A study was made of the medium conditioned by spontaneously transformed rat embryo fibroblasts of line Recl-sf, which are capable of unlimited reproduction in medium free of serum and of other endogenous growth factors (c-medium). Addition of c-medium to stationary cultures of non-transformed rat embryo fibroblasts (REF), spontaneously transformed REF (line Rec 1), and cells of Rec1-sf stimulated the incorporation of H-3-thymidine by 1.5-6 times. SDS-polyacrilamide-gel electrophoresis of proteins, marked by S-35-metionine of c-medium of the cell line Rec1-sf, demonstrated that this medium had proteins with molecular mass from 10 to 110 kD. The fractionating divisible by 100 ultra-concentrates of c-medium with utilization of heparin-sepharose allowed to isolate two types of heparin-binding proteins. The proteins of the first type took about 5% of all the proteins of c-medium; they were eluted with 1.1 M NaCl and stimulated the incorporation of H-3-thymidine in REF, Rec1 and Rec1-sf cultures by 1.3-1.9 times. The second type proteins took about 1% of all the proteins of c-medium and were eluted with 2M NaCl, and, like the main endogenic basic growth factor of fibroblasts, stimulated the incorporation of H-3-thymidine into REF and Rec1-sf, but not into the culture of Rec1 line cells. The results obtained are discussed in terms of a hypothesis of autocrine regulation of cell proliferation.
