Morphometric Analysis of Platelets in Bernard-Soulier Syndrome: Size and Configuration in Patients and Carriers

Actin-binding protein-280 binds the stress-activated protein kinase (SAPK) activator SEK-1 and is required for tumor necrosis factor-alpha activation of SAPK in melanoma cells

SEK-1, a dual specificity protein kinase that serves as one of the immediate upstream activators of the stress-activated protein kinases (SAPKs), associates specifically with the actin-binding protein, ABP-280, in vitro and in situ. SEK-1 binds to the carboxyl-terminal rod segment of ABP-280, upstream of the ABP carboxyl-terminal dimerization domain. Activation of SEK-1 in situ increases the SEK-1 activity bound to ABP-280 without changing the amount of SEK-1 polypeptide bound. The influence of ABP-280 on SAPK regulation was evaluated in human melanoma cells that lack ABP-280 expression, and in stable transformants of these cells expressing wild type ABP, or an actin-binding but dimerization-deficient mutant ABP (ABPDeltaCT109). ABP-280-deficient cells show an activation of SAPK in response to most stimuli that is comparable to that seen in ABP-280-replete cells; ABP-280-deficient cells, however, fail to show the brisk tumor necrosis factor-alpha (TNF-alpha) activation of SAPK seen in ABP-replete cells and have an 80% reduction in SAPK activation by lysophosphatidic acid. Expression of the dimerization-deficient mutant ABP-280 fails to correct the defective SAPK response to lysophosphatidic acid, but essentially normalizes the TNF-alpha activation of SAPK. Thus, a lack of ABP-280 in melanoma cells causes a defect in the regulation of SAPK that is selective for TNF-alpha and is attributable to the lack of ABP-280 polypeptide itself rather than to the disordered actin cytoskeleton that results therefrom. ABP-280 participates in TNF-alpha signal transduction to SAPKs, in part through the binding of SEK-1.

Studies on the megakaryocytes of a patient with the Bernard-Soulier syndrome

We have used monoclonal antibodies AP-1 (anti-GP Ib alpha). AP-2 (anti-GP IIb-IIIa) and FMC 25 (anti-GP IX) in immunofluorescence and immunocytochemical studies on megakaryocytes (MK) isolated from a Bernard-Soulier syndrome (BSS) patient whose giant platelets were characteristically deficient in GP Ib-IX complexes. Electron microscopy showed that the patient's MK were similar in size to normal MK. However, a striking feature was the variable and intermittent nature of the demarcation membrane system which was often vacuolar in appearance. Permeabilized mature MK from normal individuals were strongly positive with AP-2, AP-1 and FMC 25. Those from the BSS patient were normal for AP-2, negative for AP-1 but weakly positive with FMC 25. Binding of the monoclonal antibodies to the patient's platelets was evaluated using flow cytometry. The results confirmed the absence of GP Ib alpha from the surface membranes, but showed the presence of small amounts of GP IX distributed throughout the platelet population. Our findings confirm that the membrane lesion in BSS is also to be found in MK and further show that the defect may affect differently individual constituents of the GP-Ib-IX complex.

Twin pregnancy and parturition in a patient with the Bernard Soulier syndrome

A patient with the Bernard Soulier Syndrome was successfully delivered of twins. The pregnancy was complicated by slight bleeding from the uterus during the first 8 weeks, by cord prolapse necessitating emergency caesarean section, and by moderate post partum haemorrhage. The management of pregnancy in the Bernard Soulier Syndrome is discussed.

Platelet prothrombin converting activity in hereditary disorders of platelet function

Prothrombinase activities of platelets have been measured in diluted platelet-rich plasma using a chromogenic substrate assay and purified coagulation factors. No abnormalities in prothrombinase activities were found for platelets from patients with storage pool disease (dense-body deficiency), grey platelet syndrome, and Glanzmann's thrombasthenia. It is concluded that neither release of dense bodies and alpha-granules nor aggregation of platelets are essential prerequisites for exposure of a procoagulant surface. Platelets from patients with Bernard-Soulier syndrome, however, have approximately 10-fold higher prothrombinase activities in the non-stimulated form than normal non-stimulated platelets. The increased procoagulant activity cannot be completely ascribed to an increase in platelet size. It is suggested that the increased prothrombinase activity reflects an increased exposure of phosphatidylserine at the outer surface of non-stimulated Bernard-Soulier platelets, earlier described by Perret et al (1983).