SMIFH2 has effects on Formins and p53 that perturb the cell cytoskeleton

<p>Formin proteins are key regulators of the cytoskeleton involved in developmental and homeostatic programs, and human disease. For these reasons, small molecules interfering with Formins’ activity have gained increasing attention. Among them, small molecule inhibitor of Formin Homology 2 domains (SMIFH2) is often used as a pharmacological Formin blocker. Although SMIFH2 inhibits actin polymerization by Formins and affects the actin cytoskeleton, its cellular mechanism of action and target specificity remain unclear.<br>Here we show that SMIFH2 induces remodelling of actin filaments, microtubules and the Golgi complex as a result of its effects on Formins and p53.<br>We found that SMIFH2 triggers alternated depolymerization-repolymerization cycles of actin and tubulin, increases cell migration, causes scattering of the Golgi complex, and also cytotoxicity at high dose. Moreover, SMIFH2 reduces expression and activity of p53 through a post-transcriptional, proteasome-independent mechanism that influences remodelling of the cytoskeleton.<br>As the action of SMIFH2 may go beyond Formin inhibition, only short-term and low-dose SMIFH2 treatments minimize confounding effects induced by loss of p53 and cytotoxicity. </p

Initiation of lamellipodia and ruffles involves cooperation between mDia1 and the Arp2/3 complex

<p>High resolution figures accompanying the research article entitled: "<strong>Initiation of lamellipodia and ruffles involves cooperation between mDia1 and the Arp2/3 complex</strong>" published in Journal of Cell Science, september 2015 (Isogai et al., 2015; doi: 10.1242/jcs.176768)</p

Isogai et al., JCS 2015 Figure 4

<p><strong>Fig. 4. Full-length mDia1 cooperates with the Arp2/3 complex to form branched actin networks.</strong> (A) Representative Coomassie gels showing purified recombinant wild-type (WT) and mutant (MA) mDia1 (1.5 μg) (top) and WAVE2 (2 μg) (bottom). (B–E) mDia1 promotes both nucleation and elongation of linear actin filaments in the presence of profilin. (B,C) Representative frames extracted from TIRFm time-lapse imaging of actin polymerization at the indicated time and concentration of either mDia1 WT or its MA mutant. Profilin-bound actin (2.5 μM actin+5 μM profilin) was polymerized with the indicated concentration of mDia1 WT (B) or mDia1 MA (C). Scale bars: 10 μm. (D) At least ten filaments (thin lines) were tracked to determine filament length (mean±s.d., thick lines) versus time as described in the Materials and Methods. (E) Elongation rates were derived from D as described in the Materials and Methods. Scatter dot plots show average filament elongation rates. ****P<0.0001 (one-way ANOVA with Bonferroni’s multiple comparison test; n=10–12 filaments). (F) mDia1 accelerates polymerization of branched actin filaments induced by the Arp2/3 complex. The Arp2/3 complex (20 nM) activated by WAVE2 (25 nM) was used to stimulate polymerization of profilin–actin (5 μM and 2.5 μM, respectively), either alone or with increasing concentrations of mDia1 MA. Representative frames extracted from TIRFm time-lapse movies illustrate actin polymerization at the indicated time (s) and concentration of mDia1 MA. Scale bar: 10 μm. (G) mDia1 cooperates with the Arp2/3 complex in making branched actin filaments. The area filled with filaments was quantified as described in the Materials and Methods. A representative dose–response experiment carried out on the same day is shown.</p

Quantitative Proteomics Illuminates a Functional Interaction between mDia2 and the Proteasome

Formin mDia2 is a cytoskeleton-regulatory protein that switches reversibly between a closed, autoinhibited and an open, active conformation. Although the open conformation of mDia2 induces actin assembly thereby controlling many cellular processes, mDia2 possesses also actin-independent and conformation-insensitive scaffolding roles related to microtubules and p53, respectively. Thus, we hypothesize that mDia2 may have other unappreciated functions and regulatory modes. Here we identify and validate proteasome and Ubiquitin as mDia2-interacting partners using stable isotope labeling with amino acids in cell culture-based quantitative proteomics and biochemistry, respectively. Although mDia2 is ubiquitinated, binds ubiquitinated proteins and free Ubiquitin, it is not a proteasome substrate. Surprisingly, knockdown of mDia2 increases the activity of the proteasome in vitro, whereas mDia2 overexpression has opposite effects only when it adopts the open conformation and cannot induce actin assembly. Consistently, a combination of candidate and unbiased proteome-wide analyses indicates that mDia2 regulates the cellular levels of proteasome substrate β-catenin and a number of ubiquitinated actin-regulatory proteins. Hence, these findings add more complexity to the mDia2 activity cycle by showing that the open conformation may control actin dynamics also through actin-independent regulation of the proteasome

Quantitative Proteomics Illuminates a Functional Interaction between mDia2 and the Proteasome

Formin mDia2 is a cytoskeleton-regulatory protein that switches reversibly between a closed, autoinhibited and an open, active conformation. Although the open conformation of mDia2 induces actin assembly thereby controlling many cellular processes, mDia2 possesses also actin-independent and conformation-insensitive scaffolding roles related to microtubules and p53, respectively. Thus, we hypothesize that mDia2 may have other unappreciated functions and regulatory modes. Here we identify and validate proteasome and Ubiquitin as mDia2-interacting partners using stable isotope labeling with amino acids in cell culture-based quantitative proteomics and biochemistry, respectively. Although mDia2 is ubiquitinated, binds ubiquitinated proteins and free Ubiquitin, it is not a proteasome substrate. Surprisingly, knockdown of mDia2 increases the activity of the proteasome in vitro, whereas mDia2 overexpression has opposite effects only when it adopts the open conformation and cannot induce actin assembly. Consistently, a combination of candidate and unbiased proteome-wide analyses indicates that mDia2 regulates the cellular levels of proteasome substrate β-catenin and a number of ubiquitinated actin-regulatory proteins. Hence, these findings add more complexity to the mDia2 activity cycle by showing that the open conformation may control actin dynamics also through actin-independent regulation of the proteasome

Quantitative Proteomics Illuminates a Functional Interaction between mDia2 and the Proteasome

Formin mDia2 is a cytoskeleton-regulatory protein that switches reversibly between a closed, autoinhibited and an open, active conformation. Although the open conformation of mDia2 induces actin assembly thereby controlling many cellular processes, mDia2 possesses also actin-independent and conformation-insensitive scaffolding roles related to microtubules and p53, respectively. Thus, we hypothesize that mDia2 may have other unappreciated functions and regulatory modes. Here we identify and validate proteasome and Ubiquitin as mDia2-interacting partners using stable isotope labeling with amino acids in cell culture-based quantitative proteomics and biochemistry, respectively. Although mDia2 is ubiquitinated, binds ubiquitinated proteins and free Ubiquitin, it is not a proteasome substrate. Surprisingly, knockdown of mDia2 increases the activity of the proteasome in vitro, whereas mDia2 overexpression has opposite effects only when it adopts the open conformation and cannot induce actin assembly. Consistently, a combination of candidate and unbiased proteome-wide analyses indicates that mDia2 regulates the cellular levels of proteasome substrate β-catenin and a number of ubiquitinated actin-regulatory proteins. Hence, these findings add more complexity to the mDia2 activity cycle by showing that the open conformation may control actin dynamics also through actin-independent regulation of the proteasome