Abstract
It was reported in our previous studies that the "spongy degeneration-like" changes of human tumor cells were detected by coculture with human embryonic fibroblasts in vitro. It was discovered that the degenerative changes were mediated by a factor secreted from human em-bryonic fibroblasts. This factor was named the tumor-degenerating factor (TDF). The present study found that fibronectin inhibited TDF activity while TDF inhibited cell attachment mediated by fibronectin. It was possible that these mutual inhibitions were due to the direct binding of the TDF molecule to the fibrOnectin molecule. Since it is well known that fibronectin is composed of multiple domains which differ in their biological activities, this study also at-tempted to clarify which domain(s) inhibit TDF activity, through the use oftrypsin, thermolysin and 2-nitro-5-thiocyanobenzoic acid (NTCB). It is conclud-ed that multiple domains of fibronectin are required for the inhibition of TDF activity.
