title: Suppression of integrin activation by the membrane-distal sequence of the integrin alphaIIb cytoplasmic tail.
abstract: Integrin cytoplasmic tails regulate integrin activation including an increase in integrin affinity for ligands. Although there is ample evidence that the membrane-proximal regions of the alpha and beta tails interact with each other to maintain integrins in a low-affinity state, little is known about the role of the membrane-distal region of the alpha tail in regulation of integrin activation. We report a critical sequence for regulation of integrin activation in the membrane-distal region of the alphaIIb tail. Alanine substitution of the RPP residues in the alphaIIb tail rendered alphaIIbbeta3 constitutively active in a metabolic energy-dependent manner. Although an alphaIIb/alpha6Abeta3 chimaeric integrin, in which the alphaIIb tail was replaced by the alpha6A tail, was in an energy-dependent active state to bind soluble ligands, introduction of the RPP sequence into the alpha6A tail inhibited binding of an activation-dependent antibody PAC1. In alphaIIb/alpha6Abeta3, deleting the TSDA sequence from the alpha6A tail or single amino acid substitutions of the TSDA residues inhibited alphaIIb/alpha6Abeta3 activation and replacing the membrane-distal region of the alphaIIb tail with TSDA rendered alphaIIbbeta3 active, suggesting a stimulatory role of TSDA in energy-dependent integrin activation. However, adding TSDA to the alphaIIb tail containing the RPP sequence of the membrane-distal region failed to activate alphaIIbbeta3. These results suggest that the RPP sequence after the GFFKR motif of the alphaIIb tail suppresses energy-dependent alphaIIbbeta3 activation. These findings provide a molecular basis for the regulation of energy-dependent integrin activation by alpha subunit tails.
authors.affiliation: Department of Internal Medicine 1, Ehime University School of Medicine, Shigenobu, Ehime 791-0295, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Yamanouchi
authors.forename: Takaaki
authors.initials: T
authors.lastname: Hato
authors.forename: Tatsushiro
authors.initials: T
authors.lastname: Tamura
authors.forename: Shigeru
authors.initials: S
authors.lastname: Fujita
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D039503:Integrin alpha6 / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D040201:Platelet Membrane Glycoprotein IIb / Q000737:chemistry* / Q000235:genetics
chemical_list: D039503:Integrin alpha6; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D040201:Platelet Membrane Glycoprotein IIb