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Vol. 15, Issue 7, 3181-3195, July 2004

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Clathrin Isoform CHC22, a Component of Neuromuscular and Myotendinous Junctions, Binds Sorting Nexin 5 and Has Increased Expression during Myogenesis and Muscle Regeneration

Mhairi C. Towler ^*, Paul A. Gleeson , Sachiko Hoshino , Paavo Rahkila , Venus Manalo ^*, Norio Ohkoshi , Charles Ordahl ^||, Robert G. Parton ^¶, and Frances M. Brodsky ^* #

^* The G.W. Hooper Foundation, Department of Microbiology and Immunology and Departments of Biopharmaceutical Sciences and Pharmaceutical Chemistry, University of California, San Francisco, California 94143-0552; The Russell Grimwade School of Biochemistry and Molecular Biology, University of Melbourne, Victoria 3010, Melbourne, Australia; Department of Neurology, Institute of Clinical Medicine, University of Tsukuba, Tsukuba City, Japan; Kuusitie 67, Fin-40800 Vaajakoski, Finland; ^|| Department of Anatomy and Cardiovascular Research Institute, University of California, San Francisco, California, 94143-0452; and ^¶ Institute for Molecular Biosciences, Center for Microscopy and Microanalysis, and School of Biomedical Sciences, University of Queensland, Brisbane 4072, Australia

Submitted March 23, 2004; Revised April 23, 2004; Accepted April 26, 2004
Monitoring Editor: Juan S. Bonifacino

The muscle isoform of clathrin heavy chain, CHC22, has 85% sequence identity to the ubiquitously expressed CHC17, yet its expression pattern and function appear to be distinct from those of well-characterized clathrin-coated vesicles. In mature muscle CHC22 is preferentially concentrated at neuromuscular and myotendinous junctions, suggesting a role at sarcolemmal contacts with extracellular matrix. During myoblast differentiation, CHC22 expression is increased, initially localized with desmin and nestin and then preferentially segregated to the poles of fused myoblasts. CHC22 expression is also increased in regenerating muscle fibers with the same time course as embryonic myosin, indicating a role in muscle repair. CHC22 binds to sorting nexin 5 through a coiled-coil domain present in both partners, which is absent in CHC17 and coincides with the region on CHC17 that binds the regulatory light-chain subunit. These differential binding data suggest a mechanism for the distinct functions of CHC22 relative to CHC17 in membrane traffic during muscle development, repair, and at neuromuscular and myotendinous junctions.

Abbreviations used: BngTx, bungarotoxin; CCVs, clathrin-coated vesicles; CHC, clathrin heavy chain; LC, light chain; ECM, extracellular matrix; GLUT4, glucose transporter 4; MTJ, myotendinous junction; NMJ, neuromuscular junction; PX, phox homology; SNX, sorting nexin.

Online version of this article contains supporting material. Online version is available at www.molbiolcell.org.

^# Corresponding author. E-mail address: fmarbro{at}itsa.ucsf.edu.

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