Clarin-1, encoded by the Usher Syndrome III causative gene, forms a membranous microdomain: possible role of clarin-1 in organizing the actin cytoskeleton.
Clarin-1 is the protein product encoded by the gene mutated in Usher syndrome III. Although the molecular function of clarin-1 is unknown, its primary structure predicts four transmembrane domains similar to a large family of membrane proteins that include tetraspanins. Here we investigated the role of clarin-1 by using heterologous expression and in vivo model systems. When expressed in HEK293 cells, clarin-1 localized to the plasma membrane and concentrated in low density compartments distinct from lipid rafts. Clarin-1 reorganized actin filament structures and induced lamellipodia. This actin-reorganizing function was absent in the modified protein encoded by the most prevalent North American Usher syndrome III mutation, the N48K form of clarin-1 deficient in N-linked glycosylation. Proteomics analyses revealed a number of clarin-1-interacting proteins involved in cell-cell adhesion, focal adhesions, cell migration, tight junctions, and regulation of the actin cytoskeleton. Consistent with the hypothesized role of clarin-1 in actin organization, F-actin-enriched stereocilia of auditory hair cells evidenced structural disorganization in Clrn1(-/-) mice. These observations suggest a possible role for clarin-1 in the regulation and homeostasis of actin filaments, and link clarin-1 to the interactive network of Usher syndrome gene products.
Tian
Guilian
G
Department of Pharmacology, Case Western Reserve University, Cleveland, Ohio 44106-4965, USA.
Zhou
Yun
Y
Hajkova
Dagmar
D
Miyagi
Masaru
M
Dinculescu
Astra
A
Hauswirth
William W
WW
Palczewski
Krzysztof
K
Geng
Ruishuang
R
Alagramam
Kumar N
KN
Isosomppi
Juha
J
Sankila
Eeva-Marja
EM
Flannery
John G
JG
Imanishi
Yoshikazu
Y
D000199:Actins / Q000737:chemistry*; D000818:Animals; D002448:Cell Adhesion; D002462:Cell Membrane / Q000378:metabolism; D022001:Focal Adhesions / Q000378:metabolism; D006198:Hair Cells, Auditory / Q000378:metabolism; D006801:Humans; D021962:Membrane Microdomains / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D017434:Protein Structure, Tertiary; D014415:Tunicamycin / Q000494:pharmacology; D052245:Usher Syndromes / Q000378:metabolism*
D000199:Actins; C437067:CLRN1 protein, human; D008565:Membrane Proteins; D014415:Tunicamycin