Interaction of acidic isoferritins with human promyelocytic HL60 cells

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Abstract
We have used undifferentiated human promyelocytic HL60 cells to study the binding of radioiodinated human ferritin in vitro. Specific binding of human heart ferritin could be demonstrated at 37°C, whereas no binding of liver ferritin could be found. The uptake of labelled heart ferritin was abolished by incubation at 4°C, by prior treatment of the HL60 cells with pronase and by the addition of human plasma to the medium. On the other hand, the addition of excess unlabelled human liver or rat liver ferritin had no effect on the uptake of labelled human heart ferritin. Dissociation studies showed that about 55% of the bound heart ferritin radioactivity could be released by incubation with medium alone and at least 90% with excess unlabelled heart ferritin. Over 70% of the dissociated ferritin could be precipitated with polyclonal anti-ferritin serum or trichloroacetic acid. More than two-thirds of the radioactivity which could not be released after washing in medium alone was recovered in the soluble intracellular fraction following cell lysis. Almost all of the soluble radioactivity could be precipitated with the polyclonal antiserum, indicating that very little lysosomal degradation of internalized heart ferritin had occurred. The present studies demonstrate a proteinmediated binding mechanism for acidic isoferritins on HL60 cells. These observations agree with published evidence that ferritin is often associated with cell membranes and are consistent with a possible role for the protein in the regulation of haematopoiesis or in iron transfer.

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