Human platelets contain SNARE proteins and a Sec1p homologue that interacts with syntaxin 4 and is phosphorylated after thrombin activation

Implications for platelet secretion

Guy Reed, Aiilyan K. Houng, Michael L. Fitzgerald

Research output: Contribution to journalArticle

84 Citations (Scopus)

Abstract

In response to thrombin and other extracellular activators, platelets secrete molecules from large intracellular vesicles (granules) to initiate thrombosis. Little is known about the molecular machinery responsible for vesicle docking and secretion in platelets and the linkage of that machinery to cell activation. We found that platelet membranes contain a full complement of interacting proteins - VAMP, SNAP-25, and syntaxin 4 - that are necessary for vesicle docking and fusion with the plasma membrane. Platelets also contain an uncharacterized homologue of the Sec1p family that appears to regulate vesicle docking through its binding with a cognate syntaxin. This platelet Sec1 protein (PSP) bound to syntaxin 4 and thereby excluded the binding of SNAP-25 with syntaxin 4, an interaction critical to vesicle docking. As predicted by its sequence, PSP was detected predominantly in the platelet cytosol and was phosphorylated in vitro by protein kinase C (PKC), a secretion-linked kinase, incorporating 0.87 ± 0.11 mol of PO4 per mole of protein. PSP was also specifically phosphorylated in permeabilized platelets after cellular stimulation by phorbol esters or thrombin and this phosphorylation was blocked by the PKC inhibitor Ro-31-8220. Phosphorylation by PKC in vitro inhibited PSP from binding to syntaxin 4. Taken together, these studies indicate that platelets, like neurons and other cells capable of regulated secretion, contain a unique complement of interacting vesicle docking proteins and PSP, a putative regulator of vesicle docking. The PKC- dependent phosphorylation of PSP in activated platelets and its inhibitory effects on syntaxin 4 binding provide a novel functional link that may be important in coupling the processes of cell activation, intracellular signaling, and secretion.

Original languageEnglish (US)
Pages (from-to)2617-2626
Number of pages10
JournalBlood
Volume93
Issue number8
StatePublished - Apr 15 1999

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Qa-SNARE Proteins
SNARE Proteins
Platelet Activation
Platelets
Thrombin
Blood Platelets
Chemical activation
Protein Kinase C
Phosphorylation
Proteins
Machinery
Protein C Inhibitor
Phorbol Esters
Cell membranes
Protein Kinase Inhibitors

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Immunology
  • Hematology
  • Cell Biology

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Human platelets contain SNARE proteins and a Sec1p homologue that interacts with syntaxin 4 and is phosphorylated after thrombin activation : Implications for platelet secretion. / Reed, Guy; Houng, Aiilyan K.; Fitzgerald, Michael L.

In: Blood, Vol. 93, No. 8, 15.04.1999, p. 2617-2626.

Research output: Contribution to journalArticle

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