Production of plasminogen activator by synchronized normal and rous sarcoma virus-transformed chicken fibroblasts in culture

We studied intracellular activity of the plasminogen activator within the cell cycle of chemically synchronized normal and RSV-transformed chick fibrolasts in culture. Consideration has also been given to the relationship between the plasminogen activator activity and cycles of DNA synthesis or mitosis in cycling fibroblasts after viral infection. The plasminogen activator activity of the cell lysates was assayed on ¹²⁵I]fibrin-coated Petri dishes and was expressed as the radioactivity released from the plates. Normal fibroblasts produced detectable levels of plasminogen activator in the S-phase and late G₂-phase or mitosis of the cell cycle. In contrast, RSV-transformed cells produced high levels of this activator throughout the entire cell cycle although this activity fluctuated and reached a maximum in the G₂-M periods. We also found that the level of plasminogen activator activity in the transformed fibroblasts is influenced by the cycles of DNA synthesis and that cell division is required for the appearance of plasminogen activator activity in the ‘de novo’ virus-infected cultures.