calyculin-a and mezerein

Neutrophils contain a 21-kDa phosphoprotein that undergoes rapid dephosphorylation upon stimulation of these cells with the chemoattractant N-fMet-Leu-Phe (fMLP), activators of protein kinase C [e.g., 4 beta-phorbol 12-myristate 13-acetate (PMA)] or the calcium ionophore A23187. This phosphoprotein was identified as the non-muscle form of cofilin by peptide sequencing and immunoblotting with specific antibodies. Evidence is presented that in neutrophils cofilin is regulated by a continual cycle of phosphorylation and dephosphorylation, and that the phosphatase undergoes activation during cell stimulation. Experiments with a wide variety of antagonists further suggested that the protein kinase that participates in these reactions may be a novel enzyme. The kinetics of cofilin dephosphorylation in neutrophils stimulated with fMLP or PMA were very similar to those observed for superoxide (O2-) release. Immunofluorescent studies revealed that cofilin was present throughout the cytosol of resting neutrophils and underwent rapid translocation to the F-actin-rich, ruffled membranes of stimulated cells. Cytochemical analysis further revealed that the ruffled membranes also contained large amounts of hydrogen peroxide (H2O2), a product of the O2-/H2O2-generating activity of stimulated neutrophils (NADPH oxidase). Cofilin is therefore well placed to participate in the continual polymerization and depolymerization of F-actin that is thought to give rise to the oscillatory pattern of H2O2 production observed under certain conditions.

Topics: Actin Depolymerizing Factors; Actins; Amino Acid Sequence; Animals; Calcimycin; Cell Membrane; Diglycerides; Diterpenes; Guinea Pigs; Humans; Hydrogen Peroxide; Immunoblotting; Marine Toxins; Microfilament Proteins; Molecular Sequence Data; N-Formylmethionine Leucyl-Phenylalanine; NADPH Oxidases; Neutrophil Activation; Neutrophils; Okadaic Acid; Oxazoles; Oxides; Phosphorylation; Staurosporine; Terpenes; Tetradecanoylphorbol Acetate