Phosphorylation of Ser-3 of cofilin regulates its essential function on actin

Genes Cells. 1996 Jan;1(1):73-86. doi: 10.1046/j.1365-2443.1996.05005.x.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Depolymerizing Factors
  • Actins / metabolism
  • Amino Acid Sequence
  • Animals
  • Cell Line
  • Genes, Fungal
  • Humans
  • In Vitro Techniques
  • Microfilament Proteins / chemistry*
  • Microfilament Proteins / genetics
  • Microfilament Proteins / metabolism*
  • Molecular Sequence Data
  • Mutation
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Phosphatidylinositol 4,5-Diphosphate / metabolism
  • Phosphorylation
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism
  • Serine / chemistry
  • Swine


  • Actin Depolymerizing Factors
  • Actins
  • Microfilament Proteins
  • Nerve Tissue Proteins
  • Phosphatidylinositol 4,5-Diphosphate
  • Serine