Inhibition by corticosteroids of epidermal growth factor‐induced recovery of cyclooxygenase after aspirin inactivation

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Abstract
Cultures of vascular smooth muscle cells superfused with [ 14 C]arachidonic acid synthesized the antiplatelet substance prostacyclin as the major cyclooxygenase product. Prostacyclin synthesis was inactivated by aspirin, which irreversibly acetylates cyclooxygenase. Aspirin‐treated cells recovered within 2 h by a process that was blocked by cycloheximide but not by actinomycin D, and that required a serum component identified as epidermal growth factor (EGF). EGF‐induced recovery of cyclooxygenase was greatly potentiated by type β transforming growth factor (TGF‐β). Incubation with EGF and TGF‐β in the 0.1‐1.0 nanomolar range stimulated cyclooxygenase recovery up to 20‐fold without increasing [ 35 S]methionine incorporation into other cell proteins. Induction of cyclooxygenase by EGF and TGF‐β also was prevented by cycloheximide but not by actinomycin D. EGF‐dependent recovery was blocked by preincubation with dexamethasone (2 μM), an effect that was duplicated by pure lipocortin (2‐4 μg/ml). Incubation of membrane preparations from these cells with EGF selectively activated phosphorylation of a 35‐kDa cellular protein that comigrated with lipocortin. The results suggest that cyclooxygenase recovery in aspirin‐inactivated vascular smooth muscle cells is mediated by an EGF‐dependent translational control that is inhibited by corticosteroids. The findings also provide a new mechanism whereby corticosteroids suppress inflammatory prostaglandins.— P ash , J. M.; B ailey , J. M. Inhibition by corticosteroids of epidermal growth factor‐induced recovery of cyclooxygenase after aspirin inactivation. FASEB J. 2: 2613‐2618; 1988.

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