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J Tschopp, DE Jenne, S Hertig, KT Preissner, H Morgenstern, AP Sapino and L French
Institute of Biochemistry, University of Lausanne, Epalinges, Switzerland.
Clusterin, a 70-Kd disulfide-linked two-chain plasma glycoprotein
circulates in blood as a high-density lipoprotein particle and is highly
induced after tissue injury and tissue remodeling. In this study,
peripheral blood leukocytes were assayed for clusterin expression. The
protein was predominantly detectable in human platelets by immune
cytochemistry. The content of clusterin was determined and amounts to 2.5
+/- 1.3 micrograms/10(9) platelets, thus representing about 2% of the blood
pool. Clusterin purified from human platelets had the same molecular weight
as plasma clusterin under nonreducing conditions and was composed of two
disulfide-linked nonidentical subunits of the same size. Both preparations
were sensitive to reduction yielding the two subunits of 35 Kd. In contrast
to plasma clusterin, the platelet form was not complexed to apolipoprotein
A-I. By immunogold labeling, alpha-granule localization of clusterin was
observed. Complete release of platelet clusterin occurred at optimal doses
of A23187, phorbol myristate acetate (PMA), and thrombin. Because clusterin
mRNA was detected by hybridization in situ in bone marrow- derived
megakaryocytes, platelet clusterin is most likely produced and packaged
into alpha-granules during megakaryocyte development.
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| Copyright © 1993 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
