Intermediate filaments in normal thyrocytes: modulation of vimentin expression in primary cultures

In dog thyrocyte primary cultures, the antagonistic effects of thyrotropin (TSH) and epidermal growth factor (EGF) on differentiation expression were accompagnied by distinct long-term morphological changes: TSH-treated cells showed an epitheloid morphology; EGF reversibly induced a fusiform shape. Using indirect immunofluorescence microscopy and two-dimensional gel electrophoresis, we studied the modifications in the distribution and synthesis of the intermediate filament proteins of the cytoskeleton in response to TSH and EGF. These factors had little effect on the expression of cytokeratins 8 and 18, which were expressed in 98% of cells. However, TSH induced a profound redistribution of cytokeratins (and actin) with the appearance of a marked staining of cell junctions. Vimentin was coexpressed with cytokeratins in about 40% of cells from normal thyroid follicles freshly isolated by collagenase. During culture, immunostained vimentin network progressively developed in 90% of control and EGF-treated cells simultaneously with vimentin synthesis. In contrast, only 20% of TSH-treated cells reacted with vimentin antibody and we observed a marked decrease in vimentin synthesis in response to TSH. Therefore, vimentin synthesis, which should occur in at least some normal thyroid follicles in vivo, was inhibited in vitro by TSH which promotes differentiation expression. However, EGF-treated cells thereafter cultured with TSH regained an epitheloid morphology and differentiation in spite of the persistency of a complete network of vimentin.