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A NATURAL MUTATION AND SPECIFIC ARTIFICIAL DELETIONS IN THE BETA3 CYTOPLASMIC TAIL PREVENT ANTIBODY-MEDIATED ACTIVATION OF INTEGRIN ALPHAIIB-BETA3
Abstract number: P-T-281
Hauschner1 H., Rosenberg1 N., Seligsohn1 U.
1Amalia Biron Research Institute of Thrombosis and Hemostasis, Chaim Sheba Medical Center, Tel-Hashomer, Israel
How-to-cite Hauschner H, Rosenberg N, Seligsohn U. A NATURAL MUTATION AND SPECIFIC ARTIFICIAL DELETIONS IN THE BETA3 CYTOPLASMIC TAIL PREVENT ANTIBODY-MEDIATED ACTIVATION OF INTEGRIN ALPHAIIB-BETA3. J Thromb Haemost 2007; 5 Supplement 2: P-T-281
Abstract
Introduction:aIIb and b3 cytoplasmic tails of integrin aIIbb3 are associated by noncovalently interactions that stabilize the integrin in its inactive conformation. Expression of mutations that disrupt these interactions yield aIIbb3 in the activate state. We recently identified variant Glanzmann thrombasthenia in a patient whose platelets expressed 50% of normal aIIbb3 but did not bind fibrinogen. A splice site AG insertion in the last exon of b3 was identified predicting a frame-shift with extension of the cytoplasmic tail by 61 residues beyond 742 residue1.
Since the mutant does not bind fibrinogen, the defect could be in the inside-out signaling. In this study we examined fibrinogen binding capacity of the mutant by using antiLIBS6 and PT25-2 antibodies that directly activate the aIIbb3 independently from inside-out signaling.
Methods:b3-742ins - the natural mutant, b3-D742 – a truncated mutant, and b3-D749 – a truncated mutant that preserves an NPXY conserved sequence were created and introduced into BHK cells along with wild type (WT)-aIIb.
Results: FACS analysis revealed that cells harboring each mutant exhibited more than 70% of normal aIIbb3 surface expression. However, upon activation by antiLIBS6 or PT25-2 antibodies, cells harboring aIIbb3-742ins, -D742 or -D749 only bound a mean of 16%, 41% and 22% of fibrinogen that bound to WT cells, respectively. The differences between each mutant and WT cells were highly significant (p<0.001). Among the mutants, the natural mutation (b3-742ins) and b3-D749 had a significantly more pronounced effect compared to b3-D742 (p=0.0012 and 0.0066, respectively).
Conclusions: Three changes in the 742-762 sequence of the b3 cytoplasmic tail, a natural frameshift mutation causing tail extension, or 2 artificial deletions significantly reduce aIIbb3 activation by antiLIBS and PT25-2 antibodies. These findings support the evidence that b3 cytoplasmic tail from residue 742 onward is essential for aIIbb3 activation.
References: Rosenberg et al. 2005 JTH 3:2764
To cite this abstract use the following format:
Journal of Thrombosis and Haemostasis 2007; Volume 5, Supplement 2: abstract number
Session Details
| Date: |
01/08/2007
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| Time: |
00:00-00:00
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| Session name: |
XXIst ISTH Congress |
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| Location: |
Oxford, UK |
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