Membrane‐cytoskeleton interactions and the regulation of chemotactic peptide‐induced activation of human granulocytes: The effects of dihydrocytochalasin B

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Abstract
When N‐formyl chemotaclic peptides bind to granulocyte receptors at 37°C they rapidly form a high‐affinity ligand‐receptor complex whose coisolation with cyto‐skeletal residues of Triton X‐100–extracted cells is under cellular control [Jesaitis et al: J Cell Biol 98:1378, 1984]. Experiments were performed to investigate the significance of this coisolation. When the granulocytes were preincubated with dihydrocytochalasin B (dhCB) for 10 min at 37°C and then stimulated with 50 nM N‐formyl‐Met‐Leu‐[3H]Phe, the rate of uptake of the radioligand by the cells was inhibited. Colocalization of the retained peptide with the Triton X‐100 fraction of these cells was also reduced relative to this fraction of the untreated cells. This inhibition was apparent before the onset of FMLP endocytosis. The inhibition was 50% effective at 0.25 μg dhCB/ml. Maximal inhibition (80–90%) occurred at doses of dhCB > 1 μg/ml. The 90% retention of two plasma membrane markers by the cytoskeleton was marginally affected. These results support the hypothesis that coisolation of the high‐affinity receptor‐peptide complexes with granulocyte cytoskeletons occurs because of specific association of the complexes with the cytoskeleton at the cell surface. In addition, since these events precede internalization, they suggest that formation of the association between the ligand‐receptor complex and cytoskeleton may be necessary for ligand‐receptor endocytosis. Experiments were also performed to evaluate other functional consequences of cytoskeletal disruption on chemotactic peptide‐stimulated functions. f‐Met‐Leu‐Phe stimulation of O production was potentiated due to prolongation of and increase in the rate of O production. This potentiation has the same dose dependency as the inhibition of receptor modulation. The possible relationship of these various functions is discussed.