| Abstract | The oncogenic pp60v-src product of ASV (avian sarcoma virus) is shown to be a potent endogenous mitogen, which, unlike mitogens such as PDGF (platelet derived growth factor), is able to stimulate host cell proliferation without the help of other growth factors. Thus, NRK rat cells, infected with a temperature-sensitive ASV mutant which produces an abnormally thermolabile pp60v-src became proliferatively quiescent at a pp60v-src-inactivating 40°C in medium containing either 0.2% calf serum or no serum at all. Adding PDGF stimulated the quiescent tsASV-NRK cells at 40°C to initiate DNA replication in medium containing 0.2% serum, but not in serum-free medium. By contrast, activating internal pp60v-src by dropping the temperature to a permissive 36°C stimulated these quiescent cells to transit G1, initiate DNA replication and to enter mitosis even in serum-free medium. Thus, relative to PDGF, endogenous pp60v-src behaves as a complete mitogen. |
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