Carcinogenesis Advance Access published online on August 14, 2003
Carcinogenesis, doi:10.1093/carcin/bgg138
© 2003 by Oxford University Press
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CANCER BIOLOGY
1 Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, Alabama 35294-6630; Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, Alabama 35294-6630
* Corresponding author. E-mail: plchang{at}uab.edu.
Received 12 May 2003
; revised 16 July 2003
; accepted 29 July 2003
Osteopontin (OPN) is a secreted, adhesive glycoprotein. Elevated expression of osteopontin OPN in malignant and benign tumors is postulated to play a role in tumorigenesis. To determine whether OPN induction is required for tumor promotion, we used the in vitro JB6 model known to correlate with tumor promotion in vivo. The skin tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induces irreversible transformation of JB6 Cl41.5a cells. Concomitantly, TPA markedly stimulates early and persistent OPN expression and secretion for at least 4 days (the time required for these cells to begin to acquire the transformed phenotype) and increases cells' adhesion to OPN. Here, we demonstrated that dexamethasone, a synthetic analog of glucocorticoid, known to inhibit tumor promotion in vivo, not only suppressed TPA-induced OPN mRNA expression and inhibited tumorigenic transformation of JB6 Cl41.5a cells (as previously shown in JB6 Cl22 and Cl41 cells), but also that the addition of OPN partially restored dexamethasone suppression of TPA-induced cell transformation. Therefore, we tested the hypothesis that OPN induction is required for tumor promoter-induced transformation of JB6 cells by examining (1) whether the addition of OPN will induce transformation, (2) whether antisense OPN expression will inhibit TPA-induced transformation and (3) if the latter experiment showed inhibition of TPA-induced transformation whether the addition of OPN will rescue this effect. Results indicated that the addition of purified OPN induced a dose-dependent transformation of JB6 cells, as assessed by anchorage-independent growth assay and that this induction was suppressed by antibody to OPN. Furthermore, antisense OPN expressing JB6 clones suppressed TPA-induced OPN synthesis and secretion and inhibited TPA-induced anchorage-independent growth, which was partially rescued by the addition of OPN. In conclusion, OPN induction is required and can be sufficient to induce in vitro cellular transformation of a preneoplastic murine JB6 cell line.
Osteopontin induction is required for tumor promoter-induced transformation of preneoplastic mouse cells
2 School of Dentistry, University of Alabama at Birmingham, Birmingham, Alabama 35294-6630
3 Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, Alabama 35294-6630
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