Co-localization of CD9 and GPIIb-IIIa (·IIb ·3 integrin) on activated platelet pseudopods and ·-granule membranes |
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Authors: | C Brisson D O Azorsa L K Jennings S Moog J P Cazenave and F Lanza |
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Institution: | (1) Institut Pasteur de Lyon, URA 1459 CNRS, Avenue Tony Garnier, 69365 Lyon Cedex 07, France;(2) Etablissement de Transfusion Sanguine, INSERM U.311, Strasbourg, France;(3) University of Tennessee, Memphis, TN, USA |
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Abstract: | Summary CD9 is a 24-kDa membrane glycoprotein expressed on the surface of human platelets and potentially involved in cellular activation
and adhesion functions. This protein belongs to a recently delineated family of cell-surface antigens that span the membrane
four times, called tetraspans, and found mainly in leucocytes and tumour cells. As a first approach to clarify the function
of CD9, we used immunoelectron microscopy to determine the localization of this antigen in human platelets, and compared its
distribution with that of the GPIIb-IIIa integrin, the platelet receptor for fibrinogen. Monoclonal antibodies against CD9
(MAb7) and GPIIb-IIIa (HP1-1D) coupled to colloidal gold of different sizes (5 and 15 nm) were incubated with intact platelets
in suspension or on ultrathin sections of platelets embedded in LR white. CD9 was found in association with GPIIb-IIIa on
the inner face of ·-granule membranes. These two antigens also co-localized on pseudopods of activated platelets and in contact
regions between adjacent platelets. CD63, another member of the tetraspan family, was absent from ·-granules but was associated
with lysosomal structures. Flow cytometric analysis of platelet CD9 with a series of monoclonal antibodies revealed an increased
expression upon thrombin stimulation, confirming the presence of an intracellular granular pool. The observation that CD9
and GPIIb-IIIa are stored in the same intracellular structures and migrate to the same activation zones after platelet stimulation
lends support to previous suggestions of a close association between CD9 and GPIIb-IIIa in human platelets and of a possible
involvement of CD9 in adhesive functions of platelets.
This revised version was published online in November 2006 with corrections to the Cover Date. |
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