title: Distinct subcellular localisations of the putative inositol 1,3,4,5-tetrakisphosphate receptors GAP1IP4BP and GAP1m result from the GAP1IP4BP PH domain directing plasma membrane targeting.
abstract: Inositol 1,3,4,5-tetrakisphosphate (IP4), is a ubiquitous inositol phosphate that has been suggested to function as a second messenger. Recently, we purified and cloned a putative IP4 receptor, termed GAP1(IP4BP)[1], which is also a member of the GAP1 family of GTPase-activating proteins for the Ras family of GTPases. A homologue of GAP1(IP4BP), called GAP1(m), has been identified [2] and here we describe the cloning of a GAP1(m) cDNA from a human circulating-blood cDNA library. We found that a deletion mutant of GAP1(m), in which the putative phospholipid-binding domains (C2A and C2B) have been removed, binds to IP4 with a similar affinity and specificity to that of the corresponding GAP1(IP4BP) mutant. Expression studies of the proteins in either COS-7 or HeLa cells showed that, whereas GAP1(IP4BP) is located solely at the plasma membrane, GAP1(m) seems to have a distinct perinuclear localisation. By mutational analysis, we have shown that the contrast in subcellular distribution of these two closely related proteins may be a function of their respective pleckstrin homology (PH) domains. This difference in localisation has fundamental significance for our understanding of the second messenger functions of IP4.
authors.affiliation: Laboratory of Molecular Studies on Cell Regulation, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Lockyer
authors.forename: J R
authors.initials: JR
authors.lastname: Bottomley
authors.forename: J S
authors.initials: JS
authors.lastname: Reynolds
authors.forename: T J
authors.initials: TJ
authors.lastname: McNulty
authors.forename: K
authors.initials: K
authors.lastname: Venkateswarlu
authors.forename: B V
authors.initials: BV
authors.lastname: Potter
authors.forename: C E
authors.initials: CE
authors.lastname: Dempsey
authors.forename: P J
authors.initials: PJ
authors.lastname: Cullen
mesh_terms: D000818:Animals; D001665:Binding Sites; D001798:Blood Proteins / Q000737:chemistry; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D010750:Phosphoproteins; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D013329:Structure-Activity Relationship; D013347:Subcellular Fractions / Q000378:metabolism; D020703:ras GTPase-Activating Proteins
chemical_list: D001798:Blood Proteins; D007295:Inositol Phosphates; D010750:Phosphoproteins; D011506:Proteins; C102193:RASA2 protein, human; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; C061107:inositol-1,3,4,5-tetrakisphosphate receptor; C039077:platelet protein P47; D020703:ras GTPase-Activating Proteins; C081655:inositol-1,3,4,5-tetrakisphosphate