Shedding of heparan sulfate proteoglycan by stimulated endothelial cells: Evidence for proteolysis of cell‐surface molecules

Abstract

Activation of endothelial cells by cytokines and endotoxin causes procoagulant and pro-inflammatory changes over a period of hours. We postulated that the same functional state might be achieved more rapidly by changes in the metabolism of heparan sulfate, which supports many of the normal functions of endothelial cells. We previously found that binding of anti-endothelial cell antibodies and activation of complement on endothelial cells causes the rapid shedding of endothelial cell heparan sulfate. Here we report the biochemical mechanism responsible for the release of the heparan sulfate. Stimulation of endothelial cells by anti-endothelial cell antibodies and complement resulted in the release of 35S-heparan sulfate proteoglycan and partially degraded 35S-heparan sulfate chains. Degradation of the 35S-heparan sulfate chains was not necessary for release since heparin and suramin prevented cleavage of the heparan sulfate but did not inhibit release from stimulated endothelial cells. The 35S-heparan sulfate proteoglycan released from endothelial cells originated from the cell surface and had a core protein similar in size (70.5 kD) to syndecan-1. Release was due to proteolytic cleavage of the protein core by serine and/or cysteine proteinases since the release of heparan sulfate was inhibited 87% by antipain and 53% by leupeptin. Release of heparan sulfate coincided with a decrease of approximately 7 kD in the mass of the protein core and with a loss of hydrophobicity of the proteoglycan, consistent with the loss of the hydrophobic transmembrane domain. The cleavage and release of cell-surface 35S-heparan sulfate proteoglycan might be a novel mechanism by which endothelial cells may rapidly acquire the functional properties of activated endothelial cells.

Phenotypic and Functional Maturation of Dendritic Cells Mediated by Heparan Sulfate

“…Solubilization of heparan sulfate might be brought about by enzymatic cleavage of the protein core, the glycosaminoglycan chains, or, in the case of glypican, the lipid anchor (25,(27)(28)(29). For example, in injured or inflamed tissue, heparanase released from platelets and stabilized by acidic pH could mediate cleavage of heparanase sulfate (25,30).…”

“…Structural modifications of the saccharide residues, especially sulfation, confer manifold biological activities, including regulation of cell adhesion, proliferation, development, anticoagulant, and chemical mediator functions (18 -21). Injury of tissues (22) or exposure of endothelial cells and, perhaps, other cells to activated complement or to neutrophils or platelets causes rapid cleavage and shedding of heparan sulfate proteoglycans and glycosaminoglycan fragments (23)(24)(25)(26). The release of heparan sulfate is postulated to be mediated by proteolytic cleavage of the protein core or by endoglycolytic cleavage of the heparan sulfate chains (25,(27)(28)(29).…”

Characterization of potential CD138 negative myeloma "stem cells"

“…On MM cells, there is a rapid turnover of surface CD138 5,6 and the rapid loss of CD138 on apoptotic cells is probably caused by a combination of decreased protein synthesis and increased proteolytic cleavage in these cells. [7][8][9] Furthermore, neither flow cytometry nor qPCR was able to identify a differential expression of CD19 and CD20 between the CD138 -and CD138 + subpopulations ( Figure 2D). We conclude that the CD138 -cellular subset reported seems to represent an apoptotic artifact probably due to sample handling and procedures.…”

The Complement Inhibitor Low Molecular Weight Dextran Sulfate Prevents TLR4-Induced Phenotypic and Functional Maturation of Human Dendritic Cells

“…HS proteoglycans are rapidly released under conditions of inflammation and tissue damage (17)(18)(19). The release of HS is mediated by proteolytic cleavage of the protein core or by endoglycolytic cleavage of the HS chains (18,20).…”