Аннотация: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 overexpression of wild‐type or S3A‐cofilin in cultured cells caused disruption of pre‐existing 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 overexpression 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 Δ 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 functions of unphosphorylated cofilin for viability.
