DIFFERENTIAL REGULATION OF GLUTATHIONE-PEROXIDASE BY SELENOMETHIONINEAND HYPEROXIA IN ENDOTHELIAL-CELLS

We have studied the effect of selenomethionine (SeMet) and hyperoxia o n the expression of glutathione peroxidase (GP) in human umbilical vei n endothelial cells. Incubation of HUVEC with 1 x 10(-6) M SeMet for 2 4 h and 48 h caused a 65% and 86% increase in GP activity respectively . The same treatment did not result in significant changes in GP gene transcription and mRNA levels. Pactamycin, a specific inhibitor of the initiation step of translation, prevented the rise in GP activity ind uced by SeMet and caused an increase in GP mRNA in both cells grown in normal and SeMet-supplemented medium. Interestingly, SeMet supplement ation stimulated the recruitment of GP mRNA from an untranslatable poo l on to polyribosomes, so that the concentration of GP mRNA in polyrib osomal translatable pools was 50% higher in cells grown in SeMet-suppl emented medium than in cells grown in normal medium. On the other hand , cells exposed to 95% O-2 for 3 days in normal medium showed a 60%, 3 94% and 81% increase in GP gene transcription rate, mRNA levels and ac tivity respectively. Hyperoxia also stabilized GP mRNA. Hyperoxic cell s grown in SeMet-supplemented medium did not show any change in GP gen e transcription and mRNA levels, but expressed an 81% and 100% increas e in GP activity and amount of GP mRNA associated with polyribosomes r espectively, when compared with hyperoxic cells maintained in normal m edium. Thus, GP appeared to be regulated posttranscriptionally, most p robably co-translationally, in response to selenium availability, and transcriptionally and post-transcriptionally in response to oxygen.