Studies on roles of cofilin (actin/PIP2-binding protein) in activation of phagocytes

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Cofilin, an actin/PLP2-binding phosphoprotein, plays important roles in various cells and tisssues through cytoskeletal reorganization. We studied the roles of cofiln in phagocyte functions using neutrophil-like HL-60 cells and macrophage-like U937 cells. Our major results are as follows :(1)Opsonized zymosan (OZ) induced rapid dephosphorylation of cofilin and its translocation to plasma membranes on which superoxide was generated and/or OZ particles were engulfed.(2)Okadaic acid (OA) which is a potent inhibitor for phosphoprotein phosphatase type 2A and type 1, did not inhibit the stimulus-dependent dephosphorylation and translocation of cofilin at 1muM, an enhancing concentration for OZ-induced superoxide production,(3)To the contrary, OA 5muM, an inhibitory concentration for the OZ-induced respiratory burst, inhibited completely the stimulus-dependent dephosphorylation and translocation of cofilin.(4)OZ induced decrease in intracellular pH in differentiated U937 cells from 7.3 to 6.8. In the phagocytes, the changes in pH may be an important factor that regulate the F-actin-depolymerizing activity of cofilin.These results suggest that the stimuli-dependent dephosphorylation and translocation of cofillin are crucial for the activation of phagocytes.