Epidermal growth factor-stimulated DNA synthesis requires an influx of extracellular calcium.
The dependency of normal cell proliferation on adequate extracellular Ca2+ levels was further investigated by determining the role of Ca2+ influx in epidermal growth factor (EGF)-induced rat liver epithelial (T51B) cell DNA synthesis. Fura-2-loaded T51B cells responded with an increase in [Ca2+]i to EGF (5-50 ng/ml) that was blocked by low (25 microM) extracellular Ca2+ or by pretreatment with 50 microM La3+ to inhibit plasma membrane Ca2+ flux. Confluent T51B cells treated for 24 h with EGF (0.1-50 ng/ml) dose-dependently incorporated [3H]-thymidine into cell nuclei. Low extracellular Ca2+ or addition of La3+ prevented the EGF-stimulated rise in labeled nuclei, indicating that a movement of Ca2+ into the cell was required for DNA synthesis. This was supported by our findings that bradykinin, which induced a rise in [Ca2+]i by opening plasma membrane Ca2+ channels in T51B cells (but not A23187, thrombin or ATP, which raise [Ca2+]i primary through mobilization of intracellular Ca2+ stores), potentiated DNA synthesis stimulated by submaximal doses of EGF. Potentiation of the action of EGF by the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA), indicates that activation of protein kinase C and an influx of Ca2+ share a common mechanism for initiating DNA synthesis.
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Cancer Research Center of Hawaii, University of Hawaii, Honolulu 96813.
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D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000493:pharmacokinetics; D015220:Calcium Channels; D002455:Cell Division; D002462:Cell Membrane / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002120:Calcium Channel Agonists; D015220:Calcium Channels; D004815:Epidermal Growth Factor; D004247:DNA; D013755:Tetradecanoylphorbol Acetate; D001920:Bradykinin; D002118:Calcium