Fodrin in the human polymorphonuclear leucocyte: redistribution induced by the chemotactic peptide

Fodrin, a membrane skeletal protein, was found to accumulate in the posterior portion of human neutrophils polarized morphologically after stimulation by the chemotactic peptide, N-formylmethionyl-leucylphenylalanine (FMLP). In most (greater than 90%) unstimulated neutrophils, the distribution of fodrin was found to be uniform by immunofluorescence microscopy. When FMLP (10(-8)M) was applied at 25 degrees C, fodrin became polarized in about 40% of cells by 1 min, about 70% by 2 min, and about 80% by 10 min. The cells with polarized distribution decreased thereafter to about 60% of the cells at 20 min and about 20% at 60 min. Using the under-agarose system, it was confirmed that the concentration of fodrin occurred in the region opposite to the direction of chemoattraction in moving cells. By immunoelectron microscopy, most of the labeling for fodrin was observed in the filamentous cell cortex and not associated with the plasma membrane itself. In cells polarized morphologically by FMLP, the fodrin labeling became concentrated in the posterior portion of the cell; the labeling was found most densely in the granule-rich cytoplasm, while the filamentous tail region was not labeled intensely. The lamellipodium in the head region was also labeled only sparsely. The results indicate that in human neutrophils fodrin exists as a cytoskeletal protein rather than as a membrane protein and that the protein accumulates in the endoplasm of the posterior portion in migrating cells. The rearrangement is likely to modulate the organization of the actin-rich cell cortex for cell locomotion.