title: The inositol 5-phosphatase SHIP1 is a nucleo-cytoplasmic shuttling protein and enzymatically active in cell nuclei.
abstract: The inositol 5-phosphatase SHIP1 is a negative regulator of signaling processes in hematopoietic cells. SHIP1 mediates its regulatory function after relocalization from the cytoplasm to the plasma membrane where it converts its substrate PI(3,4,5)P(3) to PI(3,4)P(2) thereby terminating PI3-kinase mediated signaling. In addition, SHIP1 converts Ins(1,3,4,5)P(4) to Ins(1,3,4)P(3) thereby regulating inositol phosphate metabolism. Here we report, that SHIP1 can be detected in nuclear puncta of Jurkat cells by confocal microscopy after expression of SHIP1 from a tetracycline inducible vector. SHIP1-containing nuclear puncta partially co-localize with FLASH, a multifunctional nuclear protein that has been linked to apoptotic signaling and transcriptional control. Nuclear localization was confirmed for endogenously expressed SHIP1 in the myeloid leukemia cell line TF1. In addition, enzymatically active SHIP1 was found in nuclear fractions of Jurkat cells with a similar specific activity as cytoplasmic SHIP1. Further analysis revealed that SHIP1 is a nucleocytoplasmic shuttling protein which is actively imported into and exported out of the nucleus. Nuclear import is mediated by two canonical nuclear localization signals (NLS) i.e. K(327)KSK and K(547)KLR. Mutational inactivation of each NLS motif inhibited nuclear import and reduced the proliferation of cells indicating a functional role of nuclear SHIP1 for cell growth. Our data indicate that SHIP1 is partly localized in the nucleus and suggest that SHIP1 plays a role for nuclear phosphoinositide and/or nuclear inositol phosphate signaling.
authors.affiliation: Institute of Biochemistry and Signal Transduction, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Marcus M
authors.initials: MM
authors.lastname: Nalaskowski
authors.forename: Anja
authors.initials: A
authors.lastname: Metzner
authors.forename: Maria A
authors.initials: MA
authors.lastname: Brehm
authors.forename: Sena
authors.initials: S
authors.lastname: Labiadh
authors.forename: Helena
authors.initials: H
authors.lastname: Brauer
authors.forename: Nicole
authors.initials: N
authors.lastname: Grabinski
authors.forename: Georg W
authors.initials: GW
authors.lastname: Mayr
authors.forename: Manfred
authors.initials: M
authors.lastname: Jücker
mesh_terms: D020816:Amino Acid Motifs; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000201:enzymology*; D049109:Cell Proliferation; D006801:Humans; D000072181:Inositol Polyphosphate 5-Phosphatases; D016297:Mutagenesis, Site-Directed; D019913:Nuclear Localization Signals / Q000378:metabolism; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D051017:Apoptosis Regulatory Proteins; C485604:CASP8AP2 protein, human; D002135:Calcium-Binding Proteins; D019913:Nuclear Localization Signals; D011993:Recombinant Fusion Proteins; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases; C000606430:INPP5D protein, human; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases