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

Abstract

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.

SNX15 links clathrin endocytosis to the PtdIns(3)P early endosome independent of the APPL1 endosome

“…The disordered region between the SH3 and PX domains of SNX9 directly binds CHC, possibly through non-canonical PWSAW and DWDEDW clathrin boxes, although binding is only observed in truncated and not full length SNX9 (Lundmark and Carlsson, 2003). SNX5 binds a specific clathrin isoform, CHC22, through a binding site located within residues 239-309 of the SNX5 BAR domain (Towler et al, 2004), and an inverted clathrin box, EFELL, present in the SNX-PX domains of SNX1, SNX2, SNX3 and SNX4 has been argued to facilitate clathrin binding (Skånland et al, 2009), although another study has failed to observe these associations (McGough and Cullen, 2013). The equivalent DFRKL (box 1 in SNX15) certainly plays no role in direct binding of SNX15 to CHC.…”

A loss-of-function screen reveals SNX5 and SNX6 as potential components of the mammalian retromer

“…SNX6 has previously been suggested to regulate the function of the transforming growth factor ␤ (TGF-␤) family of receptors (Parks et al, 2001), the oncogene Pim-1 (Ishibashi et al, 2001) and the translationally controlled tumor protein TCTP (Yoon et al, 2006). SNX5 has been proposed to regulate epidermal growth factor (EGF) receptor degradation (Liu et al, 2006), play a role in macropinosome formation (Kerr et al, 2006) and act as an adaptor for the clathrin isoform CHC22 (Towler et al, 2004). However, this is the first evidence providing a functional link between the two proteins and the retromer complex.…”

Huntingtin-interacting Protein 1 (Hip1) and Hip1-related Protein (Hip1R) Bind the Conserved Sequence of Clathrin Light Chains and Thereby Influence Clathrin Assembly in Vitro and Actin Distribution in Vivo

“…Human 293T cells grown on coverslips were transfected with the GFP constructs for 2 days, and prepared as described (26). Hip1R and cortactin were labeled, respectively, with monoclonal anti-Hip1R (BD Biosciences) and anti-cortactin (4F11, Upstate Biotechnology) antibodies, followed by Alexa Fluor 647-conjugated goat anti-mouse IgG (Molecular Probes).…”