Blood, 15 January 2001, Vol. 97, No. 2, pp. 449-458
HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY
Synthesis, secretion, and subcellular localization of
serglycin proteoglycan in human endothelial cells
Barbara P. Schick,
Joel F. Gradowski, and
James D. San Antonio
From the Cardeza Foundation for Hematologic Research,
Department of Medicine, Jefferson Medical College of Thomas Jefferson
University, Philadelphia, PA.
The serglycin proteoglycan is best known as a hematopoietic
cell granule proteoglycan. It has been found that serglycin is synthesized by endothelial cells, is localized to cytoplasmic vesicles, and is constitutively secreted. Serglycin
messenger RNA in human umbilical vein endothelial cells
(HUVECs) and cultured human aortic endothelial cells was detected by
reverse transcription-polymerase chain reaction.
35S-sulfate-labeled secreted and intracellular
proteoglycans were analyzed. It was found that 85% of the
proteoglycans synthesized during culture were secreted. A core
protein of the appropriate size for serglycin was detected by analysis
of the chondroitinase-digested 35S-sulfate-labeled HUVEC
proteoglycans. This was the major core protein of the secreted
chondroitin sulfate proteoglycans. Recombinant serglycin core protein
was used to generate an antibody in chickens. A core protein identified
by Western blotting of chondroitinase digests of HUVEC proteoglycans
corresponded to the major 35S-sulfate- labeled core
protein. Identical results were obtained with 2 hematopoietic cell
lines. Cyto-immunofluorescence showed cytoplasmic vesicular and
perinuclear labeling in hematopoietic cells and HUVECs. The
serglycin-containing vesicles in HUVECs are distinct from the
Weibel-Palade bodies, which contain von Willebrand factor. Confocal
microscopy showed that tissue plasminogen activator was distributed
similarly to serglycin. Serglycin may be important for the function of
these vesicles and, once secreted, for the modulation of the activity
of their constituents.
