Rous sarcoma virus-transformed fibroblasts and cells of monocytic origin display a peculiar dot-like organization of cytoskeletal proteins involved in microfilament-membrane interactions.

By immunofluorescence and interference reflection microscopy (IRM) we found that F-actin and a group of cytoskeletal proteins involved in microfilament-membrane interaction, including vinculin, alpha-actinin, fimbrin and talin, are specifically organized in discrete dot-like structures corresponding to cell-substratum contact sites in both monocytes and monocyte-derived cells such as macrophages and osteoclasts. These proteins have a precise topological distribution; vinculin and talin form a doughnut-like ring, while actin, fimbrin and alpha-actinin are organized in dots matching the rings. An identical dot-like organization of F-actin and associated cytoskeletal proteins was also detected in malignant fibroblasts transformed by Rous Sarcoma virus (RSV) but not in the corresponding untransformed cells in culture. It is concluded that RSV transformation induces fibroblasts to express a cytoskeletal organization and a pattern of adhesion that are normally found in cells of monocytic origin. We propose that the occurrence of this cytoskeletal organization in RSV-transformed fibroblasts and in monocyte-derived cells may reflect a common ability to migrate across anatomical boundaries.