Characterization of the ferritin receptors of human T lymphoid (MOLT-4) cells.

We have previously demonstrated that distinct binding sites exist for human recombinant H ferritin (HrHF) and human liver ferritin (HLF) on human T lymphoid cells (MOLT-4). This study demonstrates that these binding sites have the characteristics of receptors specific for HrHF, and the binding characteristics and internalization of HrHF to MOLT-4 cells have now been examined. Iodinated HrHF was displaced by an excess of unlabeled HrHF. Heavy ferritin was the major subunit bound with only a small amount of light-ferritin binding, consistent with our immunofluorescence studies. Scatchard plot analysis of the competitive binding data for HrHF revealed an association constant of 6.3 to 6.7 x 10(7) L/mol with approximately 6000 to 15,000 receptor sites per MOLT-4 cell. Internalization of HrHF was demonstrated with pronase. Chloroquine substantially reduced the uptake of HrHF. Release of internalized HrHF was not observed when cells were rewarmed to 37 degrees C. These results indicate that HrHF is internalized by a mechanism consistent with receptor-mediated endocytosis, with possible involvement of the lysosome. The internalized HrHF remains associated with the cell. Although lymphoid cell growth and differentiation were not examined in this study, the presence of the demonstrated receptors may indicate a regulatory role for heavy ferritin in such cells.