β-1 tubulin R307H SNP alters microtubule dynamics and affects severity of a hereditary thrombocytopenia

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Abstract

Background:

Single nucleotide polymorphisms (SNPs) in platelet-associated genes partly explain inherent variability in platelet counts. Patients with monoallelic Bernard Soulier syndrome due to the Bolzano mutation (GPIBA A156V) have variable platelet counts despite a common mutation for unknown reasons.

Objectives:

We investigated the effect of the most common SNP (R307H) in the hematopoietic-specific tubulin isotype β-1 in these Bernard Soulier patients and potential microtubule-based mechanisms of worsened thrombocytopenia.

Patients/Methods:

Ninety-four monoallelic Bolzano mutation patients were evaluated for the R307H β-1 SNP and had platelet counts measured by three methods; the Q43P SNP was also evaluated. To investigate possible mechanisms underlying this association, we used molecular modeling of β-1 tubulin with and without the R307H SNP. We transfected SNP or non-SNP β-1 tubulin into MCF-7 and CMK cell lines and measured microtubule regrowth after nocodazole-induced depolymerization.

Results:

We found that patients with at least one R307H SNP allele had significantly worse thrombocytopenia; manual platelet counting revealed a median platelet count of 124 in non-SNP patients and 76 in SNP patients (both ×109 L−1; P < 0.01). The Q43P SNP had no significant association with platelet count. Molecular modeling suggested a structural relationship between the R307H SNP and microtubule stability via alterations in the M-loop of β tubulin; in vitro microtubule recovery assays revealed that cells transfected with R307H SNP β-1 had significantly impaired microtubule recovery.

Conclusions:

Our data show that the R307H SNP is significantly associated with the degree of thrombocytopenia in congenital and acquired platelet disorders, and may affect platelets by altering microtubule behavior.

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