title: Metabolism of thrombospondin 2. Binding and degradation by 3t3 cells and glycosaminoglycan-variant Chinese hamster ovary cells.
abstract: Thrombospondin 1 (TSP1) and thrombospondin 2 (TSP2) are members of the thrombospondin family that have a similar structural organization but somewhat different functional activities. Iodinated recombinant mouse TSP2 bound to NIH 3T3 cells and was internalized and degraded through a chloroquine-inhibitable pathway. TSP2 degradation was saturable, specific, and similar to the kinetics of degradation of TSP1. Human platelet TSP1, recombinant mouse TSP1, and recombinant mouse TSP2 cross-competed with one another for degradation by 3T3 cells. Degradation of TSP2 was less sensitive to inhibition by heparin than degradation of TSP1. This is in agreement with differences in heparin-binding affinity of the two TSPs. Degradation of TSP2 was slower in cultures of Chinese hamster ovary (CHO) cells lacking heparan sulfate proteoglycans than in wild type CHO cells or in cultures of 3T3 cells treated with heparitinase than in untreated 3T3 cells. Degradation of TSP2 was inhibited by antibodies against the low density lipoprotein receptor-related protein (LRP) or by the 39-kDa receptor-associated protein, a known antagonist of LRP. This study indicates that TSP2 and TSP1 are metabolized by a common internalization and degradation pathway involving heparan sulfate proteoglycan and LRP. Competition for this pathway is a possible mechanism whereby cells can control the levels and ratio of TSP1 and TSP2 in the extracellular milieu.
authors.affiliation: Department of Medicine, University of Wisconsin, Madison, 53706, USA.
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: D K
authors.initials: DK
authors.lastname: Strickland
authors.forename: D F
authors.initials: DF
authors.lastname: Mosher
mesh_terms: D016475:3T3 Cells; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001667:Binding, Competitive; D001792:Blood Platelets / Q000502:physiology*; D016466:CHO Cells; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002738:Chloroquine / Q000494:pharmacology; D006224:Cricetinae; D019084:Fluorescent Antibody Technique, Indirect; D014644:Genetic Variation; D006025:Glycosaminoglycans / Q000378:metabolism*; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate / Q000172:deficiency / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D011485:Protein Binding; D011509:Proteoglycans / Q000172:deficiency / Q000378:metabolism; D011971:Receptors, Immunologic / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology; D011973:Receptors, LDL / Q000037:antagonists & inhibitors / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D019699:Thrombospondins
chemical_list: D000906:Antibodies; D015815:Cell Adhesion Molecules; D002738:Chloroquine; D006025:Glycosaminoglycans; D019812:Heparan Sulfate Proteoglycans; D006497:Heparan Sulfate; D007457:Iodine Radioisotopes; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008562:Membrane Glycoproteins; D011509:Proteoglycans; D011971:Receptors, Immunologic; D011973:Receptors, LDL; D011994:Recombinant Proteins; D019699:Thrombospondins