title: Thrombin-cleaved fragments of osteopontin are overexpressed in malignant glial tumors and provide a molecular niche with survival advantage.
abstract: Osteopontin (OPN), which is highly expressed in malignant glioblastoma (GBM), possesses inflammatory activity modulated by proteolytic cleavage by thrombin and plasma carboxypeptidase B2 (CPB2) at a highly conserved cleavage site. Full-length OPN (OPN-FL) was elevated in cerebrospinal fluid (CSF) samples from all cancer patients compared with noncancer patients. However, thrombin-cleaved OPN (OPN-R) and thrombin/CPB2-double-cleaved OPN (OPN-L) levels were markedly increased in GBM and non-GBM gliomas compared with systemic cancer and noncancer patients. Cleaved OPN constituted ∼23 and ∼31% of the total OPN in the GBM and non-GBM CSF samples, respectively. OPN-R was also elevated in GBM tissues. Thrombin-antithrombin levels were highly correlated with cleaved OPN, but not OPN-FL, suggesting that the cleaved OPN fragments resulted from increased thrombin and CPB2 in this extracellular compartment. Levels of VEGF and CCL4 were increased in CSF of GBM and correlated with the levels of cleaved OPN. GBM cell lines were more adherent to OPN-R and OPN-L than OPN-FL. Adhesion to OPN altered gene expression, in particular genes involved with cellular processes, cell cycle regulation, death, and inflammation. OPN and its cleaved forms promoted motility of U-87 MG cells and conferred resistance to apoptosis. Although functional mutation of the RGD motif in OPN largely abolished these functions, OPN(RAA)-R regained significant cell binding and signaling function, suggesting that the SVVYGLR motif in OPN-R may substitute for the RGD motif if the latter becomes inaccessible. OPN cleavage contributes to GBM development by allowing more cells to bind in niches where they acquire anti-apoptotic properties.
authors.affiliation: Division of Hematology, Department of Medicine, Stanford University School of Medicine, Stanford, California 94305, USA.
authors.forename: Yasuto
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Zhifei
authors.initials: Z
authors.lastname: Shao
authors.forename: Shadi
authors.initials: S
authors.lastname: Sharif
authors.forename: Xiao-Yan
authors.initials: XY
authors.lastname: Du
authors.forename: Timothy
authors.initials: T
authors.lastname: Myles
authors.forename: Milton
authors.initials: M
authors.lastname: Merchant
authors.forename: Griffith
authors.initials: G
authors.lastname: Harsh
authors.forename: Michael
authors.initials: M
authors.lastname: Glantz
authors.forename: Lawrence
authors.initials: L
authors.lastname: Recht
authors.forename: John
authors.initials: J
authors.lastname: Morser
authors.forename: Lawrence L K
authors.initials: LL
authors.lastname: Leung
mesh_terms: D000595:Amino Acid Sequence; D000990:Antithrombin III / Q000378:metabolism; D017209:Apoptosis / Q000235:genetics; D014408:Biomarkers, Tumor / Q000134:cerebrospinal fluid; D001932:Brain Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics; D002470:Cell Survival; D054405:Chemokine CCL3 / Q000378:metabolism; D054407:Chemokine CCL4 / Q000378:metabolism; D017124:Conserved Sequence; D015972:Gene Expression Regulation, Neoplastic; D005910:Glioma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D014411:Neoplastic Stem Cells / Q000378:metabolism / Q000473:pathology; D009842:Oligopeptides / Q000378:metabolism; D053495:Osteopontin / Q000134:cerebrospinal fluid / Q000737:chemistry / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D059748:Proteolysis; D016415:Sequence Alignment; D018709:Statistics, Nonparametric; D013917:Thrombin / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; C515429:CCL3 protein, human; C066507:CCL4 protein, human; D054405:Chemokine CCL3; D054407:Chemokine CCL4; D009842:Oligopeptides; D010446:Peptide Fragments; D042461:Vascular Endothelial Growth Factor A; C046193:antithrombin III-protease complex; D053495:Osteopontin; C047981:arginyl-glycyl-aspartic acid; D000990:Antithrombin III; D010447:Peptide Hydrolases; D013917:Thrombin