IDENTIFICATION AND CHARACTERIZATION OF A NOVEL HUMAN NEUTROPHIL PROTEIN RELATED TO THE S100 FAMILY

A rabbit polyclonal antibody raised against myeloid-related protein 8 (MRP-8), a protein of the S100 family, recognized another S100 protein (MRP-14) as well as a protein of 6.5 kDa (p6) in the cytosol of resti ng neutrophils. p6 was found to be a novel member of the S100 family. It consisted of two isoforms with pi values of 6.2 (the minor form, p6 a) and 6.3 (the major form, p6b) and constituted 5% of the total cytos olic proteins. Both isoforms were also demonstrated in the cytosol of monocytes, but not in lymphocytes, as previously shown for MRP-8 and M RP-14. Only the major isoform bound radioactive Ca2+, as also observed for MRP-8, whereas the different variants of MRP-14 were all labelled . On neutrophil activation with opsonized zymosan, a stimulant known t o require extracellular Ca2+, 58% of p6a and 42% of p6b was translocat ed to the membrane. With phorbol 12-myristate 13-acetate, a Ca2+-indep endent stimulant, no translocation was detected. This translocation pa ttern was similar to that observed with MRP-8 and MRP-14. In addition, p6, MRP-8 and MRP-14 were specifically associated with the cytoskelet al fraction of the membrane. The Ca2+-dependent translocation of the n ovel S100 protein in parallel with MRP-8 and MRP-14 suggests a role fo r these proteins in regulating the Ca2+ signal to the membrane cytoske leton and thus in regulating neutrophil activation.