Transcriptional regulation of ferritin H and L subunits in adult erythroid and liver cells from the mouse. Unambiguous identification of mouse ferritin subunits and in vitro formation of the ferritin shells.

Ferritin H and L subunits present cell-specific features of structure, function, and transcriptional regulation. Mouse Friend erythroleukemia cells offer an interesting model to analyze the erythroid-specific expression of ferritin genes for comparison with the liver, an iron-storing tissue. cDNA clones for mouse ferritin H and L subunits have been isolated and sequenced. The two subunits have very similar calculated masses, 20.9 and 20.6 kDa for H and L, respectively. Electrophoretic analysis of the subunits encoded by the cDNA 1) allows unambiguous identification of mouse ferritin subunits; 2) clearly shows that mouse H and L chains can make heteropolymers in vitro; and 3) demonstrates that, at least in vitro, free subunits can coexist with subunits polymerized into complete shells. The mouse ferritin gene family displays a variable degree of complexity, ranging from three homologous sequences for the H genes to 10-14 homologous loci for the L genes. Transcription of ferritin genes exhibits tissue-specific difference. Nuclear transcriptional run-off experiments show that the L gene is more actively transcribed in the liver than in Friend erythroleukemia cells at different stages of maturation. The accumulation of the H subunit mRNA which results from dimethyl sulfoxide induction of Friend cells is the consequence of an increase in the transcription rate of the H gene. However, the H gene mRNA is transcribed at a similar rate in the liver and in induced Friend cells although 5-fold more mRNA accumulates in these cells. Therefore, there is a tissue-specific regulation of mouse ferritin expression at both the transcription and mRNA stability levels.