Novel nonsense mutation in the platelet glycoprotein Ibβ gene associated with Bernard‐Soulier syndrome

Kunishima, Shinji; Matsushita, Tadashi; Ito, Takahiko; Kamiya, Tadashi; Saito, Hidehiko

doi:10.1002/ajh.10230

Cited by 17 publications

(13 citation statements)

References 22 publications

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“…Several of the GP Ib␤ gene mutations that have been described are missense mutations. 23,[28][29][30] In general, these mutations might be expected to have a minimal effect on transcript stability. However, in the case of Watanabe et al, 8 who observed abnormal vesicles, the mutation is a 13-bp deletion within the signal peptide coding region of the GP Ib␤ gene.…”

Section: Discussionmentioning

confidence: 99%

Genetic deletion of mouse platelet glycoprotein Ibβ produces a Bernard-Soulier phenotype with increased α-granule size

Kato

Martínez

Russell

et al. 2004

Blood

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Here we report the characterization of a mouse model of the Bernard-Soulier syndrome generated by a targeted disruption of the gene encoding the glycoprotein (GP) Ib␤ subunit of the GP Ib-IX complex. Similar to a Bernard-Soulier model generated by disruption of the mouse GP Ib␣ subunit, GP Ib␤ Null mice display macrothrombocytopenia and a severe bleeding phenotype. When examined by transmission electron microscopy, the large platelets produced by a GP Ib␤ Null genotype revealed ␣-granules with increased size as compared with the ␣-granules from control mouse platelets. Data are presented linking the overexpression of a septin protein, SEPT5, to the presence of larger ␣-granules in the GP Ib␤ Null platelet. The SEPT5 gene resides approximately 250 nucleotides 5 to the GP Ib␤ gene and has been associated with modulating exocytosis from neurons and platelets as part of a presynaptic protein complex. Fusion mRNA transcripts present in megakaryocytes can contain both the SEPT5 and GP Ib␤ coding sequences as a result in an imperfect polyadenylation signal within the 3 end of both the human and mouse SEPT5 genes. We observed a 2-to 3-fold increase in SEPT5 protein levels in platelets from GP Ib␤ Null mice. These results implicate SEPT5 levels in the maintenance of normal ␣-granule size and may explain the variant granules associated with human GP Ib␤ mutations and the Bernard-Soulier syndrome.

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Section: Discussionmentioning

confidence: 99%

Genetic deletion of mouse platelet glycoprotein Ibβ produces a Bernard-Soulier phenotype with increased α-granule size

Kato

Martínez

Russell

et al. 2004

Blood

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“…40 Some are frameshifting or nonsense mutations, resulting in a typically truncated and nonfunctional protein product. [41][42][43] In this study, we have for the first time systematically characterized all the reported missense BSS mutations in GPIb␤ and observed distinct mechanisms that underlie the pathogenesis of the disease (Figure 2). Six of the 8 missense mutations are detrimental to proper tertiary folding or secretion of GPIb␤ E .…”

Section: Different Pathways To Bssmentioning

confidence: 95%

Quaternary organization of GPIb-IX complex and insights into Bernard-Soulier syndrome revealed by the structures of GPIbβ and a GPIbβ/GPIX chimera

McEwan

Yang

Carr

et al. 2011

Blood

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Platelet GPIb-IX receptor complex has 3 subunits GPIb␣, GPIb␤, and GPIX, which assemble with a ratio of 1:2:1. Dysfunction in surface expression of the complex leads to Bernard-Soulier syndrome. We have crystallized the GPIb␤ ectodomain (GPIb␤ E ) and determined the structure to show a single leucine-rich repeat with Nand C-terminal disulphide-bonded capping regions. The structure of a chimera of GPIb␤ E and 3 loops (a,b,c) taken from the GPIX ectodomain sequence was also determined. The chimera (GPIb␤ Eabc ), but not GPIb␤ E , forms a tetramer in the crystal, showing a quaternary interface between GPIb␤ and GPIX. Central to this interface is residue Tyr106 from GPIb␤, which inserts into a pocket generated by 2 loops (b,c) from GPIX. Mutagenesis studies confirmed this interface as a valid representation of interactions between GPIb␤ and GPIX in the full-length complex. Eight GPIb␤ missense mutations identified from patients with BernardSoulier syndrome were examined for changes to GPIb-IX complex surface expression. Two mutations, A108P and P74R, were found to maintain normal secretion/folding of GPIb␤ E but were unable to support GPIX surface expression. The close structural proximity of these mutations to Tyr106 and the GPIb␤ E interface with GPIX indicates they disrupt the quaternary organization of the GPIb-IX complex. (Blood. 2011;118(19):5292-5301) IntroductionGPIb-IX-V complex is an abundant membrane receptor complex on the platelet surface that plays a critical role in mediating platelet adhesion to the damaged vessel wall under conditions of high shear stress. 1 Platelets adhere, and integrins are subsequently activated by interactions of GPIb-IX-V with VWF bound to the subendothelium. How GPIb-IX-V transmits the VWF-binding signal across the membrane is not clear, partly because the structure and organization of this complex receptor remain to be elucidated. Because GPV is only weakly associated with the receptor complex and is not essential for complex expression, assembly, VWF binding, or signal transduction, 2,3 we focus on the GPIb-IX complex here.The GPIb-IX complex contains 3 subunits, GPIb␣, GPIb␤, and GPIX, with a 1:2:1 stoichiometry. 4 Each subunit is a type I transmembrane (TM) protein, containing an ectodomain with leucine-rich repeats (LRRs), 5 a single TM helix, and a relatively short cytoplasmic tail. The GPIb␣ ectodomain contains binding sites for a growing list of hemostatically important ligands, including VWF and thrombin. 6-8 Covalent and noncovalent interactions are important to the quaternary stabilization of the receptor. GPIb␣ links to 2 GPIb␤ subunits through membrane-proximal disulfide bonds to constitute the GPIb complex. 4 GPIX tightly associates with GPIb through noncovalent interactions. 9 Assembly of these subunits into a tightly integrated complex is also supported by genetic evidence. Bernard-Soulier syndrome (BSS) is a hereditary bleeding disorder that is characterized in most cases by giant platelets, low platelet counts, and little or no expression of GPIb-IX on the p...

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“…It is not evident, however, whether the Ib␤ TM domain is as important as its counterparts in GP Ib␣ and IX. No mutations within the Ib␤ TM domain have been reported to prevent surface expression of the receptor complex, although a nonsense mutation effectively removing the entire TM and cytoplasmic domains of GP Ib␤ has (20).…”

Section: Lack Of Expression Of Glycoprotein (Gp)mentioning

confidence: 99%

The Transmembrane Domain of Glycoprotein Ibβ Is Critical to Efficient Expression of Glycoprotein Ib-IX Complex in the Plasma Membrane

Padilla

et al. 2006

Journal of Biological Chemistry

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Lack of expression of glycoprotein (GP)Ib Platelet glycoprotein (GP)2 Ib-IX-V complex mediates the initial tethering and rolling of platelets on von Willebrand factor (vWF) localized at the vascular injury site (1, 2). Upon ligation with the A1 domain of vWF, the GP Ib-IX-V complex transmits inward a signal that leads to activation of integrin ␣IIb␤3 and eventual platelet activation and aggregation (3, 4).Although the GP Ib-IX-V complex is widely considered to comprise GP Ib␣, GP Ib␤, GP IX, and GP V with a 2:2:2:1 stoichiometry (5-7), it is not clear how these subunits assemble into a functional receptor complex in the membrane, partly because intersubunit interactions are largely unknown.Abnormally low expression of the GP Ib-IX-V complex in human platelets can result from mutations in either GP Ib␣, GP Ib␤, or GP IX, but not GP V (8). Such phenomena can be reproduced in transfected Chinese hamster ovary (CHO) cells; missing any of the three subunits leads to no or significantly lowered surface expression of the GP Ib-IX complex (9, 10). In contrast, GP V is not required for efficient expression of the GP Ib-IX complex, although there are mixed reports on whether it enhances the complex expression (11, 12). Furthermore, it has been shown in transfected cells that the GP Ib-IX complex assembles in the endoplasmic reticulum before being transported as a single entity to the plasma membrane. Failure of proper complex assembly results in prompt degradation of GP Ib␣ in the lysosome and accumulation of nonnative GP IX inside the cell (13,14).Although the interdependence among the subunits in the GP Ib-IX complex is well documented, the underlying reasons are not clear. The requirement of all three subunits to efficient surface expression of the complex posits the importance of intersubunit interactions to the proper assembly and therefore stability of the receptor complex. Based on the effects of mutations in GP Ib␤ on the expression level of GP IX, the N-terminal cysteine knot region in GP Ib␤ was suggested to mediate the interaction with GP IX (15). It helps to explain the dependence of GP IX expression on GP Ib␤. Why the expression of GP Ib␣ is dependent on GP Ib␤ and/or IX nonetheless remains unclear.The transmembrane (TM) domains of GP Ib␣ and IX may be important to efficient surface expression of the GP Ib-IX complex. Deletion of either the extracellular or cytoplasmic domain of GP Ib␣ does not significantly affect complex expression in transfected cells (16,17). Consistently, the Ib␣ extracellular domain, but not the combined extracellular and TM domains, can be replaced with counterparts from the interleukin-4 receptor while maintaining reasonable expression level of the receptor complex (18). In addition, a single-site mutation in the IX TM domain was recently identified to cause decreased expression of the GP Ib-IX

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Novel nonsense mutation in the platelet glycoprotein Ibβ gene associated with Bernard‐Soulier syndrome

Cited by 17 publications

References 22 publications

Genetic deletion of mouse platelet glycoprotein Ibβ produces a Bernard-Soulier phenotype with increased α-granule size

Genetic deletion of mouse platelet glycoprotein Ibβ produces a Bernard-Soulier phenotype with increased α-granule size

Quaternary organization of GPIb-IX complex and insights into Bernard-Soulier syndrome revealed by the structures of GPIbβ and a GPIbβ/GPIX chimera

The Transmembrane Domain of Glycoprotein Ibβ Is Critical to Efficient Expression of Glycoprotein Ib-IX Complex in the Plasma Membrane

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