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RB Jenkins, WL Nichols, KG Mann and LA Solberg
Human megakaryocytes have been shown by immunofluorescent techniques to
express platelet glycoprotein IIb/IIIa antigen. We report evidence that
megakaryocytes derived from human committed megakaryocytic progenitor cells
in vitro (CFU-M) synthesize glycoproteins IIb and IIIa. Nonadherent
light-density human bone marrow cells were cultured in human plasma and
methylcellulose using conditions that promote large megakaryocytic
colonies. On day 13 the megakaryocytic colonies were picked, pooled, and
pulsed with 35S-methionine in methionine-free media. Populations of
approximately 100,000 cells with greater than or equal to 95% viability and
containing 70% to 90% megakaryocytes were obtained reliably for study.
After the radioactive pulse, the cell suspension was solubilized with
nonionic detergent. To reduce nonspecific binding of 35S-labeled proteins
to agarose, the lysate was chromatographed sequentially on glycine-quenched
Affi-gel and antihuman factor X-Sepharose. The unbound material from these
resins was then chromatographed on an antiglycoprotein IIb/IIIa monoclonal
antibody resin (HP1-1D-Sepharose) or on a control monoclonal antibody
resin. Bound fractions were eluted and analyzed by polyacrylamide gel
electrophoresis and autoradiography. Autoradiograms of diethylamine eluates
from HP1-1D-Sepharose revealed two labeled proteins with electrophoretic
mobilities identical with those of human platelet membrane glycoproteins
IIb and IIIa, isolated using similar conditions. Autoradiograms of material
synthesized by control macrophages from the same donors revealed no
significant labeling of proteins in the glycoprotein IIb/IIIa molecular
weight range, nor were such proteins bound by HP1-1D-Sepharose. Our
observations show that protein synthesis by CFU-M-derived human
megakaryocytes can be readily studied using a small amount of bone marrow
aspirate as starting material. This approach will allow the study of
protein synthesis by megakaryocytes from normal subjects or from subjects
with clinical disorders, and it will circumvent the need to obtain large
amounts of bone marrow to prepare enriched populations of megakaryocytes.
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| Copyright © 1986 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||