Regulation of mitotic spindle formation by the RhoA guanine nucleotide exchange factor ARHGEF10

RhoA-ROCK2 signaling possesses complex pathophysiological functions in cancer progression and shows promising therapeutic potential

The Rho GTPase signaling pathway is responsible for cell-specific processes, including actin cytoskeleton organization, cell motility, cell division, and the transcription of specific genes. The implications of RhoA and the downstream effector ROCK2 in cancer epithelial-mesenchymal transition, migration, invasion, and therapy resistance associated with stem cells highlight the potential of targeting RhoA/ROCK2 signaling in therapy. Tumor relapse can occur due to cancer cells that do not fully respond to adjuvant chemoradiotherapy, targeted therapy, or immunotherapy. Rho signaling-mediated mitotic defects and cytokinesis failure lead to asymmetric cell division, allowing cells to form polyploids to escape cytotoxicity and promote tumor recurrence and metastasis. In this review, we elucidate the significance of RhoA/ROCK2 in the mechanisms of cancer progression and summarize their inhibitors that may improve treatment strategies.

RhoA downregulation in the murine intestinal epithelium results in chronic Wnt activation and increased tumorigenesis

Rho GTPases are molecular switches regulating multiple cellular processes. To investigate the role of RhoA in normal intestinal physiology, we used a conditional mouse model overexpressing a dominant negative RhoA mutant (RhoAT19N) in the intestinal epithelium. Although RhoA inhibition did not cause an overt phenotype, increased levels of nuclear β-catenin were observed in the small intestinal epithelium of RhoAT19N mice, and the overexpression of multiple Wnt target genes revealed a chronic activation of Wnt signaling. Elevated Wnt signaling in RhoAT19N mice and intestinal organoids did not affect the proliferation of intestinal epithelial cells but significantly interfered with their differentiation. Importantly, 17-month-old RhoAT19N mice showed a significant increase in the number of spontaneous intestinal tumors. Altogether, our results indicate that RhoA regulates the differentiation of intestinal epithelial cells and inhibits tumor initiation, likely through the control of Wnt signaling, a key regulator of proliferation and differentiation in the intestine.

Inhibitors of Rho kinases (ROCK) induce multiple mitotic defects and synthetic lethality in BRCA2-deficient cells

The trapping of Poly-ADP-ribose polymerase (PARP) on DNA caused by PARP inhibitors (PARPi) triggers acute DNA replication stress and synthetic lethality (SL) in BRCA2-deficient cells. Hence, DNA damage is accepted as a prerequisite for SL in BRCA2-deficient cells. In contrast, here we show that inhibiting ROCK in BRCA2-deficient cells triggers SL independently from acute replication stress. Such SL is preceded by polyploidy and binucleation resulting from cytokinesis failure. Such initial mitosis abnormalities are followed by other M phase defects, including anaphase bridges and abnormal mitotic figures associated with multipolar spindles, supernumerary centrosomes and multinucleation. SL was also triggered by inhibiting Citron Rho-interacting kinase, another enzyme that, similarly to ROCK, regulates cytokinesis. Together, these observations demonstrate that cytokinesis failure triggers mitotic abnormalities and SL in BRCA2-deficient cells. Furthermore, the prevention of mitotic entry by depletion of Early mitotic inhibitor 1 (EMI1) augmented the survival of BRCA2-deficient cells treated with ROCK inhibitors, thus reinforcing the association between M phase and cell death in BRCA2-deficient cells. This novel SL differs from the one triggered by PARPi and uncovers mitosis as an Achilles heel of BRCA2-deficient cells.

Key role of Rho GTPases in motor disorders associated with neurodevelopmental pathologies

Growing evidence suggests that Rho GTPases and molecules involved in their signaling pathways play a major role in the development of the central nervous system (CNS). Whole exome sequencing (WES) and de novo examination of mutations, including SNP (Single Nucleotide Polymorphism) in genes coding for the molecules of their signaling cascade, has allowed the recent discovery of dominant autosomic mutations and duplication or deletion of candidates in the field of neurodevelopmental diseases (NDD). Epidemiological studies show that the co-occurrence of several of these neurological pathologies may indeed be the rule. The regulators of Rho GTPases have often been considered for cognitive diseases such as intellectual disability (ID) and autism. But, in a remarkable way, mild to severe motor symptoms are now reported in autism and other cognitive NDD. Although a more abundant litterature reports the involvement of Rho GTPases and signaling partners in cognitive development, molecular investigations on their roles in central nervous system (CNS) development or degenerative CNS pathologies also reveal their role in embryonic and perinatal motor wiring through axon guidance and later in synaptic plasticity. Thus, Rho family small GTPases have been revealed to play a key role in brain functions including learning and memory but their precise role in motor development and associated symptoms in NDD has been poorly scoped so far, despite increasing clinical data highlighting the links between cognition and motor development. Indeed, early impairements in fine or gross motor performance is often an associated feature of NDDs, which then impact social communication, cognition, emotion, and behavior. We review here recent insights derived from clinical developmental neurobiology in the field of Rho GTPases and NDD (autism spectrum related disorder (ASD), ID, schizophrenia, hypotonia, spastic paraplegia, bipolar disorder and dyslexia), with a specific focus on genetic alterations affecting Rho GTPases that are involved in motor circuit development.

Tumor necrosis factor-induced ArhGEF10 selectively activates RhoB contributing to human microvascular endothelial cell tight junction disruption

Capillary endothelial cells (ECs) maintain a semi-permeable barrier between the blood and tissue by forming inter-EC tight junctions (TJs), regulating selective transport of fluid and solutes. Overwhelming inflammation, as occurs in sepsis, disrupts these TJs, leading to leakage of fluid, proteins, and small molecules into the tissues. Mechanistically, disruption of capillary barrier function is mediated by small Rho-GTPases, such as RhoA, -B, and -C, which are activated by guanine nucleotide exchange factors (GEFs) and disrupted by GTPase-activating factors (GAPs). We previously reported that a mutation in a specific RhoB GAP (p190BRhoGAP) underlays a hereditary capillary leak syndrome. Tumor necrosis factor (TNF) treatment disrupts TJs in cultured human microvascular ECs, a model of capillary leak. This response requires new gene transcription and involves increased RhoB activation. However, the specific GEF that activates RhoB in capillary ECs remains unknown. Transcriptional profiling of cultured tight junction-forming human dermal microvascular endothelial cells (HDMECs) revealed that 17 GEFs were significantly induced by TNF. The function of each candidate GEF was assessed by short interfering RNA depletion and trans-endothelial electrical resistance screening. Knockown of ArhGEF10 reduced the TNF-induced loss of barrier which was phenocopied by RhoB or dual ArhGEF10/RhoB knockdown. ArhGEF10 knockdown also reduced the extent of TNF-induced RhoB activation and disruption at tight junctions. In a cell-free assay, immunoisolated ArhGEF10 selectively catalyzed nucleotide exchange to activate RhoB, but not RhoA or RhoC. We conclude ArhGEF10 is a TNF-induced RhoB-selective GEF that mediates TJ disruption and barrier loss in human capillary endothelial cells.

RhoA Pathway and Actin Regulation of the Golgi/Centriole Complex

In vertebrate cells, the Golgi apparatus is located in close proximity to the centriole. The architecture of the Golgi/centriole complex depends on a multitude of factors, including the actin filament cytoskeleton. In turn, both the Golgi and centriole act as the actin nucleation centers. Actin organization and polymerization also depend on the small GTPase RhoA pathway. In this chapter, we summarize the most current knowledge on how the genetic, magnetic, or pharmacologic interference with RhoA pathway and actin cytoskeleton directly or indirectly affects architecture, structure, and function of the Golgi/centriole complex.

Hepatocellular Carcinoma Outcome Is Predicted by Expression of Neuronal Calcium Sensor 1

Background: Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related death worldwide. There is an urgent demand for prognostic biomarkers that facilitate early tumor detection, as the incidence of HCC has tripled in the United States in the last three decades. Biomarkers to identify populations at risk would have significant impact on survival. We recently found that expression of Neuronal Calcium Sensor 1 (NCS1), a Ca2+-dependent signaling molecule, predicted disease outcome in breast cancer, but its predictive value in other cancer types is unknown. This protein is potentially useful because increased NCS1 regulates Ca2+ signaling and increased Ca2+ signaling is a hallmark of metastatic cancers, conferring cellular motility and an increasingly aggressive phenotype to tumors.Methods: We explored the relationship between NCS1 expression levels and patient survival in two publicly available liver cancer cohorts and a tumor microarray using data mining strategies.Results: High NCS1 expression levels are significantly associated with worse disease outcome in Asian patients within these cohorts. In addition, a variety of Ca2+-dependent and tumor growth-promoting genes are transcriptionally coregulated with NCS1 and many of them are involved in cytoskeleton organization, suggesting that NCS1 induced dysregulated Ca2+ signaling facilitates cellular motility and metastasis.Conclusions: We found NCS1 to be a novel biomarker in HCC. Furthermore, our study identified a pharmacologically targetable signaling complex that can influence tumor progression in HCC.Impact: These results lay the foundation for using NCS1 as a prognostic biomarker in prospective cohorts of HCC patients and for further functional assessment of the characterized signaling axis. Cancer Epidemiol Biomarkers Prev; 27(9); 1091-100. ©2018 AACR.

Genomic convergence of locus-based GWAS meta-analysis identifies AXIN1 as a novel Parkinson's gene

Parkinson's disease (PD) is a common, disabling neurodegenerative disorder with significant genetic underpinnings. Multiple genome-wide association studies (GWAS) have been conducted with identification of several PD loci. However, these only explain about 25% of PD genetic risk indicating that additional loci of modest effect remain to be discovered. Association clustering methods such as gene-based tests are more powerful than single-variant analysis for identifying modest genetic effects. Combined with the locus-based algorithm, OASIS, the most significant association signals can be homed in. Here, two dbGAP GWAS datasets (7415 subjects (2750 PD and 4845 controls) genotyped for 0.78 million SNPs) were analyzed using combined clustering algorithms to identify 88 PD candidate genes in 24 loci. These were further investigated for gene expression in substantia nigra (SN) of PD and control subjects on GEO datasets. Expression differences were also assessed in normal brains SN versus white matter on BRAINEAC datasets. This genetic and functional analysis identified AXIN1, a key regulator of Wnt/β-catenin signaling, as a novel PD gene. This finding links PD with inflammation. Other significantly associated genes were CSMD1, CLDN1, ZNF141, ZNF721, RHOT2, RICTOR, KANSL1, and ARHGAP27. Novel PD genes were identified using genomic convergence of gene-wide and locus-based tests and expression studies on archived datasets.

Pan-cancer analysis of homozygous deletions in primary tumours uncovers rare tumour suppressors

Homozygous deletions are rare in cancers and often target tumour suppressor genes. Here, we build a compendium of 2218 primary tumours across 12 human cancer types and systematically screen for homozygous deletions, aiming to identify rare tumour suppressors. Our analysis defines 96 genomic regions recurrently targeted by homozygous deletions. These recurrent homozygous deletions occur either over tumour suppressors or over fragile sites, regions of increased genomic instability. We construct a statistical model that separates fragile sites from regions showing signatures of positive selection for homozygous deletions and identify candidate tumour suppressors within those regions. We find 16 established tumour suppressors and propose 27 candidate tumour suppressors. Several of these genes (including MGMT, RAD17, and USP44) show prior evidence of a tumour suppressive function. Other candidate tumour suppressors, such as MAFTRR, KIAA1551, and IGF2BP2, are novel. Our study demonstrates how rare tumour suppressors can be identified through copy number meta-analysis.

Homozygous deletions are rare in cancers and often target tumour suppressor genes. Here, the authors conduct pan-cancer analyses and apply statistical modelling to identify 27 candidate tumour suppressors, including MAFTRR, KIAA1551, and IGF2BP2.

Genetic variants associated with mosaic Y chromosome loss highlight cell cycle genes and overlap with cancer susceptibility

The Y chromosome is frequently lost in hematopoietic cells, which represents the most common somatic alteration in men. However, the mechanisms that regulate mosaic loss of chromosome Y (mLOY), and its clinical relevance, are unknown. We used genotype-array-intensity data and sequence reads from 85,542 men to identify 19 genomic regions (P < 5 × 10-8) that are associated with mLOY. Cumulatively, these loci also predicted X chromosome loss in women (n = 96,123; P = 4 × 10-6). Additional epigenome-wide methylation analyses using whole blood highlighted 36 differentially methylated sites associated with mLOY. The genes identified converge on aspects of cell proliferation and cell cycle regulation, including DNA synthesis (NPAT), DNA damage response (ATM), mitosis (PMF1, CENPN and MAD1L1) and apoptosis (TP53). We highlight the shared genetic architecture between mLOY and cancer susceptibility, in addition to inferring a causal effect of smoking on mLOY. Collectively, our results demonstrate that genotype-array-intensity data enables a measure of cell cycle efficiency at population scale and identifies genes implicated in aneuploidy, genome instability and cancer susceptibility.

Involvement of ARHGEF10, GEF for RhoA, in Rab6/Rab8-mediating membrane traffic

Small GTPases play crucial roles in the maintenance of a homeostatic environment and appropriate movements of the cell. In these processes, the direct or indirect interaction between distinct small GTPases could be required for regulating mutual signaling pathways. In our recent study, ARHGEF10, known as a guanine nucleotide exchange factor (GEF) for RhoA, was indicated to interact with Rab6A and Rab8A, which are known to function in the exocytotic pathway, and colocalized with these Rabs at exocytotic vesicles. Moreover, it was suggested that ARHGEF10 is involved in the regulation of Rab6A and Rab8A localization and invasion of breast carcinoma cells, in which Rab8 also acts via regulation of membrane trafficking. These results may reveal the existence of a novel small GTPase cascade which connects the signaling of these Rabs with RhoA during membrane trafficking. In this mini-review, we consider the possible functions of ARHGEF10 and RhoA in the Rab6- and Rab8-mediated membrane trafficking pathway.

ARHGEF10 directs the localization of Rab8 to Rab6-positive executive vesicles

The function of ARHGEF10, a known guanine nucleotide exchange factor (GEF) for RhoA with proposed roles in various diseases, is poorly understood. To understand the precise function of this protein, we raised a monoclonal antibody against ARHGEF10 and determined its localization in HeLa cells. ARHGEF10 was found to localize to vesicles containing Rab6 (of which there are three isoforms, Rab6a, Rab6b and Rab6c), Rab8 (of which there are two isoforms, Rab8a and Rab8b), and/or the secretion marker neuropeptide Y (NPY)-Venus in a Rab6-dependent manner. These vesicles were known to originate from the Golgi and contain secreted or membrane proteins. Ectopic expression of an N-terminal-truncated ARHGEF10 mutant led to the generation of large vesicle-like structures containing both Rab6 and Rab8. Additionally, small interfering (si)RNA-mediated knockdown of ARHGEF10 impaired the localization of Rab8 to these exocytotic vesicles. Furthermore, the invasiveness of MDA-MB231 cells was markedly decreased by knockdown of ARHGEF10, as well as of Rab8. From these results, we propose that ARHGEF10 acts in exocytosis and tumor invasion in a Rab8-dependent manner.

Dock8 interacts with Nck1 in mediating Schwann cell precursor migration

During embryonic development of the peripheral nervous system (PNS), Schwann cell precursors migrate along neuronal axons to their final destinations, where they will myelinate the axons after birth. While the intercellular signals controlling Schwann cell precursor migration are well studied, the intracellular signals controlling Schwann cell precursor migration remain elusive. Here, using a rat primary cell culture system, we show that Dock8, an atypical Dock180-related guanine-nucleotide exchange factor (GEF) for small GTPases of the Rho family, specifically interacts with Nck1, an adaptor protein composed only of Src homology (SH) domains, to promote Schwann cell precursor migration induced by platelet-derived growth factor (PDGF). Knockdown of Dock8 or Nck1 with its respective siRNA markedly decreases PDGF-induced cell migration, as well as Rho GTPase activation, in precursors. Dock8, through its unique N-terminal proline-rich motif, interacts with the SH3 domain of Nck1, but not with other adaptor proteins composed only of SH domains, e.g. Grb2 and CrkII, and not with the adaptor protein Elmo1. Reintroduction of the proline-rich motif mutant of Dock8 in Dock8 siRNA-transfected Schwann cell precursors fails to restore their migratory abilities, whereas that of wild-type Dock8 does restore these abilities. These results suggest that Nck1 interaction with Dock8 mediates PDGF-induced Schwann cell precursor migration, demonstrating not only that Nck1 and Dock8 are previously unanticipated intracellular signaling molecules involved in the regulation of Schwann cell precursor migration but also that Dock8 is among the genetically-conservative common interaction subset of Dock family proteins consisting only of SH domain adaptor proteins.

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Dock8, a Rho family GEF, regulates Schwann cell precursor migration.

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Nck1 adaptor protein regulates Schwann cell precursor migration.

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Dock8 uniquely interacts with Nck1.

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The interaction of Dock8 with Nck1 contributes to migration.

The leukemia-associated Rho guanine nucleotide exchange factor LARG is required for efficient replication stress signaling

We previously identified and characterized TELO2 as a human protein that facilitates efficient DNA damage response (DDR) signaling. A subsequent yeast 2-hybrid screen identified LARG; Leukemia-Associated Rho Guanine Nucleotide Exchange Factor (also known as Arhgef12), as a potential novel TELO2 interactor. LARG was previously shown to interact with Pericentrin (PCNT), which, like TELO2, is required for efficient replication stress signaling. Here we confirm interactions between LARG, TELO2 and PCNT and show that a sub-set of LARG co-localizes with PCNT at the centrosome. LARG-deficient cells exhibit replication stress signaling defects as evidenced by; supernumerary centrosomes, reduced replication stress-induced γH2AX and RPA nuclear foci formation, and reduced activation of the replication stress signaling effector kinase Chk1 in response to hydroxyurea. As such, LARG-deficient cells are sensitive to replication stress-inducing agents such as hydroxyurea and mitomycin C. Conversely we also show that depletion of TELO2 and the replication stress signaling kinase ATR leads to RhoA signaling defects. These data therefore reveal a level of crosstalk between the RhoA and DDR signaling pathways. Given that mutations in both ATR and PCNT can give rise to the related primordial dwarfism disorders of Seckel Syndrome and Microcephalic osteodysplastic primordial dwarfism type II (MOPDII) respectively, which both exhibit defects in ATR-dependent checkpoint signaling, these data also raise the possibility that mutations in LARG or disruption to RhoA signaling may be contributory factors to the etiology of a sub-set of primordial dwarfism disorders.

RhoGEFs in cell motility: novel links between Rgnef and focal adhesion kinase

Rho guanine exchange factors (GEFs) are a large, diverse family of proteins defined by their ability to catalyze the exchange of GDP for GTP on small GTPase proteins such as Rho family members. GEFs act as integrators from varied intra- and extracellular sources to promote spatiotemporal activity of Rho GTPases that control signaling pathways regulating cell proliferation and movement. Here we review recent studies elucidating roles of RhoGEF proteins in cell motility. Emphasis is placed on Dbl-family GEFs and connections to development, integrin signaling to Rho GTPases regulating cell adhesion and movement, and how these signals may enhance tumor progression. Moreover, RhoGEFs have additional domains that confer distinctive functions or specificity. We will focus on a unique interaction between Rgnef (also termed Arhgef28 or p190RhoGEF) and focal adhesion kinase (FAK), a non-receptor tyrosine kinase that controls migration properties of normal and tumor cells. This Rgnef-FAK interaction activates canonical GEF-dependent RhoA GTPase activity to govern contractility and also functions as a scaffold in a GEF-independent manner to enhance FAK activation. Recent studies have also brought to light the importance of specific regions within the Rgnef pleckstrin homology (PH) domain for targeting the membrane. As revealed by ongoing Rgnef-FAK investigations, exploring GEF roles in cancer will yield fundamental new information on the molecular mechanisms promoting tumor spread and metastasis.

Controlling the switches: Rho GTPase regulation during animal cell mitosis

Animal cell division is a fundamental process that requires complex changes in cytoskeletal organization and function. Aberrant cell division often has disastrous consequences for the cell and can lead to cell senescence, neoplastic transformation or death. As important regulators of the actin cytoskeleton, Rho GTPases play major roles in regulating many aspects of mitosis and cytokinesis. These include centrosome duplication and separation, generation of cortical rigidity, microtubule-kinetochore stabilization, cleavage furrow formation, contractile ring formation and constriction, and abscission. The ability of Rho proteins to function as regulators of cell division depends on their ability to cycle between their active, GTP-bound and inactive, GDP-bound states. However, Rho proteins are inherently inefficient at fulfilling this cycle and require the actions of regulatory proteins that enhance GTP binding (RhoGEFs), stimulate GTPase activity (RhoGAPs), and sequester inactive Rho proteins in the cytosol (RhoGDIs). The roles of these regulatory proteins in controlling cell division are an area of active investigation. In this review we will delineate the current state of knowledge of how specific RhoGEFs, RhoGAPs and RhoGDIs control mitosis and cytokinesis, and highlight the mechanisms by which their functions are controlled.

Gem GTPase acts upstream Gmip/RhoA to regulate cortical actin remodeling and spindle positioning during early mitosis

Gem is a small guanosine triphosphate (GTP)-binding protein within the Ras superfamily, involved in the regulation of voltage-gated calcium channel activity and cytoskeleton reorganization. Gem overexpression leads to stress fiber disruption, actin and cell shape remodeling and neurite elongation in interphase cells. In this study, we show that Gem plays a crucial role in the regulation of cortical actin cytoskeleton that undergoes active remodeling during mitosis. Ectopic expression of Gem leads to cortical actin disruption and spindle mispositioning during metaphase. The regulation of spindle positioning by Gem involves its downstream effector Gmip. Knockdown of Gmip rescued Gem-induced spindle phenotype, although both Gem and Gmip accumulated at the cell cortex. In addition, we implicated RhoA GTPase as an important effector of Gem/Gmip signaling. Inactivation of RhoA by overexpressing dominant-negative mutant prevented normal spindle positioning. Introduction of active RhoA rescued the actin and spindle positioning defects caused by Gem or Gmip overexpression. These findings demonstrate a new role of Gem/Gmip/RhoA signaling in cortical actin regulation during early mitotic stages.

Rho GTPase-independent regulation of mitotic progression by the RhoGEF Net1

Neuroepithelial transforming gene 1 (Net1) is a RhoA-subfamily-specific guanine nucleotide exchange factor that is overexpressed in multiple human cancers and is required for proliferation. Molecular mechanisms underlying its role in cell proliferation are unknown. Here we show that overexpression or knockdown of Net1 causes mitotic defects. Net1 is required for chromosome congression during metaphase and generation of stable kinetochore microtubule attachments. Accordingly, inhibition of Net1 expression results in spindle assembly checkpoint activation. The ability of Net1 to control mitosis is independent of RhoA or RhoB activation, as knockdown of either GTPase does not phenocopy effects of Net1 knockdown on nuclear morphology, and effects of Net1 knockdown are effectively rescued by expression of catalytically inactive Net1. We also observe that Net1 expression is required for centrosomal activation of p21-activated kinase and its downstream kinase Aurora A, which are critical regulators of centrosome maturation and spindle assembly. These results identify Net1 as a novel regulator of mitosis and indicate that altered expression of Net1, as occurs in human cancers, may adversely affect genomic stability.

PLCε cooperates with the NF-κB pathway to augment TNFα-stimulated CCL2/MCP1 expression in human keratinocyte

Phospholipase Cε (PLCε) is a unique class of PLC regulated by both Ras family small GTPases and heterotrimeric G proteins. We previously showed by using mice bearing its null or transgenic allele that PLCε plays a crucial role in various forms of skin inflammation through upregulation of proinflammatory cytokine production from keratinocytes. However, molecular mechanisms how PLCε augments cytokine production were largely unknown. We show here using cultured human keratinocyte PHK16-0b cells that induction of the expression of chemokine (C-C motif) ligand 2 (CCL2) following stimulation with tumor necrosis factor (TNF)α, which primarily depends on the activation of the NF-κB pathway, is abrogated by small interfering RNA-mediated knockdown of PLCε. Enforced expression of PLCε causes substantial CCL2 expression and cooperates with low level TNFα stimulation to induce marked overexpression of CCL2, both of which are only partially blocked by pharmacological inhibition of the NF-κB signaling. However, PLCε knockdown exhibits no effect on both the NF-κB-cis-element-mediated transcription per se and the post-translational modifications of NF-κB implicated in transcriptional regulation, suggesting that PLCε constitutes a yet unknown signaling pathway distinct from the NF-κB pathway. This pathway can cooperate with the NF-κB pathway to achieve a synergistic TNFα-stimulated CCL2 induction in keratinocytes.

Identification of a negative regulatory region for the exchange activity and characterization of T332I mutant of Rho guanine nucleotide exchange factor 10 (ARHGEF10)

The T332I mutation in Rho guanine nucleotide exchange factor 10 (ARHGEF10) was previously found in persons with slowed nerve conduction velocities and thin myelination of peripheral nerves. However, the molecular and cellular basis of the T332I mutant is not understood. Here, we show that ARHGEF10 has a negative regulatory region in the N terminus, in which residue 332 is located, and the T332I mutant is constitutively active. An N-terminal truncated ARHGEF10 mutant, ARHGEF10 ΔN (lacking amino acids 1-332), induced cell contraction that was inhibited by a Rho kinase inhibitor Y27632 and had higher GEF activity for RhoA than the wild type. The T332I mutant also showed the phenotype similar to the N-terminal truncated mutant. These data suggest that the ARHGEF10 T332I mutation-associated phenotype observed in the peripheral nerves is due to activated GEF activity of the ARHGEF10 T332I mutant.

4-Methyl-3-nitro-benzoic acid, a migration inhibitor, prevents breast cancer metastasis in SCID mice

Metastasis remains a formidable problem in malignant tumors. In this study, MTT assay revealed that 4-methyl-3-nitro-benzoic acid (MNBA) had no effect on cell viability and did not interfere with cell cycle in any breast cancer cell lines tested. However, treatment with MNBA on breast cancer cells can inhibit EGF-induced migration and chemotaxis in vitro. In vivo assay demonstrated that MNBA and Paclitaxel synergistically inhibited tumor growth and metastasis in breast cancer SCID mice xenografts. These results suggest that MNBA is a potent inhibitor cancer cell chemotaxis and may be developed into a novel anti-metastasis drug.

High-resolution analysis of genomic alteration on chromosome arm 8p in urothelial carcinoma

Loss of chromosome arm 8p, sometimes in combination with amplification of proximal 8p, is found in urothelial carcinoma (UC) and other epithelial cancers and is associated with more advanced tumor stage. We carried out array comparative genomic hybridization on 174 UC and 33 UC cell lines to examine breakpoints and copy number. This was followed by a detailed analysis of the cell lines using fluorescence in situ hybridization (FISH) and, in some cases, M-FISH, to refine breakpoints and determine translocation partners, heterozygosity analysis, and analysis of expression of selected genes. We showed an overall pattern of 8p loss with reduced heterozygosity and reduced gene expression. Amplification was seen in some samples and shown in the cell line JMSU1 to correlate with overexpression of ZNF703, ERLIN2, PROSC, GPR124, and BRF2. Apart from the centromere, no single breakpoint was overrepresented, and we postulate that frequent complex changes without consistent breakpoints reflect the need for alterations of combinations of genes. The region around 2 Mb, which was homozygously deleted in one cell line and includes the gene ARHGEF10 and the micro-RNA hsa-mir-596, is one candidate tumor suppressor gene region.

RhoA and RhoC are both required for the ROCK II-dependent promotion of centrosome duplication

CDK2-cyclin E triggers centrosome duplication, and nucleophosmin (NPM/B23) is found to be one of its targets. NPM/B23 phosphorylated by CDK2-cyclin E acquires a high binding affinity to Rho-associated kinase (ROCK II), and physically associates with ROCK II. The NPM/B23-binding results in super-activation of ROCK II, which is a critical event for initiation of centrosome duplication. The activation of ROCK II also requires the binding of Rho small GTPase to the auto-inhibitory region; hence the availability of the active Rho protein is an important aspect of the centrosomally localized ROCK II to properly initiate centrosome duplication. There are three isoforms of Rho (RhoA, B, and C), all of which are capable of binding to and priming the activation of ROCK II. Here, we investigated which Rho isoform(s) are involved in the activation of ROCK II in respect to the initiation of centrosome duplication. We found that both RhoA and RhoC, but not RhoB, were required for initiation of centrosome duplication, and over-activation of RhoA as well as RhoC, but not RhoB, promoted centrosome duplication and centrosome amplification.