Fibroblast growth regulatory factor inhibits DNA synthesis in BALB/c 3T3 cells by arresting in G1.

A cell surface macromolecular component from quiescent BALB/c 3T3 mouse cells (designated tibroblast growth regulatory factor, FGRF) inhibits DNA synthesis and cell division in growing 3T3 cells. Addition of FGRF to synchronized populations of growing 3T3 cells in the late Gl or early S phase did not inhibit DNA synthesis in the immediate S phase. However, a significant inhibition was observed in the S phase of the next round of cell cycle. Cells exposed to the regulatory factor in late S/early G2 or early Gl showed reduced DNA synthesis in the upcoming S phase; the late S/early G2 cells were more sensitive to inhibition than the cells in the Gl. Further, the regulatory factor delayed the progression of GO/Gl-arrested cells into the next S phase. These results suggest that the physiological effect of FGRF is to arrest cells in early Gl, thus preventing their entry into a new round of cell cycle. In contrast to untransformed 3T3 cells, mouse cells transformed by SV40 were not subjected to growth-arrest by the regulatory factor, although the transformed cells contain active FGRF that inhibits DNA synthesis in growing 3T3 cells.