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Myopalladin, a novel 145-kilodalton sarcomeric protein with multiple roles in Z-disc and I-band protein assemblies.

Bang ML, Mudry RE, McElhinny AS, Trombitás K, Geach AJ, Yamasaki R, Sorimachi H, Granzier H, Gregorio CC, Labeit S - J. Cell Biol. (2001)

Bottom Line: Both sites are highly homologous with those found in palladin, a protein described recently required for actin cytoskeletal assembly (Parast, M.M., and C.A.Overexpression of myopalladin's NH(2)-terminal CARP-binding region in live cardiac myocytes resulted in severe disruption of all sarcomeric components studied, suggesting that the myopalladin-CARP complex in the central I-band may have an important regulatory role in maintaining sarcomeric integrity.Our data also suggest that myopalladin may link regulatory mechanisms involved in Z-line structure (via alpha-actinin and nebulin/nebulette) to those involved in muscle gene expression (via CARP).

View Article: PubMed Central - PubMed

Affiliation: European Molecular Biology Laboratory, Heidelberg 69117, Germany.

ABSTRACT
We describe here a novel sarcomeric 145-kD protein, myopalladin, which tethers together the COOH-terminal Src homology 3 domains of nebulin and nebulette with the EF hand motifs of alpha-actinin in vertebrate Z-lines. Myopalladin's nebulin/nebulette and alpha-actinin-binding sites are contained in two distinct regions within its COOH-terminal 90-kD domain. Both sites are highly homologous with those found in palladin, a protein described recently required for actin cytoskeletal assembly (Parast, M.M., and C.A. Otey. 2000. J. Cell Biol. 150:643-656). This suggests that palladin and myopalladin may have conserved roles in stress fiber and Z-line assembly. The NH(2)-terminal region of myopalladin specifically binds to the cardiac ankyrin repeat protein (CARP), a nuclear protein involved in control of muscle gene expression. Immunofluorescence and immunoelectron microscopy studies revealed that myopalladin also colocalized with CARP in the central I-band of striated muscle sarcomeres. Overexpression of myopalladin's NH(2)-terminal CARP-binding region in live cardiac myocytes resulted in severe disruption of all sarcomeric components studied, suggesting that the myopalladin-CARP complex in the central I-band may have an important regulatory role in maintaining sarcomeric integrity. Our data also suggest that myopalladin may link regulatory mechanisms involved in Z-line structure (via alpha-actinin and nebulin/nebulette) to those involved in muscle gene expression (via CARP).

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Immunoelectron microscopy reveals colocalization of myopalladin and CARP in mouse cardiac myofibrils. (A–C) Isolated myofibrils from mouse were prepared and stretched according to Trombitás et al. 1995; immunoelectron microscopy with affinity-purified antimyopalladin antibodies reveals that myopalladin is detected both within the periphery of the Z-line (A) and in the central I-band region (A–C). In stretched sarcomeres (B), the Z-line to I-band distance increases. A, unstretched; B, slightly stretched; C, high magnification view of Z-disc in stretched myofibrils. (D) The distances of I-band–bound CARP and myopalladin from the Z-disk were measured from immunoelectron micrographs at different sarcomere lengths (29 micrographs were analyzed for CARP; 54 micrographs for myopalladin). Both CARP and myopalladin colocalize in the central I-band and their epitope distances (in μm) from the Z-disc were dependent on sarcomeric length (SL).
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Figure 8: Immunoelectron microscopy reveals colocalization of myopalladin and CARP in mouse cardiac myofibrils. (A–C) Isolated myofibrils from mouse were prepared and stretched according to Trombitás et al. 1995; immunoelectron microscopy with affinity-purified antimyopalladin antibodies reveals that myopalladin is detected both within the periphery of the Z-line (A) and in the central I-band region (A–C). In stretched sarcomeres (B), the Z-line to I-band distance increases. A, unstretched; B, slightly stretched; C, high magnification view of Z-disc in stretched myofibrils. (D) The distances of I-band–bound CARP and myopalladin from the Z-disk were measured from immunoelectron micrographs at different sarcomere lengths (29 micrographs were analyzed for CARP; 54 micrographs for myopalladin). Both CARP and myopalladin colocalize in the central I-band and their epitope distances (in μm) from the Z-disc were dependent on sarcomeric length (SL).

Mentions: Consistent with the immunofluorescence data, immunoelectron microscopy studies with myopalladin-specific antibodies detected myopalladin both within the periphery of the Z-line (Fig. 8 A) and in the central I-band (Fig. 8, A–C). In fact, measurements of the CARP and myopalladin epitopes from the Z-disc revealed that the two proteins colocalized within the central I-band (Fig. 8 D). Interestingly, for both I-band–bound myopalladin and CARP the distances of their epitopes from the Z-line were dependent on stretch (i.e., sarcomere length). In contrast, the Z-line–bound myopalladin remained in a fixed position. This raises the possibility that CARP and the I-band–bound myopalladin are attached to the elastic titin filament, whereas the Z-line–bound myopalladin is an integral component within Z-lines.


Myopalladin, a novel 145-kilodalton sarcomeric protein with multiple roles in Z-disc and I-band protein assemblies.

Bang ML, Mudry RE, McElhinny AS, Trombitás K, Geach AJ, Yamasaki R, Sorimachi H, Granzier H, Gregorio CC, Labeit S - J. Cell Biol. (2001)

Immunoelectron microscopy reveals colocalization of myopalladin and CARP in mouse cardiac myofibrils. (A–C) Isolated myofibrils from mouse were prepared and stretched according to Trombitás et al. 1995; immunoelectron microscopy with affinity-purified antimyopalladin antibodies reveals that myopalladin is detected both within the periphery of the Z-line (A) and in the central I-band region (A–C). In stretched sarcomeres (B), the Z-line to I-band distance increases. A, unstretched; B, slightly stretched; C, high magnification view of Z-disc in stretched myofibrils. (D) The distances of I-band–bound CARP and myopalladin from the Z-disk were measured from immunoelectron micrographs at different sarcomere lengths (29 micrographs were analyzed for CARP; 54 micrographs for myopalladin). Both CARP and myopalladin colocalize in the central I-band and their epitope distances (in μm) from the Z-disc were dependent on sarcomeric length (SL).
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Related In: Results  -  Collection

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Figure 8: Immunoelectron microscopy reveals colocalization of myopalladin and CARP in mouse cardiac myofibrils. (A–C) Isolated myofibrils from mouse were prepared and stretched according to Trombitás et al. 1995; immunoelectron microscopy with affinity-purified antimyopalladin antibodies reveals that myopalladin is detected both within the periphery of the Z-line (A) and in the central I-band region (A–C). In stretched sarcomeres (B), the Z-line to I-band distance increases. A, unstretched; B, slightly stretched; C, high magnification view of Z-disc in stretched myofibrils. (D) The distances of I-band–bound CARP and myopalladin from the Z-disk were measured from immunoelectron micrographs at different sarcomere lengths (29 micrographs were analyzed for CARP; 54 micrographs for myopalladin). Both CARP and myopalladin colocalize in the central I-band and their epitope distances (in μm) from the Z-disc were dependent on sarcomeric length (SL).
Mentions: Consistent with the immunofluorescence data, immunoelectron microscopy studies with myopalladin-specific antibodies detected myopalladin both within the periphery of the Z-line (Fig. 8 A) and in the central I-band (Fig. 8, A–C). In fact, measurements of the CARP and myopalladin epitopes from the Z-disc revealed that the two proteins colocalized within the central I-band (Fig. 8 D). Interestingly, for both I-band–bound myopalladin and CARP the distances of their epitopes from the Z-line were dependent on stretch (i.e., sarcomere length). In contrast, the Z-line–bound myopalladin remained in a fixed position. This raises the possibility that CARP and the I-band–bound myopalladin are attached to the elastic titin filament, whereas the Z-line–bound myopalladin is an integral component within Z-lines.

Bottom Line: Both sites are highly homologous with those found in palladin, a protein described recently required for actin cytoskeletal assembly (Parast, M.M., and C.A.Overexpression of myopalladin's NH(2)-terminal CARP-binding region in live cardiac myocytes resulted in severe disruption of all sarcomeric components studied, suggesting that the myopalladin-CARP complex in the central I-band may have an important regulatory role in maintaining sarcomeric integrity.Our data also suggest that myopalladin may link regulatory mechanisms involved in Z-line structure (via alpha-actinin and nebulin/nebulette) to those involved in muscle gene expression (via CARP).

View Article: PubMed Central - PubMed

Affiliation: European Molecular Biology Laboratory, Heidelberg 69117, Germany.

ABSTRACT
We describe here a novel sarcomeric 145-kD protein, myopalladin, which tethers together the COOH-terminal Src homology 3 domains of nebulin and nebulette with the EF hand motifs of alpha-actinin in vertebrate Z-lines. Myopalladin's nebulin/nebulette and alpha-actinin-binding sites are contained in two distinct regions within its COOH-terminal 90-kD domain. Both sites are highly homologous with those found in palladin, a protein described recently required for actin cytoskeletal assembly (Parast, M.M., and C.A. Otey. 2000. J. Cell Biol. 150:643-656). This suggests that palladin and myopalladin may have conserved roles in stress fiber and Z-line assembly. The NH(2)-terminal region of myopalladin specifically binds to the cardiac ankyrin repeat protein (CARP), a nuclear protein involved in control of muscle gene expression. Immunofluorescence and immunoelectron microscopy studies revealed that myopalladin also colocalized with CARP in the central I-band of striated muscle sarcomeres. Overexpression of myopalladin's NH(2)-terminal CARP-binding region in live cardiac myocytes resulted in severe disruption of all sarcomeric components studied, suggesting that the myopalladin-CARP complex in the central I-band may have an important regulatory role in maintaining sarcomeric integrity. Our data also suggest that myopalladin may link regulatory mechanisms involved in Z-line structure (via alpha-actinin and nebulin/nebulette) to those involved in muscle gene expression (via CARP).

Show MeSH