Abstract
Alström syndrome (ALMS) is a progressive multi-systemic disorder characterized by cone-rod dystrophy, sensorineural hearing loss, childhood obesity, insulin resistance and cardiac, renal, and hepatic dysfunction. The gene responsible for Alström syndrome, ALMS1, is ubiquitously expressed and has multiple splice variants. The protein encoded by this gene has been implicated in ciliary function, cell cycle control, and intracellular transport. To gain better insight into the pathways through which ALMS1 functions, we carried out a yeast two hybrid (Y2H) screen in several mouse tissue libraries to identify ALMS1 interacting partners. The majority of proteins found to interact with the murine carboxy-terminal end (19/32) of ALMS1 were α-actinin isoforms. Interestingly, several of the identified ALMS1 interacting partners (α-actinin 1, α-actinin 4, myosin Vb, rad50 interacting 1 and huntingtin associated protein1A) have been previously associated with endosome recycling and/or centrosome function. We examined dermal fibroblasts from human subjects bearing a disruption in ALMS1 for defects in the endocytic pathway. Fibroblasts from these patients had a lower uptake of transferrin and reduced clearance of transferrin compared to controls. Antibodies directed against ALMS1 N- and C-terminal epitopes label centrosomes and endosomal structures at the cleavage furrow of dividing MDCK cells, respectively, suggesting isoform-specific cellular functions. Our results suggest a role for ALMS1 variants in the recycling endosome pathway and give us new insights into the pathogenesis of a subset of clinical phenotypes associated with ALMS.
Highlights
Alstrom syndrome (ALMS; OMIM#203800) is a monogenic disorder characterized by a combination of features including obesity, insulin resistance, type 2 diabetes and retinal and cochlear degeneration that progress as patients age
Since the majority of mutations in both ALMS patients and mouse models reside in exons 8, 10 and 16, we used the carboxy-terminal region of mouse ALMS1 (ALMS1-C1) as bait (Fig. 1A)
To investigate whether ALMS1 may have a role in endosome recycling during cytokinesis, we examined the staining pattern of ALMS1 by using antibodies raised against the N-terminal (ALMS1-Ntr) and C-terminal (ALMS1-C) ends, respectively, in Madin-Darby Canine Kidney Epithelial (MDCK) cells undergoing late cytokinesis
Summary
Alstrom syndrome (ALMS; OMIM#203800) is a monogenic disorder characterized by a combination of features including obesity, insulin resistance, type 2 diabetes and retinal and cochlear degeneration that progress as patients age. ALMS1 is a ubiquitous protein that localizes to centrosomes and basal bodies of ciliated cells [5,6,7]. ALMS1 expresses a number of splice variants. The splicing patterns and functions of ALMS1 are not fully understood, previous studies have suggested roles for the protein in intracellular trafficking and ciliary function [6,7,8,9]. A-Actinin as well as other members of the endosome recycling pathway were identified as direct interactors with ALMS1 To gain insight into the molecular pathways in which ALMS1 is involved, we performed a yeast-twohybrid (Y2H) screen in three mouse tissue libraries using a bait specific for the murine C-terminus of ALMS1. a-Actinin as well as other members of the endosome recycling pathway were identified as direct interactors with ALMS1
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