Oligomerization of the diaphanous-related formin FHOD1 requires a coiled-coil motif critical for its cytoskeletal and transcriptional activities

The diaphanous-related formin homology 2 domain containing protein 1 (FHOD1) interacts with the Rac GTPase and activates the Rho-ROCK cascade leading to the formation of actin stress fibers. Here, we report the detection of homotypic interactions of FHOD1 in the yeast two-hybrid system, by co-immunoprecipitation and co-localization in mammalian cells. A predicted coiled-coil motif C-terminal to the core FH2 domain, but not the core FH2 domain itself, was critical for self-association of FHOD1. Deletion of both the coiled-coil motif and the core FH2 domain abrogated formation of actin stress fibers and activation of transcription of the serum response element by FHOD1. In contrast, these motifs were dispensable for the physical and functional interaction of FHOD1 with Rac1. Together, these results indicate that oligomerization of FHOD1 via the coiled-coil motif is a critical parameter for its biological activities.