| Abstract: | Solo (ARHGEF40) is a RhoA‐targeting guanine nucleotide exchange factor that regulates tensional force‐induced cytoskeletal reorganization. Solo binds to keratin 8/keratin 18 (K8/K18) filaments through multiple sites, but the roles of these interactions in the localization and mechanotransduction‐regulating function of Solo remain unclear. Here, we constructed two Solo mutants (L14R/L17R and L49R/L52R) with leucine‐to‐arginine replacements in the N‐terminal conserved region (which we termed the Solo domain) and analyzed their K18‐binding activities. These mutations markedly decreased the K18‐binding ability of the N‐terminal fragment (residues 1–329) of Solo but had no apparent effect on the K18‐binding ability of full‐length (FL) Solo. When expressed in cultured cells, wild‐type Solo‐FL showed a unique punctate localization near the ventral surface of cells and caused the reinforcement of actin filaments. In contrast, despite retaining the K18‐binding ability, the L14R/L17R and L49R/L52R mutants of Solo‐FL were diffusely distributed in the cytoplasm and barely induced actin cytoskeletal reinforcement. Furthermore, wild‐type Solo‐FL promoted traction force generation against extracellular matrices and tensional force‐induced stress fiber reinforcement, but its L14R/L17R and L49R/L52R mutants did not. These results suggest that the K18‐binding ability of the N‐terminal Solo domain is critical for the ventral localization of Solo and its function in regulating mechanotransduction. |
