Late signals are required for the stimulation of D

Authors: HaiLan Chen Philip S Rudland John A Smith David G Fernig

Publish Date: 1996/06/01

Volume: 16, Issue: 3, Pages: 249-263

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Abstract

Maximal stimulation of DNA synthesis in quiescent rat mammary Rama 27 fibroblasts is elicited by epidermal growth factor EGF or basic fibroblast growth factor bFGF 18 h after the initial addition of the growth factorsthe ‘lag’ period At maximallystimulating concentrations EGF and bFGF are interchangeable 9 h after their initial addition When the initial concentration of growth factor is below that required to elicit a maximal response it is possible to increase the level of DNA synthesis by increasing the concentration of growth factor 9 h after its initial addition When the initial concentration of growth factor is high substitution by a lower concentration of growth factor after 9 h allows a greater proportion of cells to synthesize DNA than would be expected from a continuous low dose of growth factor Similar results are obtained when both the growth factor and its concentration are changed 9 h after the initial addition of growth factor However when EGF at a low concentration is substituted for a high concentration of EGF or bFGF the resulting increase in the levels of DNA synthesis is greater when EGF rather than bFGF is added for a second time The halflife of the growthstimulatory signals delivered by EGF and by bFGF 9 h after their initial addition is 1–2 h These results suggest that to stimulate DNA synthesis i EGF or bFGF must deliver a signals continuously ii the initial signals produced by EGF and bFGF are equivalent iii the signals produced between 9–18 h by EGF may be different to those produced by bFGF

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