title: Regulation of PI4,5P2 synthesis by nuclear-cytoplasmic shuttling of the Mss4 lipid kinase.
abstract: The essential phospholipid PI4,5P(2) is generated by a well conserved PI4P 5-kinase, Mss4, in yeast. Balanced production and turnover of PI4,5P(2) is important for normal organization of the actin cytoskeleton and cell viability. Previous studies have shown that multiple PI phosphatases can regulate PI4,5P(2) levels. We report a new, unexpected regulatory mechanism for PI4,5P(2) homeostasis, directed by nuclear-cytoplasmic shuttling of the lipid kinase. We show that Mss4 is a phosphoprotein, which contains a functional nuclear localization signal (NLS) and can shuttle between the cytoplasm and the nucleus. Temperature-conditional mss4 cells that accumulate Mss4 protein in the nucleus exhibit reduced levels of PI4,5P(2), depolarization of the actin cytoskeleton and a block in Mss4 phosphorylation, suggesting an essential role for phosphorylated Mss4 at the plasma membrane. Through the isolation of gene dosage-dependent suppressors of mss4 mutants, we identified Bcp1, a protein enriched in the nucleus, which is required for Mss4 nuclear export and is related to the mammalian BRCA2-interacting protein BCCIP. Together, these studies suggest a new mechanism for lipid kinase regulation through regulated nuclear-cytoplasmic shuttling.
authors.affiliation: Department of Cellular and Molecular Medicine, University of California, San Diego, School of Medicine, La Jolla, CA 92093-0668, USA.
authors.forename: Anjon
authors.initials: A
authors.lastname: Audhya
authors.forename: Scott D
authors.initials: SD
authors.lastname: Emr
mesh_terms: D000199:Actins / Q000378:metabolism; D001693:Biological Transport, Active; D047388:Casein Kinases; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism*; D002472:Cell Transformation, Viral; D003593:Cytoplasm / Q000201:enzymology / Q000378:metabolism*; D018628:Gene Dosage; D015971:Gene Expression Regulation, Enzymologic; D016153:Genes, Suppressor; D008954:Models, Biological; D009154:Mutation; D019913:Nuclear Localization Signals / Q000737:chemistry / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates / Q000096:biosynthesis* / Q000235:genetics; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011494:Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013539:Simian virus 40 / Q000235:genetics; D013696:Temperature
chemical_list: D000199:Actins; C477607:Bcp1 protein, S cerevisiae; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D011506:Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D010770:Phosphotransferases; D011494:Protein Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); C489795:MSS4 protein, S cerevisiae; D047388:Casein Kinases