Increased expression of urokinase plasminogen activator in Quebec platelet disorder is linked to megakaryocyte differentiation

Abstract

Quebec platelet disorder (QPD) is an inherited bleeding disorder associated with increased urokinase plasminogen activator (uPA) in platelets but not in plasma, intraplatelet plasmin generation, and ␣-granule protein degradation. These abnormalities led us to investigate uPA expression by QPD CD34 ؉ progenitors, cultured megakaryocytes, and platelets, and whether uPA was stored in QPD ␣-granules. Although QPD CD34 ؉ progenitors expressed normal amounts of uPA, their differentiation into megakaryocytes abnormally increased expression of the uPA gene but not the flanking genes for vinculin or calcium/calmodulindependent protein kinase II␥ on chromosome 10. The increased uPA production by cultured QPD megakaryocytes mirrored their production of ␣-granule proteins, which was normal. uPA was localized to QPD ␣-granules and it showed extensive colocalization with ␣-granule proteins in both cultured QPD megakaryocytes and platelets, and with plasminogen in QPD platelets. In QPD megakaryocytes, cultured without or with plasma as a source of plasminogen, ␣-granule proteins were stored undegraded and this was associated with much less uPAplasminogen colocalization than in QPD platelets. Our studies indicate that the overexpression of uPA in QPD emerges with megakaryocyte differentiation, without altering the expression of flanking genes, and that uPA is costored with ␣-granule proteins prior to their proteolysis in QPD. (Blood. 2009;113:1535-1542)

Plasminogen associates with phosphatidylserine-exposing platelets and contributes to thrombus lysis under flow

“…14 Like PAI-1, 15 plasminogen is contained in platelet a granules 16,17 and is released upon thrombin stimulation. 18 Platelet-bound plasminogen supports single-chain urokinase PA (scuPA)-mediated plasma clot lysis, 19 suggesting that despite being at a low concentration (0.2 nM), it is a functionally active pool.…”

Genetic basis of congenital platelet disorders

“…40 Quebec platelet disorder, another autosomal-dominant inherited platelet disorder with linkage to chromosome 10 (10q24), is characterized by a gain-of-function defect in fibrinolysis and increased platelet stores of urokinase plasminogen activator (uPA), which results in delayed-onset bleeding after clinical challenge. [41][42][43][44] Although platelets are structurally normal and platelet counts minimally reduced to normal, there is plasminmediated degradation of ␣-granule proteins and increased uPA released from activated platelets in Quebec platelet disorder, resulting in decreased aggregation and accelerated clot lysis. 45 Sequencing of the candidate gene PLAU, which encodes uPA, did not reveal putative coding or regulatory mutations, although it was observed that there was disproportionate allelic expression in patients, suggesting a cis regulatory defect.…”

Improving blood disorder diagnosis: reflections on the challenges

“…Thromboelastography is excluded as a possible diagnostic screening test [19] 2008 Quebec platelet disorder is reported to have minimal effect on urinary uPA [24] 2009 Quebec platelet disorder is linked to PLAU (uPA gene) with increased expression of uPA, by the linked allele, during megakaryocyte differentiation [22]. uPA is demonstrated to be targeted to a-granules in the disorder [23]. a-granule proteins are identified to be stored undegraded in Quebec platelet disorder megakaryocytes grown in culture, which do not contain plasminogen, confirming that their proteolysis in the disorder reflects intraplatelet plasmin generation [23] 2010 Quebec platelet disorder mutation is associated with a highly specific mutation: tandem duplication of a 78-kb genomic segment on chromosome 10 that includes PLAU [25].…”