ARHGAP21 associates with FAK and PKCζ and is redistributed after cardiac pressure overload

Detection of Cancer-Associated Gene Mutations in Urinary Cell-Free DNA among Prostate Cancer Patients in South Africa

Prostate cancer (PCa) is the most common cause of cancer death among African men. The presence of tumor-specific variations in cell-free DNA (cfDNA), such as mutations, microsatellite instability, and DNA methylation, has been explored as a source of biomarkers for cancer diagnosis. In this study, we investigated the diagnostic role of cfDNA among South African PCa patients. We performed whole exome sequencing (WES) of urinary cfDNA. We identified a novel panel of 31 significantly deregulated somatic mutated genes between PCa and benign prostatic hyperplasia (BPH). Additionally, we performed whole-genome sequencing (WGS) on matching PCa and normal prostate tissue in an independent PCa cohort from South Africa. Our results suggest that the mutations are of germline origin as they were also found in the normal prostate tissue. In conclusion, our study contributes to the knowledge of cfDNA as a biomarker for diagnosing PCa in the South African population.

ARHGAP17 inhibits pathological cyclic strain-induced apoptosis in human periodontal ligament fibroblasts via Rac1/Cdc42

Rho GTPase-activating protein (Rho-GAP) and Rho GDP dissociation inhibitor (Rho- GDI) are two main negative regulators of Rho GTPase. Our previous work has found that Rho-GDI and Rho GTPase are involved in the response of human periodontal ligament (PDL) cells to mechanical stress. However, whether Rho-GAP also has a role in this process remains unknown. Here, we attempted to find the Rho-GAP gene that may be involved in pathological stretch-induced apoptosis of PDL cells. Human PDL fibroblasts were exposed to 20% cyclic strain for 6 hours or 24 hours, after which the expression levels of ARHGAP10, ARHGAP17, ARHGAP21, ARHGAP24 and ARHGAP28 were determined. Results showed that ARHGAP17 expression decreased the most obviously after treatment of stretch. In addition, ARHGAP17 overexpression abolished 20% cyclic strain-induced apoptosis. Therefore, ARHGAP17 has an important role in pathological stretch-induced apoptosis of human PDL fibroblasts. Moreover, we found that ARHGAP17 overexpression also alleviated cyclic strain-induced activation of Rac1/Cdc42, a major downstream target of ARHGAP17. Furthermore, two Rac1 inhibitors, NSC23766 and EHT 1864, both attenuated ARHGAP17 knockdown-mediated apoptosis in human PDL fibroblasts. Collectively, our data demonstrate that ARHGAP17 inhibits pathological cyclic strain-induced apoptosis in human PDL fibroblasts through inactivating Rac1/Cdc42. This study highlights the importance of Rho signalling in the response of human PDL fibroblasts to mechanical stress.

Sirtuin 1 represses PKC-ζ activity through regulating interplay of acetylation and phosphorylation in cardiac hypertrophy

BACKGROUND AND PURPOSE

Activation of PKC-ζ is closely linked to the pathogenesis of cardiac hypertrophy. PKC-ζ can be activated by certain lipid metabolites such as phosphatidylinositol (3,4,5)-trisphosphate and ceramide. However, its endogenous negative regulators are not well defined. Here, the role of the sirtuin1-PKC-ζ signalling axis and the underlying molecular mechanisms were investigated in cardiac hypertrophy.

EXPERIMENTAL APPROACH

Cellular hypertrophy in cultures of cardiac myocytes, from neonatal Sprague-Dawley rats, was monitored by measuring cell surface area and the mRNA levels of hypertrophic biomarkers. Interaction between sirtuin1 and PKC-ζ was investigated by co-immunoprecipitation and confocal immunofluorescence microscopy. Sirtuin1 activation was enhanced by resveratrol treatment or Ad-sirtuin1 transfection. A model of cardiac hypertrophy in Sprague-Dawley rats was established by abdominal aortic constriction surgery or induced by isoprenaline in vivo.

KEY RESULTS

Overexpression of PKC-ζ led to cardiac hypertrophy and increased activity of NF-κB, ERK1/2 and ERK5, which was ameliorated by sirtuin1 overexpression. Enhancement of sirtuin1 activity suppressed acetylation of PKC-ζ, hindered its binding to phosphoinositide-dependent kinase 1 and inhibited PKC-ζ phosphorylation in cardiac hypertrophy. Consequently, the downstream pathways of PKC-ζ' were suppressed in cardiac hypertrophy. This regulation loop suggests a new role for sirtuin1 in mediation of cardiac hypertrophy.

CONCLUSIONS AND IMPLICATIONS

Sirtuin1 is an endogenous negative regulator for PKC-ζ and mediates its activity via regulating the acetylation and phosphorylation in the pathogenesis of cardiac hypertrophy. Targeting the sirtuin1-PKC-ζ signalling axis may suggest a novel therapeutic approach against cardiac hypertrophy.

Oleanonic acid ameliorates pressure overload-induced cardiac hypertrophy in rats: The role of PKCζ-NF-κB pathway

It has been reported that inflammation is closely related with cardiac hypertrophy. Some inflammatory cytokines such as tumor necrosis factor-α, interleukin-1β, and interleukin-6 directly induce cardiac hypertrophy, which is associated with the activation of nuclear factorkappa B (NF-κB). Thus, NF-κB is an attractive target for cardiac hypertrophy. In the present study, oleanonic acid inhibited the elevation of transcriptional activity of NF-κB and reduced the mRNA expressions of hypertrophic genes such as atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) in a concentration-dependent manner in phenylephrine (PE)-treated cardiomyocytes. Furthermore, we found that oleanonic acid inhibited the phosphorylation of protein kinase C ζ (PKCζ) at Thr410 site and then reduced the activation of NF-κB using gain- and loss-of-function approaches in PE-treated cardiomyocytes. In vivo, similar results were observed in abdominal aortic constriction (AAC) rats that were intragastrically administered with oleanonic acid, and the pathological changes accompanying cardiac hypertrophy were relieved. In conclusion, oleanonic acid can effectively ameliorate cardiac hypertrophy by inhibiting PKCζ-NF-κB signaling pathway.

miR-3174 Contributes to Apoptosis and Autophagic Cell Death Defects in Gastric Cancer Cells by Targeting ARHGAP10

Gastric cancer (GC) is a major health problem worldwide because of its high morbidity and mortality. Considering the well-established roles of miRNA in the regulation of GC carcinogenesis and progression, we screened differentially expressed microRNAs (miRNAs) by using The Cancer Genome Atlas (TCGA) and the GEO databases. We found that miR-3174 was the most significantly differentially expressed miRNA in GC. Ectopic miR-3174 expression was also detected in clinical GC patient samples and cell lines and associated with poor patient prognosis. Apoptosis and autophagic cell death are two types of programmed cell death, whereas both are deficient in gastric cancer. Our functional analyses demonstrated that miR-3174 inhibited mitochondria-dependent apoptosis and autophagic cell death in GC. Moreover, high expression of miR-3174 also resulted in Cisplatin resistance in GC cells. Using bioinformatics analyses combined with in vitro and in vivo experiments, we determined that miR-3174 directly targets ARHGAP10. Notably, ARHGAP10 promoted mitochondria-dependent apoptosis by enhancing p53 expression, which was followed by Bax trans-activation and caspase cleavage. ARHGAP10 also facilitated autophagic cell death by suppressing mammalian target of rapamycin complex 1 (mTOC1) activity. Our results reveal a potential miRNA-based clinical therapeutic target that may also serve as a predictive marker for GC.

The roles of ARHGAP10 in the proliferation, migration and invasion of lung cancer cells

Lung cancer is a leading cause of cancer-related mortalities worldwide. In the present study, a comparison of To determine the roles of ARHGAP10 in the proliferation, migration and invasion of lung cancer cells expression levels between normal lung tissues and lung cancer tissues were compared using immunoblotting, and CCK-8 and Transwell assays. Lung cancer tissues had a decreased ARHGAP10 mRNA expression level compared to the adjacent normal tissues. The ectopic expression of ARHGAP10 significantly suppressed the migration, invasion and proliferation of lung cancer cells. Gene set enrichment analysis revealed that metastasis and Wnt signaling pathways were negatively correlated with ARHGAP10 expression. Immunoblotting analysis revealed that ARHGAP10 overexpression inhibited metastasis [matrix metalloproteinase (MMP)-2, MMP-9 and VEGF] and the expression of Wnt pathway-related proteins (β-catenin and c-Myc). Moreover, the stimulation effects of lithium chloride, a GSK3β inhibitor, on the accumulation of β-catenin were notably suppressed by ARHGAP10 overexpression. Collectively, ARHGAP10 acts to suppress tumor within lung cancer by affecting metastasis and Wnt signaling pathways. The results therefore suggest that ARHGAP10 is a potentially attractive target for the treatment of lung cancer.

ARHGAP10, downregulated in ovarian cancer, suppresses tumorigenicity of ovarian cancer cells

Rho GTPase-activating proteins (RhoGAPs) are implicated in the development and progression of ovarian cancer. ARHGAP10 is a member of RhoGAP proteins and inactivates Cdc42 by converting GTP-bound form to GDP-bound form. Here, we aimed to evaluate ARHGAP10 expression profile and functions in ovarian cancer. The decreased expression of ARHGAP10 was found in 77.3% (58/75) of ovarian cancer tissues, compared with their non-tumorous counterparts. Furthermore, overall survival in ovarian cancer patients with higher expression of ARHGAP10 was longer than those with lower expression. Ectopic expression of ARHGAP10 in two ovarian cancer cell lines with lower expression of ARHGAP10 (A2780 and HO-8910) dramatically suppressed cell proliferation in vitro. In nude mice, its stable overexpression significantly inhibited the tumorigenicity of A2780 cells. We further demonstrated that overexpression of ARHGAP10 significantly inhibited cell adhesion, migration and invasion, resulted in cell arrest in G1 phase of cell cycle and a significant increase of apoptosis. Moreover, ARHGAP10 interacted with Cdc42 and overexpression of ARHGAP10 inhibited the activity of Cdc42 in A2780 cells. Gene set enrichment analysis on The Cancer Genome Atlas dataset showed that KEGG cell cycle, replication and base excision repair (BER) pathways were correlatively with the ARHGAP10 expression, which was further confirmed in ovarian cancer cells by western blotting. Hence, ARHGAP10 may serve as a tumor suppressor through inactivating Cdc42, as well as inhibiting cell cycle, replication and BER pathways. Our data suggest an important role of ARHGAP10 in the molecular etiology of cancer and implicate the potential application of ARHGAP10 in cancer therapy.

ARHGAP21 prevents abnormal insulin release through actin rearrangement in pancreatic islets from neonatal mice

AIMS

ARHGAP21 is a Rho GTPase-activating protein (RhoGAP) that associates with many proteins and modulates several cellular functions, including actin cytoskeleton rearrangement in different tissues. However, it is unknown whether ARHGAP21 is expressed in pancreatic beta cells and its function in these cells. Herein, we assess the participation of ARHGAP21 in insulin secretion.

MAIN METHODS

Neonatal mice were treated with anti-sense oligonucleotide against ARHG AP21 (AS) for 2 days, resulting in a reduction of the protein's expression of about 60% in the islets. F-actin depolimerization, insulin secretion,mRNA level of genes involved in insulin secretion, maturation and proliferation were evaluated in islets from both control and AS-treated mice.

KEY FINDINGS

ARHGAP21 co-localized with actin inMIN6 beta cells and with insulin in neonatal pancreatic islets. F-actin was reduced in AS-islets, as judged by lower phalloidin intensity. Insulin secretion was increased in islets from AS-treated mice, however no differences were observed in the GSIS (glucose-stimulated insulin secretion). In these islets, the pERK1/2 was increased, as well as the gene expressions of VAMP2 and SNAP25, proteins that are present in the secretory machinery. Maturation and cell proliferation were not affected in islets from AS-treated mice.

SIGNIFICANCE

In conclusion, our data show, for the first time, that ARHGAP21 is expressed and participates in the secretory process of pancreatic beta cells. Its effect is probably via pERK1/2, which modulates the rearrangement of the cytoskeleton. ARHGAP21 also controls the expression of genes that encodes proteins of the secretory machinery.

Gαq signalling: the new and the old

In the last few years the interactome of Gαq has expanded considerably, contributing to improve our understanding of the cellular and physiological events controlled by this G alpha subunit. The availability of high-resolution crystal structures has led the identification of an effector-binding region within the surface of Gαq that is able to recognise a variety of effector proteins. Consequently, it has been possible to ascribe different Gαq functions to specific cellular players and to identify important processes that are triggered independently of the canonical activation of phospholipase Cβ (PLCβ), the first identified Gαq effector. Novel effectors include p63RhoGEF, that provides a link between G protein-coupled receptors and RhoA activation, phosphatidylinositol 3-kinase (PI3K), implicated in the regulation of the Akt pathway, or the cold-activated TRPM8 channel, which is directly inhibited upon Gαq binding. Recently, the activation of ERK5 MAPK by Gq-coupled receptors has also been described as a novel PLCβ-independent signalling axis that relies upon the interaction between this G protein and two novel effectors (PKCζ and MEK5). Additionally, the association of Gαq with different regulatory proteins can modulate its effector coupling ability and, therefore, its signalling potential. Regulators include accessory proteins that facilitate effector activation or, alternatively, inhibitory proteins that downregulate effector binding or promote signal termination. Moreover, Gαq is known to interact with several components of the cytoskeleton as well as with important organisers of membrane microdomains, which suggests that efficient signalling complexes might be confined to specific subcellular environments. Overall, the complex interaction network of Gαq underlies an ever-expanding functional diversity that puts forward this G alpha subunit as a major player in the control of physiological functions and in the development of different pathological situations.

ARHGAP21 is a RhoGAP for RhoA and RhoC with a role in proliferation and migration of prostate adenocarcinoma cells

BACKGROUND

Several Rho GTPase-activating proteins (RhoGAPs) are implicated in tumor progression through their effects on Rho GTPase activity. ARHGAP21 is a RhoGAP with increased expression in head and neck squamous cell carcinoma and with a possible role in glioblastoma tumor progression, yet little is known about the function of ARHGAP21 in cancer cells. Here we studied the role of ARHGAP21 in two prostate adenocarcinoma cell lines, LNCaP and PC3, which respectively represent initial and advanced stages of prostate carcinogenesis.

RESULTS

ARHGAP21 is located in the nucleus and cytoplasm of both cell lines and its depletion resulted in decreased proliferation and increased migration of PC3 cells but not LNCaP cells. In PC3 cells, ARHGAP21 presented GAP activity for RhoA and RhoC and induced changes in cell morphology. Moreover, its silencing altered the expression of genes involved in cell proliferation and cytoskeleton organization, as well as the endothelin-1 canonical pathway.

CONCLUSIONS

Our results reveal new functions and signaling pathways regulated by ARHGAP21, and indicate that it could contribute to prostate cancer progression.

ErbB/integrin signaling interactions in regulation of myocardial cell-cell and cell-matrix interactions

Neuregulin (Nrg)/ErbB and integrin signaling pathways are critical for the normal function of the embryonic and adult heart. Both systems activate several downstream signaling pathways, with different physiological outputs: cell survival, fibrosis, excitation-contraction coupling, myofilament structure, cell-cell and cell-matrix interaction. Activation of ErbB2 by Nrg1β in cardiomycytes or its overexpression in cancer cells induces phosphorylation of FAK (Focal Adhesion Kinase) at specific sites with modulation of survival, invasion and cell-cell contacts. FAK is also a critical mediator of integrin receptors, converting extracellular matrix alterations into intracellular signaling. Systemic FAK deletion is lethal and is associated with left ventricular non-compaction whereas cardiac restriction in adult hearts is well tolerated. Nevertheless, these hearts are more susceptible to stress conditions like trans-aortic constriction, hypertrophy, and ischemic injury. As FAK is both downstream and specifically activated by integrins and Nrg-1β, here we will explore the role of FAK in the heart as a protective factor and as possible mediator of the crosstalk between the ErbB and Integrin receptors. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

Protein kinase C (PKC)ζ-mediated Gαq stimulation of ERK5 protein pathway in cardiomyocytes and cardiac fibroblasts

Gq-coupled G protein-coupled receptors (GPCRs) mediate the actions of a variety of messengers that are key regulators of cardiovascular function. Enhanced Gα(q)-mediated signaling plays an important role in cardiac hypertrophy and in the transition to heart failure. We have recently described that Gα(q) acts as an adaptor protein that facilitates PKCζ-mediated activation of ERK5 in epithelial cells. Because the ERK5 cascade is known to be involved in cardiac hypertrophy, we have investigated the potential relevance of this pathway in cardiovascular Gq-dependent signaling using both cultured cardiac cell types and chronic administration of angiotensin II in mice. We find that PKCζ is required for the activation of the ERK5 pathway by Gq-coupled GPCR in neonatal and adult murine cardiomyocyte cultures and in cardiac fibroblasts. Stimulation of ERK5 by angiotensin II is blocked upon pharmacological inhibition or siRNA-mediated silencing of PKCζ in primary cultures of cardiac cells and in neonatal cardiomyocytes isolated from PKCζ-deficient mice. Moreover, upon chronic challenge with angiotensin II, these mice fail to promote the changes in the ERK5 pathway, in gene expression patterns, and in hypertrophic markers observed in wild-type animals. Taken together, our results show that PKCζ is essential for Gq-dependent ERK5 activation in cardiomyocytes and cardiac fibroblasts and indicate a key cardiac physiological role for the Gα(q)/PKCζ/ERK5 signaling axis.

Focal adhesion kinase -- the basis of local hypertrophic signaling domains

Focal adhesion kinase (FAK), a broadly expressed non-receptor tyrosine kinase which transduces signals from integrins, growth and hormonal factors, is a key player in many fundamental biological processes and functions, including cell adhesion, migration, proliferation and survival. The involvement of FAK in this range of functions supports its role in important aspects of organismal development and disease, such as central nervous system and cardiovascular development, cancer, cardiac hypertrophy and tissue fibrosis. Many functions of FAK are correlated with its tyrosine kinase activity, which is temporally and spatially controlled by complex intra-molecular autoinhibitory conformation and inter-molecular interactions with protein and lipid partners. The inactivation of FAK in mice results in embryonic lethality attributed to the lack of proper development and function of the heart. Accordingly, embryonic FAK myocyte-specific knockout mice display lethal cardiac defects such as thin ventricle wall and ventricular septum defects. Emerging data also support a role for FAK in the reactive hypertrophy and failure of adult hearts. Moreover, the mechanisms that regulate FAK in differentiated cardiac myocytes to biomechanical stress and soluble factors are beginning to be revealed and are discussed here together with data that connect FAK to its downstream effectors. This article is part of a Special Issue entitled "Local Signaling in Myocytes".

β-Arrestin 1 inhibits the GTPase-activating protein function of ARHGAP21, promoting activation of RhoA following angiotensin II type 1A receptor stimulation

Activation of the small GTPase RhoA following angiotensin II stimulation is known to result in actin reorganization and stress fiber formation. Full activation of RhoA, by angiotensin II, depends on the scaffolding protein β-arrestin 1, although the mechanism behind its involvement remains elusive. Here we uncover a novel partner and function for β-arrestin 1, namely, in binding to ARHGAP21 (also known as ARHGAP10), a known effector of RhoA activity, whose GTPase-activating protein (GAP) function it inhibits. Using yeast two-hybrid screening, a peptide array, in vitro binding studies, truncation analyses, and coimmunoprecipitation techniques, we show that β-arrestin 1 binds directly to ARHGAP21 in a region that transects the RhoA effector GAP domain. Moreover, we show that the level of a complex containing β-arrestin 1 and ARHGAP21 is dynamically increased following angiotensin stimulation and that the kinetics of this interaction modulates the temporal activation of RhoA. Using information gleaned from a peptide array, we developed a cell-permeant peptide that serves to inhibit the interaction of these proteins. Using this peptide, we demonstrate that disruption of the β-arrestin 1/ARHGAP21 complex results in a more active ARHGAP21, leading to less-efficient signaling via the angiotensin II type 1A receptor and, thereby, attenuation of stimulated stress fiber formation.