Regulation and functions of the RhoA regulatory guanine nucleotide exchange factor GEF-H1

Tubulin-Targeted Therapy in Melanoma Increases the Cell Migration Potential by Activation of the Actomyosin Cytoskeleton─An In Vitro Study

One of the most dangerous aspects of cancers is their ability to metastasize, which is the leading cause of death. Hence, it holds significance to develop therapies targeting the eradication of cancer cells in parallel, inhibiting metastases in cells surviving the applied therapy. Here, we focused on two melanoma cell lines─WM35 and WM266-4─representing the less and more invasive melanomas. We investigated the mechanisms of cellular processes regulating the activation of actomyosin as an effect of colchicine treatment. Additionally, we investigated the biophysical aspects of supplement therapy using Rho-associated protein kinase (ROCK) inhibitor (Y-27632) and myosin II inhibitor ((-)-blebbistatin), focusing on the microtubules and actin filaments. We analyzed their effect on the proliferation, migration, and invasiveness of melanoma cells, supported by studies on cytoskeletal architecture using confocal fluorescence microscopy and nanomechanics using atomic force microscopy (AFM) and microconstriction channels. Our results showed that colchicine inhibits the migration of most melanoma cells, while for a small cell population, it paradoxically increases their migration and invasiveness. These changes are also accompanied by the formation of stress fibers, compensating for the loss of microtubules. Simultaneous administration of selected agents led to the inhibition of this compensatory effect. Collectively, our results highlighted that colchicine led to actomyosin activation and increased the level of cancer cell invasiveness. We emphasized that a cellular pathway of Rho-ROCK-dependent actomyosin contraction is responsible for the increased invasive potential of melanoma cells in tubulin-targeted therapy.

Zearalenone promotes endometrial cancer cell migration and invasion via activation of estrogen receptor-mediated Rho/ROCK/PMLC signaling pathway

Zearalenone (ZEA), has emerged as a potential endocrine-disrupting chemical (EDC). Previous results show ZEA effects on endometrial stromal cell apoptosis, migration, and growth of endometriosis. Despite the reported presence of ZEA in Endometrial Cancer (EC) patient's blood and tissues, ZEA-induced EC promotion and its mechanism/s remain elusive. In this study, Ishikawa cells were used to investigate the ZEA effects on Ishikawa cell migration, invasion, and the underlying mechanism involved in these events. Ishikawa cells were exposed to low concentrations of ZEA (5, 25, and 125 nM) for 48 h, and morphological alterations, migration, invasion, markers associated with epithelial-mesenchymal transition (EMT), E-cadherin, Vimentin, RhoA/ROCK/PMLC pathway activation were analyzed. ZEA (25 nM) exposure caused morphological alterations like stress fiber, filopodia formation, loss of cell adhesion, and a significant increase in migration and invasive potential in extracellular matrix-coated porous membranes. Moreover, ZEA exposure also increases the Rho-GTPase activity and expression of pathway mediators, GEFH1, RhoA, ROCK1+2, CDC42, and PMLC/MLC. Furthermore, pre-treatment with specific pharmacological inhibitors for Estrogen receptor-alpha (ER-α) and ROCK attenuate the ZEA-induced stress fiber formation and altered expression of E-cadherin, Vimentin, and Rho/ROCK/PMLC pathway mediators. These findings suggest that Rho/ROCK/PMLC signaling pathways are involved in ZEA-induced Ishikawa cell migration and invasion.

I told you to stop: obscurin's role in epithelial cell migration

The giant cytoskeletal protein obscurin contains multiple cell signaling domains that influence cell migration. Here, we follow each of these pathways, examine how these pathways modulate epithelial cell migration, and discuss the cross-talk between these pathways. Specifically, obscurin uses its PH domain to inhibit phosphoinositide-3-kinase (PI3K)-dependent migration and its RhoGEF domain to activate RhoA and slow cell migration. While obscurin's effect on the PI3K pathway agrees with the literature, obscurin's effect on the RhoA pathway runs counter to most other RhoA effectors, whose activation tends to lead to enhanced motility. Obscurin also phosphorylates cadherins, and this may also influence cell motility. When taken together, obscurin's ability to modulate three independent cell migration pathways is likely why obscurin knockout cells experience enhanced epithelial to mesenchymal transition, and why obscurin is a frequently mutated gene in several types of cancer.

Regulation of the RhoA exchange factor GEF-H1 by profibrotic stimuli through a positive feedback loop involving RhoA, MRTF, and Sp1

RhoA and its effectors, the transcriptional coactivators myocardin-related transcription factor (MRTF) and serum response factor (SRF), control epithelial phenotype and are indispensable for profibrotic epithelial reprogramming during fibrogenesis. Context-dependent control of RhoA and fibrosis-associated changes in its regulators, however, remain incompletely characterized. We previously identified the guanine nucleotide exchange factor GEF-H1 as a central mediator of RhoA activation in renal tubular cells exposed to inflammatory or fibrotic stimuli. Here we found that GEF-H1 expression and phosphorylation were strongly elevated in two animal models of fibrosis. In the Unilateral Ureteral Obstruction mouse kidney fibrosis model, GEF-H1 was upregulated predominantly in the tubular compartment. GEF-H1 was also elevated and phosphorylated in a rat pulmonary artery banding (PAB) model of right ventricular fibrosis. Prolonged stimulation of LLC-PK1 tubular cells with tumor necrosis factor (TNF)-α or transforming growth factor (TGF)-β1 increased GEF-H1 expression and activated a luciferase-coupled GEF-H1 promoter. Knockdown and overexpression studies revealed that these effects were mediated by RhoA, cytoskeleton remodeling, and MRTF, indicative of a positive feedback cycle. Indeed, silencing endogenous GEF-H1 attenuated activation of the GEF-H1 promoter. Of importance, inhibition of MRTF using CCG-1423 prevented GEF-H1 upregulation in both animal models. MRTF-dependent increase in GEF-H1 was prevented by inhibition of the transcription factor Sp1, and mutating putative Sp1 binding sites in the GEF-H1 promoter eliminated its MRTF-dependent activation. As the GEF-H1/RhoA axis is key for fibrogenesis, this novel MRTF/Sp1-dependent regulation of GEF-H1 abundance represents a potential target for reducing renal and cardiac fibrosis.NEW & NOTEWORTHY We show that expression of the RhoA regulator GEF-H1 is upregulated in tubular cells exposed to fibrogenic cytokines and in animal models of kidney and heart fibrosis. We identify a pathway wherein GEF-H1/RhoA-dependent MRTF activation through its noncanonical partner Sp1 upregulates GEF-H1. Our data reveal the existence of a positive feedback cycle that enhances Rho signaling through control of both GEF-H1 activation and expression. This feedback loop may play an important role in organ fibrosis.

Targeting guanine nucleotide exchange factors for novel cancer drug discovery

INTRODUCTION

Guanine nucleotide exchange factors (GEFs) regulate the activation of small GTPases (G proteins) of the Ras superfamily proteins controlling cellular functions. Ras superfamily proteins act as 'molecular switches' that are turned 'ON' by guanine exchange. There are five major groups of Ras family GTPases: Ras, Ran, Rho, Rab and Arf, with a variety of different GEFs regulating their GTP loading. GEFs have been implicated in various diseases including cancer. This makes GEFs attractive targets to modulate signaling networks controlled by small GTPases.

AREAS COVERED

In this review, the roles and mechanisms of GEFs in malignancy are outlined. The mechanism of guanine exchange activity by GEFs on a small GTPase is illustrated. Then, some examples of GEFs that are significant in cancer are presented with a discussion on recent progress in therapeutic targeting efforts using a variety of approaches.

EXPERT OPINION

Recently, GEFs have emerged as potential therapeutic targets for novel cancer drug development. Targeting small GTPases is challenging; thus, targeting their activation by GEFs is a promising strategy. Most GEF-targeted drugs are still in preclinical development. A deeper biological understanding of the underlying mechanisms of GEF activity and utilizing advanced technology are necessary to enhance drug discovery for GEFs in cancer.

ZO-1 Regulates Hippo-Independent YAP Activity and Cell Proliferation via a GEF-H1- and TBK1-Regulated Signalling Network

Tight junctions are a barrier-forming cell-cell adhesion complex and have been proposed to regulate cell proliferation. However, the underlying mechanisms are not well understood. Here, we used cells deficient in the junction scaffold ZO-1 alone or together with its paralog ZO-2, which disrupts the junctional barrier. We found that ZO-1 knockout increased cell proliferation, induced loss of cell density-dependent proliferation control, and promoted apoptosis and necrosis. These phenotypes were enhanced by double ZO-1/ZO-2 knockout. Increased proliferation was dependent on two transcriptional regulators: YAP and ZONAB. ZO-1 knockout stimulated YAP nuclear translocation and activity without changes in Hippo-dependent phosphorylation. Knockout promoted TANK-binding kinase 1 (TBK1) activation and increased expression of the RhoA activator GEF-H1. Knockdown of ZO-3, another paralog interacting with ZO1, was sufficient to induce GEF-H1 expression and YAP activity. GEF-H1, TBK1, and mechanotransduction at focal adhesions were found to cooperate to activate YAP/TEAD in ZO-1-deficient cells. Thus, ZO-1 controled cell proliferation and Hippo-independent YAP activity by activating a GEF-H1- and TBK1-regulated mechanosensitive signalling network.

Rac1 promotes kidney collecting duct repair by mechanically coupling cell morphology to mitotic entry

Prolonged obstruction of the ureter, which leads to injury of the kidney collecting ducts, results in permanent structural damage, while early reversal allows for repair. Cell structure is defined by the actin cytoskeleton, which is dynamically organized by small Rho guanosine triphosphatases (GTPases). In this study, we identified the Rho GTPase, Rac1, as a driver of postobstructive kidney collecting duct repair. After the relief of ureteric obstruction, Rac1 promoted actin cytoskeletal reconstitution, which was required to maintain normal mitotic morphology allowing for successful cell division. Mechanistically, Rac1 restricted excessive actomyosin activity that stabilized the negative mitotic entry kinase Wee1. This mechanism ensured mechanical G2-M checkpoint stability and prevented premature mitotic entry. The repair defects following injury could be rescued by direct myosin inhibition. Thus, Rac1-dependent control of the actin cytoskeleton integrates with the cell cycle to mediate kidney tubular repair by preventing dysmorphic cells from entering cell division.

Bone resorption by osteoclasts involves fine tuning of RHOA activity by its microtubule-associated exchange factor GEF-H1

Bone health is controlled by the balance between bone formation by osteoblasts and degradation by osteoclasts. A disequilibrium in favor of bone resorption leads to osteolytic diseases characterized by decreased bone density. Osteoclastic resorption is dependent on the assembly of an adhesion structure: the actin ring, also called podosome belt or sealing zone, which is composed of a unique patterning of podosomes stabilized by microtubules. A better understanding of the molecular mechanisms regulating the crosstalk between actin cytoskeleton and microtubules network is key to find new treatments to inhibit bone resorption. Evidence points to the importance of the fine tuning of the activity of the small GTPase RHOA for the formation and maintenance of the actin ring, but the underlying mechanism is not known. We report here that actin ring disorganization upon microtubule depolymerization is mediated by the activation of the RHOA-ROCK signaling pathway. We next show the involvement of GEF-H1, one of RHOA guanine exchange factor highly expressed in osteoclasts, which has the particularity of being negatively regulated by sequestration on microtubules. Using a CRISPR/Cas9-mediated GEF-H1 knock-down osteoclast model, we demonstrate that RHOA activation upon microtubule depolymerization is mediated by GEF-H1 release. Interestingly, although lower levels of GEF-H1 did not impact sealing zone formation in the presence of an intact microtubule network, sealing zone was smaller leading to impaired resorption. Altogether, these results suggest that a fine tuning of GEF-H1 through its association with microtubules, and consequently of RHOA activity, is essential for osteoclast sealing zone stability and resorption function.

CCDC88B interacts with RASAL3 and ARHGEF2 and regulates dendritic cell function in neuroinflammation and colitis

CCDC88B is a risk factor for several chronic inflammatory diseases in humans and its inactivation causes a migratory defect in DCs in mice. CCDC88B belongs to a family of cytoskeleton-associated scaffold proteins that feature protein:protein interaction domains. Here, we identified the Rho/Rac Guanine Nucleotide Exchange Factor 2 (ARHGEF2) and the RAS Protein Activator Like 3 (RASAL3) as CCDC88B physical and functional interactors. Mice defective in Arhgef2 or Rasal3 show dampened neuroinflammation, and display altered cellular response and susceptibility to colitis; ARHGEF2 maps to a human Chromosome 1 locus associated with susceptibility to IBD. Arhgef2 and Rasal3 mutant DCs show altered migration and motility in vitro, causing either reduced (Arhgef2) or enhanced (Rasal3) migratory properties. The CCDC88B/RASAL3/ARHGEF2 complex appears to regulate DCs migration by modulating activation of RHOA, with ARHGEF2 and RASAL3 acting in opposite regulatory fashions, providing a molecular mechanism for the involvement of these proteins in DCs immune functions.

βPix Guanine Nucleotide Exchange Factor Regulates Regeneration of Injured Peripheral Axons

Axon regeneration is essential for successful recovery after peripheral nerve injury. Although growth cone reformation and axonal extension are crucial steps in axonal regeneration, the regulatory mechanisms underlying these dynamic processes are poorly understood. Here, we identify βPix (Arhgef7), the guanine nucleotide exchange factor for Rac1 GTPase, as a regulator of axonal regeneration. After sciatic nerve injury in mice, the expression levels of βPix increase significantly in nerve segments containing regenerating axons. In regrowing axons, βPix is localized in the peripheral domain of the growth cone. Using βPix neuronal isoform knockout (NIKO) mice in which the neuronal isoforms of βPix are specifically removed, we demonstrate that βPix promotes neurite outgrowth in cultured dorsal root ganglion neurons and in vivo axon regeneration after sciatic nerve crush injury. Activation of cJun and STAT3 in the cell bodies is not affected in βPix NIKO mice, supporting the local action of βPix in regenerating axons. Finally, inhibiting Src, a kinase previously identified as an activator of the βPix neuronal isoform, causes axon outgrowth defects in vitro, like those found in the βPix NIKO neurons. Altogether, these data indicate that βPix plays an important role in axonal regrowth during peripheral nerve regeneration.

HUNK inhibits epithelial-mesenchymal transition of CRC via direct phosphorylation of GEF-H1 and activating RhoA/LIMK-1/CFL-1

Epithelial-mesenchymal transition (EMT) is associated with the invasive and metastatic phenotypes in colorectal cancer (CRC). However, the mechanisms underlying EMT in CRC are not completely understood. In this study, we find that HUNK inhibits EMT and metastasis of CRC cells via its substrate GEF-H1 in a kinase-dependent manner. Mechanistically, HUNK directly phosphorylates GEF-H1 at serine 645 (S645) site, which activates RhoA and consequently leads to a cascade of phosphorylation of LIMK-1/CFL-1, thereby stabilizing F-actin and inhibiting EMT. Clinically, the levels of both HUNK expression and phosphorylation S645 of GEH-H1 are not only downregulated in CRC tissues with metastasis compared with that without metastasis, but also positively correlated among these tissues. Our findings highlight the importance of HUNK kinase direct phosphorylation of GEF-H1 in regulation of EMT and metastasis of CRC.

Lfc subcellular localization and activity is controlled by αv-class integrin

Fibronectin (FN)-binding integrins control a variety of cellular responses through Rho GTPases. The FN-binding integrins, αvβ3 and α5β1, are known to induce different effects on cell morphology and motility. Here, we report that FN-bound αvβ3 integrin, but not FN-bound α5β1 integrin, triggers the dissociation of the RhoA GEF Lfc (also known as GEF-H1 and ARHGEF2 in humans) from microtubules (MTs), leading to the activation of RhoA, formation of stress fibres and maturation of focal adhesions (FAs). Conversely, loss of Lfc expression decreases RhoA activity, stress fibre formation and FA size, suggesting that Lfc is the major GEF downstream of FN-bound αvβ3 that controls RhoA activity. Mechanistically, FN-engaged αvβ3 integrin activates a kinase cascade involving MARK2 and MARK3, which in turn leads to phosphorylation of several phospho-sites on Lfc. In particular, S151 was identified as the main site involved in the regulation of Lfc localization and activity. Our findings indicate that activation of Lfc and RhoA is orchestrated in FN-adherent cells in an integrin-specific manner.

Targeting the RhoA-GEF-H1 pathway of mast cells attenuates experimental airway allergy

Mast cells are the major effector cells in allergic diseases. RhoA and its downstream pathway is associated with the pathogenesis of airway allergy. The objective of this study is to test a hypothesis that modulating the RhoA-GEF-H1 axis in mast cells can attenuate airway allergy. An airway allergic disorder (AAD) mouse model was employed. Mast cells were isolated from AAD mouse airway tissues to be analyzed by RNA sequencing. We observed that mast cells isolated from the respiratory tract of AAD mice were resistant to apoptosis. Mast cell mediator levels in nasal lavage fluid were correlated with apoptosis resistance in AAD mice. Activation of RhoA in AAD mast cells was related to resistance to apoptosis. Mast cells isolated from the airway tissues in AAD mouse exhibited strong RhoA-GEF-H1 expression. The RhoA-GEF-H1 axis was associated with the lower FasL expression in AAD mast cells. Activation of the RhoA-GEF-H1 axis promoted the production of mediators in mast cells. Inhibition of GEF-H1 facilitated the SIT-induced mast cell apoptosis and enhanced the therapeutic efficacy of AAD. In conclusion, RhoA-GEF-H1 activities are associated with resistance to apoptosis in mast cells isolated from sites of allergic lesions. The state of apoptosis resistance in mast cells is associated with the state of AAD disease. Inhibition of GEF-H1 restores the sensitivity of mast cells to apoptosis inducers, and alleviates experimental AAD in mice.

Epimedin C protects dexamethasone-induced osteoblasts through NRF1/RhoA pathway

Osteoporosis (OP) is a metabolic bone disease that leads to decrease of bone strength and increase bone brittle and fracture. Dexamethasone (DXMS) usage is a common risk factor of OP. In present study, we found that the Epimedin C protect the DXMS-induced OP, Ras Homolog Family Member A transforming protein (RhoA) was increased in osteoblasts (OBs) and OP models. We further revealed that Nrf1 is a transcription factor that responds to Epimedin C and DXMS in modulating RhoA promoter. The results collectively demonstrate that Epimedin C functions as a positive modifier of RhoA via alteration of Nrf1 transcriptional activity on RhoA promoter, thereby, protecting OBs against OP. Our work is the first study identifying the Epimedin C function in balancing the OBs in OP model via Nrf1-RhoA.

GEF-H1 Transduces FcεRI Signaling in Mast Cells to Activate RhoA and Focal Adhesion Formation during Exocytosis

When antigen-stimulated, mast cells release preformed inflammatory mediators stored in cytoplasmic granules. This occurs via a robust exocytosis mechanism termed degranulation. Our previous studies revealed that RhoA and Rac1 are activated during mast cell antigen stimulation and are required for mediator release. Here, we show that the RhoGEF, GEF-H1, acts as a signal transducer of antigen stimulation to activate RhoA and promote mast cell spreading via focal adhesion (FA) formation. Cell spreading, granule movement, and exocytosis were all reduced in antigen-stimulated mast cells when GEF-H1 was depleted by RNA interference. GEF-H1-depleted cells also showed a significant reduction in RhoA activation, resulting in reduced stress fiber formation without altering lamellipodia formation. Ectopic expression of a constitutively active RhoA mutant restored normal morphology in GEF-H1-depleted cells. FA formation during antigen stimulation required GEF-H1, suggesting it is a downstream target of the GEF-H1-RhoA signaling axis. GEF-H1 was activated by phosphorylation in conjunction with antigen stimulation. Syk kinase is linked to the FcεRI signaling pathway and the Syk inhibitor, GS-9973, blocked GEF-H1 activation and also suppressed cell spreading, granule movement, and exocytosis. We concluded that during FcεRI receptor stimulation, GEF-H1 transmits signals to RhoA activation and FA formation to facilitate the exocytosis mechanism.

Growth cone advance requires EB1 as revealed by genomic replacement with a light-sensitive variant

A challenge in analyzing dynamic intracellular cell biological processes is the dearth of methodologies that are sufficiently fast and specific to perturb intracellular protein activities. We previously developed a light-sensitive variant of the microtubule plus end-tracking protein EB1 by inserting a blue light-controlled protein dimerization module between functional domains. Here, we describe an advanced method to replace endogenous EB1 with this light-sensitive variant in a single genome editing step, thereby enabling this approach in human induced pluripotent stem cells (hiPSCs) and hiPSC-derived neurons. We demonstrate that acute and local optogenetic EB1 inactivation in developing cortical neurons induces microtubule depolymerization in the growth cone periphery and subsequent neurite retraction. In addition, advancing growth cones are repelled from areas of blue light exposure. These phenotypes were independent of the neuronal EB1 homolog EB3, revealing a direct dynamic role of EB1-mediated microtubule plus end interactions in neuron morphogenesis and neurite guidance.

TF-Prioritizer: a Java pipeline to prioritize condition-specific transcription factors

BACKGROUND

Eukaryotic gene expression is controlled by cis-regulatory elements (CREs), including promoters and enhancers, which are bound by transcription factors (TFs). Differential expression of TFs and their binding affinity at putative CREs determine tissue- and developmental-specific transcriptional activity. Consolidating genomic datasets can offer further insights into the accessibility of CREs, TF activity, and, thus, gene regulation. However, the integration and analysis of multimodal datasets are hampered by considerable technical challenges. While methods for highlighting differential TF activity from combined chromatin state data (e.g., chromatin immunoprecipitation [ChIP], ATAC, or DNase sequencing) and RNA sequencing data exist, they do not offer convenient usability, have limited support for large-scale data processing, and provide only minimal functionality for visually interpreting results.

RESULTS

We developed TF-Prioritizer, an automated pipeline that prioritizes condition-specific TFs from multimodal data and generates an interactive web report. We demonstrated its potential by identifying known TFs along with their target genes, as well as previously unreported TFs active in lactating mouse mammary glands. Additionally, we studied a variety of ENCODE datasets for cell lines K562 and MCF-7, including 12 histone modification ChIP sequencing as well as ATAC and DNase sequencing datasets, where we observe and discuss assay-specific differences.

CONCLUSION

TF-Prioritizer accepts ATAC, DNase, or ChIP sequencing and RNA sequencing data as input and identifies TFs with differential activity, thus offering an understanding of genome-wide gene regulation, potential pathogenesis, and therapeutic targets in biomedical research.

MICAL1 activation by PAK1 mediates actin filament disassembly

The MICAL1 monooxygenase is an important regulator of filamentous actin (F-actin) structures. Although MICAL1 has been shown to be regulated via protein-protein interactions at the autoinhibitory carboxyl terminus, a link between actin-regulatory RHO GTPase signaling pathways and MICAL1 has not been established. We show that the CDC42 GTPase effector PAK1 associates with and phosphorylates MICAL1 on two serine residues, leading to accelerated F-actin disassembly. PAK1 binds to the amino-terminal catalytic monooxygenase and calponin homology domains, distinct from the autoinhibitory carboxyl terminus. Extracellular ligand stimulation leads to PAK-dependent phosphorylation, linking external signals to MICAL1 phosphorylation. Mass spectrometry indicates that MICAL1 co-expression with CDC42 and PAK1 increases MICAL1 association with hundreds of proteins, including the previously described MICAL1-interacting proteins RAB10 and RAB7A. These results provide insights into a redox-mediated pathway linking extracellular signals to cytoskeleton regulation via a RHO GTPase and indicate a means of communication between RHO and RAB GTPases.

CDKL5 deficiency disorder: molecular insights and mechanisms of pathogenicity to fast-track therapeutic development

CDKL5 deficiency disorder (CDD) is an X-linked brain disorder of young children and is caused by pathogenic variants in the cyclin-dependent kinase-like 5 (CDKL5) gene. Individuals with CDD suffer infantile onset, drug-resistant seizures, severe neurodevelopmental impairment and profound lifelong disability. The CDKL5 protein is a kinase that regulates key phosphorylation events vital to the development of the complex neuronal network of the brain. Pathogenic variants identified in patients may either result in loss of CDKL5 catalytic activity or are hypomorphic leading to partial loss of function. Whilst the progressive nature of CDD provides an excellent opportunity for disease intervention, we cannot develop effective therapeutics without in-depth knowledge of CDKL5 function in human neurons. In this mini review, we summarize new findings on the function of CDKL5. These include CDKL5 phosphorylation targets and the consequence of disruptions on signaling pathways in the human brain. This new knowledge of CDKL5 biology may be leveraged to advance targeted drug discovery and rapid development of treatments for CDD. Continued development of effective humanized models will further propel our understanding of CDD biology and may permit the development and testing of therapies that will significantly alter CDD disease trajectory in young children.

Interphase microtubule disassembly is a signaling cue that drives cell rounding at mitotic entry

At mitotic entry, reorganization of the actomyosin cortex prompts cells to round-up. Proteins of the ezrin, radixin, and moesin family (ERM) play essential roles in this process by linking actomyosin forces to the plasma membrane. Yet, the cell-cycle signal that activates ERMs at mitotic entry is unknown. By screening a compound library using newly developed biosensors, we discovered that drugs that disassemble microtubules promote ERM activation. We further demonstrated that disassembly of interphase microtubules at mitotic entry directs ERM activation and metaphase cell rounding through GEF-H1, a Rho-GEF inhibited by microtubule binding, RhoA, and its kinase effector SLK. We finally demonstrated that GEF-H1 and Ect2, another Rho-GEF previously identified to control actomyosin forces, act together to drive activation of ERMs and cell rounding in metaphase. In summary, we report microtubule disassembly as a cell-cycle signal that controls a signaling network ensuring that actomyosin forces are efficiently integrated at the plasma membrane to promote cell rounding at mitotic entry.

Therapeutic Validation of GEF-H1 Using a De Novo Designed Inhibitor in Models of Retinal Disease

Inflammation and fibrosis are important components of diseases that contribute to the malfunction of epithelia and endothelia. The Rho guanine nucleotide exchange factor (GEF) GEF-H1/ARHGEF-2 is induced in disease and stimulates inflammatory and fibrotic processes, cell migration, and metastasis. Here, we have generated peptide inhibitors to block the function of GEF-H1. Inhibitors were designed using a structural in silico approach or by isolating an inhibitory sequence from the autoregulatory C-terminal domain. Candidate inhibitors were tested for their ability to block RhoA/GEF-H1 binding in vitro, and their potency and specificity in cell-based assays. Successful inhibitors were then evaluated in models of TGFβ-induced fibrosis, LPS-stimulated endothelial cell-cell junction disruption, and cell migration. Finally, the most potent inhibitor was successfully tested in an experimental retinal disease mouse model, in which it inhibited blood vessel leakage and ameliorated retinal inflammation when treatment was initiated after disease diagnosis. Thus, an antagonist that blocks GEF-H1 signaling effectively inhibits disease features in in vitro and in vivo disease models, demonstrating that GEF-H1 is an effective therapeutic target and establishing a new therapeutic approach.

Molecular determinants of αVβ5 localization in flat clathrin lattices: Role of αVβ5 in cell adhesion and proliferation

The vitronectin receptor integrin αVβ5 can reside in two distinct adhesion structures: focal adhesions (FAs) and flat clathrin lattices (FCLs). Here we investigated the mechanism that regulates the subcellular distribution of β5 in keratinocytes and show that β5 has approximately 7- and 5-fold higher affinity for the clathrin adaptors ARH and Numb, respectively, than for talin; all proteins that bind to the membrane-proximal NPxY motif of the β5 cytoplasmic domain. Using mass spectrometry, we identified β5 interactors including the Rho GEFs p115Rho-GEF and GEF-H1, and the serine protein kinase MARK2; depletion of which diminishes the clustering of β5 in FCLs. Substitution of two serines (S759/762) in the β5 cytoplasmic domain with phospho-mimetic glutamates causes a shift in the localization of β5 from FAs into FCLs without affecting the interactions with MARK2, p115Rho-GEF or GEF-H1. Instead, we demonstrate that changes in the actomyosin-based cellular contractility by ectopic expression of activated Rho or disruption of microtubules regulates β5 localization. Finally, we present evidence that β5 in either FAs or FCLs functions to promote adhesion to vitronectin, cell spreading, and proliferation.

MRTF: Basic Biology and Role in Kidney Disease

A lesser known but crucially important downstream effect of Rho family GTPases is the regulation of gene expression. This major role is mediated via the cytoskeleton, the organization of which dictates the nucleocytoplasmic shuttling of a set of transcription factors. Central among these is myocardin-related transcription factor (MRTF), which upon actin polymerization translocates to the nucleus and binds to its cognate partner, serum response factor (SRF). The MRTF/SRF complex then drives a large cohort of genes involved in cytoskeleton remodeling, contractility, extracellular matrix organization and many other processes. Accordingly, MRTF, activated by a variety of mechanical and chemical stimuli, affects a plethora of functions with physiological and pathological relevance. These include cell motility, development, metabolism and thus metastasis formation, inflammatory responses and—predominantly-organ fibrosis. The aim of this review is twofold: to provide an up-to-date summary about the basic biology and regulation of this versatile transcriptional coactivator; and to highlight its principal involvement in the pathobiology of kidney disease. Acting through both direct transcriptional and epigenetic mechanisms, MRTF plays a key (yet not fully appreciated) role in the induction of a profibrotic epithelial phenotype (PEP) as well as in fibroblast-myofibroblast transition, prime pathomechanisms in chronic kidney disease and renal fibrosis.

Natriuretic peptide receptor-C releases and activates guanine nucleotide-exchange factor H1 in a ligand-dependent manner

Although natriuretic peptide receptor-C (NPR-C) is involved in the clearance of natriuretic peptides from plasma, it also possesses other physiological functions, such as inhibition of adenylyl cyclase activity through Gαi. However, the physiological roles and intracellular signaling pathways of NPR-C have yet been not fully elucidated. In this study, we identified a RhoA-specific guanine nucleotide-exchange factor, GEF-H1, as a novel binding protein of NPR-C. We demonstrated that endogenous NPR-C interacted with GEF-H1 in HeLa cells, and that the interaction between NPR-C and GEF-H1 was dependent on a 37-amino acid cytoplasmic region of NPR-C. In contrast, another natriuretic peptide receptor, NPR-A, which includes the kinase homology and guanylyl cyclase domains in the intracellular region, did not interact with GEF-H1. We also revealed that the ligands of NPR-C (i.e., ANP, CNP, and osteocrin) caused dissociation of GEF-H1 from NPR-C. Furthermore, osteocrin treatment induced phosphorylation of GEF-H1 at Ser-886, enhanced the interaction of GEF-H1 with 14-3-3, and increased the amount of activated GEF-H1. These findings strongly supported that NPR-C may be involved in diverse physiological roles by regulating GEF-H1 signaling.

Network Analysis Identifies Drug Targets and Small Molecules to Modulate Apoptosis Resistant Cancers

Programed cell death or apoptosis fails to induce cell death in many recalcitrant cancers. Thus, there is an emerging need to activate the alternate cell death pathways in such cancers. In this study, we analyzed the apoptosis-resistant colon adenocarcinoma, glioblastoma multiforme, and small cell lung cancers transcriptome profiles. We extracted clusters of non-apoptotic cell death genes from each cancer to understand functional networks affected by these genes and their role in the induction of cell death when apoptosis fails. We identified transcription factors regulating cell death genes and protein-protein interaction networks to understand their role in regulating cell death mechanisms. Topological analysis of networks yielded FANCD2 (ferroptosis, negative regulator, down), NCOA4 (ferroptosis, up), IKBKB (alkaliptosis, down), and RHOA (entotic cell death, down) as potential drug targets in colon adenocarcinoma, glioblastoma multiforme, small cell lung cancer phenotypes respectively. We also assessed the miRNA association with the drug targets. We identified tumor growth-related interacting partners based on the pathway information of drug-target interaction networks. The protein-protein interaction binding site between the drug targets and their interacting proteins provided an opportunity to identify small molecules that can modulate the activity of functional cell death interactions in each cancer. Overall, our systematic screening of non-apoptotic cell death-related genes uncovered targets helpful for cancer therapy.