Osteopontin Undergoes Polymerization in Vivo and Gains Chemotactic Activity for Neutrophils Mediated by Integrin 9 1

Cell-Matrix Frontier Laboratory, Biomedical Research Unit, Hiroshima University, Minamiku, Hiroshima, Japan.
Journal of Biological Chemistry (Impact Factor: 4.57). 02/2011; 286(13):11170-8. DOI: 10.1074/jbc.M110.189258
Source: PubMed


Osteopontin (OPN) is an integrin-binding inflammatory cytokine that undergoes polymerization catalyzed by transglutaminase 2. We have previously reported that polymeric OPN (polyOPN), but not unpolymerized OPN (OPN*), attracts neutrophils in vitro by presenting an acquired binding site for integrin α9β1. Among many in vitro substrates for transglutaminase 2, only a few have evidence for in vivo polymerization and concomitant function. Although polyOPN has been identified in bone and aorta, the in vivo functional significance of polyOPN is unknown. To determine whether OPN polymerization contributes to neutrophil recruitment in vivo, we injected OPN* into the peritoneal space of mice. Polymeric OPN was detected by immunoblotting in the peritoneal wash of mice injected with OPN*, and both intraperitoneal and plasma OPN* levels were higher in mice injected with a polymerization-incompetent mutant, confirming that OPN* polymerizes in vivo. OPN* injection induced neutrophil accumulation, which was significantly less following injection of a mutant OPN that was incapable of polymerization. The importance of in vivo polymerization was further confirmed with cystamine, a transglutaminase inhibitor, which blocked the polymerization and attenuated OPN*-mediated neutrophil recruitment. The thrombin-cleaved N-terminal fragment of OPN, another ligand for α9β1, was not responsible for neutrophil accumulation because a thrombin cleavage-incompetent mutant recruited similar numbers of neutrophils as wild type OPN*. Neutrophil accumulation in response to both wild type and thrombin cleavage-incompetent OPN* was reduced in mice lacking the integrin α9 subunit in leukocytes, indicating that α9β1 is required for polymerization-induced recruitment. We have illustrated a physiological role of molecular polymerization by demonstrating acquired chemotactic properties for OPN.

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    Stem Cell Research & Therapy 02/2014; 5(1):29. DOI:10.1186/scrt418 · 3.37 Impact Factor
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    • "The intramolecular structure, RGD (Arg-Gly-Asp), is an unique sequence that improves cell adhesion in proteins. Through the RGD cell adhesion sequence, OPN may interact with important tumor metastasis factors, including integrin, CD44, vascular endothelial growth factor/epidermal growth factor receptor (VEGF/EGFR), matrix metalloproteinases (MMPs), fibronectin (FN), survivin, transforming growth factor (TGF), tumor necrosis factor (TNF) and urokinase-type plasminogen activator (uPA) to promote cell chemotaxis, adhesion and migration (8–17). Budhu et al(18) and Pan et al(19) put forward the theory that OPN was a significant factor in hepatocellular carcinoma metastasis and that it may be a molecular marker of intrahepatic metastasis. "
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    ABSTRACT: The aim of the present study was to investigate the inhibitory effects of thalidomide in the hepatocellular carcinoma nude mouse model in order to provide new insights into a comprehensive clinical intervention for hepatocellular carcinoma. MHCC97 cells were routinely cultured, passaged and adjusted to a single cell suspension with a concentration of 2×10(7)/ml. Six-week-old, BALB/C male nude mice were anesthetized and fixed in the prone position, then a subcapsular injection of the single cell suspension was administered into the spleen and their abdomens were closed. A laparotomy and left hepatic lobectomy was performed 14 days later and the abdomens were closed once again. Subsequent to the establishment of the hepatocellular carcinoma model, the nude mice were randomly divided into three groups, each consisting of 12 mice. The early intervention group were immediately provided with the post-operative thalidomide intervention, the late intervention group were provided with the post-operative thalidomide intervention one week subsequent to the surgery, and the negative control group were provided with a placebo intervention (0.9% physiological saline). Each intervention was continuously administered once per day for one week. The osteopontin (OPN) content of the liver tumors was detected using immunohistochemistry. The data were analyzed using an analysis of variance (ANOVA) test. There were significant differences in the OPN levels of the tumors among the early intervention, late intervention and negative control groups. Thalidomide may inhibit the generation of OPN and thereby inhibit the infiltration and metastasis of tumors; the immediate use of thalidomide following hepatectomy in the present study may block the invasion and metasis for liver cancer more effectively.
    Experimental and therapeutic medicine 05/2013; 5(5):1403-1407. DOI:10.3892/etm.2013.1010 · 1.27 Impact Factor
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    • "OPN is highly expressed in chronic inflammatory diseases and possesses chemotactic activity for macrophages and neutrophils [165–167]. Elevated OPN expression in breast, myeloma, and prostate cancers is associated with poor prognosis [168–170]. OPN is secreted by host stromal cells and cancer cells; however, the role of OPN in metastasis is dependent on the site of production. "
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    Journal of Oncology 02/2012; 2012(3):351089. DOI:10.1155/2012/351089
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