title: Phosphorylation of glycosyl-phosphatidylinositol by phosphatidylinositol 3-kinase changes its properties as a substrate for phospholipases.
abstract: Phosphatidylinositol 3-kinases (PI3K) phosphorylate the 3-position of the inositol ring of phosphatidylinositol-4,5-bisphosphate to produce phosphatidylinositol-3,4,5-trisphosphate. It is not clear whether PI3K can phosphorylate the inositol group in other biomolecules. We sought to determine whether PI3K was able to use glycosyl-phosphatidylinositol (GPI) as a substrate. This phospholipid may exist either in free form (GPIfree) or forming a lipid anchor (GPIanchor) for the attachment of extracellular proteins to the plasma membrane. We demonstrate the specific PI3K-mediated phosphorylation of the inositol 3-hydroxyl group within both types of GPI by incubating this phospholipid with immunoprecipitated PI3K. The phosphorylated product behaves in HPLC as a derivative of a PI3K lipid product. To our knowledge, this is the first demonstration that PI3K uses lipid substrates other than phosphoinositides. Further, we show that this has potential functional consequences. When GPIfree is phosphorylated, it becomes a poorer substrate for GPI-specific phospholipase D, but a better substrate for phosphatidylinositol-specific phospholipase C. These phosphorylation events may constitute the basis of a previously undescribed signal transduction mechanism.
authors.affiliation: Department of Cell Signalling, Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Científicas, Arturo Duperier 4, 28029 Madrid, Spain. djones@nki.nl
authors.forename: David R
authors.initials: DR
authors.lastname: Jones
authors.forename: Covadonga
authors.initials: C
authors.lastname: Pañeda
authors.forename: Ana Victoria
authors.initials: AV
authors.lastname: Villar
authors.forename: Alicia
authors.initials: A
authors.lastname: Alonso
authors.forename: Félix M
authors.initials: FM
authors.lastname: Goñi
authors.forename: Peter
authors.initials: P
authors.lastname: Bütikofer
authors.forename: Urs
authors.initials: U
authors.lastname: Brodbeck
authors.forename: Peter R
authors.initials: PR
authors.lastname: Shepherd
authors.forename: Isabel
authors.initials: I
authors.lastname: Varela-Nieto
mesh_terms: D000818:Animals; D017261:Glycosylphosphatidylinositols / Q000737:chemistry / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010739:Phospholipase D / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D017261:Glycosylphosphatidylinositols; D019869:Phosphatidylinositol 3-Kinases; D010738:Type C Phospholipases; D010739:Phospholipase D