Search tips
Search criteria

Results 1-13 (13)

Clipboard (0)

Select a Filter Below

Year of Publication
Document Types
author:("Hu, jinhua")
1.  Molecular views of Arf-like small GTPases in cilia and ciliopathies 
Experimental cell research  2013;319(15):2316-2322.
The primary cilia are microtubule-based organelles that protrude from most of the eukaryotic cells. Recognized as the cell’s antenna, primary cilia function as a signaling hub for many physiologically and developmentally important signaling cascades. Ciliary dysfunction causes a wide spectrum of syndromic human genetic diseases collectively termed "ciliopathies”. Mounting evidences have shown that various small GTPases have been implicated in the context of cilia as well as human ciliopathies. However, how these small GTPases affect cilia formation and function remains poorly understood. Here we review and discuss the ciliary role of three Arf-like small GTPases (Arls), Arl3, Arl6, and Arl13b.
PMCID: PMC3742637  PMID: 23548655
2.  The emerging role of Arf/Arl Small GTPases in Cilia and Ciliopathies 
Journal of cellular biochemistry  2012;113(7):2201-2207.
Once overlooked as an evolutionary vestige, the primary cilium has recently been the focus of intensive studies. Mounting data show that this organelle is a hub for various signaling pathways during vertebrate embryonic development and pattern formation. However, how cilia form and how cilia execute the sensory function still remain poorly understood. Cilia dysfunction is correlated with a wide spectrum of human diseases, now termed ciliopathies. Various small GTPases, including the members in Arf/Arl, Rab, and Ran subfamilies, have been implicated in cilia formation and/or function. Here we review and discuss the role of one particular group of small GTPase, Arf/Arl, in the context of cilia and ciliopathy.
PMCID: PMC4133128  PMID: 22389062
Arf/Arl; cilia; ciliopathies
3.  Transition fibre protein FBF1 is required for the ciliary entry of assembled intraflagellar transport complexes 
Nature communications  2013;4:10.1038/ncomms3750.
Sensory organelle cilia play critical roles in mammalian embryonic development and tissue homeostasis. Intraflagellar transport (IFT) machinery is required for the assembly and maintenance of cilia. Yet how this large complex passes through the size-dependent barrier at the ciliary base remains enigmatic. Here we report that FBF1, a highly conserved transition fibre protein, is required for the ciliary import of assembled IFT particles at the cilia base. We cloned dyf-19, the C. elegans homolog of human FBF1, in a whole-genome screen for ciliogenesis mutants. DYF-19 localizes specifically to transition fibres and interacts directly with the IFT-B component DYF-11/IFT54. Although not a structural component of transition fibres, DYF-19 is essential for the transit of assembled IFT particles through the ciliary base. Furthermore, we found that human FBF1 shares conserved localization and function with its worm counterpart. We conclude that FBF1 is a key functional transition fibre component that facilitates the ciliary entry of assembled IFT machinery.
PMCID: PMC3856926  PMID: 24231678
4.  Small GTPases and cilia 
Protein & cell  2011;2(1):10.1007/s13238-011-1004-7.
Small GTPases are key molecular switches that bind and hydrolyze GTP in diverse membrane- and cytoskeleton-related cellular processes. Recently, mounting evidences have highlighted the role of various small GTPases, including the members in Arf/Arl, Rab, and Ran subfamilies, in cilia formation and function. Once overlooked as an evolutionary vestige, the primary cilium has attracted more and more attention in last decade because of its role in sensing various extracellular signals and the association between cilia dysfunction and a wide spectrum of human diseases, now called ciliopathies. Here we review recent advances about the function of small GTPases in the context of cilia, and the correlation between the functional impairment of small GTPases and ciliopathies. Understanding of these cellular processes is of fundamental importance for broadening our view of cilia development and function in normal and pathological states and for providing valuable insights into the role of various small GTPases in disease processes, and their potential as therapeutic targets.
PMCID: PMC3858892  PMID: 21337006
Small GTPase; cilia; ciliopathy
5.  SUMOylation of the small GTPase ARL-13 promotes ciliary targeting of sensory receptors 
The Journal of Cell Biology  2012;199(4):589-598.
SUMOylation of the small GTPase ARL13 is required for the proper ciliary targeting of sensory receptors and corresponding sensory functions.
Primary cilia serve as cellular antenna for various sensory signaling pathways. However, how the sensory receptors are properly targeted to the ciliary surface remains poorly understood. Here, we show that UBC-9, the sole E2 small ubiquitin-like modifier (SUMO)-conjugating enzyme, physically interacts with and SUMOylates the C terminus of small GTPase ARL-13, the worm orthologue of ARL13B that mutated in ciliopathy Joubert syndrome. Mutations that totally abolish the SUMOylation of ARL-13 do not affect its established role in ciliogenesis, but fail to regulate the proper ciliary targeting of various sensory receptors and consequently compromise the corresponding sensory functions. Conversely, constitutively SUMOylated ARL-13 fully rescues all ciliary defects of arl-13–null animals. Furthermore, SUMOylation modification of human ARL13B is required for the ciliary entry of polycystin-2, the protein mutated in autosomal dominant polycystic kidney disease. Our data reveal a novel but conserved role for the SUMOylation modification of ciliary small GTPase ARL13B in specifically regulating the proper ciliary targeting of various sensory receptors.
PMCID: PMC3494855  PMID: 23128241
6.  The BBSome controls IFT assembly and turnaround in cilia 
Nature cell biology  2012;14(9):950-957.
The bidirectional movement of intraflagellar transport (IFT) particles, which are composed of motors, IFT-A and IFT-B subcomplexes, and cargos, is required for cilia biogenesis and signaling 1, 2. A successful IFT cycle depends on the massive IFT particle to be properly assembled at the ciliary base and turned around from anterograde to retrograde transport at the ciliary tip. However, how IFT assembly and turnaround are regulated in vivo remains elusive. From a whole-genome mutagenesis screen in C. elegans, we identified two hypomorphic mutations in dyf-2 and bbs-1 as the only mutants showing normal anterograde IFT transport but defective IFT turnaround at the ciliary tip. Further analyses revealed that the BBSome 3, 4, a group of conserved proteins affected in human Bardet-Biedl syndrome (BBS) 5, assembles IFT complexes at the ciliary base, then binds to anterograde IFT particle in a DYF-2- (an ortholog of human WDR19) and BBS-1-dependent manner, and lastly reaches the ciliary tip to regulate proper IFT recycling. Our results unravel the BBSome as the key player regulating IFT assembly and turnaround in cilia.
PMCID: PMC3434251  PMID: 22922713
8.  An association between type Iγ PI4P 5-kinase and Exo70 directs E-cadherin clustering and epithelial polarization 
Molecular Biology of the Cell  2012;23(1):87-98.
Type Iγ phosphatidylinositol-4-phosphate 5-kinase and Exo70 cooperate in the directed targeting of E-cadherin on the plasma membrane to newly formed adherens junctions. This promotes the regional accumulation of E-cadherin, expansion and maturation of adherens junctions, and differentiation of the lateral membrane domain.
E-Cadherin–mediated formation of adherens junctions (AJs) is essential for the morphogenesis of epithelial cells. However, the mechanisms underlying E-cadherin clustering and AJ maturation are not fully understood. Here we report that type Iγ phosphatidylinositol-4-phosphate 5-kinase (PIPKIγ) associates with the exocyst via a direct interaction with Exo70, the exocyst subunit that guides the polarized targeting of exocyst to the plasma membrane. By means of this interaction, PIPKIγ mediates the association between E-cadherin and Exo70 and determines the targeting of Exo70 to AJs. Further investigation revealed that Exo70 is necessary for clustering of E-cadherin on the plasma membrane and extension of nascent E-cadherin adhesions, which are critical for the maturation of cohesive AJs. In addition, we observed phosphatidylinositol-4,5-bisphosphate (PI4,5P2) accumulation at E-cadherin clusters during the assembly of E-cadherin adhesions. PIPKIγ-generated PI4,5P2 is required for recruiting Exo70 to newly formed E-cadherin junctions and facilitates the assembly and maturation of AJs. These results support a model in which PIPKIγ and PIPKIγ-generated PI4,5P2 pools at nascent E-cadherin contacts cue Exo70 targeting and orient the tethering of exocyst-associated E-cadherin. This could be an important mechanism that regulates E-cadherin clustering and AJ maturation, which is essential for the establishment of solid, polarized epithelial structures.
PMCID: PMC3248907  PMID: 22049025
9.  Candidate exome capture identifies mutation of SDCCAG8 as the cause of a retinal-renal ciliopathy 
Nature genetics  2010;42(10):840-850.
Nephronophthisis-related ciliopathies (NPHP-RC) are recessive disorders featuring dysplasia or degeneration preferentially in kidney, retina, and cerebellum. Here we combine homozygosity mapping with candidate gene analysis by performing “ciliopathy candidate exome capture” followed by massively-parallel sequencing. We detect 12 different truncating mutations of SDCCAG8 in 10 NPHP-RC families. We demonstrate that SDCCAG8 is localized at both centrioles and directly interacts with NPHP-RC-associated OFD1. Depletion of sdccag8 causes kidney cysts and a body axis defect in zebrafish and induces cell polarity defects in 3D renal cell cultures. This work identifies SDCCAG8 loss of function as a novel cause of a retinal-renal ciliopathy and validates exome capture analysis for broadly heterogeneous single-gene disorders.
PMCID: PMC2947620  PMID: 20835237
10.  The small GTPases ARL-13 and ARL-3 coordinate intraflagellar transport and ciliogenesis 
The Journal of Cell Biology  2010;189(6):1039-1051.
Cilia intraflagellar transport and ciliogenesis are regulated by two small GTPases that maintain binding between IFT subcomplexes.
Intraflagellar transport (IFT) machinery mediates the bidirectional movement of cargos that are required for the assembly and maintenance of cilia. However, little is known about how IFT is regulated in vivo. In this study, we show that the small guanosine triphosphatase (GTPase) adenosine diphosphate ribosylation factor–like protein 13 (ARL-13) encoded by the Caenorhabditis elegans homologue of the human Joubert syndrome causal gene ARL13B, localizes exclusively to the doublet segment of the cilium. arl-13 mutants have shortened cilia with various ultrastructural deformities and a disrupted association between IFT subcomplexes A and B. Intriguingly, depletion of ARL-3, another ciliary small GTPase, partially suppresses ciliogenesis defects in arl-13 mutants by indirectly restoring binding between IFT subcomplexes A and B. Rescue of arl-13 mutants by ARL-3 depletion is mediated by an HDAC6 deacetylase-dependent pathway. Thus, we propose that two conserved small GTPases, ARL-13 and ARL-3, coordinate to regulate IFT and that perturbing this balance results in cilia deformation.
PMCID: PMC2886347  PMID: 20530210
11.  STAM and Hrs Down-Regulate Ciliary TRP Receptors 
Molecular Biology of the Cell  2007;18(9):3277-3289.
Cilia are endowed with membrane receptors, channels, and signaling components whose localization and function must be tightly controlled. In primary cilia of mammalian kidney epithelia and sensory cilia of Caenorhabditis elegans neurons, polycystin-1 (PC1) and transient receptor polycystin-2 channel (TRPP2 or PC2), function together as a mechanosensory receptor-channel complex. Despite the importance of the polycystins in sensory transduction, the mechanisms that regulate polycystin activity and localization, or ciliary membrane receptors in general, remain poorly understood. We demonstrate that signal transduction adaptor molecule STAM-1A interacts with C. elegans LOV-1 (PC1), and that STAM functions with hepatocyte growth factor–regulated tyrosine kinase substrate (Hrs) on early endosomes to direct the LOV-1-PKD-2 complex for lysosomal degradation. In a stam-1 mutant, both LOV-1 and PKD-2 improperly accumulate at the ciliary base. Conversely, overexpression of STAM or Hrs promotes the removal of PKD-2 from cilia, culminating in sensory behavioral defects. These data reveal that the STAM-Hrs complex, which down-regulates ligand-activated growth factor receptors from the cell surface of yeast and mammalian cells, also regulates the localization and signaling of a ciliary PC1 receptor-TRPP2 complex.
PMCID: PMC1951776  PMID: 17581863
12.  Casein Kinase II and Calcineurin Modulate TRPP Function and Ciliary LocalizationD⃞ 
Molecular Biology of the Cell  2006;17(5):2200-2211.
Cilia serve as sensory devices in a diversity of organisms and their defects contribute to many human diseases. In primary cilia of kidney cells, the transient receptor potential polycystin (TRPP) channels polycystin-1 (PC-1) and polycystin-2 (PC-2) act as a mechanosensitive channel, with defects resulting in autosomal dominant polycystic kidney disease. In sensory cilia of Caenorhabditis elegans male-specific neurons, the TRPPs LOV-1 and PKD-2 are required for mating behavior. The mechanisms regulating TRPP ciliary localization and function are largely unknown. We identified the regulatory subunit of the serine-threonine casein kinase II (CK2) as a binding partner of LOV-1 and human PC-1. CK2 and the calcineurin phosphatase TAX-6 modulate male mating behavior and PKD-2 ciliary localization. The phospho-defective mutant PKD-2S534A localizes to cilia, whereas a phospho-mimetic PKD-2S534D mutant is largely absent from cilia. Calcineurin is required for PKD-2 ciliary localization, but is not essential for ciliary gene expression, ciliogenesis, or localization of cilium structural components. This unanticipated function of calcineurin may be important for regulating ciliary protein localization. A dynamic phosphorylation-dephosphorylation cycle may represent a mechanism for modulating TRPP activity, cellular sensation, and ciliary protein localization.
PMCID: PMC1446073  PMID: 16481400
13.  ATP-2 Interacts with the PLAT Domain of LOV-1 and Is Involved in Caenorhabditis elegans Polycystin Signaling 
Molecular Biology of the Cell  2005;16(2):458-469.
Caenorhabditis elegans is a powerful model to study the molecular basis of autosomal dominant polycystic kidney disease (ADPKD). ADPKD is caused by mutations in the polycystic kidney disease (PKD)1 or PKD2 gene, encoding polycystin (PC)-1 or PC-2, respectively. The C. elegans polycystins LOV-1 and PKD-2 are required for male mating behaviors and are localized to sensory cilia. The function of the evolutionarily conserved polycystin/lipoxygenase/α-toxin (PLAT) domain found in all PC-1 family members remains an enigma. Here, we report that ATP-2, the β subunit of the ATP synthase, physically associates with the LOV-1 PLAT domain and that this interaction is evolutionarily conserved. In addition to the expected mitochondria localization, ATP-2 and other ATP synthase components colocalize with LOV-1 and PKD-2 in cilia. Disrupting the function of the ATP synthase or overexpression of atp-2 results in a male mating behavior defect. We further show that atp-2, lov-1, and pkd-2 act in the same molecular pathway. We propose that the ciliary localized ATP synthase may play a previously unsuspected role in polycystin signaling.
PMCID: PMC545878  PMID: 15563610

Results 1-13 (13)