Expression of Messenger RNA Species Coding for a Mr 43,000 Peptide Associated with Ferritin in Human Leukemia-K562 Cells and Its Down Regulation during Differentiation1

In the current study it was found that K-562 erythroleukemia cells express the superheavy (S) inKNA and the 43Kd S peptide which were recently discovered in activated T-lymphocytes. The S mRNA was iden tified by its cross-hybridization with ferritin H complementary DNA probe and the S peptide (M, 43,000) was identified by its immunoprecipitation with CM-H-9 monoclonal antibody specific for placenta! isoferritin. During terminal differentiation by hemin the level of S mRNA decreased below detection, with a concomitant diminution in the biosyn thesis of the S peptide. In contrast, a significant increase in the level of ferritin light (L) and heavy (H) mRNAs was observed, resulting in an increase in the rate of biosynthesis of the H and L ferritin subunits. Removal of iron by desferrioxamine reduced the biosynthesis of ferritin L and H chains without altering the level of the corresponding mRNAs. Treatment with desferrioxamine did not affect either the level of S mRNA or the biosynthesis of the S peptide. This is a demonstration of a new mRNA species which is expressed in leukemic cells and is down-regulated during cell differentiation.