[The release of transforming growth factors by cells resistant to ethidium bromide and growing on a serum-free...

350sf and 625sf cells growing in serum free medium secrete transforming growth factors (TGFs) that induce NIH 3T3 indicator cells to form colonies in soft agar. The addition of 2 ng/ml of EGF increases twice the number of colonies of NIH 3T3 indicator cells. The TGFs secreted by 350sf and 625 sf cells do not compete with 125I EGF for binding to EGF receptors on human A-431 cells. The number of EGF receptors on 350 sf and 625 sf and 625 sf cells continuously grown in serum-free medium do not differ from that of EGF receptors on parental Lebr-350 and Lebr-625 cells continuously grown in the presence of 10% serum. These results suggest that TGFs produced by 350 sf and 625 sf cells are not alpha TGF. It is possible that cells secrete beta TGFs of yet unknown type.