Disruption of the productive encounter complex results in dysregulation of DIAPH1 activity.

The diaphanous-related formin, Diaphanous 1 (DIAPH1), is required for the assembly of Filamentous (F)-actin structures. DIAPH1 is an intracellular effector of the receptor for advanced glycation end products (RAGE) and contributes to RAGE signaling and effects such as increased cell migration upon RAGE stimulation. Mutations in DIAPH1, including those in the basic "RRKR" motif of its autoregulatory domain, diaphanous autoinhibitory domain (DAD), are implicated in hearing loss, macrothrombocytopenia, and cardiovascular diseases. The solution structure of the complex between the N-terminal inhibitory domain, DID, and the C-terminal DAD, resolved by NMR spectroscopy shows only transient interactions between DID and the basic motif of DAD, resembling those found in encounter complexes. Cross-linking studies placed the RRKR motif into the negatively charged cavity of DID. Neutralizing the cavity resulted in a 5-fold decrease in the binding affinity and 4-fold decrease in the association rate constant of DAD for DID, indicating that the RRKR interactions with DID form a productive encounter complex. A DIAPH1 mutant containing a neutralized RRKR binding cavity shows excessive colocalization with actin and is unresponsive to RAGE stimulation. This is the first demonstration of a specific alteration of the surfaces responsible for productive encounter complexation with implications for human pathology.

N-terminal acetylation and arginylation of actin determines the architecture and assembly rate of linear and branched actin networks.

The great diversity in actin network architectures and dynamics is exploited by cells to drive fundamental biological processes, including cell migration, endocytosis, and cell division. While it is known that this versatility is the result of the many actin-remodeling activities of actin-binding proteins, such as Arp2/3 and cofilin, recent work also implicates posttranslational acetylation or arginylation of the actin N terminus itself as an equally important regulatory mechanism. However, the molecular mechanisms by which acetylation and arginylation alter the properties of actin are not well understood. Here, we directly compare how processing and modification of the N terminus of actin affects its intrinsic polymerization dynamics and its remodeling by actin-binding proteins that are essential for cell migration. We find that in comparison to acetylated actin, arginylated actin reduces intrinsic as well as formin-mediated elongation and Arp2/3-mediated nucleation. By contrast, there are no significant differences in cofilin-mediated severing. Taken together, these results suggest that cells can employ these differently modified actins to regulate actin dynamics. In addition, unprocessed actin with an N-terminal methionine residue shows very different effects on formin-mediated elongation, Arp2/3-mediated nucleation, and severing by cofilin. Altogether, this study shows that the nature of the N terminus of actin can promote distinct actin network dynamics, which can be differentially used by cells to locally finetune actin dynamics at distinct cellular locations, such as at the leading edge.

Proximal-tubule molecular relay from early Protein diaphanous homolog 1 to late Rho-associated protein kinase 1 regulates kidney function in obesity-induced kidney damage.

The small GTPase protein RhoA has two effectors, ROCK (Rho-associated protein kinase 1) and mDIA1 (protein diaphanous homolog 1), which cooperate reciprocally. However, temporal regulation of RhoA and its effectors in obesity-induced kidney damage remains unclear. Here, we investigated the role of RhoA activation in the proximal tubules at the early and late stages of obesity-induced kidney damage. In mice, a three-week high-fat-diet induced proximal tubule hypertrophy and damage without increased albuminuria, and RhoA/mDIA1 activation without ROCK activation. Conversely, a 12-week high-fat diet induced proximal tubule hypertrophy, proximal tubule damage, increased albuminuria, and RhoA/ROCK activation without mDIA1 elevation. Proximal tubule hypertrophy resulting from cell cycle arrest accompanied by downregulation of the multifunctional cyclin-dependent kinase inhibitor p27Kip1 was elicited by RhoA activation. Mice overexpressing proximal tubule-specific and dominant-negative RHOA display amelioration of high-fat diet-induced kidney hypertrophy, cell cycle abnormalities, inflammation, and renal impairment. In human proximal tubule cells, mechanical stretch mimicking hypertrophy activated ROCK, which triggered inflammation. In human kidney samples from normal individuals with a body mass index of about 25, proximal tubule cell size correlated with body mass index, proximal tubule cell damages, and mDIA1 expression. Thus, RhoA activation in proximal tubules is critical for the initiation and progression of obesity-induced kidney damage. Hence, the switch in the downstream RhoA effector in proximal tubule represents a transition from normal to pathogenic kidney adaptation and to body weight gain, leading to obesity-induced kidney damage.

Loss of mDia1 and Fhod1 impacts platelet formation but not platelet function.

An organized and dynamic cytoskeleton is required for platelet formation and function. Formins are a large family of actin regulatory proteins which are also able to regulate microtubule dynamics. There are four formin family members expressed in human and mouse megakaryocytes and platelets. We have previously shown that the actin polymerization activity of formin proteins is required for cytoskeletal dynamics and platelet spreading using a small molecule inhibitor. In the current study, we analyze transgenic mouse models deficient in two of these proteins, mDia1 and Fhod1, along with a model lacking both proteins. We demonstrate that double knockout mice display macrothrombocytopenia which is due to aberrant megakaryocyte function and a small decrease in platelet lifespan. Platelet function is unaffected by the loss of these proteins. This data indicates a critical role for formins in platelet and megakaryocyte function.

Formin mDia1 contributes to migration and epithelial-mesenchymal transition of tubular epithelial cells exposed to TGF-ß1.

Renal tubular epithelial cells may undergo epithelial-mesenchymal transition (EMT) in response to stimuli, such as transforming growth factor (TGF)-ß1, leading to myofibroblast activation and renal fibrosis. The formin mDia1 is required for nucleation and polymerization of actin and the microtubule cytoskeleton. The present study sought to explore the role of mDia1 in EMT of tubular epithelial cells. A rat model of unilateral ureteral obstruction (UUO) was established. The expression of TGF-ß1, collagen I, collagen III, and mDia1 in the kidneys was examined at day 7 after surgery. The effect of mDia1 on EMT was explored in NRK-52E cells by exposing them to TGF-ß1. Increased expression of TGF-ß1, collagen I, collagen III, and mDia1 was found in obstructive kidneys of UUO model rats. Exposing rat tubular epithelial cells to TGF-ß1 promoted collagen I and collagen III expression but had no effect on mDia1 expression. Silencing mDia1 expression impeded epithelial cell migration as well as reduced TGF-ß1, collagen, and Profilin1 expression, whereas mDia1 overexpression exerted an opposite effect. Furthermore, mDia1 regulated the expression of vimentin, α-smooth muscle actin, and E-cadherin and focal adhesion-kinase (FAK)/Src activation through Profilin1. Inhibition of the mDia1 activator RhoA by fasudil reversed EMT, and FAK/Src activation induced by mDia1. In conclusion, mDia1 regulated tubular epithelial cell migration, collagen expression, and EMT in NRK-52E cells exposed to TGF-ß1. Thus, suppression of mDia1 activation might be a strategy to counteract renal fibrosis.

RhoC regulates the actin remodeling required for phagosome formation during FcγR-mediated phagocytosis.

Phagosome formation is a complicated process that requires spatiotemporally regulated actin reorganization. We found that RhoC GTPase is a critical regulator of FcγR-mediated phagocytosis in macrophages. Our live-cell imaging revealed that RhoC, but not RhoA, is recruited to phagocytic cups engulfing IgG-opsonized erythrocytes (IgG-Es). RhoC silencing through RNAi, CRISPR/Cas-mediated RhoC knockout, and the expression of dominant-negative or constitutively active RhoC mutants suppressed the phagocytosis of IgG-Es. Moreover, RhoC-GTP pulldown experiments showed that endogenous RhoC is transiently activated during phagosome formation. Notably, actin-driven pseudopod extension, which is required for the formation of phagocytic cups, was severely impaired in cells expressing the constitutively active mutant RhoC-G14V, which induced abnormal F-actin accumulation underneath the plasma membrane. mDia1 (encoded by DIAPH1), a Rho-dependent actin nucleation factor, and RhoC were colocalized at the phagocytic cups. Similar to what was seen for RhoC, mDia1 silencing through RNAi inhibited phagosome formation. Additionally, the coexpression of mDia1 with constitutively active mutant RhoC-G14V or expression of active mutant mDia1-ΔN3 drastically inhibited the uptake of IgG-Es. These data suggest that RhoC modulates phagosome formation be modifying actin cytoskeletal remodeling via mDia1.

Intranuclear Actin Structure Modulates Mesenchymal Stem Cell Differentiation.

Actin structure contributes to physiologic events within the nucleus to control mesenchymal stromal cell (MSC) differentiation. Continuous cytochalasin D (Cyto D) disruption of the MSC actin cytoskeleton leads to osteogenic or adipogenic differentiation, both requiring mass transfer of actin into the nucleus. Cyto D remains extranuclear, thus intranuclear actin polymerization is potentiated by actin transfer: we asked whether actin structure affects differentiation. We show that secondary actin filament branching via the Arp2/3 complex is required for osteogenesis and that preventing actin branching stimulates adipogenesis, as shown by expression profiling of osteogenic and adipogenic biomarkers and unbiased RNA-seq analysis. Mechanistically, Cyto D activates osteoblast master regulators (e.g., Runx2, Sp7, Dlx5) and novel coregulated genes (e.g., Atoh8, Nr4a3, Slfn5). Formin-induced primary actin filament formation is critical for Arp2/3 complex recruitment: osteogenesis is prevented by silencing of the formin mDia1, but not its paralog mDia2. Furthermore, while inhibition of actin, branching is a potent adipogenic stimulus, silencing of either mDia1 or mDia2 blocks adipogenic gene expression. We propose that mDia1, which localizes in the cytoplasm of multipotential MSCs and traffics into the nucleus after cytoskeletal disruption, joins intranuclear mDia2 to facilitate primary filament formation before mediating subsequent branching via Arp2/3 complex recruitment. The resulting intranuclear branched actin network specifies osteogenic differentiation, while actin polymerization in the absence of Arp2/3 complex-mediated secondary branching causes adipogenic differentiation. Stem Cells 2017;35:1624-1635.

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

Protrusion of lamellipodia and ruffles requires polymerization of branched actin filaments by the Arp2/3 complex. Although regulation of Arp2/3 complex activity has been extensively investigated, the mechanism of initiation of lamellipodia and ruffles remains poorly understood. Here, we show that mDia1 acts in concert with the Arp2/3 complex to promote initiation of lamellipodia and ruffles. We find that mDia1 is an epidermal growth factor (EGF)-regulated actin nucleator involved in membrane ruffling using a combination of knockdown and rescue experiments. At the molecular level, mDia1 polymerizes linear actin filaments, activating the Arp2/3 complex, and localizes within nascent and mature membrane ruffles. We employ functional complementation experiments and optogenetics to show that mDia1 cooperates with the Arp2/3 complex in initiating lamellipodia and ruffles. Finally, we show that genetic and pharmacological interference with this cooperation hampers ruffling and cell migration. Thus, we propose that the lamellipodium- and ruffle-initiating machinery consists of two actin nucleators that act sequentially to regulate membrane protrusion and cell migration.

Interaction between mDia1 and ROCK in Rho-induced migration and adhesion of human dental pulp cells.

AIM: To investigate the effects of mammalian homologue of Drosophila diaphanous-1(mDia1) and Rho-associated coiled-coil-containing protein kinase (ROCK) on the migration and adhesion of dental pulp cells (DPCs). METHODOLOGY: Lysophosphatidic acid (LPA) was used to activate Rho signalling. mDia1 and ROCK were inhibited by short interfering RNA and the specific inhibitor, Y-27632, respectively. The migration of DPCs was assessed using the transwell migration assay and scratch test. Formation of cytoskeleton and focal adhesions(FAs) was observed by confocal laser scanning microscopy. Cell adhesion and spreading assays were performed. Phosphorylation of focal adhesion kinase (FAK) and paxillin was detected by Western blotting, and the bands were analysed using Adobe Photoshop CS5 software. All experiments were performed at least three times, and data were analysed with one-way anova and a post hoc test. RESULTS: LPA-triggered activation of Rho and inhibition of ROCK significantly increased the cell migration rate. Cell migration was inhibited by silencing mDia1. mDia1 silencing and ROCK inhibition suppressed the LPA-induced formation of the cytoskeleton, FA and phosphorylation of FAK and paxillin. Inhibition of ROCK or mDia1 facilitated early cell adhesion and spreading; by contrast, the combined inhibition of ROCK and mDia1 neutralized these effects. CONCLUSIONS: mDia1 promoted RhoA-induced migration of DPCs, but ROCK had an opposite effect. Both mDia1 and ROCK participated in cytoskeleton formation and adhesion of DPCs. The interactions between mDia1 and ROCK might influence dental pulp repair by determining the migration and adhesion of DPCs.

Structural and Biochemical Basis for the Inhibitory Effect of Liprin-α3 on Mouse Diaphanous 1 (mDia1) Function.

Diaphanous-related formins are eukaryotic actin nucleation factors regulated by an autoinhibitory interaction between the N-terminal RhoGTPase-binding domain (mDiaN) and the C-terminal Diaphanous-autoregulatory domain (DAD). Although the activation of formins by Rho proteins is well characterized, its inactivation is only marginally understood. Recently, liprin-α3 was shown to interact with mDia1. Overexpression of liprin-α3 resulted in a reduction of the cellular actin filament content. The molecular mechanisms of how liprin-α3 exerts this effect and counteracts mDia1 activation by RhoA are unknown. Here, we functionally and structurally define a minimal liprin-α3 core region, sufficient to recapitulate the liprin-α3 determined mDia1-respective cellular functions. We show that liprin-α3 alters the interaction kinetics and thermodynamics of mDiaN with RhoA·GTP and DAD. RhoA displaces liprin-α3 allosterically, whereas DAD competes with liprin-α3 for a highly overlapping binding site on mDiaN. Liprin-α3 regulates actin polymerization by lowering the regulatory potency of RhoA and DAD on mDiaN. We present a model of a mechanistically unexplored and new aspect of mDiaN regulation by liprin-α3.

Formin mDia1, a downstream molecule of FMNL1, regulates Profilin1 for actin assembly and spindle organization during mouse oocyte meiosis.

Mammalian diaphanous1 (mDia1) is a homologue of Drosophila diaphanous and belongs to the Formin-homology family of proteins that catalyze actin nucleation and polymerization. Although Formin family proteins, such as Drosophila diaphanous, have been shown to be essential for cytokinesis, whether and how mDia1 functions during meiosis remain uncertain. In this study, we explored possible roles and the signaling pathway involved for mDia1 using a mouse oocyte model. mDia1 depletion reduced polar body extrusion, which may have been due to reduced cortical actin assembly. mDia1 and Profilin1 had similar localization patterns in mouse oocytes and mDia1 knockdown resulted in reduced Profilin1 expression. Depleting FMNL1, another Formin family member, resulted in reduced mDia1 expression, while RhoA inhibition did not alter mDia1 expression, which indicated that there was a FMNL1-mDia1-Profilin1 signaling pathway in mouse oocytes. Additionally, mDia1 knockdown resulted in disrupting oocyte spindle morphology, which was confirmed by aberrant p-MAPK localization. Thus, these results demonstrated indispensable roles for mDia1 in regulating mouse oocyte meiotic maturation through its effects on actin assembly and spindle organization.

The Aß1₋42 peptide regulates microtubule stability independently of tau.

Interference with microtubule stability by beta-amyloid peptide (Aß) has been shown to disrupt dendritic function and axonal trafficking, both early events in Alzheimer's disease. However, it is unclear whether Aß regulation of microtubule dynamics can occur independently of its action on tau. RhoA has been implicated in neurotoxicity by Aß but the mechanism by which this activation generates cytoskeletal changes is also unclear. We found that oligomeric Aß1-42 induced the formation of stable detyrosinated microtubules in NIH3T3 cells and this function resulted from the activation of a RhoA-dependent microtubule stabilization pathway regulated by integrin signaling and the formin mDia1. Induction of microtubule stability by Aß was also initiated by dimerization of APP and required caspase activity, two previously characterized regulators of neurotoxicity downstream of Aß. Finally, we found that this function was conserved in primary neurons and abolished by Rho inactivation, reinforcing a link between induction of stable detyrosinated microtubules and neuropathogenesis by Aß. Our study reveals a novel activity of Aß on the microtubule cytoskeleton that is independent of tau and associated with pathways linked to microtubule stabilization and Aß-mediated neurotoxicity.

The Rho-mDia1 signaling pathway is required for cyclic strain-induced cytoskeletal rearrangement of human periodontal ligament cells.

Tooth movement is the result of periodontal tissue reconstruction. The biomechanical effects produced by orthopedic forces can affect the cytoskeletal rearrangement of human periodontal ligament cells (hPDLCs). However, the mechanisms responsible for the cytoskeletal rearrangement are not completely understood. To analyze the effect, we investigated the role of the Rho-mDia1 signaling pathway in cyclic strain-induced cytoskeletal rearrangement of hPDLCs in detail. We cultured hPDLCs on collagen I-coated six-well Bioflex plates and then exposed them to cyclic strain with physiological loading (10%) at a frequency of 0.1Hz for 6 or 24h using a Flexercell Tension Plus system. Notably, the cells cultured on the Bioflex plates showed increased expression levels of RhoA-GTP, profilin-1 protein, and the combination of RhoA and mDia1, whereas the expression levels of Rho-GDIa were reduced compared with a static control group. Furthermore, the cytoskeletal rearrangement of cells was enhanced. However, profilin-1 protein expression and cytoskeletal reorganization under cyclic strain can decrease due to the overexpression of Rho-GDIa or mDia1-siRNA transfection, whereas Rho-GDIa siRNA transfection has the opposite effect on hPDLCs. Together, our results demonstrate that the Rho-mDia1 signaling pathway is involved in the cytoskeletal rearrangement of hPDLCs induced by cyclic strain. These observations may enable a more in-depth understanding of orthodontic tooth movement and the reconstruction of PDL and alveolar bone.

The diaphanous-related formins promote protrusion formation and cell-to-cell spread of Listeria monocytogenes.

The Gram-positive bacterium Listeria monocytogenes is a facultative intracellular pathogen whose virulence depends on its ability to spread from cell to cell within an infected host. Although the actin-related protein 2/3 (Arp2/3) complex is necessary and sufficient for Listeria actin tail assembly, previous studies suggest that other actin polymerization factors, such as formins, may participate in protrusion formation. Here, we show that Arp2/3 localized to only a minor portion of the protrusion. Moreover, treatment of L. monocytogenes-infected HeLa cells with a formin FH2-domain inhibitor significantly reduced protrusion length. In addition, the Diaphanous-related formins 1-3 (mDia1-3) localized to protrusions, and knockdown of mDia1, mDia2, and mDia3 substantially decreased cell-to-cell spread of L. monocytogenes. Rho GTPases are known to be involved in formin activation. Our studies also show that knockdown of several Rho family members significantly influenced bacterial cell-to-cell spread. Collectively, these findings identify a Rho GTPase-formin network that is critically involved in the cell-to-cell spread of L. monocytogenes.

Impaired slow axonal transport in diabetic peripheral nerve is independent of RAGE.

Diabetic peripheral nerve dysfunction is a common complication occurring in 30-50% of long-term diabetic patients. The pathogenesis of this dysfunction remains unclear but growing evidence suggests that it might be attributed, in part, to alteration in axonal transport. Our previous studies demonstrated that RAGE (Receptor for Advanced Glycation Endproducts) contributes to the pathogenesis of diabetic peripheral neuropathy and impairs nerve regeneration consequent to sciatic nerve crush, particularly in diabetes. We hypothesize that RAGE plays a role in axonal transport impairment via the interaction of its cytoplasmic domain with mammalian Diaphanous 1 (mDia1) - actin interacting molecule. Studies showed that mDia1-RAGE interaction is necessary for RAGE-ligand-dependent cellular migration, AKT phosphorylation, macrophage inflammatory response and smooth muscle migration. Here, we studied RAGE, mDia1 and markers of axonal transport rates in the peripheral nerves of wild-type C57BL/6 and RAGE null control and streptozotocin-injected diabetic mice at 1, 3 and 6 h after sciatic nerve crush. The results show that in both control and diabetic nerves, the amount of RAGE accumulated at the proximal and distal side of the crush area is similar, indicating that the recycling rate for RAGE is very high and that it is evenly transported from and towards the neuronal cell body. Furthermore, we show that slow axonal transport of proteins such as Neurofilament is affected by diabetes in a RAGE-independent manner. Finally, our study demonstrates that mDia1 axonal transport is impaired in diabetes, suggesting that diabetes-related changes affecting actin binding proteins occur early in the course of the disease.

Ena/VASP proteins at the crossroads of actin nucleation pathways in dendritic cell migration.

As sentinels of our immune system dendritic cells (DCs) rely on efficient cell migration for patrolling peripheral tissues and delivering sampled antigens to secondary lymphoid organs for the activation of T-cells. Dynamic actin polymerization is key to their macropinocytic and migratory properties. Both major actin nucleation machineries, formins and the Arp2/3 complex, are critical for different aspects of DC functionality, by driving the generation of linear and branched actin filaments, respectively. However, the importance of a third group of actin nucleators, the Ena/VASP family, has not been addressed yet. Here, we show that the two family members Evl and VASP are expressed in murine DCs and that their loss negatively affects DC macropinocytosis, spreading, and migration. Our interactome analysis reveals Ena/VASP proteins to be ideally positioned for orchestrating the different actin nucleation pathways by binding to the formin mDia1 as well as to the WAVE regulatory complex, a stimulator of Arp2/3. In fact, Evl/VASP deficient murine DCs are more vulnerable to inhibition of Arp2/3 demonstrating that Ena/VASP proteins contribute to the robustness and efficiency of DC migration.

Quantitation of RhoA activation: differential binding to downstream effectors.

The small GTPase RhoA controls many important cellular processes through its ability to activate multiple downstream effector pathways. Most RhoA effectors contain a Rho-binding domain (RBD), and interaction between active RhoA and the RBD typically induces a conformational change in effectors that stimulates their recruitment or activity. Isolated GTPase binding domains fused to GST have been widely used in so-called pulldown assays to measure the activation state of other GTPases in cell lysates. Similarly, GST fusions containing the RBD of the RhoA effector Rhotekin have been widely adopted as a standardized tool for the measurement of RhoA activation. RBDs have also been used to generate fluorescent reporter constructs to localize sites of GTPase activation in intact cells. In this report, we demonstrate that not all forms of active RhoA are capable of interacting with the Rhotekin RBD. A constitutively active RhoA-G14V mutant, which interacted with the RBDs of ROCK2 and mDIA1, was unable to bind the Rhotekin RBD as evidenced by both conventional GST pulldown assay and our newly established BRET assay. Furthermore, active RhoA induced by different stimuli in cells also displayed binding preference for its diverse effectors. Our data demonstrate that RhoA may undergo effector-specific activation for differential regulation of its downstream pathways, and that RhoA activation should not be defined solely by its interaction with Rhotekin.

Formin Activity and mDia1 Contribute to Maintain Axon Initial Segment Composition and Structure.

The axon initial segment (AIS) is essential for maintaining neuronal polarity, modulating protein transport into the axon, and action potential generation. These functions are supported by a distinctive actin and microtubule cytoskeleton that controls axonal trafficking and maintains a high density of voltage-gated ion channels linked by scaffold proteins to the AIS cytoskeleton. However, our knowledge of the mechanisms and proteins involved in AIS cytoskeleton regulation to maintain or modulate AIS structure is limited. In this context, formins play a significant role in the modulation of actin and microtubules. We show that pharmacological inhibition of formins modifies AIS actin and microtubule characteristics in cultured hippocampal neurons, reducing F-actin density and decreasing microtubule acetylation. Moreover, formin inhibition diminishes sodium channels, ankyrinG and ßIV-spectrin AIS density, and AIS length, in cultured neurons and brain slices, accompanied by decreased neuronal excitability. We show that genetic downregulation of the mDia1 formin by interference RNAs also decreases AIS protein density and shortens AIS length. The ankyrinG decrease and AIS shortening observed in pharmacologically inhibited neurons and neuron-expressing mDia1 shRNAs were impaired by HDAC6 downregulation or EB1-GFP expression, known to increase microtubule acetylation or stability. However, actin stabilization only partially prevented AIS shortening without affecting AIS protein density loss. These results suggest that mDia1 maintain AIS composition and length contributing to the stability of AIS microtubules.

Inhibition of Sema4D/PlexinB1 signaling alleviates vascular dysfunction in diabetic retinopathy.

Diabetic retinopathy (DR) is a common complication of diabetes and leads to blindness. Anti-VEGF is a primary treatment for DR. Its therapeutic effect is limited in non- or poor responders despite frequent injections. By performing a comprehensive analysis of the semaphorins family, we identified the increased expression of Sema4D during oxygen-induced retinopathy (OIR) and streptozotocin (STZ)-induced retinopathy. The levels of soluble Sema4D (sSema4D) were significantly increased in the aqueous fluid of DR patients and correlated negatively with the success of anti-VEGF therapy during clinical follow-up. We found that Sema4D/PlexinB1 induced endothelial cell dysfunction via mDIA1, which was mediated through Src-dependent VE-cadherin dysfunction. Furthermore, genetic disruption of Sema4D/PlexinB1 or intravitreal injection of anti-Sema4D antibody reduced pericyte loss and vascular leakage in STZ model as well as alleviated neovascularization in OIR model. Moreover, anti-Sema4D had a therapeutic advantage over anti-VEGF on pericyte dysfunction. Anti-Sema4D and anti-VEGF also conferred a synergistic therapeutic effect in two DR models. Thus, this study indicates an alternative therapeutic strategy with anti-Sema4D to complement or improve the current treatment of DR.

Anillin Promotes Cell Contractility by Cyclic Resetting of RhoA Residence Kinetics.

RhoA stimulates cell contractility by recruiting downstream effectors to the cortical plasma membrane. We now show that direct binding by anillin is required for effective signaling: this antagonizes the otherwise labile membrane association of GTP-RhoA to promote effector recruitment. However, since its binding to RhoA blocks access by other effectors, we demonstrate that anillin must also concentrate membrane phosphoinositide-4,5-P2 (PIP2) to promote signaling. We propose and test a sequential pathway where GTP-RhoA first binds to anillin and then is retained at the membrane by PIP2 after it disengages from anillin. Importantly, re-binding of membrane GTP-RhoA to anillin, regulated by the cortical density of anillin, creates cycles through this pathway. These cycles repeatedly reset the dissociation kinetics of GTP-RhoA, substantially increasing its dwell time to recruit effectors. Thus, anillin regulates RhoA signaling by a paradigm of kinetic scaffolding that may apply to other signals whose efficacy depends on their cortical dwell times.