title: Inositol(1,4,5)P3 3-kinase isoenzymes: Catalytic properties and importance of targeting to F-actin to understand function.
abstract: Inositol(1,4,5)trisphosphate (Ins(1,4,5)P3) 3-kinases (Itpks) catalyze the phosphorylation of inositol(1,4,5)trisphosphate into inositol(1,3,4,5)tetrakisphosphate (Ins(1,3,4,5)P4). Three isoenzymes Itpka/b and c have been identified in human, rat and mouse. They share a catalytic domain relatively well conserved at the C-terminal end and a quite isoenzyme specific regulatory domain at the N-terminal end of the protein. Activity determined in cell homogenates with Ins(1,4,5)P3 and ATP as substrate is generally very low compared to Ins(1,4,5)P3 5-phosphatase, except in a few tissues such as brain, testis, thymus or intestine. Activity is very much Ca(2+) sensitive and increased in the presence of Ca(2+)/calmodulin (CaM) as compared to EGTA alone. When challenged after receptor activation, activity could be further activated several fold, e.g. in rat brain cortical slices stimulated by carbachol or in human astrocytoma cells stimulated by purinergic agonists. Two of the three isoenzymes show an unexpected cytoskeletal localization for Itpka/b or at the leading edge for Itpkb. This is explained by the presence of an F-actin binding site at the N-terminal part of the two isoenzymes. This interaction confers to Itpka the properties of an F-actin bundling protein with two major consequences: i) it can reorganize the cytoskeletal network, particularly in dendritic spines, and ii) can provide an opportunity for Ins(1,3,4,5)P4 to act very locally as second messenger.
authors.affiliation: Interdisciplinary Research Institute (IRIBHM), Université Libre de Bruxelles, Campus Erasme, Bldg C, 808 Route de Lennik, 1070 Brussels, Belgium. Electronic address: cerneux@ulb.ac.be.
authors.forename: Christophe
authors.initials: C
authors.lastname: Erneux
authors.affiliation: Interdisciplinary Research Institute (IRIBHM), Université Libre de Bruxelles, Campus Erasme, Bldg C, 808 Route de Lennik, 1070 Brussels, Belgium.
authors.forename: Somadri
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Interdisciplinary Research Institute (IRIBHM), Université Libre de Bruxelles, Campus Erasme, Bldg C, 808 Route de Lennik, 1070 Brussels, Belgium.
authors.forename: Sandra
authors.initials: S
authors.lastname: Koenig
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D055162:Biocatalysis; D020134:Catalytic Domain; D006801:Humans; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051379:Mice; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051381:Rats
chemical_list: D000199:Actins; D007527:Isoenzymes; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase
keywords: Inositol trisphosphate 3-kinase; Inositol(1,3,4,5)tetrakisphosphate; Inositol(1,4,5)trisphosphate; Signal transduction