Actin architecture of cultured human thyroid cancer cells: predictor of differentiation?
 The actin cytoskeleton is important for cell structure and motility.
 A disordered actin architecture has been correlated with a high metastatic potential in melanoma, fibrosarcoma, and colon cancer models.
 Thyrotropin is known to induce growth and differentiation in cultured thyroid cells, whereas the carcinogenic phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) causes dedifferentiation and malignant transformation in many cell lines.
 We therefore assessed the effect of thyrotropin and TPA on the actin architecture of FTC-133 human follicular thyroid cancer cells in continuous culture.
 Staining of filamentous actin with rhodamine phalloidin showed that 1 mU/ml or 30 mU/ml thyrotropin-induced actin polymerization was detectable at 1 hour but more notable at 24 hours.
 Similarly TPA (0.008 to 10 mumol/L) caused rapid actin fiber disruption and redistribution to the cell periphery.
 Secondary antibody staining for alpha-actinin, a protein that binds and crosslinks actin, was more prominent after treatment with thyrotropin but decreased after TPA.
 These findings indicate that the actin cytoskeleton has a dynamic response to trophic factors.
 Thyrotropin promoted actin polymerization, but TPA caused depolymerization.
 These effects may correlate with cellular alpha-actinin levels.
 Actin architecture may therefore reflect the state of differentiation of thyroid tumor cells.
