SPARC: a Ca2+-binding extracellular protein associated with endothelial cell injury and proliferation.
SPARC (Secreted Protein that is Acidic and Rich in Cysteine) is a Ca2+-binding, stress-related protein released in vitro by both malignant and normal cells derived from all primordial germ layers. It is specifically elevated in endothelial cells as a result of "culture shock" (characterized by high levels of proliferation and migration) and exhibits density-dependent secretion. Exposure of bovine aortic endothelial cells to endotoxin results in a 70-100% increase in secreted protein, with a three-fold increase in SPARC. Immunofluorescence histochemistry on mouse tissues revealed (a) a preferential association of SPARC with highly proliferative cells (e.g., gut epithelia, mammary gland, and epidermis), (b) a cell surface or stromal location in thymus, lung, and salivary gland, (c) staining of epididymidal epithelium and testicular cells, and (d) an association with somites of 14 d mouse embryos. We envision SPARC as an extracellular modulator of Ca2+ and other cation-sensitive proteins/proteinases, that facilitates cellular proliferation in response to injury and to developmental signals.
Sage
H
H
Department of Biological Structure, University of Washington, Seattle 98195.
Decker
J
J
Funk
S
S
Chow
M
M
D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002455:Cell Division; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism; D051379:Mice; D015676:Osteonectin; D014018:Tissue Distribution
D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D015676:Osteonectin