Participation of cofilin in opsonized zymosan-triggered activation of neutrophil-like HL-60 cells through rapid dephosphorylation and translocation to plasma membranes.

We studied the roles of cofilin, an actin-binding phosphoprotein, in superoxide production of neutrophil-like HL-60 cells triggered by opsonized zymosan (OZ). OZ caused dephosphorylation of cofilin as well as a transient increase of F-actin. Both reactions were complete within 30 s. Okadaic acid (OA) magnified the OZ-triggered O2--production 3.3-fold at 1 microM, but inhibited it completely at 5 microM. We used these critical concentrations to study the effects of OA on changes in phosphorylation and intracellular localization of cofilin. The OZ-induced dephosphorylation of cofilin was inhibited by 5 microM OA but not by 1 microM OA. Subcellular fractionation and immunoblotting revealed that 1 microM OA increased cofilin on the phagosomal membranous fraction but 5 microM OA decreased it. At 1 microM, OA increased translocation of p47phox to membranes, which may explain in part the enhancing effect of 1 microM OA. Confocal laser scanning microscopy showed that: (i) Cofilin diffused throughout the cytosol of resting cells, but accumulated at the plasma membranes forming phagocytic vesicles in activated cells. (ii) At 1 microM, OA had little effect on the OZ-evoked translocation of cofilin, whereas 5 microM OA suppressed it completely. (iii) OA alone, which could not trigger the phagocytic respiratory burst, did not cause any change in the distribution of cofilin at such concentrations. Furthermore, in a superoxide-producing cell-free system employing membranous and cytosolic fractions, affinity-purified anti-cofilin antibody showed an enhancing effect. These results suggest that cofilin participates in the superoxide production of the OZ-activated phagocytes through dephosphorylation and translocation. The roles of cofilin in the activated leukocytes will be discussed.