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  • Title: Phosphorylation of Ser-3 of cofilin regulates its essential function on actin.
    Author: Moriyama K, Iida K, Yahara I.
    Journal: Genes Cells; 1996 Jan; 1(1):73-86. PubMed ID: 9078368.
    Abstract:
    BACKGROUND: Cofilin is a low-molecular weight actin-modulating protein, and is structurally and functionally conserved in eucaryotes from yeast to mammals. The functions of cofilin appear to be regulated by phosphorylation and dephosphorylation. RESULTS: A proteolytic study of phosphorylated porcine cofilin and expression of a mutated cofilin in cultured cells revealed that Ser-3 is the unique phosphorylation site. Phosphorylated cofilin was found not to bind to either F- or G-actin while unphosphorylated cofilin binds to both. S3D-cofilin, in which Ser-3 was replaced with Asp, did not bind in vitro to actin while S3A-cofilin did. The transient over-expression of wild-type or S3A-cofilin in cultured cells caused disruption of preexisting actin structures and induced cytoplasmic actin bundles. Heat shock-induced nuclear or NaCl buffer-induced cytoplasmic actin/cofilin rods contained the expressed cofilin. In contrast, the over-expression of S3D-cofilin did not alter the actin structures. Induced actin rods did not contain S3D-cofilin. S3D-porcine cofilin did not complement the lethality associated with delta cof1 mutations in Saccharomyces cerevisiae while wild-type and S3A-cofilin did. Furthermore, we found that S2A/S4D- and S2D/S4D-yeast cofilin mutants were not viable. CONCLUSION: We conclude that the function of cofilin is negatively regulated in vivo by phosphorylation of Ser-3 and that cells require the function of unphosphorylated cofilin for viability.
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