Fibrin clot retraction in normal and transformed avian fibroblasts

Normal avian embryo fibroblasts induced retraction of a fibrin clot. The expression of high levels of this activity was associated with the exponential growth phase of the cell division cycle. Cells transformed by avian sarcoma virus (ASV) and other agents lost this activity regardless of the cell cycle phase. Cultures infected with transformation-defective ASV mutants retained a high level of fibrin clot retraction. However, this activity could not be recovered when temperature-sensitive, virus-transformed cells were shifted to a nonpermissive temperature (41°C). The results indicated that, in this cell system, loss of fibrin clot retraction could be considered a reliable parameter of cell transformation.