Epidermal growth factor (EGF) is required only during the traverse of early G1 in PDGF stimulated density-arrested BALB/c-3T3 cells.
Density-arrested BALB/c-3T3 cells that had received a transient exposure to PDGF and were then transferred to medium containing only EGF and somatomedin C (Sm-C) began DNA synthesis after the G0/G1 lag. Supraphysiological concentrations of insulin could be employed to replace the Sm-C requirement. This G0/G1 lag phase was bisected by the requirement for the exogenous presence of EGF. Our data indicated that EGF was required during the traverse of only the first half of G0/G1 phase (6 h) and not during the traverse of late G1. Subphysiological serum concentrations of Sm-C were also necessary to be present with EGF for progression through early G0/G1; however, traverse of the final half of G0/G1 and commitment to DNA synthesis required the presence of Sm-C. It was found that physiological concentrations of Sm-C were required for the traverse late G1. The requirement for Sm-C for G0/G1 traverse of BALB/c-3T3 cells as opposed to human fibroblasts or glial cells may be due to a difference in endogenous synthesis of an insulin-like growth factor. Our data are in close agreement with previous reports that EGF is only required for approximately the first 8 h during traverse of the G0/G1 phase. The requirement for EGF to be present for the first 6 h of G0/G1 could result from a continued or repetitious event or by more than one distinct EGF-requiring event.
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology; D007399:Interphase; D051379:Mice; D008807:Mice, Inbred BALB C; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*
D010982:Platelet-Derived Growth Factor; D004815:Epidermal Growth Factor