Cytoplasmic γ Actin as a Z-Disc Protein

Nakata, Takashi; Nishina, Yasushi; Yorifuji, Hiroshi

doi:10.1006/bbrc.2001.5353

Cited by 20 publications

(22 citation statements)

References 18 publications

(23 reference statements)

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“…Our results closely match ␥-actin localization in chicken skeletal muscle (16) and also the staining pattern observed in human skeletal muscle with antibodies to Aplysia actin that reacted with mammalian cytoplasmic actins but not muscle actin (26). Others have reported ␥-actin immunoreactivity most predominantly associated with the Z-disk (27,28). We cannot explain this difference other than to note that predominant sarcolemmal staining was consistently observed with antibodies raised against whole protein (Fig.…”

Section: Discussionsupporting

confidence: 87%

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Cytoplasmic γ-actin contributes to a compensatory remodeling response in dystrophin-deficient muscle

Hanft

Rybakova

Patel

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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Dystrophin mechanically links the costameric cytoskeleton and sarcolemma, yet dystrophin-deficient muscle exhibits abnormalities in cell signaling, gene expression, and contractile function that are not clearly understood. We generated new antibodies specific for cytoplasmic ␥-actin and confirmed that ␥-actin most predominantly localized to the sarcolemma and in a faint reticular lattice within normal muscle cells. However, we observed that ␥-actin levels were increased 10-fold at the sarcolemma and within the cytoplasm of striated muscle cells from dystrophin-deficient mdx mice. Transgenic overexpression of the dystrophin homologue utrophin, or functional dystrophin constructs in mdx muscle, restored ␥-actin to normal levels, whereas ␥-actin remained elevated in mdx muscle expressing nonfunctional dystrophin constructs. We conclude that increased cytoplasmic ␥-actin in dystrophin-deficient muscle may be a compensatory response to fortify the weakened costameric lattice through recruitment of parallel mechanical linkages. However, the presence of excessive myoplasmic ␥-actin may also contribute to altered cell signaling or gene expression in dystrophin-deficient muscle.costamere ͉ muscular dystrophy ͉ sarcolemma D uchenne muscular dystrophy is caused by mutations in the gene encoding dystrophin (1). Dystrophin functions as part of a large complex of sarcolemmal proteins including dystroglycans, sarcoglycans, dystrobrevins, syntrophins, and sarcospan (2, 3). This dystrophin-glycoprotein complex is thought to link the actin-based costameric cytoskeleton with the extracellular matrix and mechanically stabilize the sarcolemma against shear stresses imposed during muscle activity (4). When dystrophin is absent the link between the costamere and sarcolemma is disrupted, resulting in compromised sarcolemma integrity (4).Dystrophin is anchored to the sarcolemma primarily through direct interaction with ␤-dystroglycan (5, 6). Regarding its interaction with costameres, the amino-terminal calponin homology domain and a cluster of basic spectrin repeats within the middle rod domain of dystrophin bind directly to actin filaments (7-10). Cytoplasmic ␥-actin filaments are retained in a costameric pattern on sarcolemma peeled from single myofibers of normal mouse muscle but are absent from all sarcolemma of dystrophin-deficient mdx muscle (11). Thus, dystrophin is necessary for a mechanically strong link between the sarcolemma and costameric actin filaments.Here we peeled sarcolemma from several lines of transgenic mdx mice expressing deletion constructs of dystrophin, and we report that either actin binding domain is sufficient to retain costameric actin on peeled sarcolemma. We generated new polyclonal antibodies (pAbs) and mAbs to cytoplasmic ␥-actin, and we demonstrate that ␥-actin levels are elevated 10-fold in dystrophin-deficient striated muscle. We hypothesize that elevated ␥-actin levels contribute to a compensatory remodeling of the dystrophin-deficient costameric cytoskeleton. Our results also provide the basis for s...

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Section: Discussionsupporting

confidence: 87%

“…We cannot explain this difference other than to note that predominant sarcolemmal staining was consistently observed with antibodies raised against whole protein (Fig. 2) (16, 26), whereas Z-disk staining was observed exclusively with antibodies to synthetic peptides (27,28).…”

Section: Discussionmentioning

confidence: 93%

Cytoplasmic γ-actin contributes to a compensatory remodeling response in dystrophin-deficient muscle

Hanft

Rybakova

Patel

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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“…In transverse sections FHL3 co-localized with ␣-actinin at the plasma membrane and at punctate structures within the muscle fiber (Fig. 4, vii-xii), as shown previously for ␣-actinin localization (61). In transverse sections FHL3 co-localized with actin (Fig.…”

Section: Fhl3 Localizes To the Nucleus And Stress Fibers In C2c12supporting

confidence: 85%

FHL3 Is an Actin-binding Protein That Regulates α-Actinin-mediated Actin Bundling

Coghill

Brown²,

Cottle

et al. 2003

Journal of Biological Chemistry

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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 pulldown 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 ␣-actinin-mediated actin bundling. These studies reveal FHL3 as a significant regulator of actin cytoskeletal dynamics in skeletal myoblasts.The LIM superfamily of proteins is defined by the presence of one or more LIM domains, which represent a cysteinerich double zinc finger motif denoted by the sequence (CX 2 -CX 17-19 HX 2 C)X 2 (CX 2 CX 16 -20 CX 2 (H/D/C)) (1). The LIM zinc finger does not interact with DNA but functions as a proteinprotein binding module (2, 3). LIM proteins localize to the nucleus and scaffold the assembly of transcription factors and thereby regulate transcription. In the cytoplasm LIM proteins facilitate the complex association of signaling proteins with the actin cytoskeleton (3).A subset of LIM proteins are the LIM-only proteins, which comprise solely multiple copies of LIM domains. The family of four and a half LIM domain (FHL) 1 proteins all contain a single N-terminal LIM-type zinc finger followed by four sequential LIM domains and no other modular domains (4). This group of proteins includes FHL1 (also called SLIM1) and its alternatively spliced isoforms SLIMMER and KyoT2, FHL2 (also called DRAL for "down-regulated in rhabdomyosarcoma" or SLIM3), FHL3 (also called SLIM2), FHL4, and ACT. FHL1, FHL2, and FHL3 are highly expressed in striated muscle, whereas ACT is expressed only in the testis (4 -12).FHL1 is strongly implicated in the pathogenesis of human cardiomyopathy. Microarray analysis has demonstrated FHL1 mRNA levels are decreased in failing human hearts with dilated cardiomyopathy and significantly increased in hypertrophic cardiomyopathy (13,14). Mouse models of hypertrophic cardiomyopathy induced by transverse aortic constriction also show elevated expression of FHL1, suggesting FHL1 may play a significant role in regulating the heart muscle cytoarchitecture (15). In skeletal myoblasts FHL1 localizes in...

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“…However, nocodazole did not change the subsarcolemmal localization or the cross-striated distribution pattern of the transcripts at concentrations that destroyed microtubules ( Figure 5). Although the presence of subsarcolemmal gamma actin filaments in myofibers has been recently questioned (Nakata et al 2001), we analyzed whether cytochalasin D or latrunculin that disassembles actin filaments altered the transcripts distribution. These drugs did not have any marked effect (not shown).…”

Section: Northern Analysismentioning

confidence: 99%

Restricted Distribution of mRNAs Encoding a Sarcoplasmic Reticulum or Transverse Tubule Protein in Skeletal Myofibers

Nissinen

Kaisto

Salmela

et al. 2005

J Histochem Cytochem.

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S U M M A R Y Calsequestrin (CSQ) and dihydropyridine receptor (DHPR) are muscle cell proteins that are directed into the endoplasmic reticulum (ER) during translation. The former is subsequently found in the sarcoplasmic reticulum (SR) and the latter in the transverse tubule membrane. To elucidate the potential role of mRNA targeting within muscle cells, we have analyzed the localization of CSQ and DHPR proteins and mRNAs in primary cultured rat myotubes, in skeletal muscle cryosections, and in isolated flexor digitorum brevis muscle fibers. In the myotube stage of differentiation, the mRNAs distributed throughout the cell, mimicking the distribution of the endogenous ER marker proteins. In the adult skeletal myofibers, however, both CSQ and DHPR ␣ 1 transcripts located perinuclearly and in cross-striations flanking Z lines beneath the sarcolemma, a distribution pattern that sharply contrasted the interfibrillar distribution of typical ER proteins. Interestingly, all nuclei of the myofibers were transcriptionally active. In summary, the mRNAs encoding either a resident SR protein or a transverse tubule protein were located beneath the sarcolemma, implying that translocation of the respective proteins to the lumen of ER takes place at this location.

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Cytoplasmic γ Actin as a Z-Disc Protein

Cited by 20 publications

References 18 publications

Cytoplasmic γ-actin contributes to a compensatory remodeling response in dystrophin-deficient muscle

Cytoplasmic γ-actin contributes to a compensatory remodeling response in dystrophin-deficient muscle

FHL3 Is an Actin-binding Protein That Regulates α-Actinin-mediated Actin Bundling

Restricted Distribution of mRNAs Encoding a Sarcoplasmic Reticulum or Transverse Tubule Protein in Skeletal Myofibers

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