title: Heterozygous ITGA2B R995W mutation inducing constitutive activation of the αIIbβ3 receptor affects proplatelet formation and causes congenital macrothrombocytopenia.
abstract: Congenital macrothrombocytopenia is a genetically heterogeneous group of rare disorders. αIIbβ3 has not been implicated in these conditions. We identified a novel, conserved heterozygous ITGA2B R995W mutation in 4 unrelated families. The surface expression of platelet αIIbβ3 was decreased to 50% to 70% of control. There was spontaneous PAC-1 and fibrinogen binding to resting platelets without CD62p expression. The activation state of αIIbβ3 in 293T cells was higher for αIIb-W995 than for β3-H723 but was weaker than for β3-N562. FAK was spontaneously phosphorylated in αIIb-W995/β3-transfected 293T cells. These results indicate that αIIb-W995/β3 has a constitutive, activated conformation but does not induce platelet activation. αIIb-W995/β3-transfected CHO cells developed membrane ruffling and abnormal cytoplasmic protrusions. The increased size and decreased number of proplatelet tips in αIIb-W995/β3-transduced mouse fetal liver-derived megakaryocytes indicate defective pro-platelet formation. We propose that activating mutations in ITGA2B and ITGB3 represent the etiology of a subset of congenital macrothrombocytopenias.
authors: Department of Advanced Diagnosis, Clinical Research Center, National Hospital Organization Nagoya Medical Center, 4-1-1 Sannomaru, Naka-ku, Nagoya, Japan. kunishis@nnh.hosp.go.jp
authors: Shinji
authors: S
authors: Kunishima
authors: Hirokazu
authors: H
authors: Kashiwagi
authors: Makoto
authors: M
authors: Otsu
authors: Naoya
authors: N
authors: Takayama
authors: Koji
authors: K
authors: Eto
authors: Masafumi
authors: M
authors: Onodera
authors: Yuji
authors: Y
authors: Miyajima
authors: Yasushi
authors: Y
authors: Takamatsu
authors: Junji
authors: J
authors: Suzumiya
authors: Kousaku
authors: K
authors: Matsubara
authors: Yoshiaki
authors: Y
authors: Tomiyama
authors: Hidehiko
authors: H
authors: Saito
mesh_terms: D000328:Adult; D019943:Amino Acid Substitution; D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D002648:Child; D002675:Child, Preschool; D006224:Cricetinae; D003412:Cricetulus; D004252:DNA Mutational Analysis; D005260:Female; D006579:Heterozygote; D006801:Humans; D007223:Infant; D039421:Integrin alpha2 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D039661:Integrin beta3 / Q000235:genetics / Q000378:metabolism; D008297:Male; D008533:Megakaryocytes / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008875:Middle Aged; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013921:Thrombocytopenia / Q000097:blood / Q000151:congenital* / Q000235:genetics*; D014162:Transfection; D055815:Young Adult
chemical_list: C056564:ITGA2B protein, human; C061248:ITGB3 protein, human; D039421:Integrin alpha2; D039661:Integrin beta3; D050505:Mutant Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011994:Recombinant Proteins