Golgi bypass of ciliary proteins

Witzgall, Ralph

doi:10.1016/j.semcdb.2018.03.010

Cited by 16 publications

(14 citation statements)

References 59 publications

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“…Sstr3 mislocalisation has previously been reported in the Bbs2 À/À mouse model due to a complete failure to localise to the ciliary axoneme despite high expression levels [64]. Its localisation is known to be dependent on the BBSome complex [65]. In WT dermal fibroblasts we detected SSTR3 at the basal body, directly connecting to the ciliary axoneme, although not entering the cilium.…”

Section: Discussionsupporting

confidence: 52%

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Translational readthrough of ciliopathy genes BBS2 and ALMS1 restores protein, ciliogenesis and function in patient fibroblasts

Eintracht¹,

Forsythe

May-Simera³

et al. 2021

EBioMedicine

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Background Ciliary dysfunction underlies a range of genetic disorders collectively termed ciliopathies, for which there are no treatments available. Bardet-Biedl syndrome (BBS) is characterised by multisystemic involvement, including rod-cone dystrophy and renal abnormalities. Together with Alström syndrome (AS), they are known as the ‘obesity ciliopathies’ due to their common phenotype. Nonsense mutations are responsible for approximately 11% and 40% of BBS and AS cases, respectively. Translational readthrough inducing drugs (TRIDs) can restore full-length protein bypassing in-frame premature termination codons, and are a potential therapeutic approach for nonsense-mediated ciliopathies. Methods Patient fibroblasts harbouring nonsense mutations from two different ciliopathies (Bardet-Biedl Syndrome and Alström Syndrome) were treated with PTC124 (ataluren) or amlexanox. Following treatment, gene expression, protein levels and ciliogenesis were evaluated. The expression of intraflagellar transport protein IFT88 and G-protein coupled receptor SSTR3 was investigated as a readout of ciliary function. Findings mRNA expression was significantly increased in amlexanox-treated patient fibroblasts, and full-length BBS2 or ALMS1 protein expression was restored in PTC124- and amlexanox-treated fibroblasts. Treatment with TRIDs significantly improved ciliogenesis defects in BBS2 Y24*/R275* fibroblasts. Treatment recovered IFT88 expression and corrected SSTR3 mislocalisation in BBS2 Y24*/R275* and ALMS1 S1645*/S1645* fibroblasts, suggesting rescue of ciliary function. Interpretation The recovery of full-length BBS2 and ALMS1 expression and correction of anatomical and functional ciliary defects in BBS2 Y24*/R275* and ALMS1 S1645*/S1645* fibroblasts suggest TRIDs are a potential therapeutic option for the treatment of nonsense-mediated ciliopathies.

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Section: Discussionsupporting

confidence: 52%

“…Sstr3 mislocalisation has previously been reported in the Bbs2 −/− mouse model due to a complete failure to localise to the ciliary axoneme despite high expression levels [64] . Its localisation is known to be dependent on the BBSome complex [65] .…”

Section: Discussionmentioning

confidence: 99%

Translational readthrough of ciliopathy genes BBS2 and ALMS1 restores protein, ciliogenesis and function in patient fibroblasts

Eintracht¹,

Forsythe

May-Simera³

et al. 2021

EBioMedicine

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“…In polarized epithelial cells a primary cilium protruding from the apical membrane is anchored at the basal body, a structure consisting of the mother and daughter centrioles of the centrosome that during cell polarization relocated to the apical membrane, losing most of its pericentriolar material and ability to nucleate MTs (Figure 5C). Notably, newly synthesized proteins that are delivered to the ciliary membrane in a Rab11-, Rab8- and exocyst-dependent manner frequently follow pathways that bypass the Golgi stacks (Tian et al, 2014; Bernabé-Rubio and Alonso, 2017; Gilder et al, 2018; Witzgall, 2018). This transport is likely to involve a circular membrane compartment surrounding the base of the cilium that contains Rab11 and the IC/ cis -Golgi protein GM130 (Kim et al, 2010; He et al, 2012; Stoops et al, 2015).…”

Section: Golgi Remodeling By Differentiated Cellsmentioning

confidence: 99%

A New Look at the Functional Organization of the Golgi Ribbon

Saraste

Prydz

2019

Front. Cell Dev. Biol.

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A characteristic feature of vertebrate cells is a Golgi ribbon consisting of multiple cisternal stacks connected into a single-copy organelle next to the centrosome. Despite numerous studies, the mechanisms that link the stacks together and the functional significance of ribbon formation remain poorly understood. Nevertheless, these questions are of considerable interest, since there is increasing evidence that Golgi fragmentation – the unlinking of the stacks in the ribbon – is intimately connected not only to normal physiological processes, such as cell division and migration, but also to pathological states, including neurodegeneration and cancer. Challenging a commonly held view that ribbon architecture involves the formation of homotypic tubular bridges between the Golgi stacks, we present an alternative model, based on direct interaction between the biosynthetic (pre-Golgi) and endocytic (post-Golgi) membrane networks and their connection with the centrosome. We propose that the central domains of these permanent pre- and post-Golgi networks function together in the biogenesis and maintenance of the more transient Golgi stacks, and thereby establish “linker compartments” that dynamically join the stacks together. This model provides insight into the reversible fragmentation of the Golgi ribbon that takes place in dividing and migrating cells and its regulation along a cell surface – Golgi – centrosome axis. Moreover, it helps to understand transport pathways that either traverse or bypass the Golgi stacks and the positioning of the Golgi apparatus in differentiated neuronal, epithelial, and muscle cells.

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“…Alternatively, given the broader distribution of the ER (Fig. 4a), the receptors might follow a Golgi-independent route from the ER to the sensory compartment, as described for other cilia membrane proteins [38]. Regardless, neither EGFP:IR8a ∆CREL nor EGFP:IR8a N669Q displayed Golgi localisation, indicating that their inability to localise to sensory cilia is not due to transport arrest in the Golgi.…”

Section: Resultsmentioning

confidence: 90%

In vivo assembly and trafficking of olfactory Ionotropic Receptors

et al. 2019

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Background Ionotropic receptors (IRs) are a large, divergent subfamily of ionotropic glutamate receptors (iGluRs) that are expressed in diverse peripheral sensory neurons and function in olfaction, taste, hygrosensation and thermosensation. Analogous to the cell biological properties of their synaptic iGluR ancestors, IRs are thought to form heteromeric complexes that localise to the ciliated dendrites of sensory neurons. IR complexes are composed of selectively expressed ‘tuning’ receptors and one of two broadly expressed co-receptors (IR8a or IR25a). While the extracellular ligand-binding domain (LBD) of tuning IRs is likely to define the stimulus specificity of the complex, the role of this domain in co-receptors is unclear. Results We identify a sequence in the co-receptor LBD, the ‘co-receptor extra loop’ (CREL), which is conserved across IR8a and IR25a orthologues but not present in either tuning IRs or iGluRs. The CREL contains a single predicted N -glycosylation site, which we show bears a sugar modification in recombinantly expressed IR8a. Using the Drosophila olfactory system as an in vivo model, we find that a transgenically encoded IR8a mutant in which the CREL cannot be N -glycosylated is impaired in localisation to cilia in some, though not all, populations of sensory neurons expressing different tuning IRs. This defect can be complemented by the presence of endogenous wild-type IR8a, indicating that IR complexes contain at least two IR8a subunits and that this post-translational modification is dispensable for protein folding or complex assembly. Analysis of the subcellular distribution of the mutant protein suggests that its absence from sensory cilia is due to a failure in exit from the endoplasmic reticulum. Protein modelling and in vivo analysis of tuning IR and co-receptor subunit interactions by a fluorescent protein fragment complementation assay reveal that the CREL N -glycosylation site is likely to be located on the external face of a heterotetrameric IR complex. Conclusions Our data reveal an important role for the IR co-receptor LBD in control of intracellular transport, provide novel insights into the stoichiometry and assembly of IR complexes and uncover an unexpected heterogeneity in the trafficking regulation of this sensory receptor family. Electronic supplementary material The online version of this article (10.1186/s12915-019-0651-7) contains supplementary material, which is available to authorized users.

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Golgi bypass of ciliary proteins

Cited by 16 publications

References 59 publications

Translational readthrough of ciliopathy genes BBS2 and ALMS1 restores protein, ciliogenesis and function in patient fibroblasts

Translational readthrough of ciliopathy genes BBS2 and ALMS1 restores protein, ciliogenesis and function in patient fibroblasts

A New Look at the Functional Organization of the Golgi Ribbon

In vivo assembly and trafficking of olfactory Ionotropic Receptors

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