R to Q amino acid substitution in the GFFKR sequence of the cytoplasmic domain of the integrin IIb subunit in a patient with a Glanzmann's thrombasthenia-like syndrome.
The integrin IIbbeta3 mediates platelet aggregation through its fibrinogen and adhesive protein-binding properties. Particular interest concerns the role of the cytoplasmic domains of IIb and beta3. We now report the molecular analysis of IIbbeta3 from a patient with a Glanzmann's thrombasthenia-like syndrome for whom the principal characteristics are an approximate 50% total platelet content of IIbbeta3 but with a much lower proportion in the surface pool (Hardisty et al, Blood 80:696, 1992). Polymerase chain reaction (PCR) single-strand conformational polymorphism and DNA sequencing showed a heterozygous mutation giving rise to amino acid substitution R995 to Q in the GFFKR sequence of the cytoplasmic domain of IIb. Reverse transcriptase-PCR and polymorphism analysis only detected mRNA for the mutated allele of the IIb gene and a single allele of the beta3 gene in his platelets, suggesting other unidentified defects. Site-directed mutagenesis followed by transient expression of the mutated IIb together with wild-type beta3 in Cos-7 cells resulted in a markedly decreased expression of the complex at the cell surface when compared with cells transfected with wild-type IIb and beta3. Flow cytometry with PAC-1 and a stable Chinese hamster ovary-transfected cell line showed that the mutated receptor was not locked into a high activation state, although it became so in the presence of the activating antibody, anti-LIBS6. This is the first reported natural mutation in the highly conserved GFFKR sequence of the IIb cytoplasmic domain.
Peyruchaud
O
O
The UMR 5533 CNRS, Hôpital Cardiologique, Pessac, France.
Nurden
A T
AT
Milet
S
S
Macchi
L
L
Pannochia
A
A
Bray
P F
PF
Kieffer
N
N
Bourre
F
F
D019943:Amino Acid Substitution; D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D006224:Cricetinae; D006801:Humans; D008297:Male; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics*; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D013915:Thrombasthenia / Q000235:genetics*
D019039:Platelet Glycoprotein GPIIb-IIIa Complex