signal has evolved in the catalytic domain either de novo (IP3K-A) or as a substitute for an earlier evolved corresponding N-terminal signal (IP3K-B and IP3K-C). In higher vertebrates, and in particular in primates, re-export of nuclear IP3K activity may be guaranteed by the mechanism discovered.
authors.affiliation: Institut für Biochemie und Molekularbiologie I: Zelluläre Signaltransduktion, Universitätsklinikum Hamburg-Eppendorf, Martinistr. 52, D-20246 Hamburg, Germany.
authors.forename: Marcus M
authors.initials: MM
authors.lastname: Nalaskowski
authors.forename: Sabine
authors.initials: S
authors.lastname: Windhorst
authors.forename: Malte C
authors.initials: MC
authors.lastname: Stockebrand
authors.forename: Georg W
authors.initials: GW
authors.lastname: Mayr
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D019556:COS Cells; D020134:Catalytic Domain / Q000235:genetics / Q000502:physiology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D049452:Green Fluorescent Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence / Q000379:methods; D008969:Molecular Sequence Data; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D007295:Inositol Phosphates; D007527:Isoenzymes; D011993:Recombinant Fusion Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D015544:Inositol 1,4,5-Trisphosphate; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase