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Jayo, AsierAutor o coautorMartinez, ConstantinoAutor o coautor

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L718P mutation in the membrane-proximal cytoplasmic tail of beta 3 promotes abnormal alpha IIb beta 3 clustering and lipid microdomain coalescence, and associates with a thrombasthenia-like phenotype

Publicat a:Haematologica. 95 (7): 1158-1166 - 2010-07-01 95(7), DOI: 10.3324/haematol.2009.018572

Autors: Jayo, Asier; Conde, Isabel; Lastres, Pedro; Martinez, Constantino; Rivera, Jose; Vicente, Vicente; Gonzalez-Manchon, Consuelo

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Support for the role of transmembrane and membrane-proximal domains of alpha IIb beta 3 integrin in the maintenance of receptor low affinity comes from mutational studies showing that activating mutations can induce constitutive bi-directional transmembrane signaling.We report the functional characterization of a mutant alpha IIb beta 3 integrin carrying the Leu718Pro mutation in the membrane-proximal region of the beta 3 cytoplasmic domain, identified in heterozygosis in a patient with a severe bleeding phenotype and defective platelet aggregation and adhesion.Transiently transfected cells expressed similar levels of normal and mutant alpha IIb beta 3, but surface expression of mutant alpha v beta 3 was reduced due to its retention in intracellular compartments. Cells stably expressing mutant alpha IIb beta 3 showed constitutive binding to soluble multivalent ligands as well as spontaneous fibrinogen-dependent aggregation, but their response to DTT was markedly reduced. Fibrinogen-adherent cells exhibited a peculiar spreading phenotype with long protrusions. Immunofluorescence analysis revealed the formation of alpha IIb beta 3 clusters underneath the entire cell body and the presence of atypical high-density patches of clustered alpha IIb beta 3 containing encircled areas devoid of integrin that showed decreased affinity for the fluorescent lipid analog DiIC(16) and were disrupted in cholesterol-depleted cells.These findings are consistent with an important role of the membrane-proximal region of beta 3 in modulating alpha IIb beta 3 clustering and lateral redistribution of membrane lipids. Since the beta 3 mutant was associated with a thrombasthenic phenotype in a patient carrying one normal beta 3 allele, these results support a dominant role of clustering in regulating integrin alpha IIb beta 3 functions in vivo.

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