REGULATION OF ORNITHINE DECARBOXYLASE IN A TRANSFORMED-CELL LINE THATOVEREXPRESSES TRANSLATION INITIATION-FACTOR EIF-4E

pMV7-4E cells (4E-P2), derived from NIH-3T3 cells, overexpress eIF-4E and exhibit characteristics of transformation, possibly due to transla tional relief of mRNAs encoding proteins that regulate cell growth. Or nithine decarboxylase (ODC), the rate-limiting enzyme in polyamine bio synthesis, is induced in 4E-P2 cells, and this induction appears to be related to the transformed phenotype of these cells, ODC mRNA contain s extensive secondary structure in its 5' untranslated region (5'UTR) and may be regulated by eIF-4E, which melts mRNA secondary structure, To better understand this regulation, cDNA constructs containing the m ild-type 5'UTR of ODC or deletion mutants inserted ahead of the lucife rase gene mere transfected into 4E-P2 and 3T3 cells, Expression of luc iferase was higher in 4E-P2 cells in all cases, suggesting that the se condary structure of the ODC 5'UTR inhibits expression in 3T3 cells, a nd this inhibition is overcome by the high eIF-4E levels in 4E-P2 cell s, When a small open reading frame present in the 5'UTR of ODC was des troyed by a point mutation, this luciferase construct was expressed ab out 6-fold over that containing the mild-type 5'UTR in both cell lines , although both of these 5'UTRs contain the same predicted secondary s tructure, Thus, factors in addition to eIF-4E may be involved in the r egulation of ODC, To examine the differences in ODC regulation by poly amines in normal and transformed cells, the effect of N-1,N-12-bis(eth yl)spermine (BE-3-4-3) on the synthesis and degradation of ODC was exa mined, ODC activity in 4E-P2 cells was 10 times less sensitive to redu ction by BE-3-4-3 compared to 3T3 cells, suggesting that high ODC leve ls in eIF-4E-overexpressing cells are the result of decreased regulati on by polyamines as well as relief of translational regulation by eIF- 4E.