Article

A myopathy-linked desmin mutation perturbs striated muscle actin filament architecture.

Department of Cell Biology and Anatomy, University of Arizona, Tucson, AZ 85724, USA.
Molecular biology of the cell (Impact Factor: 5.98). 12/2008; 20(3):834-45. DOI: 10.1091/mbc.E08-07-0753
Source: PubMed

ABSTRACT Desmin interacts with nebulin establishing a direct link between the intermediate filament network and sarcomeres at the Z-discs. Here, we examined a desmin mutation, E245D, that is located within the coil IB (nebulin-binding) region of desmin and that has been reported to cause human cardiomyopathy and skeletal muscle atrophy. We show that the coil IB region of desmin binds to C-terminal nebulin (modules 160-164) with high affinity, whereas binding of this desmin region containing the E245D mutation appears to enhance its interaction with nebulin in solid-phase binding assays. Expression of the desmin-E245D mutant in myocytes displaces endogenous desmin and C-terminal nebulin from the Z-discs with a concomitant increase in the formation of intracellular aggregates, reminiscent of a major histological hallmark of desmin-related myopathies. Actin filament architecture was strikingly perturbed in myocytes expressing the desmin-E245D mutant because most sarcomeres contained elongated or shorter actin filaments. Our findings reveal a novel role for desmin intermediate filaments in modulating actin filament lengths and organization. Collectively, these data suggest that the desmin E245D mutation interferes with the ability of nebulin to precisely regulate thin filament lengths, providing new insights into the potential molecular consequences of expression of certain disease-associated desmin mutations.

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These findings are important for understanding myotilin-linked muscle diseases and designing treatments for these disorders. Lihaksen rakennetta ja toimintaa säätelevät useat valkuaisaineet, joiden avulla aktiini- ja myosiinisäikeiden tuottama supistusvoima synkronoidaan ja siirretään tukikudoksiin. Myotiliini on lihaksen rakenneproteiini ja osa lihaksen supistusyksikköä, sarkomeeriä. Myotiliinin perityt pistemutaatiot aikaansaavat luuranko- ja sydänlihaksen häiriöitä, eli myotilinopatioita. Vaikka myotilinopatian perinnöllinen tausta tunnetaan, on vielä selvittämättä, kuinka myotiliinin muutokset johtavat lihasten surkastumiseen. Solutasolla tiedämme, että myotilinopatiapotilailla on vakavia sarkomeerin rakennehäiriöitä, ja että viallisen myotiliinin ilmentäminen lihassoluissa johtaa sarkomeerirakenteen hajoamiseen. Tässä tutkimuksessa selvitettiin myotiliinin toimintamekanismeja. Myotiliinin päätehtävänä lienee aktiinisäikeiden yhteenliittäminen sarkomeerin Z-levyssä. 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Näitä proteiinien vuorovaikutuksia voidaan säädellä fosforylaation avulla. Vuorovaikutukset ovat osa mekanismia, jolla lihassolun sisäinen viestintä tapahtuu. Myotilinopatioille tyypillisiä lihaksen rakennevirheitä ovat Z-levyn muutokset ja tiheän säiemäisen materiaalin keräytyminen. Kertymien syytä ja mekanismia ei tunneta, mutta yksi syy tähän voisi olla proteiinien puutteellinen hajoaminen. Osoitimme, että kalpaiini-proteaasi pilkkoo myotiliinin lihassoluissa ja että myotiliini hajoaa pienempiin rakenneosiin proteasomireitin välityksellä. Määritimme myös ensimmäisen toiminnallisen eron normaalin ja mutatoituneen myotiliinin välillä, sillä myotilinopatioissa mutatoitunut myotiliini hajoaa huomattavasti normaalia hitaammin. Lisäksi näytimme, että mikäli myotiliinin hajoamista estetään kemikaaleilla, seurauksena on proteiinikertymiä, jotka muistuttavat potilasnäytteissä nähtäviä muutoksia. 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