A variant thrombasthenic phenotype associated with compound heterozygosity of integrin beta3-subunit: (Met124Val)beta3 alters the subunit dimerization rendering a decreased number of constitutive active alphaIIbbeta3 receptors.
We report the analysis of a variant case of thrombasthenic phenotype that is a compound heterozygote for two mutations located within the metal ion dependent adhesion site (MIDAS) of the beta3 subunit. The patient inherited a maternal allele carrying the Met124Val substitution and a paternal allele that changes Asp119 to Tyr. Phenotyping of the human platelet antigen 1 (HPA-1) showed that the platelet alphaIIbbeta3 complex in the patient was mostly accounted for by the Asp 119Tyr allele that does not bind to fibrinogen (Fg). The patient showed agonistinduced binding of platelets to Fg but neither binding to PAC-1 nor cell aggregation could be detected, most likely due to the minute expression (< or = 5%) of alphaIIb(124Val)beta3 receptors. CHO cells expressing (124Val)beta3 showed a diminished surface expression of alphaIIbbeta3, enhanced adhesion to immobilized Fg, and spontaneous aggregation in the presence of soluble Fg, suggesting that (124Val)beta3 may confer constitutive activity to the alphaIIb(124Val)beta3 receptors. A distinct feature of these cells is the failure of DTT to enhance the binding to soluble Fg and the formation of cell aggregates. The substitution of (124Met)beta3 by either a polar or a positively charged amino acid restored the surface exposure and function of the alphaIIbbeta3 receptors whereas a negatively charged residue did not.
González-Manchón
Consuelo
C
Department of Physiopathology and Human Molecular Genetics, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu, 9, 28040-Madrid, Spain.
Butta
Nora
N
Larrucea
Susana
S
Arias-Salgado
Elena G
EG
Alonso
Sonia
S
López
Angela
A
Parrilla
Roberto
R
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D016824:Antigens, Human Platelet / Q000235:genetics / Q000276:immunology; D001483:Base Sequence; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism; D015153:Blotting, Western; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D004252:DNA Mutational Analysis; D018076:DNA, Complementary / Q000378:metabolism; D019281:Dimerization; D005192:Family Health; D005260:Female; D005340:Fibrinogen / Q000378:metabolism; D005434:Flow Cytometry; D005822:Genetic Vectors; D006579:Heterozygote; D006801:Humans; D015151:Immunoblotting; D007223:Infant; D039661:Integrin beta3 / Q000737:chemistry* / Q000235:genetics*; D008297:Male; D051379:Mice; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D010641:Phenotype; D010973:Platelet Adhesiveness; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry* / Q000235:genetics*; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D013915:Thrombasthenia / Q000097:blood* / Q000473:pathology*; D013997:Time Factors; D014162:Transfection
D016824:Antigens, Human Platelet; D018076:DNA, Complementary; D039661:Integrin beta3; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D012333:RNA, Messenger; D005340:Fibrinogen