title: Loss of pleckstrin defines a novel pathway for PKC-mediated exocytosis.
abstract: Pleckstrin, the platelet and leukocyte C kinase substrate, is a prominent substrate of PKC in platelets, monocytes, macrophages, lymphocytes, and granulocytes. Pleckstrin accounts for 1% of the total protein in these cells, but it is best known for containing the 2 prototypic Pleckstrin homology, or PH, domains. Overexpressed pleckstrin can affect polyphosphoinositide second messenger-based signaling events; however, its true in vivo role has been unknown. Here, we describe mice containing a null mutation within the pleckstrin gene. Platelets lacking pleckstrin exhibit a marked defect in exocytosis of delta and alpha granules, alphaIIbbeta3 activation, actin assembly, and aggregation after exposure to the PKC stimulant, PMA. Pleckstrin-null platelets aggregate normally in response to thrombin, but they fail to aggregate in response to thrombin in the presence of PI3K inhibitors, suggesting that a PI3K-dependent signaling pathway compensates for the loss of pleckstrin. Although pleckstrin-null platelets merged their granules in response to stimulation of PKC, they failed to empty their contents into the open canalicular system. This might be attributable to impaired actin assembly present in cells lacking pleckstrin. These data show that pleckstrin regulates the fusion of granules to the cell membrane and is an essential component of PKC-mediated exocytosis.
authors.affiliation: Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
authors.forename: Lurong
authors.initials: L
authors.lastname: Lian
authors.forename: Yanfeng
authors.initials: Y
authors.lastname: Wang
authors.forename: Matthew
authors.initials: M
authors.lastname: Flick
authors.forename: John
authors.initials: J
authors.lastname: Choi
authors.forename: Edward W
authors.initials: EW
authors.lastname: Scott
authors.forename: Jay
authors.initials: J
authors.lastname: Degen
authors.forename: Mark A
authors.initials: MA
authors.lastname: Lemmon
authors.forename: Charles S
authors.initials: CS
authors.lastname: Abrams
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D001798:Blood Proteins / Q000235:genetics / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D008561:Membrane Fusion / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D016296:Mutagenesis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D015539:Platelet Activation / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D000199:Actins; D001798:Blood Proteins; D010750:Phosphoproteins; C039077:platelet protein P47; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C