title: Genetic ablation of phosphatidylinositol transfer protein function in murine embryonic stem cells.
abstract: Phosphatidylinositol transfer proteins (PITPs) regulate the interface between signal transduction, membrane-trafficking, and lipid metabolic pathways in eukaryotic cells. The best characterized mammalian PITPs are PITP alpha and PITP beta, two highly homologous proteins that are encoded by distinct genes. Insights into PITP alpha and PITP beta function in mammalian systems have been gleaned exclusively from cell-free or permeabilized cell reconstitution and resolution studies. Herein, we report for the first time the use of genetic approaches to directly address the physiological functions of PITP alpha and PITP beta in murine cells. Contrary to expectations, we find that ablation of PITP alpha function in murine cells fails to compromise growth and has no significant consequence for bulk phospholipid metabolism. Moreover, the data show that PITP alpha does not play an obvious role in any of the cellular activities where it has been reconstituted as an essential stimulatory factor. These activities include protein trafficking through the constitutive secretory pathway, endocytic pathway function, biogenesis of mast cell dense core secretory granules, and the agonist-induced fusion of dense core secretory granules to the mast cell plasma membrane. Finally, the data demonstrate that PITP alpha-deficient cells not only retain their responsiveness to bulk growth factor stimulation but also retain their pluripotency. In contrast, we were unable to evict both PITP beta alleles from murine cells and show that PITP beta deficiency results in catastrophic failure early in murine embryonic development. We suggest that PITP beta is an essential housekeeping PITP in murine cells, whereas PITP alpha plays a far more specialized function in mammals than that indicated by in vitro systems that show PITP dependence.
authors.affiliation: Department of Cell and Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7090, USA.
authors.forename: James G
authors.initials: JG
authors.lastname: Alb
authors.forename: Scott E
authors.initials: SE
authors.lastname: Phillips
authors.forename: Kathleen
authors.initials: K
authors.lastname: Rostand
authors.forename: Xiaoxia
authors.initials: X
authors.lastname: Cui
authors.forename: Jef
authors.initials: J
authors.lastname: Pinxteren
authors.forename: Laura
authors.initials: L
authors.lastname: Cotlin
authors.forename: Timothy
authors.initials: T
authors.lastname: Manning
authors.forename: Shuling
authors.initials: S
authors.lastname: Guo
authors.forename: John D
authors.initials: JD
authors.lastname: York
authors.forename: Harald
authors.initials: H
authors.lastname: Sontheimer
authors.forename: James F
authors.initials: JF
authors.lastname: Collawn
authors.forename: Vytas A
authors.initials: VA
authors.lastname: Bankaitis
mesh_terms: D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D002470:Cell Survival; D004705:Endocytosis / Q000502:physiology; D005089:Exocytosis / Q000502:physiology; D005434:Flow Cytometry; D018390:Gene Targeting; D005838:Genotype; D007073:Immunoglobulin E / Q000378:metabolism; D008407:Mast Cells / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008819:Mice, Nude; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000378:metabolism*; D020033:Protein Isoforms; D011990:Receptors, Transferrin / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013234:Stem Cells / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D020033:Protein Isoforms; D011990:Receptors, Transferrin; D007073:Immunoglobulin E