Thymosin beta 4 (Fx peptide) is a potent regulator of actin polymerization in living cells

Proc Natl Acad Sci U S A. 1992 May 15;89(10):4678-82. doi: 10.1073/pnas.89.10.4678.


Thymosin beta 4 (beta 4) is a 5-kDa polypeptide originally identified in calf thymus. Although numerous activities have been attributed to beta 4, its physiological role remains elusive. Recently, beta 4 was found to bind actin in human platelet extracts and to inhibit actin polymerization in vitro, raising the possibility that it may be a physiological regulator of actin assembly. To examine this potential function, we have increased the cellular beta 4 concentration by microinjecting synthetic beta 4 into living epithelial cells and fibroblasts. The injection induced a diminution of stress fibers and a dose-dependent depolymerization of actin filaments as indicated by quantitative image analysis of phalloidin binding. Our results show that beta 4 is a potent regulator of actin assembly in living cells.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells
  • Actins / metabolism*
  • Animals
  • Cell Line
  • Kinetics
  • Macromolecular Substances
  • Mice
  • Microinjections
  • Microscopy, Fluorescence
  • Rats
  • Thymosin / analogs & derivatives*
  • Thymosin / chemical synthesis
  • Thymosin / pharmacology


  • Actins
  • Macromolecular Substances
  • thymosin beta(4)
  • Thymosin