Translocation of a small cytosolic calcium-binding protein (MRP-8) to plasma membrane correlates with human neutrophil activation.

To further understand the mechanisms involved in phagocyte activation in general and in NADPH oxidase activation in particular, a polyclonal antibody was raised in rabbit against a partially purified oxidase preparation. The enzyme was solubilized from zymosan-activated human neutrophils and resting cells and separated by preparative isoelectric focusing electrophoresis. A polyclonal antibody was raised in rabbit against the pI 5.0 fraction, which had the maximum superoxide-producing capacity. Analysis of the polyclonal antibody revealed marked differences between activated and resting neutrophils. The antibody recognized in particular an 8-kDa protein (p8) in resting human neutrophil cytosol and in the membrane of zymosan-activated cells. A polyclonal antibody (anti-p8) was raised against the pure cytosolic p8 protein. This anti-p8 reacted not only with p8, but also with cytosolic proteins of 14 kDa and 6 kDa. N-terminal amino acid sequence analysis of p8 revealed homology with the calcium-binding myeloid related protein (MRP-8). Upon neutrophil activation, translocation of the 8- and 14-kDa proteins to the membrane was observed with stimuli known to depend on extracellular calcium. In calcium-depleted medium, the absence of translocation correlated with a depression of superoxide production, supporting a role for the calcium-binding protein in cellular activation.