The Formin/Diaphanous-related Protein, FHOS, Interacts with Rac1 and Activates Transcription from the Serum Response Element

Abstract

FHOS is a member of the formin homology (FH) family of proteins and is expressed at high levels in splenic cells. FH proteins link cellular signaling pathways to the actin cytoskeleton and serum response factor-dependent transcription. In these studies, the role of FHOS in Rho family GTPase signaling pathways was analyzed. FHOS interacted with the polybasic domain in the Rac1 C terminus in a guanine nucleotideindependent manner but did not interact with RhoA, Cdc42Hs, Rac2, or Rac3. Intramolecular autoinhibitory interactions between the C terminus of FHOS and an N-terminal region partially overlapping the Rac1 interaction domain were also identified. FHOS truncation mutants lacking the N-or C-terminal autoregulatory domains stimulated transcription of a c-fos serum response element (SRE)-driven reporter. Overexpression of wild-type and mutant (N17 and V12) Rac1 proteins repressed SRE induction by the N-terminal FHOS deletion mutant but not by the C-terminal FHOS deletion mutant. Immunofluorescence studies indicated that the localization of the mutant FHOS proteins might contribute to their differential responses to Rac1. Wild-type FHOS and the N-terminal deletion mutant localized to the perinuclear region and membrane edges. In contrast, the C-terminal FHOS mutants were diffusely localized. These data suggest that FHOS induces transcription from SREs by multiple pathways and that Rac1 may influence the course of some FHOSinduced signaling events.

The mDial Formin Is Required for Neutrophil Polarization, Migration, and Activation of the LARG/RhoA/ROCK Signaling Axis during Chemotaxis

“…Thus, mDia1 effects on chemotaxis may reflect its modulation of both actin and microtubule components, a functional role already ascribed to the related formin homology domain-containing protein in relation to its regulation of HeLa cell elongation (41). Drfs such as mDia1 also control activities of several transcriptional activators (such as serum response factor and its cofactor, MAL) that regulate cytoskeletal-modulatory genes and, by extension, cytoskeletally-dependent functions, such as cell migration (14,42,43). The extent to which each of these functions enables mDia1 effects on chemotaxis requires further investigation, but the impaired capacity of mDia1 Ϫ/Ϫ neutrophils to generate and anteriorly polarize F-actin in response to chemoattractant stimuli suggests that the influence of mDia1 on neutrophil chemotaxis relates at least in part to its actin-nucleating function.…”

Riboproteomics of the Hepatitis C Virus Internal Ribosomal Entry Site

“…38 No hepatitis C virus proteins were detected in the HCV IRES affinity extract. Table 3 identifies proteins common to the HCV IRES and reversed IRES sequence extracts.…”

The Rac1 hypervariable region in targeting and signaling

“…Rac1, but not Rac2, Rac3 and RhoA, associates to FHOD1 (formin homology-2 domain containing protein) and frl (formin-related gene in leukocytes) in a nucleotide-independent manner. [97][98][99] In addition, the interaction required the Rac1 C-terminal HVR. 97 Moreover, an activated mutant of Rac1 recruites FHOD1 to membrane ruffles.…”

“…[97][98][99] In addition, the interaction required the Rac1 C-terminal HVR. 97 Moreover, an activated mutant of Rac1 recruites FHOD1 to membrane ruffles. 99 In the initial functional studies on this interaction, both active and inactive Rac1 mutants were found to reduce FHOD1-mediated activation of the SRE (Serum-Response Element), suggesting Rac1 signaling affects FHOD1 function in a complex fashion.…”

“…99 In the initial functional studies on this interaction, both active and inactive Rac1 mutants were found to reduce FHOD1-mediated activation of the SRE (Serum-Response Element), suggesting Rac1 signaling affects FHOD1 function in a complex fashion. 97 A subsequent study 98 showed that FHOD1 expression stimulates migration of melanoma cells on different substrates, but did not affect integrin expression or integrin-mediated adhesion. Moreover, expression of Rac1N17 as well as inhibition of RhoA or ROCK, inhibited the induction of action stress fibers in NIH3T3 cells by an activated mutant of FHOD1.…”