Intracellular localization of migration inhibitory factor-related protein (MRP) and detection of cell surface MRP...

The migration inhibitory factor-related proteins (MRPs) MRP-8 and MRP-14 were detected in differentiated human leukemia cell lines (THP-1 and HL-60) by immunocytochemical analysis. They were induced and colocalized in the cytoplasm and in lesser amounts in the nucleus when THP-1 and HL-60 cells were induced to differentiate by 1alpha,25-dihydroxyvitamin D3 or retinoic acid. In a search for a protein capable of binding MRPs, both MRPs were individually produced in insect cells (Sf21) infected with recombinant baculovirus. The purified recombinant MRPs were electrophoretically and antigenically indistinguishable from the native proteins, and their ability to form the MRP8/14 complex was retained. The presence of MRP binding sites was investigated by a binding assay using recombinant MRPs and specific monoclonal antibodies. MRP binding sites were detected on the cell membrane of the human leukemia cell lines THP-1, Raji, and MOLT-4. HL-60 cells treated with 1alpha, 25-dihydroxyvitamin D3 did not express MRP binding sites on the cell membrane, but a high level of MRPs accumulated in the cells. The occurrence of MRP binding sites on the cell surface of leukemia cell lines of monocyte and lymphocyte origin suggests that MRPs, released from neutrophils under certain conditions, may contribute to the activation and recruitment of effector cells to inflammatory lesions.