Differential Regulation of Actin Depolymerizing Factor and Cofilin in Response to Alterations in the Actin Monomer Pool*
- From the ‡ Department of Biochemistry and Molecular Biology and the Molecular, Cellular and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado 80523 and
- § The Children's Medical Research Institute, 214 Hawkesbury Road, Westmead, New South Wales 2145, Australia
- ∥Performed much of this work at the CMRI, Sydney, Australia, during a sabbatical leave from Colorado State University. To whom correspondence should be addressed. Tel.: 970-491-6096; FAX: 970-491-0494; E-mail: jbamburg{at}vines.colostate.edu
Abstract
Myoblasts, transfected with a human gene encoding a β-actin point mutation, down-regulate expression of actin depolymerizing factor (ADF) and its mRNA. Regulation is posttranscriptional. Expression of cofilin, a structurally similar protein, and profilin, CapG, and tropomodulin is not altered with increasing mutant β-actin expression. Myoblasts expressing either human γ-actin or the mutant β-actin down-regulate the endogenous mouse actin genes to keep a constant level of actin mRNA, whereas the γ-actin transfectants do not down-regulate ADF. Thus, ADF expression is regulated differently from actin expression.
The mutant β-actin binds to ADF with about the same affinity as normal actin; however, it does not assemble into normal actin filaments. The decrease in ADF expression correlates with an increase in the unassembled actin pool. When the actin monomer pool in untransfected myoblasts is increased 70% by treatment with latrunculin A, synthesis of ADF and actin are down-regulated compared with cofilin and 19 other proteins selected at random. Increasing the actin monomer pool also results in nearly complete phosphorylation of both ADF and cofilin. Thus, ADF and cofilin are coordinately regulated by posttranslational modification, but their expression is differentially regulated. Furthermore, expression of ADF is responsive to the utilization of actin by the cell.
Footnotes
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↵¶ NHMRC Senior Research Fellow.
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↵* This work was supported in part by National Institutes of Health Grants GM35126 and TW01856 (to J. R. B.) and an NHMRC grant (to P. G.). 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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↵1 The abbreviations used are:
- βsm-actin
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a single mutant actin in which Gly-244 is converted to Asp
- ADF
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actin depolymerizing factor
- DTT
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dithiothreitol
- PAGE
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polyacrylamide gel electrophoresis
- PBS
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phosphate-buffered saline
- MOPS
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3-(N-morpholino)propanesulfonate
- MES
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2-(N-morpholino)ethanesulfonic acid
- Lat A
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latrunculin A.
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- Received December 5, 1996.
- Revision received January 23, 1997.
- © 1997 by The American Society for Biochemistry and Molecular Biology, Inc.
