抄録
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 O-2-production 3.3-fold at 1 μM, but inhibited it completely at 5 μM. 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 μM OA but not by 1 μM OA. Subcellular fractionation and immunoblotting revealed that 1 μM OA increased cofilin on the phagosomal membranous fraction but 5 μM OA decreased it. At 1 μM, OA increased translocation of p47phox to membranes, which may explain in part the enhancing effect of 1 μM 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 μM, OA had little effect on the OZ-evoked translocation of cofilin, whereas 5 μM 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 cellfree 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.
