title: Alix protein is substrate of Ozz-E3 ligase and modulates actin remodeling in skeletal muscle.
abstract: Alix/AIP1 is a multifunctional adaptor protein that participates in basic cellular processes, including membrane trafficking and actin cytoskeleton assembly, by binding selectively to a variety of partner proteins. However, the mechanisms regulating Alix turnover, subcellular distribution, and function in muscle cells are unknown. We now report that Alix is expressed in skeletal muscle throughout myogenic differentiation. In myotubes, a specific pool of Alix colocalizes with Ozz, the substrate-binding component of the muscle-specific ubiquitin ligase complex Ozz-E3. We found that interaction of the two endogenous proteins in the differentiated muscle fibers changes Alix conformation and promotes its ubiquitination. This in turn regulates the levels of the protein in specific subcompartments, in particular the one containing the actin polymerization factor cortactin. In Ozz(-/-) myotubes, the levels of filamentous (F)-actin is perturbed, and Alix accumulates in large puncta positive for cortactin. In line with this observation, we show that the knockdown of Alix expression in C2C12 muscle cells affects the amount and distribution of F-actin, which consequently leads to changes in cell morphology, impaired formation of sarcolemmal protrusions, and defective cell motility. These findings suggest that the Ozz-E3 ligase regulates Alix at sites where the actin cytoskeleton undergoes remodeling.
authors.affiliation: Institute of Biomedicine and Molecular Immunology, National Research Council, 90146 Palermo, Italy. bongiovanni@ibim.cnr.it
authors.forename: Antonella
authors.initials: A
authors.lastname: Bongiovanni
authors.forename: Daniele P
authors.initials: DP
authors.lastname: Romancino
authors.forename: Yvan
authors.initials: Y
authors.lastname: Campos
authors.forename: Gaetano
authors.initials: G
authors.lastname: Paterniti
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Qiu
authors.forename: Simon
authors.initials: S
authors.lastname: Moshiach
authors.forename: Valentina
authors.initials: V
authors.lastname: Di Felice
authors.forename: Naja
authors.initials: N
authors.lastname: Vergani
authors.forename: Duran
authors.initials: D
authors.lastname: Ustek
authors.forename: Alessandra
authors.initials: A
authors.lastname: d'Azzo
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002448:Cell Adhesion; D002460:Cell Line; D002465:Cell Movement; D051356:Cortactin / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D021381:Protein Transport; D011554:Pseudopodia / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D002135:Calcium-Binding Proteins; D051356:Cortactin; C482861:Neurl2 protein, mouse; C492144:Pdcd6ip protein, mouse; D012097:Repressor Proteins; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases