title: Thrombospondin mediates calcium mobilization in fibroblasts via its Arg-Gly-Asp and carboxyl-terminal domains.
abstract: Thrombospondin is a matrix glycoprotein found in various cells that can modulate cell attachment, migration, and proliferation. We now show that intact soluble thrombospondin causes a transient [Ca2+]i increase in IMR-90 fibroblasts. This [Ca2+]i increase is mediated partly by the RGD-containing domain of thrombospondin that binds to the integrin alpha v beta 3 as demonstrated by inhibitor studies using anti-alpha v beta 3 antibody and RGD-containing peptides. A non-RGD and non-alpha v beta 3 component of this [Ca2+]i increase is mediated by the carboxyl-terminal domain of thrombospondin through an unidentified receptor on fibroblasts as shown by the antibody to the carboxyl-terminal of thrombospondin, C6.7. In addition, the carboxyl-terminal derived peptide, RFYVVMWK, also triggers [Ca2+]i increase in approximately 35% of fibroblasts. Both EGTA and Ni2+ block the entire [Ca2+]i increase indicating that this is due to an influx of extracellular Ca2+. B6H12, an antibody to the integrin-associated protein, blocks this [Ca2+]i increase by 50%, suggesting that some of the Ca2+ might be entering through an integrin-associated calcium channel. The current findings demonstrate that multiple domains on thrombospondin can trigger signal transduction events by increasing [Ca2+]i through their interactions with different cell receptors.
authors.affiliation: DuPont Merck Pharmaceutical Company, Cardiovascular Diseases Division, Wilmington, Delaware 19880-0400, USA.
authors.forename: P W
authors.initials: PW
authors.lastname: Tsao
authors.forename: S A
authors.initials: SA
authors.lastname: Mousa
mesh_terms: D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D018955:CD36 Antigens / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D039564:Integrin alphaV; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology; D015398:Signal Transduction; D019699:Thrombospondins
chemical_list: D015703:Antigens, CD; D018955:CD36 Antigens; D039564:Integrin alphaV; D008562:Membrane Glycoproteins; D009842:Oligopeptides; D010446:Peptide Fragments; D019699:Thrombospondins; C047981:arginyl-glycyl-aspartic acid; D002118:Calcium