 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. "    ///    "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. "    ///    Autocrine stimulation by osteopontin plays a pivotal role in the expression of the mitogenic and invasive phenotype of RET/PTC-transformed thyroid cells..     ///    "RET/PTC also induced a strong overexpression of CD44, a cell surface signalling receptor for OPN. "    ///    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.. "