Abstract
Formin homology‐2‐domain containing protein 1 (FHOD1) regulates gene transcription, actin‐cytoskeleton structure, and cell migration. To gain insight into the mechanisms by which FHOD1 mediates these diverse activities, a yeast‐two‐hybrid screen was performed to identify FHOD1‐binding proteins. Three proteins specifically interacted with the carboxy‐terminal two‐thirds of FHOD1, which includes the FH1, FH2, and diaphanous activating domains (DAD). The newly identified FHOD1‐binding proteins are protein kinase C binding protein 1 (PRKCBP1), cyclophilin B, and an isoform of WASP‐interacting SH3‐domain protein/diaphanous‐interacting protein 1 (WISH/DIP1), named WISH‐B. The proline‐rich FH1 domain of FHOD1 was sufficient to interact with the central portion of PRKCP1 and full‐length cyclophilin B. The FH1 domain also interacted with full‐length WISH‐B, but the extreme amino‐terminus was sufficient to associate with WISH‐B as well. WISH‐B altered the solubility of FHOD1 in vitro and a truncation mutant containing the amino‐terminal 227 residues of WISH‐B disrupted FHOD1‐induced stress fibers. WISH‐B did not affect FHOD1‐induced gene transcription through the serum response factor (SRF) recognition site on the skeletal α actin promoter (SkA). However, stabilization of F‐actin prevented FHOD1 dependent activation of this promoter in presence of high, but not low serum concentrations. Thus, the identification of a new FHOD1‐binding protein provides insight into the mechanisms by which FHOD1 regulates actin polymerization and transcription. © 2004 Wiley‐Liss, Inc.