C. elegans PAT-6/actopaxin plays a critical role in the assembly of integrin adhesion complexes in vivo.
BACKGROUND
The novel focal adhesion protein actopaxin includes tandem unconventional calponin homology (CH) domains and a less well-conserved N-terminal stretch. Dominant-negative studies have implicated actopaxin in focal adhesion formation.


RESULTS
PAT-6/actopaxin, the sole actopaxin homolog in C. elegans, is located in body wall muscle attachments that are in vivo homologs of focal adhesions. We show using pat-6 protein null alleles that PAT-6/actopaxin has critical nonredundant roles during attachment maturation. It is required to recruit UNC-89 and myofilaments to newly forming attachments, and also to reposition the attachments so that they form the highly ordered array of dense body and M line attachments that are characteristic of mature muscle cells. PAT-6/actopaxin is not required for the deposition of UNC-52/perlecan in the basal lamina, nor for the initiation of attachment assembly, including the clustering of integrin into foci and the recruitment of attachment proteins PAT-4/ILK, UNC-112, and DEB-1/vinculin from the cytosol. PAT-6/actopaxin, PAT-4/ILK, and UNC-112 are each required for the same steps during attachment assembly in vivo, consistent with the notion that they work together in multiprotein complex. Supporting this idea, PAT-4/ILK can simultaneously bind to PAT-6/actopaxin and UNC-112, forming a ternary complex, in yeast three-hybrid assays. Finally, we show that both calponin homology domains are required for PAT-6/actopaxin's critical functions during attachment assembly in vivo.


CONCLUSIONS
We show directly by loss-of-function genetics that PAT-6/actopaxin plays essential roles during the maturation of integrin-mediated muscle attachments in vivo.
Lin
Xinyi
X
Department of Cell and Structural Biology, University of Illinois at Urbana-Champaign, 601 South Goodwin Avenue, Urbana, IL 61801, USA.
Qadota
Hiroshi
H
Moerman
Donald G
DG
Williams
Benjamin D
BD
D000185:Actinin; D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D022001:Focal Adhesions; D020869:Gene Expression Profiling; D015151:Immunoblotting; D016023:Integrins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000235:genetics* / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism; D011509:Proteoglycans / Q000378:metabolism; D034622:RNA Interference; D000096985:Calponins
D000185:Actinin; D029742:Caenorhabditis elegans Proteins; D016023:Integrins; D008565:Membrane Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D011509:Proteoglycans; C486590:PARVA protein, human; D000096985:Calponins; C098932:Unc-89 protein, C elegans; C082396:unc-52 protein, C elegans