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  • Title: Autocrine stimulation by osteopontin plays a pivotal role in the expression of the mitogenic and invasive phenotype of RET/PTC-transformed thyroid cells.
    Author: Castellone MD, Celetti A, Guarino V, Cirafici AM, Basolo F, Giannini R, Medico E, Kruhoffer M, Orntoft TF, Curcio F, Fusco A, Melillo RM, Santoro M.
    Journal: Oncogene; 2004 Mar 18; 23(12):2188-96. PubMed ID: 14981541.
    Abstract:
    Papillary thyroid carcinomas are characterized by rearrangements of the RET receptor tyrosine kinase generating RET/PTC oncogenes. Here we show that osteopontin (OPN), a secreted glycoprotein, is a major RET/PTC-induced transcriptional target in PC Cl 3 thyroid follicular cells. OPN upregulation depended on the integrity of the RET/PTC kinase and tyrosines Y1015 and Y1062, two major RET/PTC autophosphorylation sites. RET/PTC also induced a strong overexpression of CD44, a cell surface signalling receptor for OPN. Upregulation of CD44 was dependent on RET/PTC Y1062, as well. Constitutive OPN overexpression or treatment with exogenous recombinant OPN sharply increased proliferation, Matrigel invasion and spreading in collagen gels of RET/PTC-transformed PC Cl 3 cells. These effects were impaired by the treatment of PC Cl 3-RET/PTC cells with OPN- and CD44-locking antibodies. Thus, RET/PTC signalling triggers an autocrine loop involving OPN and CD44 that sustains proliferation and invasion of transfomed PC Cl 3 thyrocytes.
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