Regulation of ferritin H-chain expression in differentiating Friend leukemia cells.

The mechanisms that regulate the expression of ferritin, the iron storage protein, have been investigated in Friend erythroleukemia cells (FLCs) induced to differentiate by several chemical compounds. In differentiating FLCs, administration of hemin increases the steady-state level of ferritin mRNA about 15-fold and the ferritin content about 20- to 25-fold. Conversely, iron salts have only mild stimulatory effects on these parameters and iron chelators only slightly inhibited the stimulatory effect of hemin. Transient transfection experiments with a construct in which the human ferritin H-chain promoter drives the expression of the indicator chloramphenicol acetyltransferase (CAT) gene show that the increase in mRNA content is mainly due to enhanced transcription. In addition to transcriptional effects, translational regulation resulting in the further increase in ferritin synthesis is shown by CAT assays from cells transiently transfected with a construct containing the coding region for the indicator CAT mRNA under the translational control of the mRNA ferritin iron-responsive element. We conclude that, in FLCs induced to differentiate, hemin acts synergistically with the differentiation inducers, increasing ferritin expression. Both transcriptional and translational mechanisms are responsible for this synergistic effect, which appears to be characteristic of differentiated erythroid cells because it is not observed in other cell types (ie, fibroblastic cell lines).