A novel Pro126His beta propeller mutation in integrin alphaIIb causes Glanzmann thrombasthenia by impairing progression of pro-alphaIIbbeta3 from endoplasmic reticulum to Golgi.
BACKGROUND
Glanzmann thrombasthenia (GT) is an autosomal recessive bleeding disorder characterized by lack of platelet aggregation in response to most physiological agonists and caused by either a lack or dysfunction of the platelet integrin alphaIIbbeta3 (glycoprotein IIb/IIIa).


METHODS
Mucocutaneous bleeding manifestations and platelet dysfunction consistent with GT were observed in a 20-year-old proband of a Chinese family.


OBJECTIVE
To determine the molecular basis of GT and characterize the mutation by in vitro expression studies.


RESULTS
Analysis of the patient's platelets by fluorescence-activated cell sorting demonstrated the presence of trace amounts of beta3, exposed on her platelet surface, but a complete absence of alphaIIbbeta3. Sequence analysis revealed a novel C470A transversion in exon 4 of the alphaIIb gene predicting a Pro126His alteration in the blade 2 of the alphaIIb beta propeller domain. The proband was homozygous for the mutation, the mother and the father were heterozygous, whereas 100 healthy subjects lacked this transversion. Chinese hamster ovary cells cotransfected with cDNAs of mutated alphaIIb and wild-type beta3 failed to express alphaIIbbeta3 on the cell surface as shown by FACS. Western blot analysis of the cell lysates showed no detectable mature alphaIIb. Immunoprecipitation with antibody against beta3 demonstrated pro-alphaIIb in the cells expressing the mutant alphaIIbbeta3, indicating pro-alphaIIbbeta3 complex formation. Intracellular immunofluorescence studies demonstrated the pro-alphaIIbbeta3 complex that co-localized with an ER marker, but showed minimal co-localization with a Golgi marker.


CONCLUSIONS
A novel Pro126His mutation in alphaIIb compromised transport of the pro-alphaIIbbeta3 complex from the endoplasmic reticulum to the Golgi, leading to intracellular retention. The impaired alphaIIbbeta3 transport is responsible for the thrombasthenia in this patient.
Shen
Wei-Zhang
WZ
Shanghai Institute of Hematology, Ruijin Hospital, Medical College of Shanghai Jiao Tong University, Shanghai, People's Republic of China.
Ding
Qiu-Lan
QL
Jin
Pei-Pei
PP
Wang
Xue-Feng
XF
Jiang
Yu-Zhen
YZ
Li
Shu-Mei
SM
Wang
Hong-Li
HL
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D005091:Exons / Q000235:genetics; D005190:Family; D005260:Female; D006056:Golgi Apparatus / Q000235:genetics / Q000378:metabolism; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D008297:Male; D020125:Mutation, Missense / Q000235:genetics; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D040201:Platelet Membrane Glycoprotein IIb / Q000235:genetics* / Q000378:metabolism; D021381:Protein Transport / Q000235:genetics / Q000502:physiology; D013915:Thrombasthenia / Q000209:etiology / Q000235:genetics* / Q000378:metabolism*
D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D040201:Platelet Membrane Glycoprotein IIb