C. elegans PAT-4/ILK Functions as an Adaptor Protein within Integrin Adhesion Complexes

BACKGROUND Mammalian integrin-linked kinase (ILK) was identified in a yeast two-hybrid screen for proteins binding the integrin beta(1) subunit cytoplasmic domain. ILK has been implicated in integrin-mediated signaling and is also an adaptor within integrin-associated cytoskeletal complexes. RESULTS We identified the C. elegans pat-4 gene in previous genetic screens for mutants unable to assemble integrin-mediated muscle cell attachments. Here, we report that pat-4 encodes the sole C. elegans homolog of ILK. In pat-4 null mutants, embryonic muscle cells form integrin foci, but the subsequent recruitment of vinculin and UNC-89 as well as actin and myosin filaments to these in vivo focal adhesion analogs is blocked. Conversely, PAT-4/ILK requires the ECM component UNC-52/perlecan, the transmembrane protein integrin, and the novel cytoplasmic attachment protein UNC-112 to be properly recruited to nascent attachments. Transgenically expressed "kinase-dead" ILK fully rescues pat-4 loss-of-function mutants. We also identify UNC-112 as a new binding partner for ILK. CONCLUSIONS Our data strengthens the emerging view that ILK functions primarily as an adaptor protein within integrin adhesion complexes and identifies UNC-112 as a new ILK binding partner.