Thrombospondin-1 enhances human thyroid carcinoma cell invasion through urokinase activity

Previous studies reported that modification in the expression of the matricellular multidomain glycoprotein thrombospondin-1 (TSP-1) could play a critical role in the control of tumor progression and metastasis development. The function of this multimodular protein in cancers appears highly dependent on the cellular context and thus remains to date very difficult to accurately characterize. Controversial results indeed exist reporting either pro- or anti-invasive properties of TSP-1. Since it appeared that TSP-1 could be of prognostic value for certain specific types of cancers, we examined in this study the prospective function of TSP-1 in the control of human follicular thyroid carcinoma (FTC) cell invasiveness. First, we established that the aggressive behavior of human thyroid malignant cells is closely correlated to the TSP-1 amount. We demonstrated that exogenously added TSP-1 stimulates by two-fold the capacity of FTC cells to invade Matrigel-coated wells. The use of specific anti-TSP-1 blocking antibodies led to a drastic inhibition of the basal FTC cell invasion. Zymography experiments revealed that the uPA-dependent proteolytic activity is directly controlled by TSP-1, MMPs activity is not. The TSP-1-mediated stimulation of uPA appears to occur at post-transcriptional level. Finally, we established that the TSP-1-stimulated FTC cell invasion is wholly abolished under anti-uPA blocking antibodies or aprotinin treatments whereas MMP inhibitors have no effect. All together, we evidenced in the present study that TSP-1 promotes human follicular thyroid carcinoma cell invasion mainly through up-regulation of the urokinase-dependent activity.