Suppressor Mutations Suggest a Surface on PAT-4 (Integrin Linked Kinase) that Interacts with UNC-112 (Kindlin) [Signal Transduction]

April 1st, 2014 by Qadota, H., Luo, Y., Matsunaga, Y., Park, A. S., Gernert, K. M., Benian, G. M.

Caenorhabditis elegans striated muscle cells attach to basement membrane and transmit the force of muscle contraction through integrin adhesion complexes. The cytoplasmic tail of β-integrin (PAT-3) is associated with a conserved four-protein complex that includes UNC-112 (kindlin), PAT-4 (integrin linked kinase), PAT-6 (α-parvin/actopaxin), and UNC-97 (PINCH). The proper localization of UNC-112 to muscle integrin adhesion sites requires PAT-4. A recent report (1) suggests a possible molecular mechanism for this requirement: that UNC-112 exists in closed inactive and open active conformations, and conversion to the open active form is promoted by binding to PAT-4(ILK). Previously, we also reported identification of a single missense mutation in UNC-112, D382V, which abolishes both binding to PAT-4, and normal localization to integrin adhesion sites in vivo. In this report, we describe isolation and characterization of PAT-4 missense mutations that permit binding with UNC-112 D382V, and place 9 affected residues on a homology model of PAT-4. These 9 residues cluster in two regions on the surface of PAT-4, do not overlap the likely binding surface for PAT-6 (α-parvin), and therefore may reside along the interaction surface of PAT-4 for UNC-112 (kindlin). We also show that one of these PAT-4 mutations restores the ability of UNC-112 D382V to localize to integrin adhesions and participate in complex formation.