title: Loss of PIP5KIgamma, unlike other PIP5KI isoforms, impairs the integrity of the membrane cytoskeleton in murine megakaryocytes.
abstract: Phosphatidylinositol-4,5-bisphosphate (PIP(2)) is an abundant phospholipid that contributes to second messenger formation and has also been shown to contribute to the regulation of cytoskeletal dynamics in all eukaryotic cells. Although the alpha, beta, and gamma isoforms of phosphatidylinositol-4-phosphate-5-kinase I (PIP5KI) all synthesize PIP2, mammalian cells usually contain more than one PIP5KI isoform. This raises the question of whether different isoforms of PIP5KI fulfill different functions. Given the speculated role of PIP(2) in platelet and megakaryocyte actin dynamics, we analyzed murine megakaryocytes lacking individual PIP5KI isoforms. PIP5KIgamma(-/-) megakaryocytes exhibited plasma membrane blebbing accompanied by a decreased association of the membrane with the cytoskeleton. This membrane defect was rescued by adding back wild-type PIP5KIgamma, but not by adding a catalytically inactive mutant or a splice variant lacking the talin-binding motif. Notably, both PIP5KIbeta- and PIP5KIgamma(-/-) cells had impaired PIP(2) synthesis. However, PIP5KIbeta-null cells lacked the membrane-cytoskeleton defect. Furthermore, overexpressing PIP5KIbeta in PIP5KIgamma(-/-) cells failed to revert this defect. Megakaryocytes lacking the PIP5KIgamma-binding partner, talin1, mimicked the membrane-cytoskeleton defect phenotype seen in PIP5KIgamma(-/-) cells. These findings demonstrate a unique role for PIP5KIgamma in the anchoring of the cell membrane to the cytoskeleton in megakaryocytes, probably through a pathway involving talin. These observations further demonstrate that individual PIP5KI isoforms fulfill distinct functions within cells.
authors.affiliation: Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Yanfeng
authors.initials: Y
authors.lastname: Wang
authors.forename: Rustem I
authors.initials: RI
authors.lastname: Litvinov
authors.forename: Xinsheng
authors.initials: X
authors.lastname: Chen
authors.forename: Tami L
authors.initials: TL
authors.lastname: Bach
authors.forename: Lurong
authors.initials: L
authors.lastname: Lian
authors.forename: Brian G
authors.initials: BG
authors.lastname: Petrich
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Monkley
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Kanaho
authors.forename: David R
authors.initials: DR
authors.lastname: Critchley
authors.forename: Takehiko
authors.initials: T
authors.lastname: Sasaki
authors.forename: Morris J
authors.initials: MJ
authors.lastname: Birnbaum
authors.forename: John W
authors.initials: JW
authors.lastname: Weisel
authors.forename: John
authors.initials: J
authors.lastname: Hartwig
authors.forename: Charles S
authors.initials: CS
authors.lastname: Abrams
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure*; D003599:Cytoskeleton / Q000201:enzymology / Q000648:ultrastructure*; D008297:Male; D008533:Megakaryocytes / Q000201:enzymology / Q000648:ultrastructure*; D051379:Mice; D008817:Mice, Mutant Strains; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D016608:Talin / Q000378:metabolism*
chemical_list: D019269:Phosphatidylinositol 4,5-Diphosphate; D020033:Protein Isoforms; D016608:Talin; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase