title: An isoform of GTPase regulator DOCK4 localizes to the stereocilia in the inner ear and binds to harmonin (USH1C).
abstract: The driving forces for the regulation of cell morphology are the Rho family GTPases that coordinate the assembly of the actin cytoskeleton. This dynamic feature is a result of tight coupling between the cytoskeleton and signal transduction and is facilitated by actin-binding proteins (ABPs). Mutations in the actin bundling and PDZ domain-containing protein harmonin are the causes of Usher syndrome type 1C (USH1C), a syndrome of congenital deafness and progressive blindness, as well as certain forms of non-syndromic deafness. Here, we have used the yeast two-hybrid assay to isolate molecular partners of harmonin and identified DOCK4, an unconventional guanine exchange factor for the Rho family of guanosine triphosphatases (Rho GEF GTPases), as a protein interacting with harmonin. Detailed molecular analysis revealed that a novel DOCK4 isoform (DOCK4-Ex49) is expressed in the brain, eye and inner ear tissues. We have further provided evidence that the DOCK4-Ex49 binds to nucleotide free Rac as effectively as DOCK2 and DOCK4 and it is a potent Rac activator. By immunostaining using a peptide antibody specific to DOCK4-Ex49, we showed its localization in the inner ear within the hair bundles along the stereocilia (SC). Together, our data indicate a possible Rac-DOCK4-ABP harmonin-activated signaling pathway in regulating actin cytoskeleton organization in stereocilia.
authors.affiliation: Department of Otolaryngology, University of Miami, Miami, FL 33101, USA.
authors.forename: D
authors.initials: D
authors.lastname: Yan
authors.forename: F
authors.initials: F
authors.lastname: Li
authors.forename: M L
authors.initials: ML
authors.lastname: Hall
authors.forename: C
authors.initials: C
authors.lastname: Sage
authors.forename: W-H
authors.initials: WH
authors.lastname: Hu
authors.forename: Cosmas
authors.initials: C
authors.lastname: Giallourakis
authors.forename: Geeta
authors.initials: G
authors.lastname: Upadhyay
authors.forename: X M
authors.initials: XM
authors.lastname: Ouyang
authors.forename: L L
authors.initials: LL
authors.lastname: Du
authors.forename: John R
authors.initials: JR
authors.lastname: Bethea
authors.forename: Z Y
authors.initials: ZY
authors.lastname: Chen
authors.forename: V
authors.initials: V
authors.lastname: Yajnik
authors.forename: X Z
authors.initials: XZ
authors.lastname: Liu
mesh_terms: D000199:Actins / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002460:Cell Line; D002923:Cilia / Q000201:enzymology / Q000378:metabolism; D003598:Cytoskeletal Proteins; D003599:Cytoskeleton / Q000378:metabolism; D007758:Ear, Inner / Q000201:enzymology / Q000378:metabolism*; D005091:Exons; D020690:GTPase-Activating Proteins / Q000276:immunology / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006801:Humans; D051379:Mice; D020033:Protein Isoforms / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D020798:Two-Hybrid System Techniques; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C510122:DOCK4 protein, human; C473475:Dock4 protein, mouse; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D020033:Protein Isoforms; C118970:USH1C protein, human; C492262:Ush1c protein, mouse; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins