VCP binding influences intracellular distribution of the slow Wallerian degeneration protein, Wld^S

Wallerian degeneration slow (Wld^S) mice express a chimeric protein that delays axonal degeneration. The N-terminal domain (N70), which is essential for axonal protection in vivo, binds valosin-containing protein (VCP) and targets both Wld^S and VCP to discrete nuclear foci. We characterized the formation, composition and localization of these potentially important foci. Missense mutations show that the N-terminal sixteen residues (N16) of Wld^S are essential for both VCP binding and targeting Wld^S to nuclear foci. Removing N16 abolishes foci, and VCP binding sequences from ataxin-3 or HrdI restore them. In vitro, these puncta co-localize with proteasome subunits. In vivo, Wld^S assumes a range of nuclear distribution patterns, including puncta, and its neuronal expression and intranuclear distribution is region-specific and varies between spontaneous and transgenic Wld^S models. We conclude that VCP influences Wld^S intracellular distribution, and thus potentially its function, by binding within the N70 domain required for axon protection.