Protease induction of hemoglobin synthesis but not terminal cell division in K562 cells

Several protease preparations of varied specificity increased hemoglobin levels in K562 cells. These are the first enzymes shown to stimulate this process in these cells. Hemin, at a concentration at which it did not act as a potent inducer of hemoglobin production, was found to synergistically stimulate induction by proteases. As seen in some other cell types, six different protease preparations also stimulated K562 cell yield. Hemin did not enhance the protease stimulation of cell yield, but was, instead, slightly inhibitory. Trypsin was one of the most potent inducers of the proteases tested. A combination of trypsin with a "synergistic" concentration of hemin did not decrease the size of K562 cells during induction of hemoglobin production, suggesting that these cells were not irreversibly differentiated nor induced to terminal cell division by this treatment. This was supported, although not proven, by an assay that demonstrated no progressive decrease in the rate of cell multiplication associated with the induction of hemoglobin synthesis.