ZINC IS REQUIRED FOR THE EXPRESSION OF ORNITHINE DECARBOXYLASE IN A DIFLUOROMETHYLORNITHINE-RESISTANT CELL-LINE

Dilution of quiescent L1210-DFMO(r) (difluoromethylornithine-resistant ) cells in fresh medium containing serum led to the induction of ornit hine decarboxylase (ODC) and to the expression of its mRNA, as determi ned by a sensitive solution-hybridization-RNAase-protection assay. Add ition of the chelating agent diethylenetriaminepenta-acetic acid (DTPA ) at seeding time caused an inhibition of the induction of ODC activit y by up to 90%, and only Zn2+ of the bivalent metal ions tested was ef fective in reversing this effect. The inhibition of the induction of O DC activity was accompanied by a marked decrease, prevented by Zn2+ su pplementation, of the accumulation of immunoreactive ODC protein and O DC mRNA. DTPA treatment also caused a slight acceleration of ODC turno ver. These results indicate that a restricted Zn2+ availability in L12 10-DFMO(r) cells impairs ODC induction remarkably, mainly by affecting the expression of the messenger