FHL3 Is an Actin-binding Protein That Regulates α-Actinin-mediated Actin Bundling
FHL3 LOCALIZES TO ACTIN STRESS FIBERS AND ENHANCES CELL SPREADING AND STRESS FIBER DISASSEMBLY*
- Imogen D. Coghill,
- Susan Brown‡,
- Denny L. Cottle,
- Meagan J. McGrath§,
- Paul A. Robinson,
- Harshal H. Nandurkar,
- Jennifer M. Dyson and
- Christina A. Mitchell¶
- Department of Biochemistry and Molecular Biology, Monash University, Clayton 3800, Melbourne, Victoria, Australia
- ¶To whom correspondence should be addressed. Fax: 61-3-9905-4699; E-mail: christina.mitchell{at}med.monash.edu.au.
Abstract
Four and a half LIM domain (FHL) proteins are members of the LIM protein superfamily. Several FHL proteins function as co-activators of CREM/CREB transcription factors and the androgen receptor. FHL3 is highly expressed in skeletal muscle, but its function is unknown. FHL3 localized to the nucleus in C2C12 myoblasts and, following integrin engagement, exited the nucleus and localized to actin stress fibers and focal adhesions. In mature skeletal muscle FHL3 was found at the Z-line. Actin was identified as a potential FHL3 binding partner in yeast two-hybrid screening of a skeletal muscle library. FHL3 complexed with actin both in vitro and in vivo as shown by glutathione S-transferase pull-down assays and co-immunoprecipitation of recombinant and endogenous proteins. FHL3 promoted cell spreading and when overexpressed in spread C2C12 cells disrupted actin stress fibers. Increased FHL3 expression was detected in highly motile cells migrating into an artificial wound, compared with non-motile cells. The molecular mechanism by which FHL3 induced actin stress fiber disassembly was demonstrated by low speed actin co-sedimentation assays and electron microscopy. FHL3 inhibited α-actinin-mediated actin bundling. These studies reveal FHL3 as a significant regulator of actin cytoskeletal dynamics in skeletal myoblasts.
Footnotes
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↵1 The abbreviations used are: FHL, four and a half LIM domains; AD, GAL-4 activation domain; BD, GAL-4 DNA-binding domain; DTT, dithiothreitol; GFP, green fluorescent protein; GST, glutathione S-transferase; HA, hemagglutinin; IPTG, isopropylthiogalactosidase; FITC, fluorescein isothiocyanate; TRITC, tetramethylrhodamine isothiocyanate; CREB, cAMP-response element-binding protein; TMRM, tetramethylrhodamine methyl ester perchlorate; CREM, cAMP response element modulator.
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↵* This work was supported in part by a grant from the National Health and Medical Research Council of Australia. The costs of publication of this article were defrayed in part by the payment of page charges. This 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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↵‡ Recipient of a National Heart Foundation postdoctoral fellowship.
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↵§ Recipient of a National Heart Foundation postgraduate research scholarship.
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- Received December 30, 2002.
- Revision received March 20, 2003.
- The American Society for Biochemistry and Molecular Biology, Inc.
