Diminished expression of the α5β1 integrin (fibronectin receptor) by invasive clones of a human follicular thyroid cancer cell line

Altered adhesion plaques have been observed in transformed cell lines and are associated with enhanced metastatic potential. The prototypical adhesion plaque is formed by α5β1 fibronectin receptors (FnRs) interacting with the cellular actin network. We have found differences in the actin networks of noninvasive (FTC‐133) and invasive (FTC‐236, FTC‐238) clones of a human follicular thyroid cancer cell line. Furthermore, thyroid‐stimulating hormone (TSH) induces stress fibers in FTC‐133. In order to investigate differences in adhesion plaques, expression of fibronectin (FN) and its receptor by these cells was analyzed. For these studies FTC‐133, FTC‐236, and FTC‐238 were cultured in serum‐depleted DME‐H21 medium for 24 hours before the addition of TSH 30 mU/ml. No quantitative differences were noted in FN expression on Western blot in either the conditioned medium or cellular extracts. Western blots and immunohistochemical studies indicated that TSH induced secretion of FN only in FTC‐133. Flow cytometry with an α5 antibody demonstrated a 52% and 45% reduction (p