title: Phosphatidylinositol 3-kinase c2alpha contains a nuclear localization sequence and associates with nuclear speckles.
abstract: Phosphoinositide 3-kinase C2alpha (PI3K-C2alpha) belongs to the class II phosphatidylinositol 3-kinases, which are defined by their in vitro usage of phosphatidylinositol and phosphatidylinositol 4-phosphate as substrates. All type II phosphatidylinositol 3-kinases contain at their C terminus a C2-like domain. Here we demonstrate that Homo sapiens phosphoinositide 3-kinase C2alpha (HsPI3K-C2alpha) has dual cellular localization present in the cytoplasm and in the nucleus. A distinct nuclear localization signal sequence was identified by expressing HsPI3K-C2alpha-green fluorescent protein fusion proteins in HeLa cells. The nuclear localization signal was mapped to a stretch of 11 amino acids (KRKTKISRKTR) located within C2-like domain of the kinase. In the cytoplasm and the nucleus HsPI3K-C2alpha associates with macromolecular complexes that are resistant to detergent extraction. Indirect immunofluorescence reveals that in the nucleus HsPI3K-C2alpha is enriched at distinct subnuclear domains known as nuclear speckles, which contain pre-mRNA processing factors and are functionally connected to RNA metabolism. Phosphorylation of HsPI3K-C2alpha is induced by inhibition of RNA polymerase II-dependent transcription and coincides with enlargement and rounding up of the nuclear speckles. The results suggest that phosphorylation of HsPI3K-C2alpha is inversely linked to mRNA transcription and supports the importance of phosphoinositides for nuclear activity.
authors.affiliation: Institute for Research in Biomedicine, Via Vincenzo Vela 6, CH 6500 Bellinzona, Switzerland.
authors.forename: S A
authors.initials: SA
authors.lastname: Didichenko
authors.forename: M
authors.initials: M
authors.lastname: Thelen
mesh_terms: D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000378:metabolism*; D012322:RNA Precursors / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D008164:Luminescent Proteins; D019913:Nuclear Localization Signals; D012322:RNA Precursors; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D019869:Phosphatidylinositol 3-Kinases