Effects of transforming growth factor beta on cytoskeleton structure and extracellular matrix in Mv1Lu mink epithelial cells

Previous studies have shown that transforming growth factor beta (TGF-beta) is a potent regulator of cell growth and differentiation. To study the effects of TGF-beta on cell morphology and cytoskeleton reorganization, we conducted a survey using Mv1Lu mink lung epithelial cells with antibodies to cytoskeletal proteins and an extracellular matrix protein. While the untreated cells showed a cuboidal shape of typical epithelia, the Mv1Lu cells displayed a drastic shape change in the presence of TGF-beta. This alteration was most prominent when near-confluent cells were treated with TGF-beta. Since the morphology alteration is known to be accompanied by the reorganization of cytoskeletal proteins in other cell types, we investigated the intracellular distribution of the three major cytoskeletal structures: microfilaments, microtubules, and intermediate filaments. In the microfilament system, TGF-beta induced new stress fiber formation, which was caused primarily by the polymerization of cytoplasmic G-actin. However, TGF-beta appeared not to induce any significant changes in microtubular structures and vimentin filaments as determined by indirect fluorescence microscopy. Finally we confirmed the rapid accumulation of fibronectin by immunoblot analysis and chased the protein locations by immunofluorescence microscopy.