Microfilaments and intermediate filaments in epithelial cells transformed by murine sarcoma or leukemia viruses

The murine epithelial cell line MMC-E was used to study changes in the cytoskeletal organization associated with viral transformation of epithelial cells by two different viruses. The cells were transformed with Moloney mouse sarcoma virus (MSV) or murine leukemia virus (MuLV). The expression of actin, myosin and of intermediate filament proteins in the cells was then studied. In MMC-E cells actin and myosin were organized as belt-like structures at the edges of the border cells of the cell islands and also circumferentially in the cells inside the islands. The major change after transformation was the decrease of the actomyosin containing belt extending from cell to cell at the borders of the cell islands. Both MMC-E cells and the MSV-transformed cells contained keratin as a juxtanuclear granular aggregate whereas the MuLV-transformed cells showed bright fibrillar arrays of keratin. Both virus-transformed cell lines showed enhanced vimentin-specific fluorescence and analysis of their cytoskeletal polypeptides confirmed the result. Similar molecular forms of keratin polypeptides were seen in all cells by immunoblotting. Viral transformation of MMC-E epithelial cells thus leads to different changes in their cytoskeletal organization depending on the transforming viral or cellular gene.