title: The Joubert syndrome-associated missense mutation (V443D) in the Abelson-helper integration site 1 (AHI1) protein alters its localization and protein-protein interactions.
abstract: BACKGROUND
  Missense mutations in AHI1 result in the neurodevelopmental ciliopathy called Joubert syndrome.
  
  
  RESULTS
  Mutations in AHI1 decrease cilia formation, alter its localization and stability, and change its binding to HAP1 and NPHP1.
  
  
  CONCLUSIONS
  Mutations in AHI1 affect ciliogenesis, AHI1 protein localization, and AHI1-protein interactions.
  
  
  CONCLUSIONS
  This study begins to describe how missense mutations in AHI1 can cause Joubert syndrome. Mutations in AHI1 cause Joubert syndrome (JBTS), a neurodevelopmental ciliopathy, characterized by midbrain-hindbrain malformations and motor/cognitive deficits. Here, we show that primary cilia (PC) formation is decreased in fibroblasts from individuals with JBTS and AHI1 mutations. Most missense mutations in AHI1, causing JBTS, occur in known protein domains, however, a common V443D mutation in AHI1 is found in a region with no known protein motifs. We show that cells transfected with AHI1-V443D, or a new JBTS-causing mutation, AHI1-R351L, have aberrant localization of AHI1 at the basal bodies of PC and at cell-cell junctions, likely through decreased binding of mutant AHI1 to NPHP1 (another JBTS-causing protein). The AHI1-V443D mutation causes decreased AHI1 stability because there is a 50% reduction in AHI1-V443D protein levels compared with wild type AHI1. Huntingtin-associated protein-1 (Hap1) is a regulatory protein that binds Ahi1, and Hap1 knock-out mice have been reported to have JBTS-like phenotypes, suggesting a role for Hap1 in ciliogenesis. Fibroblasts and neurons with Hap1 deficiency form PC with normal growth factor-induced ciliary signaling, indicating that the Hap1 JBTS phenotype is likely not through effects at PC. These results also suggest that the binding of Ahi1 and Hap1 may not be critical for ciliary function. However, we show that HAP1 has decreased binding to AHI1-V443D indicating that this altered binding could be responsible for the JBTS-like phenotype through an unknown pathway. Thus, these JBTS-associated missense mutations alter their subcellular distribution and protein interactions, compromising functions of AHI1 in cell polarity and cilium-mediated signaling, thereby contributing to JBTS.
authors.affiliation: Center for Neuropharmacology and Neuroscience, Albany Medical College, Albany, New York 12208, USA.
authors.forename: Karina
authors.initials: K
authors.lastname: Tuz
authors.forename: Yi-Chun
authors.initials: YC
authors.lastname: Hsiao
authors.forename: Oscar
authors.initials: O
authors.lastname: Juárez
authors.forename: Bingxing
authors.initials: B
authors.lastname: Shi
authors.forename: Erin Y
authors.initials: EY
authors.lastname: Harmon
authors.forename: Ian G
authors.initials: IG
authors.lastname: Phelps
authors.forename: Michelle R
authors.initials: MR
authors.lastname: Lennartz
authors.forename: Ian A
authors.initials: IA
authors.lastname: Glass
authors.forename: Dan
authors.initials: D
authors.lastname: Doherty
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Ferland
mesh_terms: D000015:Abnormalities, Multiple; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics* / Q000378:metabolism; D033942:Adaptor Proteins, Vesicular Transport; D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism / Q000473:pathology; D016764:Cell Polarity; D002478:Cells, Cultured; D002526:Cerebellar Diseases / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002531:Cerebellum / Q000002:abnormalities; D002923:Cilia / Q000378:metabolism / Q000473:pathology; D017124:Conserved Sequence; D003598:Cytoskeletal Proteins; D005124:Eye Abnormalities / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007365:Intercellular Junctions / Q000378:metabolism; D052177:Kidney Diseases, Cystic / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D009419:Nerve Tissue Proteins / Q000378:metabolism; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D060066:Protein Interaction Maps; D055550:Protein Stability; D021381:Protein Transport; D012160:Retina / Q000002:abnormalities / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques
chemical_list: C487178:AHI1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D003598:Cytoskeletal Proteins; C096896:HAP1 protein, human; D008565:Membrane Proteins; C108725:NPHP1 protein, human; D009419:Nerve Tissue Proteins
keywords: AHI1; Cilia; HAP1; Joubert Syndrome; Neurodevelopment; Neurological Diseases; Neurons; Protein Complexes