Phenotypic consequence of the gene abnormality in the platelet glycoprotein IX gene observed in a patient with Bernard-Soulier syndrome through mammalian cell expression system.
We previously reported a patient with Bernard-Soulier syndrome (BSS) who had a homozygous missense mutation in the GPIX gene Phe55 (TTT) to Ser (TCT) replacement in the leucine-rich motif (LRM) of the GPIX polypeptide, as a probable cause of BSS phenotype. To study the effect of this mutation on the surface expression of the GPIb/IX complex and GPIX, we introduced this mutation into the cDNA of GPIX by site-directed mutagenesis and performed in vitro transfection studies with plasmid for mutant GPIX and other plasmids for GPIb/IX complex. Mutant GPIX could not increase the surface expression of GPIb-alpha, but also surface expression of GPIX itself. Immunostaining of the CHO-K1 cells transfected with two plasmids for mutant GPIX and GPIb-beta showed that mutant GPIX was weakly but certainly detected in the cytoplasm of the transfected cells. These findings indicate that this substitution is responsible for BSS phenotype and that the LRM of GPIX is a critically important element for an efficient expression of the GPIb/IX complex. They also suggest that the failure of GPIb/IX complex expression can be caused by a mechanism other than synthetic defect of the mutant protein.
Suzuki
K
K
Third Department of Internal Medicine, Yamagata University School of Medicine, Japan.
Hayashi
T
T
Akiba
J
J
Satoh
S
S
Kato
T
T
D000818:Animals; D001606:Bernard-Soulier Syndrome / Q000097:blood / Q000235:genetics*; D016466:CHO Cells; D006224:Cricetinae; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D006801:Humans; D020125:Mutation, Missense; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000235:genetics*; D014162:Transfection
D019038:Platelet Glycoprotein GPIb-IX Complex