title: The beta3 subunit of the integrin alphaIIbbeta3 regulates alphaIIb-mediated outside-in signaling.
abstract: Bidirectional signaling is an essential feature of alphaIIbbeta3 function. The alphaIIb cytoplasmic domain negatively regulates beta3-mediated inside-out signaling, but little is known about the regulation of alphaIIb-mediated outside-in signaling. We show that alphaIIb-mediated outside-in signaling is enhanced in platelets of a patient lacking the terminal 39 residues of the beta3 cytoplasmic tail. This enhanced signaling was detected as thromboxane A(2) (TxA(2)) production and granule secretion, and required ligand cross-linking of alphaIIbbeta3 and platelet aggregation. This outside-in signaling was specifically inhibited by a palmitoylated version of a beta3 peptide corresponding to cytoplasmic domain residues R724-R734. Unlike the palmitoylated peptide, the nonpalmitoylated beta3 peptide could not cross the platelet membrane and did not inhibit this outside-in signaling. The physiologic relevance of this beta3-mediated negative regulation of alphaIIb outside-in signaling was demonstrated in normal platelets treated with the palmitoylated peptide and a physiologic agonist. Binding of alphaIIbbeta3 complexes to immobilized peptides demonstrated that a peptide corresponding to beta3 residues R724-R734 appears to bind to an alphaIIb cytoplasmic domain peptide containing residues K989-D1002, but not to control peptides. These results demonstrate that alphaIIb-mediated outside-in signaling resulting in TxA(2) production and granule secretion is negatively regulated by a sequence of residues in the membrane distal beta3 cytoplasmic domain sequence RKEFAKFEEER.
authors.affiliation: Department of Microbiology and Molecular Cell Sciences, University of Memphis, Memphis, TN 38152, USA.
authors.forename: Junling
authors.initials: J
authors.lastname: Liu
authors.forename: Carl W
authors.initials: CW
authors.lastname: Jackson
authors.forename: Ralph A
authors.initials: RA
authors.lastname: Gruppo
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Jennings
authors.forename: T Kent
authors.initials: TK
authors.lastname: Gartner
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D005089:Exocytosis; D006801:Humans; D039661:Integrin beta3 / Q000235:genetics / Q000502:physiology*; D008297:Male; D009154:Mutation; D019308:Palmitic Acid; D010449:Peptide Mapping; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000502:physiology*; D040201:Platelet Membrane Glycoprotein IIb / Q000502:physiology*; D021122:Protein Subunits / Q000502:physiology; D015398:Signal Transduction; D013915:Thrombasthenia / Q000097:blood / Q000235:genetics; D013928:Thromboxane A2 / Q000096:biosynthesis
chemical_list: D039661:Integrin beta3; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D040201:Platelet Membrane Glycoprotein IIb; D021122:Protein Subunits; D019308:Palmitic Acid; D013928:Thromboxane A2