ULTRASTRUCTURAL-LOCALIZATION OF THE S-100-LIKE PROTEINS MRP8 AND MRP14 IN MONOCYTES IS CALCIUM-DEPENDENT

MRP8 and MRP14 are members of the S-100 family of Ca2+-binding protein s and are expressed by granulocytes and monocytes. Members of this fam ily have been described to be involved in membrane and cytoskeleton in teractions; we therefore studied the subcellular distribution of MRP8/ MRP14 in cultured human monocytes at the ultrastructural Monospecific rabbit antisera against MRP8 MRP14 and a monoclonal antibody (moAb 27E 10), which exclusively recognizes the MRP8/MRP14 heterodimer but not t he monomers, were used in both immunoperoxidase/preembedding- and immu nogold/cryotechniques. Comparing non-stimulated monocytes with Ca2+ io nophore A23187-treated cells, we could demonstrate that MRP8 and MRP14 associate with membrane and cytoskeletal structures in a Ca2+-depende nt manner. Employing moAb 27E10, MRP8/MRP14 complexes were shown to be translocated to these cellular components. In addition, immunogold do uble-labelling experiments revealed a clear co-localization of MRP8/MR P14 complexes with the type III intermediate filament vimentin. Analys is of immunogold-labelled cryosections of renal allografts after acute vascular rejection demonstrated that a subpopulation of infiltrating macrophages showed a similar association of MRP8/MRP14 to the cytoskel eton in situ; this finding emphasizes the in vivo relevance of our obs ervations. We conclude that Ca2+-dependent translocation of MRP8/MRP14 occurs to distinct subcellular components suggesting a role of these proteins for the medulation of cytoskeletal and membrane interactions.