Synergy between Actin Depolymerizing Factor/Cofilin and Profilin in Increasing Actin Filament Turnover*
- From Dynamique du Cytosquelette, Laboratoire d’Enzymologie et Biochimie Structurales, CNRS, 91198 Gif-sur-Yvette, France
Abstract
The mechanism of control of the steady state of actin assembly by actin depolymerizing factor (ADF)/cofilin and profilin has been investigated. Using Tβ4 as an indicator of the concentration of ATP-G-actin, we show that ADF increases the concentration of ATP-G-actin at steady state. The measured higher concentration of ATP-G-actin is quantitatively consistent with the increase in treadmilling, caused by the large increase in the rate of depolymerization from the pointed ends induced by ADF (Carlier, M.-F., Laurent, V., Santolini, J., Didry, D., Melki, R., Xia, G.-X., Hong, Y., Chua, N.-H., and Pantaloni, D. (1997)J. Cell Biol. 136, 1307–1322). Experiments demonstrate that profilin synergizes with ADF to further enhance the turnover of actin filaments up to a value 125-fold higher than in pure F-actin solutions. Profilin and ADF act at the two ends of filaments in a complementary fashion to increase the processivity of treadmilling. Using the capping protein CapZ, we show that ADF increases the number of filaments at steady state by 1.3-fold, which cannot account for the 25-fold increase in turnover rate. Computer modeling of the combined actions of ADF and profilin on the dynamics of actin filaments using experimentally determined rate constants generates a distribution of the different actin species at steady state, which is in quantitative agreement with the data.
Footnotes
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↵* This work was supported in part by the Association pour la Recherche contre le Cancer, the Ligue Nationale contre le Cancer, and the Association Française contre les Myopathies.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed. Tel.: 33-01-69-82-34-65; Fax: 33-01-69-82-31-29; E-mail:carlier{at}lebs.cnrs-gif.fr.
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↵2 I. Gutsche-Perelroizen, submitted for publication.
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↵3 M.-F. Carlier, unpublished data.
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↵4 M.-F. Carlier and I. Perelroizen, unpublished data.
- Abbreviations:
- ADF
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actin depolymerizing factor
- Tβ4
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thymosin β4.
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- Received June 8, 1998.
- Revision received July 17, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
