G Protein-Coupled Receptor and RhoA-Stimulated Transcriptional Responses: Links to Inflammation, Differentiation, and Cell Proliferation

Inhibition of the Rho/MRTF pathway improves the response of BRAF-resistant melanoma to PD1/PDL1 blockade

Metastatic cutaneous melanoma is a fatal skin cancer. Resistance to targeted and immune therapies limits the benefits of current treatments. Identifying and adding anti-resistance agents to current treatment protocols can potentially improve clinical responses. Myocardin-related transcription factor (MRTF) is a transcriptional coactivator whose activity is indirectly regulated by actin and the Rho family of GTPases. We previously demonstrated that development of BRAF inhibitor (BRAFi) resistance frequently activates the Rho/MRTF pathway in human and mouse BRAFV600E melanomas. In clinical trials, pretreatment with BRAFi reduces the benefit of immune therapies. We aimed to test the efficacy of concurrent treatment with our MRTF pathway inhibitor CCG-257081 and anti-PD1 in vivo and to examine its effects on the melanoma immune microenvironment. Because MRTF pathway activation upregulates the expression of immune checkpoint inhibitor genes/proteins, we asked whether CCG-257081 can improve the response to immune checkpoint blockade. CCG-257081 reduced the expression of PDL1 in BRAFi-resistant melanoma cells and decreased surface PDL1 levels on both BRAFi-sensitive and -resistant melanoma cells. Using our recently described murine vemurafenib-resistant melanoma model, we found that CCG-257081, in combination with anti-PD1 immune therapy, reduced tumor growth and increased survival. Moreover, anti-PD1/CCG-257081 co-treatment increased infiltration of CD8+ T cells and B cells into the tumor microenvironment and reduced tumor-associated macrophages. Here, we propose CCG-257081 as an anti-resistance and immune therapy-enhancing anti-melanoma agent.

Untangling the role of RhoA in the heart: protective effect and mechanism

RhoA (ras homolog family member A) is a small G-protein that transduces intracellular signaling to regulate a broad range of cellular functions such as cell growth, proliferation, migration, and survival. RhoA serves as a proximal downstream effector of numerous G protein-coupled receptors (GPCRs) and is also responsive to various stresses in the heart. Upon its activation, RhoA engages multiple downstream signaling pathways. Rho-associated coiled-coil-containing protein kinase (ROCK) is the first discovered and best characterized effector or RhoA, playing a major role in cytoskeletal arrangement. Many other RhoA effectors have been identified, including myocardin-related transcription factor A (MRTF-A), Yes-associated Protein (YAP) and phospholipase Cε (PLCε) to regulate transcriptional and post-transcriptional processes. The role of RhoA signaling in the heart has been increasingly studied in last decades. It was initially suggested that RhoA signaling pathway is maladaptive in the heart, but more recent studies using cardiac-specific expression or deletion of RhoA have revealed that RhoA activation provides cardioprotection against stress through various mechanisms including the novel role of RhoA in mitochondrial quality control. This review summarizes recent advances in understanding the role of RhoA in the heart and its signaling pathways to prevent progression of heart disease.

Exercise Attenuate Diaphragm Atrophy in COPD Mice via Inhibiting the RhoA/ROCK Signaling

Background

Exercise is an indispensable component of pulmonary rehabilitation with strong anti-inflammatory effects. However, the mechanisms by which exercise prevents diaphragmatic atrophy in COPD (chronic obstructive pulmonary disease) remain unclear.

Methods

Forty male C57BL/6 mice were assigned to the control (n=16) and smoke (n=24) groups. Mice in the smoke group were exposed to the cigarette smoke (CS) for six months. They were then divided into model and exercise training groups for 2 months. Histological changes were observed in lung and diaphragms. Subsequently, agonist U46639 and antagonist Y27632 of RhoA/ROCK were subjected to mechanical stretching in LPS-treated C2C12 myoblasts. The expression levels of Atrogin-1, MuRF-1, MyoD, Myf5, IL-1β, TNF-α, and RhoA/ROCK were determined by Western blotting.

Results

Diaphragmatic atrophy and increased RhoA/ROCK expression were observed in COPD mice. Exercise training attenuated diaphragmatic atrophy, decreased the expression of MuRF-1, and increased MyoD expression in COPD diaphragms. Exercise also affects the upregulation of RhoA/ROCK and inflammation-related proteins. In in vitro experiments with C2C12 myoblasts, LPS remarkably increased the level of inflammation and protein degradation, whereas Y27632 or combined with mechanical stretching prevented this phenomenon considerably.

Conclusion

RhoA/ROCK plays an important role in the prevention of diaphragmatic atrophy in COPD.

Exploiting Cell-Based Assays to Accelerate Drug Development for G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) are relevant targets for health and disease as they regulate various aspects of metabolism, proliferation, differentiation, and immune pathways. They are implicated in several disease areas, including cancer, diabetes, cardiovascular diseases, and mental disorders. It is worth noting that about a third of all marketed drugs target GPCRs, making them prime pharmacological targets for drug discovery. Numerous functional assays have been developed to assess GPCR activity and GPCR signaling in living cells. Here, we review the current literature of genetically encoded cell-based assays to measure GPCR activation and downstream signaling at different hierarchical levels of signaling, from the receptor to transcription, via transducers, effectors, and second messengers. Singleplex assay formats provide one data point per experimental condition. Typical examples are bioluminescence resonance energy transfer (BRET) assays and protease cleavage assays (e.g., Tango or split TEV). By contrast, multiplex assay formats allow for the parallel measurement of multiple receptors and pathways and typically use molecular barcodes as transcriptional reporters in barcoded assays. This enables the efficient identification of desired on-target and on-pathway effects as well as detrimental off-target and off-pathway effects. Multiplex assays are anticipated to accelerate drug discovery for GPCRs as they provide a comprehensive and broad identification of compound effects.

Spatiotemporal Optical Control of Gαq-PLCβ Interactions

Cells experience time-varying and spatially heterogeneous chemokine signals in vivo, activating cell surface proteins including G protein-coupled receptors (GPCRs). The Gαq pathway activation by GPCRs is a major signaling axis with broad physiological and pathological significance. Compared with other Gα members, GαqGTP activates many crucial effectors, including PLCβ (Phospholipase Cβ) and Rho GEFs (Rho guanine nucleotide exchange factors). PLCβ regulates many key processes, such as hematopoiesis, synaptogenesis, and cell cycle, and is therefore implicated in terminal-debilitating diseases, including cancer, epilepsy, Huntington's Disease, and Alzheimer's Disease. However, due to a lack of genetic and pharmacological tools, examining how the dynamic regulation of PLCβ signaling controls cellular physiology has been difficult. Since activated PLCβ induces several abrupt cellular changes, including cell morphology, examining how the other pathways downstream of Gq-GPCRs contribute to the overall signaling has also been difficult. Here we show the engineering, validation, and application of a highly selective and efficient optogenetic inhibitor (Opto-dHTH) to completely disrupt GαqGTP-PLCβ interactions reversibly in user-defined cellular-subcellular regions on optical command. Using this newly gained PLCβ signaling control, our data indicate that the molecular competition between RhoGEFs and PLCβ for GαqGTP determines the potency of Gq-GPCR-governed directional cell migration.

Recent Insights in Pyrin Inflammasome Activation: Identifying Potential Novel Therapeutic Approaches in Pyrin-Associated Autoinflammatory Syndromes

Pyrin is a cytosolic protein encoded by the MEFV gene, predominantly expressed in innate immune cells. Upon activation, it forms an inflammasome, a multimolecular complex that enables the activation and secretion of IL-1β and IL-18. In addition, the Pyrin inflammasome activates Gasdermin D leading to pyroptosis, a highly pro-inflammatory cell death. Four autoinflammatory syndromes are associated with Pyrin inflammasome dysregulation: familial Mediterranean fever, hyper IgD syndrome/mevalonate kinase deficiency, pyrin-associated autoinflammation with neutrophilic dermatosis, and pyogenic arthritis, pyoderma gangrenosum, and acne syndrome. In this review, we discuss recent advances in understanding the molecular mechanisms regulating the two-step model of Pyrin inflammasome activation. Based on these insights, we discuss current pharmacological options and identify a series of existing molecules with therapeutic potential for the treatment of pyrin-associated autoinflammatory syndromes.

Gα12 signaling regulates transcriptional and phenotypic responses that promote glioblastoma tumor invasion

In silico interrogation of glioblastoma (GBM) in The Cancer Genome Atlas (TCGA) revealed upregulation of GNA12 (Gα12), encoding the alpha subunit of the heterotrimeric G-protein G12, concomitant with overexpression of multiple G-protein coupled receptors (GPCRs) that signal through Gα12. Glioma stem cell lines from patient-derived xenografts also showed elevated levels of Gα12. Knockdown (KD) of Gα12 was carried out in two different human GBM stem cell (GSC) lines. Tumors generated in vivo by orthotopic injection of Gα12KD GSC cells showed reduced invasiveness, without apparent changes in tumor size or survival relative to control GSC tumor-bearing mice. Transcriptional profiling of GSC-23 cell tumors revealed significant differences between WT and Gα12KD tumors including reduced expression of genes associated with the extracellular matrix, as well as decreased expression of stem cell genes and increased expression of several proneural genes. Thrombospondin-1 (THBS1), one of the genes most repressed by Gα12 knockdown, was shown to be required for Gα12-mediated cell migration in vitro and for in vivo tumor invasion. Chemogenetic activation of GSC-23 cells harboring a Gα12-coupled DREADD also increased THBS1 expression and in vitro invasion. Collectively, our findings implicate Gα12 signaling in regulation of transcriptional reprogramming that promotes invasiveness, highlighting this as a potential signaling node for therapeutic intervention.

Ephexin3/ARHGEF5 Together with Cell Migration Signaling Partners within the Tumor Microenvironment Define Prognostic Transcriptional Signatures in Multiple Cancer Types

Cancer cell migration involves a repertoire of signaling proteins that lead cytoskeleton reorganization as a critical step in metastatic dissemination. RhoGEFs are multidomain effectors that integrate signaling inputs to activate the molecular switches that orchestrate actin cytoskeleton reorganization. Ephexins, a group of five RhoGEFs, play oncogenic roles in invasive and metastatic cancer, leading to a mechanistic hypothesis about their function as signaling nodes assembling functional complexes that guide cancer cell migration. To identify clinically significant Ephexin signaling partners, we applied three systematic data mining strategies, based on the screening of essential Ephexins in multiple cancer cell lines and the identification of coexpressed signaling partners in the TCGA cancer patient datasets. Based on the domain architecture of encoded proteins and gene ontology criteria, we selected Ephexin signaling partners with a role in cytoskeletal reorganization and cell migration. We focused on Ephexin3/ARHGEF5, identified as an essential gene in multiple cancer cell types. Based on significant coexpression data and coessentiality, the signaling repertoire that accompanies Ephexin3 corresponded to three groups: pan-cancer, cancer-specific and coessential. To further select the Ephexin3 signaling partners likely to be relevant in clinical settings, we first identified those whose high expression was statistical linked to shorter patient survival. The resulting Ephexin3 transcriptional signatures represent significant accumulated risk, predictive of shorter survival, in 17 cancer types, including PAAD, LUAD, LGG, OSC, AML, KIRC, THYM, BLCA, LIHC and UCEC. The signaling landscape that accompanies Ephexin3 in various cancer types included the tyrosine kinase receptor MET and the tyrosine phosphatase receptor PTPRF, the serine/threonine kinases MARK2 and PAK6, the Rho GTPases RHOD, RHOF and RAC1, and the cytoskeletal regulator DIAHP1. Our findings set the basis to further explore the role of Ephexin3/ARHGEF5 as an essential effector and signaling hub in cancer cell migration.

Spatiotemporal optical control of Gαq-PLCβ interactions

Cells experience time-varying and spatially heterogeneous chemokine signals in vivo, activating cell surface proteins, including G protein-coupled receptors (GPCRs). The Gαq pathway activation by GPCRs is a major signaling axis with a broad physiological and pathological significance. Compared to other Gα members, GαqGTP activates many crucial effectors, including PLCβ (Phospholipase Cβ) and Rho GEFs (Rho guanine nucleotide exchange factors). PLCβ regulates many key processes, such as hematopoiesis, synaptogenesis, and cell cycle, and is therefore implicated in terminal - debilitating diseases, including cancer, epilepsy, Huntington's Disease, and Alzheimer's Disease. However, due to a lack of genetic and pharmacological tools, examining how the dynamic regulation of PLCβ signaling controls cellular physiology has been difficult. Since activated PLCβ induces several abrupt cellular changes, including cell morphology, examining how the other pathways downstream of Gq-GPCRs contribute to the overall signaling has also been difficult. Here we show the engineering, validation, and application of a highly selective and efficient optogenetic inhibitor (Opto-dHTH) to completely disrupt GαqGTP-PLCβ interactions reversibly in user-defined cellular-subcellular regions on optical command. Using this newly gained PLCβ signaling control, our data indicate that the molecular competition between RhoGEFs and PLCβ for GαqGTP determines the potency of Gq-GPCR-governed directional cell migration.

Guanine nucleotide exchange factors for Rho GTPases (RhoGEFs) as oncogenic effectors and strategic therapeutic targets in metastatic cancer

Metastatic cancer cells dynamically adjust their shape to adhere, invade, migrate, and expand to generate secondary tumors. Inherent to these processes is the constant assembly and disassembly of cytoskeletal supramolecular structures. The subcellular places where cytoskeletal polymers are built and reorganized are defined by the activation of Rho GTPases. These molecular switches directly respond to signaling cascades integrated by Rho guanine nucleotide exchange factors (RhoGEFs), which are sophisticated multidomain proteins that control morphological behavior of cancer and stromal cells in response to cell-cell interactions, tumor-secreted factors and actions of oncogenic proteins within the tumor microenvironment. Stromal cells, including fibroblasts, immune and endothelial cells, and even projections of neuronal cells, adjust their shapes and move into growing tumoral masses, building tumor-induced structures that eventually serve as metastatic routes. Here we review the role of RhoGEFs in metastatic cancer. They are highly diverse proteins with common catalytic modules that select among a variety of homologous Rho GTPases enabling them to load GTP, acquiring an active conformation that stimulates effectors controlling actin cytoskeleton remodeling. Therefore, due to their strategic position in oncogenic signaling cascades, and their structural diversity flanking common catalytic modules, RhoGEFs possess unique characteristics that make them conceptual targets of antimetastatic precision therapies. Preclinical proof of concept, demonstrating the antimetastatic effect of inhibiting either expression or activity of βPix (ARHGEF7), P-Rex1, Vav1, ARHGEF17, and Dock1, among others, is emerging.

Targeting small GTPases: emerging grasps on previously untamable targets, pioneered by KRAS

Small GTPases including Ras, Rho, Rab, Arf, and Ran are omnipresent molecular switches in regulating key cellular functions. Their dysregulation is a therapeutic target for tumors, neurodegeneration, cardiomyopathies, and infection. However, small GTPases have been historically recognized as "undruggable". Targeting KRAS, one of the most frequently mutated oncogenes, has only come into reality in the last decade due to the development of breakthrough strategies such as fragment-based screening, covalent ligands, macromolecule inhibitors, and PROTACs. Two KRAS^G12C covalent inhibitors have obtained accelerated approval for treating KRAS^G12C mutant lung cancer, and allele-specific hotspot mutations on G12D/S/R have been demonstrated as viable targets. New methods of targeting KRAS are quickly evolving, including transcription, immunogenic neoepitopes, and combinatory targeting with immunotherapy. Nevertheless, the vast majority of small GTPases and hotspot mutations remain elusive, and clinical resistance to G12C inhibitors poses new challenges. In this article, we summarize diversified biological functions, shared structural properties, and complex regulatory mechanisms of small GTPases and their relationships with human diseases. Furthermore, we review the status of drug discovery for targeting small GTPases and the most recent strategic progress focused on targeting KRAS. The discovery of new regulatory mechanisms and development of targeting approaches will together promote drug discovery for small GTPases.

Differential role for rapid proteostasis in Rho GTPase-mediated control of quiescent endothelial integrity

Endothelial monolayer permeability is regulated by actin dynamics and vesicular traffic. Recently, ubiquitination was also implicated in the integrity of quiescent endothelium, as it differentially controls the localization and stability of adhesion- and signaling proteins. However, the more general effect of fast protein turnover on endothelial integrity is not clear. Here, we found that inhibition of E1 ubiquitin ligases induces a rapid, reversible loss of integrity in quiescent, primary human endothelial monolayers, accompanied by increased F-actin stress fibers and the formation of intercellular gaps. Concomitantly, total protein and activity of the actin-regulating GTPase RhoB, but not its close homologue RhoA, increase ∼10-fold in 5-8 h. We determined that, the depletion of RhoB, but not of RhoA, the inhibition of actin contractility and the inhibition of protein synthesis all significantly rescue the loss of cell-cell contact induced by E1 ligase inhibition. Collectively, our data suggest that in quiescent human endothelial cells, the continuous and fast turnover of short-lived proteins that negatively regulate cell-cell contact, is essential to preserve monolayer integrity.

Overexpressed Gα13 activates serum response factor through stoichiometric imbalance with Gβγ and mislocalization to the cytoplasm

Gα13, a heterotrimeric G protein α subunit of the G12/13 subfamily, is an oncogenic driver in multiple cancer types. Unlike other G protein subfamilies that contribute to cancer progression via amino acid substitutions that abolish their deactivating, intrinsic GTPase activity, Gα13 rarely harbors such mutations in tumors and instead appears to stimulate aberrant cell growth via overexpression as a wildtype form. It is not known why this effect is exclusive to the G12/13 subfamily, nor has a mechanism been elucidated for overexpressed Gα13 promoting tumor progression. Using a reporter gene assay for serum response factor (SRF)-mediated transcription in HEK293 cells, we found that transiently expressed, wildtype Gα13 generates a robust SRF signal, approximately half the amplitude observed for GTPase-defective Gα13. When epitope-tagged, wildtype Gα13 was titrated upward in cells, a sharp increase in SRF stimulation was observed coincident with a "spillover" of Gα13 from membrane-associated to a soluble fraction. Overexpressing G protein β and γ subunits caused both a decrease in this signal and a shift of wildtype Gα13 back to the membranous fraction, suggesting that stoichiometric imbalance in the αβγ heterotrimer results in aberrant subcellular localization and signalling by overexpressed Gα13. We also examined the acylation requirements of wildtype Gα13 for signalling to SRF. Similar to GTPase-defective Gα13, S-palmitoylation of the wildtype α subunit was necessary for SRF activation but could be replaced functionally by an engineered site for N-terminal myristoylation. However, a key difference was observed between wildtype and GTPase-defective Gα13: whereas the latter protein lacking palmitoylation sites was rescued in its SRF signalling by either an engineered polybasic sequence or a C-terminal isoprenylation site, these motifs failed to restore signalling by wildtype, non-palmitoylated Gα13. These findings illuminate several components of the mechanism in which overexpressed, wildtype Gα13 contributes to growth and tumorigenic signalling, and reveal greater stringency in its requirements for post-translational modification in comparison to GTPase-defective Gα13.

Neutralization of excessive CCL28 improves wound healing in diabetic mice

Introduction: Chronic, non-healing skin wounds such as diabetic foot ulcers (DFUs) are common in patients with type 2 diabetes mellitus (T2DM) and often result in limb amputation and even death. However, mechanisms by which T2DM and inflammation negatively impact skin wound healing remains poorly understood. Here we investigate a mechanism by which an excessive level of chemokine CCL28, through its receptor CCR10, impairs wound healing in patients and mice with T2DM. Methods & Results: Firstly, a higher level of CCL28 was observed in skin and plasma in both patients with T2DM, and in obesity-induced type 2 diabetic db/db mice. Compared with WT mice, adipose tissue from db/db mice released 50% more CCL28, as well as 2- to 3-fold more IL-1β, IL-6, and TNF-α, and less VEGF, as determined by ELISA measurements. Secondly, overexpression of CCL28 with adenovirus (Adv-CCL28) caused elevation of proinflammatory cytokines as well as CCR10 expression and also reduced eNOS expression in the dorsal skin of WT mice as compared with control Adv. Thirdly, topical application of neutralizing anti-CCL28 Ab dose-dependently accelerated wound closure and eNOS expression, and decreased IL-6 level, with an optimal dose of 1 μg/wound. In addition, mRNA levels of eNOS and anti-inflammatory cytokine IL-4 were increased as shown by real-time RT-PCR. The interaction between eNOS and CCR10 was significantly reduced in diabetic mouse wounds following application of the optimal dose of anti-CCL28 Ab, and eNOS expression increased. Finally, enhanced VEGF production and increased subdermal vessel density as indicated by CD31 immunostaining were also observed with anti-CCL28 Ab. Discussion: Taken together, topical application of neutralizing anti-CCL28 Ab improved dorsal skin wound healing by reducing CCR10 activation and inflammation in part by preventing eNOS downregulation, increasing VEGF production, and restoring angiogenesis. These results indicate anti-CCL28 Ab has significant potential as a therapeutic strategy for treatment of chronic non-healing diabetic skin wounds such as DFUs.

Unveiling the biological role of sphingosine-1-phosphate receptor modulators in inflammatory bowel diseases

Inflammatory bowel disease (IBD) is chronic inflammation of the gastrointestinal tract that has a high epidemiological prevalence worldwide. The increasing disease burden worldwide, lack of response to current biologic therapeutics, and treatment-related immunogenicity have led to major concerns regarding the clinical management of IBD patients and treatment efficacy. Understanding disease pathogenesis and disease-related molecular mechanisms is the most important goal in developing new and effective therapeutics. Sphingosine-1-phosphate (S1P) receptor (S1PR) modulators form a class of oral small molecule drugs currently in clinical development for IBD have shown promising effects on disease improvement. S1P is a sphingosine-derived phospholipid that acts by binding to its receptor S1PR and is involved in the regulation of several biological processes including cell survival, differentiation, migration, proliferation, immune response, and lymphocyte trafficking. T lymphocytes play an important role in regulating inflammatory responses. In inflamed IBD tissue, an imbalance between T helper (Th) and regulatory T lymphocytes and Th cytokine levels was found. The S1P/S1PR signaling axis and metabolism have been linked to inflammatory responses in IBD. S1P modulators targeting S1PRs and S1P metabolism have been developed and shown to regulate inflammatory responses by affecting lymphocyte trafficking, lymphocyte number, lymphocyte activity, cytokine production, and contributing to gut barrier function.

The Role of Myofibroblasts in Physiological and Pathological Tissue Repair

Myofibroblasts are the construction workers of wound healing and repair damaged tissues by producing and organizing collagen/extracellular matrix (ECM) into scar tissue. Scar tissue effectively and quickly restores the mechanical integrity of lost tissue architecture but comes at the price of lost tissue functionality. Fibrotic diseases caused by excessive or persistent myofibroblast activity can lead to organ failure. This review defines myofibroblast terminology, phenotypic characteristics, and functions. We will focus on the central role of the cell, ECM, and tissue mechanics in regulating tissue repair by controlling myofibroblast action. Additionally, we will discuss how therapies based on mechanical intervention potentially ameliorate wound healing outcomes. Although myofibroblast physiology and pathology affect all organs, we will emphasize cutaneous wound healing and hypertrophic scarring as paradigms for normal tissue repair versus fibrosis. A central message of this review is that myofibroblasts can be activated from multiple cell sources, varying with local environment and type of injury, to either restore tissue integrity and organ function or create an inappropriate mechanical environment.

RhoA signaling increases mitophagy and protects cardiomyocytes against ischemia by stabilizing PINK1 protein and recruiting Parkin to mitochondria

Mitophagy, a mitochondria-specific form of autophagy, removes dysfunctional mitochondria and is hence an essential process contributing to mitochondrial quality control. PTEN-induced kinase 1 (PINK1) and the E3 ubiquitin ligase Parkin are critical molecules involved in stress-induced mitophagy, but the intracellular signaling mechanisms by which this pathway is regulated are unclear. We tested the hypothesis that signaling through RhoA, a small GTPase, induces mitophagy via modulation of the PINK1/Parkin pathway as a protective mechanism against ischemic stress. We demonstrate that expression of constitutively active RhoA as well as sphingosine-1-phosphate induced activation of endogenous RhoA in cardiomyocytes result in an accumulation of PINK1 at mitochondria. This is accompanied by translocation of Parkin to mitochondria and ubiquitination of mitochondrial proteins leading to recognition of mitochondria by autophagosomes and their lysosomal degradation. Expression of RhoA in cardiomyocytes confers protection against ischemia, and this cardioprotection is attenuated by siRNA-mediated PINK1 knockdown. In vivo myocardial infarction elicits increases in mitochondrial PINK1, Parkin, and ubiquitinated mitochondrial proteins. AAV9-mediated RhoA expression potentiates these responses and a concurrent decrease in infarct size is observed. Interestingly, induction of mitochondrial PINK1 accumulation in response to RhoA signaling is neither mediated through its transcriptional upregulation nor dependent on depolarization of the mitochondrial membrane, the canonical mechanism for PINK1 accumulation. Instead, our results reveal that RhoA signaling inhibits PINK1 cleavage, thereby stabilizing PINK1 protein at mitochondria. We further show that active RhoA localizes at mitochondria and interacts with PINK1, and that the mitochondrial localization of RhoA is regulated by its downstream effector protein kinase D. These findings demonstrate that RhoA activation engages a unique mechanism to regulate PINK1 accumulation, induce mitophagy and protect against ischemic stress, and implicates regulation of RhoA signaling as a potential strategy to enhance mitophagy and confer protection under stress conditions.

Interaction kinetics between p115-RhoGEF and Gα13 are determined by unique molecular interactions affecting agonist sensitivity

The three RH-RhoGEFs (Guanine nucleotide exchange factors) p115-RhoGEF, LARG (leukemia-associated RhoGEF) and PDZ-RhoGEF link G-protein coupled receptors (GPCRs) with RhoA signaling through activation of Gα_12/13. In order to find functional differences in signaling between the different RH-RhoGEFs we examined their interaction with Gα₁₃ in high spatial and temporal resolution, utilizing a FRET-based single cell assay. We found that p115-RhoGEF interacts significantly shorter with Gα₁₃ than LARG and PDZ-RhoGEF, while narrowing the structural basis for these differences down to a single amino acid in the rgRGS domain of p115-RhoGEF. The mutation of this amino acid led to an increased interaction time with Gα₁₃ and an enhanced agonist sensitivity, comparable to LARG, while mutating the corresponding amino acid in Gα₁₃ the same effect could be achieved. While the rgRGS domains of RH-RhoGEFs showed GAP (GTPase-activating protein) activity towards Gα₁₃ in vitro, our approach suggests higher GAP activity of p115-RhoGEF in intact cells.

A Hypothesis Regarding Neurosecretory Inhibition of Stress Mediators by Colchicine in Preventing Stress-Induced Familial Mediterranean Fever Attacks

Familial Mediterranean fever (FMF) is a monogenic autoinflammatory disease characterized by recurrent episodes of fever and serositis. Colchicine (Col) has a crucial role in the prevention of amyloidosis and FMF attacks. The effect of Col on innate immune cells is based on the inhibition of the microtubule system. The microtubule system is also very important for neurosecretory functions. The inhibitory effect of Col on neurosecretory functions is an overlooked issue. Considering that the neuroimmune cross-talk process plays a role in the development of inflammatory diseases, the effect of Col on the neuronal system becomes important. FMF attacks are related to emotional stress. Therefore, the effect of Col on stress mediators is taken into consideration. In this hypothetical review, we discuss the possible effects of Col on the central nervous systems (CNS) and peripheral nervous systems (PNS) in light of mostly experimental study findings using animal models. Studies to be carried out on this subject will shed light on the pathogenesis of FMF attacks and the other possible mechanisms of action of Col apart from the anti-inflammatory features.

Dietary patterns in association with the expression of pro-metastatic genes in primary breast cancer

PURPOSE

Metastasis is a major leading cause of mortality in female breast cancer (BrCa). Cellular motility is a pathological process of metastasis remarked by the overexpression of cortactin (CTTN), Ras homolog family member-A (RhoA), and Rho-associated kinase (ROCK) genes. Their balance is responsible for upholding the integrity of healthy epithelial cell junctions. This study aimed to explore the associations between a posteriori dietary patterns and the expression levels of pro-metastatic genes in primary BrCa.

METHODS

In this consecutive case series, 215 eligible women, newly diagnosed with histologically confirmed non-metastatic BrCa (stage I-IIIA), were recruited from Hospitals in Tabriz, Northwestern Iran (2015-2017). The tumoral expression levels of genes were quantified using real-time reverse transcription-polymerase chain reaction. Dietary data assessment was carried out using a validated food frequency questionnaire.

RESULTS

Three dietary patterns were identified using principal component analysis (KMO = 0.699). Adherence to the "vegan" pattern (vegetables, fruits, legumes, nuts, seeds, and whole grains) was inversely associated with the expression levels of RhoA (OR_Adj.T3vs.T1 = 0.24, 95%CI 0.07-0.79) and ROCK (OR_Adj.T3vs.T1 = 0.26, 95%CI 0.08-0.87). In addition, the highest adherence to the "prudent" pattern (spices, seafood, dairy, and vegetable oils) decreased the odds of overexpressions at RhoA (OR_Adj.T3vs.T1 = 0.26, 95%CI 0.08-0.84) and ROCK genes (OR_Adj.T3vs.T1 = 0.29, 95%CI 0.09-0.95). The highest adherence to "Western" pattern (meat, processed meat, hydrogenated fat, fast food, refined cereals, sweets, and soft drinks) was a risk factor associated with the overexpression of RhoA (OR_Adj.T3vs.T1 = 3.15, 95%CI 1.12-8.85).

CONCLUSION

Adherence to healthy dietary patterns was significantly associated with the downregulation of pro-metastatic genes. Findings provided new implications to advance the nutrigenomic knowledge to prevent the odds of over-regulations in pro-metastatic genes of the primary BrCa.

Intranuclear Delivery of DNA Nanostructures via Cellular Mechanotransduction

DNA nanostructures are attractive gene carriers for nanomedicine applications, yet their delivery to the nucleus remains inefficient. We present the application of extracellular mechanical stimuli to activate cellular mechanotransduction for boosting the intranuclear delivery of DNA nanostructures. Treating mammalian cells with polythymidine-rich spherical nucleic acids (poly(T) SNAs) under gentle compression by a single coverslip leads to up to ∼50% nuclear accumulation without severe endosomal entrapment, cytotoxicity, or long-term membrane damage; no chemical modification or transfection reagent is needed. Gentle compression activates Rho-ROCK mechanotransduction and causes nuclear translocation of YAP. Joint compression and treatment with poly(T) oligonucleotides upregulate genes linked to myosin, actin filament, and nuclear import. In turn, Rho-ROCK, myosin, and importin mediate the nuclear entry of poly(T) SNAs. Treatment of endothelioma cells with poly(T) SNAs bearing antisense oligonucleotides under compression inhibits an intranuclear oncogene. Our data should inspire the marriage of DNA nanotechnology and cellular biomechanics for intranuclear applications.

HNRNPC regulates RhoA to induce DNA damage repair and cancer-associated fibroblast activation causing radiation resistance in pancreatic cancer

Pancreatic cancer (PC) is one of the most lethal types of cancer due to its asymptomatic nature in the early stages and consequent late diagnosis. Its mortality rate remains high despite advances in treatment strategies, which include a combination of surgical resection and adjuvant therapy. Although these approaches may have a positive effect on prognosis, the development of chemo- and radioresistance still poses a significant challenge for successful PC treatment. Heterogeneous nuclear ribonucleoprotein C1/C2 (HNRNPC) and RhoA have been implicated in the regulation of tumour cell proliferation and chemo- and radioresistance. Our study aims to investigate the mechanism for HNRNPC regulation of PC radiation resistance via the RhoA pathway. We found that HNRNPC and RhoA mRNA and protein expression levels were significantly higher in PC tissues compared to adjacent non-tumour tissue. Furthermore, high HNRNPC expression was associated with poor patient prognosis. Using HNRNPC overexpression and siRNA interference, we demonstrated that HNRNPC overexpression promoted radiation resistance in PC cells, while HNRNPC knockdown increased radiosensitivity. However, silencing of RhoA expression was shown to attenuate radiation resistance caused by HNRNPC overexpression. Next, we identified RhoA as a downstream target of HNRNPC and showed that inhibition of the RhoA/ROCK2-YAP/TAZ pathway led to a reduction in DNA damage repair and radiation resistance. Finally, using both in vitro assays and an in vivo subcutaneous tumour xenograft model, we demonstrated that RhoA inhibition can hinder the activity of cancer-related fibroblasts and weaken PC radiation resistance. Our study describes a role for HNRNPC and the RhoA/ROCK2-YAP/TAZ signalling pathways in mediating radiation resistance and provides a potential therapeutic target for improving the treatment of PC.

Sphingosine 1-Phosphate Receptor 5 (S1P5) Deficiency Promotes Proliferation and Immortalization of Mouse Embryonic Fibroblasts

Simple Summary

Sphingosine 1-phosphate (S1P) is a lipid metabolite involved in cell proliferation, survival or migration. S1P is a ligand for five high-affinity G protein-coupled receptors (S1P1-5), which differ in their tissue distribution, and the specific effects of S1P depend on the suite of S1P receptor subtypes expressed. To date, information regarding the role of S1P5 in cell proliferation is limited and ambiguous. Our results suggest that, unlike other S1P receptors, the S1P5 receptor has an anti-proliferative function. We found that S1P5 deficiency promotes cell immortalization and proliferation by controlling the spatial activation of ERK.

Abstract

Sphingosine 1-phosphate (S1P), a bioactive lipid, interacts with five widely expressed G protein-coupled receptors (S1P1-5), regulating a variety of downstream signaling pathways with overlapping but also opposing functions. To date, data regarding the role of S1P5 in cell proliferation are ambiguous, and its role in controlling the growth of untransformed cells remains to be fully elucidated. In this study, we examined the effects of S1P5 deficiency on mouse embryonic fibroblasts (MEFs). Our results indicate that lack of S1P5 expression profoundly affects cell morphology and proliferation. First, S1P5 deficiency reduces cellular senescence and promotes MEF immortalization. Second, it decreases cell size and leads to cell elongation, which is accompanied by decreased cell spreading and migration. Third, it increases proliferation rate, a phenotype rescued by the reintroduction of exogenous S1P5. Mechanistically, S1P5 promotes the activation of FAK, controlling cell spreading and adhesion while the anti-proliferative function of the S1P/S1P5 signaling is associated with reduced nuclear accumulation of activated ERK. Our results suggest that S1P5 opposes the growth-promoting function of S1P1-3 through spatial control of ERK activation and provides new insights into the anti-proliferative function of S1P5.

Agonist-induced extracellular vesicles contribute to the transfer of functional bombesin receptor-subtype 3 to recipient cells

Extracellular vesicles (EVs) are important carriers for biomolecules in the microenvironment that greatly promote intercellular and extracellular communications. However, it is unclear whether bombesin receptor-subtype 3 (BRS-3), an orphan G-protein coupled receptor, can be packed into EVs and functionally transferred to recipient cells. In this study, we applied the synthetic agonist and antagonist to activate and inhibit the BRS-3 in HEK293-BRS-3 cells, whose EVs release was BRS-3 activation dependent. The presence of BRS-3 in harvested EVs was further confirmed by an enhanced green fluorescent protein tag. After recipient cells were co-cultured with these EVs, the presence of BRS-3 in the recipient cells was discovered, whose function was experimentally validated. Quantitative proteomics approach was utilized to decipher the proteome of the EVs derived from HEK293-BRS-3 cells after different stimulations. More than 900 proteins were identified, including 51 systematically dysregulated EVs proteins. The Ingenuity Pathway Analysis (IPA) revealed that RhoA signaling pathway was as an essential player for the secretion of EVs. Selective inhibition of RhoA signaling pathway after BRS-3 activation dramatically reversed the increased secretion of EVs. Our data, collectively, demonstrated that EVs contributed to the transfer of functional BRS-3 to the recipient cells, whose secretion was partially regulated by RhoA signaling pathway.

Regulation of Leukaemia Associated Rho GEF (LARG/ARHGEF12)

The Ras homologous (Rho) protein family of GTPases (RhoA, RhoB and RhoC) are the members of the Ras superfamily and regulate cellular processes such as cell migration, proliferation, polarization, adhesion, gene transcription and cytoskeletal structure. Rho GTPases function as molecular switches that cycle between GTP-bound (active state) and GDP-bound (inactive state) forms. Leukaemia-associated RhoGEF (LARG) is a guanine nucleotide exchange factor (GEF) that activates RhoA subfamily GTPases by promoting the exchange of GDP for GTP. LARG is selective for RhoA subfamily GTPases and is an essential regulator of cell migration and invasion. Here, we describe the mechanisms by which LARG is regulated to facilitate the understanding of how LARG mediates functions like cell motility and to provide insight for better therapeutic targeting of these functions.

The Rho kinase (ROCK) inhibitor Y-27632 reduces the β2-adrenoceptor density but enhance cAMP formation in primary equine bronchial epithelial cells

The present study addresses the effect of the Rho-kinase (ROCK) inhibitor Y-27632 on the β2-adrenoceptor density and β-agonist-stimulated intracellular second messenger cAMP formation in primary equine bronchial epithelial cells (EBEC). Y-27632 significantly decreased the β2-adrenoceptor number (Bmax) without markedly affecting the receptor affinity (dissociation constant, KD) to the radioligand [125I]-iodocyanopindolol (ICYP). In contrast, Y-27632 augmented the β-agonist-stimulated intracellular cAMP production. Herein, Y-27632 markedly increased the maximal cAMP responses (Emax) (isoproterenol > epinephrine > norepinephrine) but did not shift the β-agonist concentration-effect curves to the left. The β2-selective antagonist ICI 118.551 and the β1/β2-antagonsit propranolol but not the β1-selctive antagonist CGP 20712A reversed the isoproterenol-induced cAMP formation equally in Y-27632-treated and control EBEC, suggesting the effect was merely related to the β2-subtype. These results show that Y-27632 differentially regulates the receptor density and function. Thus, these findings provide the first evidence that the functional interaction of the β2-adrenoceptor and Rho-kinase (ROCK) signaling pathways decreases the receptor expression but enhances receptor downstream cAMP formation. This differential regulation of the receptor density and function by Y-27632 should be further reconsidered with regard to the beneficial effect of the drug in asthma therapy.

Lysophosphatidic Acid Signaling in Cancer Cells: What Makes LPA So Special?

Lysophosphatidic acid (LPA) refers to a family of simple phospholipids that act as ligands for G protein-coupled receptors. While LPA exerts effects throughout the body in normal physiological circumstances, its pathological role in cancer is of great interest from a therapeutic viewpoint. The numerous LPA receptors (LPARs) are coupled to a variety of G proteins, and more than one LPAR is typically expressed on any given cell. While the individual receptors signal through conventional GPCR pathways, LPA is particularly efficacious in stimulating cancer cell proliferation and migration. This review addresses the mechanistic aspects underlying these pro-tumorigenic effects. We provide examples of LPA signaling responses in various types of cancers, with an emphasis on those where roles have been identified for specific LPARs. While providing an overview of LPAR signaling, these examples also reveal gaps in our knowledge regarding the mechanisms of LPA action at the receptor level. The current understanding of the LPAR structure and the roles of LPAR interactions with other receptors are discussed. Overall, LPARs provide insight into the potential molecular mechanisms that underlie the ability of individual GPCRs (or combinations of GPCRs) to elicit a unique spectrum of responses from their agonist ligands. Further knowledge of these mechanisms will inform drug discovery, since GPCRs are promising therapeutic targets for cancer.

Pharmacological characterization of the imipridone anti-cancer drug ONC201 reveals a negative allosteric mechanism of action at the D2 dopamine receptor

ONC201 is a first-in-class imipridone compound that is in clinical trials for the treatment of high-grade gliomas and other advanced cancers. Recent studies identified that ONC201 antagonizes D2-like dopamine receptors at therapeutically relevant concentrations. In the current study, characterization of ONC201 using radioligand binding and multiple functional assays revealed that it was a full antagonist of the D2 and D3 receptors (D2R and D3R) with low micromolar potencies, similar to its potency for anti-proliferative effects. Curve-shift experiments using D2R-mediated b-arrestin recruitment and cAMP assays revealed that ONC201 exhibited a mixed form of antagonism. An operational model of allostery was used to analyze these data, which suggested that the predominant modulatory effect of ONC201 was on dopamine efficacy with little to no effect on dopamine affinity. To investigate how ONC201 binds to the D2R, we employed scanning mutagenesis coupled with a D2R-mediated calcium efflux assay. Eight residues were identified as being important for ONC201's functional antagonism of the D2R. Mutation of these residues followed by assessing ONC201 antagonism in multiple signaling assays highlighted specific residues involved in ONC201 binding. Together with computational modeling and simulation studies, our results suggest that ONC201 interacts with the D2R in a bitopic manner where the imipridone core of the molecule protrudes into the orthosteric binding site, but does not compete with dopamine, whereas a secondary phenyl ring engages an allosteric binding pocket that may be associated with negative modulation of receptor activity. Significance Statement ONC201 is a novel antagonist of the D2 dopamine receptor with demonstrated efficacy in the treatment of various cancers, especially high-grade glioma. In this study, we demonstrate that it antagonizes the D2 receptor with novel bitopic and negative allosteric mechanisms of action, which may explain its high selectivity and some of its clinical anti-cancer properties that are distinct from other D2 receptor antagonists widely used for the treatment of schizophrenia and other neuropsychiatric disorders.

Tumour cell CD99 regulates transendothelial migration via CDC42 and actin remodelling

Metastasis requires tumour cells to cross endothelial cell (EC) barriers using pathways similar to those used by leucocytes during inflammation. Cell surface CD99 is expressed by healthy leucocytes and ECs, and participates in inflammatory transendothelial migration (TEM). Tumour cells also express CD99, and we have analysed its role in tumour progression and cancer cell TEM. Tumour cell CD99 was required for adhesion to ECs but inhibited invasion of the endothelial barrier and migratory activity. Furthermore, CD99 depletion in tumour cells caused redistribution of the actin cytoskeleton and increased activity of the Rho GTPase CDC42, known for its role in actin remodelling and cell migration. In a xenograft model of breast cancer, tumour cell CD99 expression inhibited metastatic progression, and patient samples showed reduced expression of the CD99 gene in brain metastases compared to matched primary breast tumours. We conclude that CD99 negatively regulates CDC42 and cell migration. However, CD99 has both pro- and anti-tumour activity, and our data suggest that this results in part from its functional linkage to CDC42 and the diverse signalling pathways downstream of this Rho GTPase. This article has an associated First Person interview with the first author of the paper.

Chronic restraint stress induces changes in the cerebral Galpha 12/13 and Rho-GTPase signaling network

Background

Evidence indicates that Gα12, Gα13, and its downstream effectors, RhoA and Rac1, regulate neuronal morphology affected by stress. This study was aimed at investigating whether repeated stress influences the expression of proteins related to the Gα12/13 intracellular signaling pathway in selected brain regions sensitive to the effects of stress. Furthermore, the therapeutic impact of β(1)adrenergic receptors (β1AR) blockade was assessed.

Methods

Restraint stress (RS) model in mice (2 h/14 days) was used to assess prolonged stress effects on the mRNA expression of Gα12, Gα13, RhoA, Rac1 in the prefrontal cortex (PFC), hippocampus (HIP) and amygdala (AMY). In a separate study, applying RS model in rats (3–4 h/1 day or 14 days), we evaluated stress effects on the expression of Gα12, Gα11, Gαq, RhoA, RhoB, RhoC, Rac1/2/3 in the HIP. Betaxolol (BET), a selective β1AR antagonist, was introduced (5 mg/kg/p.o./8–14 days) in the rat RS model to assess the role of β1AR in stress effects. RT-qPCR and Western Blot were used for mRNA and protein assessments, respectively.

Results

Chronic RS decreased mRNA expression of Gα12 and increased mRNA for Rac1 in the PFC of mice. In the mice AMY, decreased mRNA expression of Gα12, Gα13 and RhoA was observed. Fourteen days of RS exposure increased RhoA protein level in the rats’ HIP in the manner dependent on β1AR activity.

Conclusions

Together, these results suggest that repeated RS affects the expression of genes and proteins known to be engaged in neural plasticity, providing potential targets for further studies aimed at unraveling the molecular mechanisms of stress-related neuropsychiatric diseases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43440-021-00294-4.

Targeting Gα13-integrin interaction ameliorates systemic inflammation

Systemic inflammation as manifested in sepsis is an excessive, life-threatening inflammatory response to severe bacterial or viral infection or extensive injury. It is also a thrombo-inflammatory condition associated with vascular leakage/hemorrhage and thrombosis that is not effectively treated by current anti-inflammatory or anti-thrombotic drugs. Here, we show that MB2mP6 peptide nanoparticles, targeting the Gα13-mediated integrin "outside-in" signaling in leukocytes and platelets, inhibited both inflammation and thrombosis without causing hemorrhage/vascular leakage. MB2mP6 improved mouse survival when infused immediately or hours after onset of severe sepsis. Furthermore, platelet Gα13 knockout inhibited septic thrombosis whereas leukocyte Gα13 knockout diminished septic inflammation, each moderately improving survival. Dual platelet/leukocyte Gα13 knockout inhibited septic thrombosis and inflammation, further improving survival similar to MB2mP6. These results demonstrate that inflammation and thrombosis independently contribute to poor outcomes and exacerbate each other in systemic inflammation, and reveal a concept of dual anti-inflammatory/anti-thrombotic therapy without exacerbating vascular leakage.

The Impact of Spaceflight and Microgravity on the Human Islet-1+ Cardiovascular Progenitor Cell Transcriptome

Understanding the transcriptomic impact of microgravity and the spaceflight environment is relevant for future missions in space and microgravity-based applications designed to benefit life on Earth. Here, we investigated the transcriptome of adult and neonatal cardiovascular progenitors following culture aboard the International Space Station for 30 days and compared it to the transcriptome of clonally identical cells cultured on Earth. Cardiovascular progenitors acquire a gene expression profile representative of an early-stage, dedifferentiated, stem-like state, regardless of age. Signaling pathways that support cell proliferation and survival were induced by spaceflight along with transcripts related to cell cycle re-entry, cardiovascular development, and oxidative stress. These findings contribute new insight into the multifaceted influence of reduced gravitational environments.

ZHX3 promotes the progression of urothelial carcinoma of the bladder via repressing of RGS2 and is a novel substrate of TRIM21

Clinically, patients with urothelial carcinoma of the bladder (UCB) with tumor metastasis are incurable. To find new therapeutic strategies, the mechanisms underlying UCB invasion and metastasis should be further investigated. In this study, zinc finger and homeobox 3 (ZHX3) was first screened as a critical oncogenic factor associated with poor prognosis in a UCB dataset from The Cancer Genome Atlas (TCGA). These results were also confirmed in a large cohort of clinical UCB clinical samples. Next, we found that ZHX3 could promote the migration and invasion capacities of UCB cells both in vitro and in vivo. Mechanistically, coimmunoprecipitation (coIP) and mass spectrometry (MS) analysis indicated that ZHX3 was a target of tripartite motif 21 (TRIM21), which mediates its ubiquitination, and subsequent degradation. Notably, RNA‐seq analysis showed that ZHX3 repressed the expression of regulator of G protein signaling 2 (RGS2). Generally, our results suggest that ZHX3 plays an oncogenic role in UCB pathogenesis and might serve as a novel therapeutic target for UCB.

Neuropeptide Y/Y5 Receptor Pathway Stimulates Neuroblastoma Cell Motility Through RhoA Activation

Neuropeptide Y (NPY) has been implicated in the regulation of cellular motility under various physiological and pathological conditions, including cancer dissemination. Yet, the exact signaling pathways leading to these effects remain unknown. In a pediatric malignancy, neuroblastoma (NB), high NPY release from tumor tissue associates with metastatic disease. Here, we have shown that NPY stimulates NB cell motility and invasiveness and acts as a chemotactic factor for NB cells. We have also identified the Y5 receptor (Y5R) as the main NPY receptor mediating these actions. In NB tissues and cell cultures, Y5R is highly expressed in migratory cells and accumulates in regions of high RhoA activity and dynamic cytoskeleton remodeling. Y5R stimulation activates RhoA and results in Y5R/RhoA-GTP interactions, as shown by pull-down and proximity ligation assays, respectively. This is the first demonstration of the role for the NPY/Y5R axis in RhoA activation and the subsequent cytoskeleton remodeling facilitating cell movement. These findings implicate Y5R as a target in anti-metastatic therapies for NB and other cancers expressing this receptor.

RGS proteins, GRKs, and beta-arrestins modulate G protein-mediated signaling pathways in asthma

Asthma is a highly prevalent disorder characterized by chronic lung inflammation and reversible airways obstruction. Pathophysiological features of asthma include episodic and reversible airway narrowing due to increased bronchial smooth muscle shortening in response to external and host-derived mediators, excessive mucus secretion into the airway lumen, and airway remodeling. The aberrant airway smooth muscle (ASM) phenotype observed in asthma manifests as increased sensitivity to contractile mediators (EC₅₀) and an increase in the magnitude of contraction (E_max); collectively these attributes have been termed "airways hyper-responsiveness" (AHR). This defining feature of asthma can be promoted by environmental factors including airborne allergens, viruses, and air pollution and other irritants. AHR reduces airway caliber and obstructs airflow, evoking clinical symptoms such as cough, wheezing and shortness of breath. G-protein-coupled receptors (GPCRs) have a central function in asthma through their impact on ASM and airway inflammation. Many but not all treatments for asthma target GPCRs mediating ASM contraction or relaxation. Here we discuss the roles of specific GPCRs, G proteins, and their associated signaling pathways, in asthma, with an emphasis on endogenous mechanisms of GPCR regulation of ASM tone and lung inflammation including regulators of G-protein signaling (RGS) proteins, G-protein coupled receptor kinases (GRKs), and β-arrestin.

Optogenetic control of small GTPases reveals RhoA mediates intracellular calcium signaling

Rho/Ras family small GTPases are known to regulate numerous cellular processes, including cytoskeletal reorganization, cell proliferation, and cell differentiation. These processes are also controlled by Ca²⁺, and consequently, cross talk between these signals is considered likely. However, systematic quantitative evaluation has not yet been reported. To fill this gap, we constructed optogenetic tools to control the activity of small GTPases (RhoA, Rac1, Cdc42, Ras, Rap, and Ral) using an improved light-inducible dimer system (iLID). We characterized these optogenetic tools with genetically encoded red fluorescence intensity-based small GTPase biosensors and confirmed these optogenetic tools’ specificities. Using these optogenetic tools, we investigated calcium mobilization immediately after small GTPase activation. Unexpectedly, we found that a transient intracellular calcium elevation was specifically induced by RhoA activation in RPE1 and HeLa cells. RhoA activation also induced transient intracellular calcium elevation in MDCK and HEK293T cells, suggesting that generally RhoA induces calcium signaling. Interestingly, the molecular mechanisms linking RhoA activation to calcium increases were shown to be different among the different cell types: In RPE1 and HeLa cells, RhoA activated phospholipase C epsilon (PLCε) at the plasma membrane, which in turn induced Ca²⁺ release from the endoplasmic reticulum (ER). The RhoA–PLCε axis induced calcium-dependent nuclear factor of activated T cells nuclear translocation, suggesting that it does activate intracellular calcium signaling. Conversely, in MDCK and HEK293T cells, RhoA–ROCK–myosin II axis induced the calcium transients. These data suggest universal coordination of RhoA and calcium signaling in cellular processes, such as cellular contraction and gene expression.

YAP/TAZ inhibition reduces metastatic potential of Ewing sarcoma cells

Ewing sarcoma (EwS) is a highly metastatic bone cancer characterized by the ETS fusion oncoprotein EWS-FLI1. EwS cells are phenotypically highly plastic and switch between functionally distinct cell states dependent on EWS-FLI1 fluctuations. Whereas EWS-FLI1^high cells proliferate, EWS-FLI1^low cells are migratory and invasive. Recently, we reported activation of MRTFB and TEAD, effectors of RhoA and Hippo signalling, upon low EWS-FLI1, orchestrating key steps of the EwS migratory gene expression program. TEAD and its co-activators YAP and TAZ are commonly overexpressed in cancer, providing attractive therapeutic targets. We find TAZ levels to increase in the migratory EWS-FLI1^low state and to associate with adverse prognosis in EwS patients. We tested the effects of the potent YAP/TAZ/TEAD complex inhibitor verteporfin on EwS cell migration in vitro and on metastasis in vivo. Verteporfin suppressed expression of EWS-FLI1 regulated cytoskeletal genes involved in actin signalling to the extracellular matrix, effectively blocked F-actin and focal-adhesion assembly and inhibited EwS cell migration at submicromolar concentrations. In a mouse EwS xenograft model, verteporfin treatment reduced relapses at the surgical site and delayed lung metastasis. These data suggest that YAP/TAZ pathway inhibition may prevent EwS cell dissemination and metastasis, justifying further preclinical development of YAP/TAZ inhibitors for EwS treatment.

Influence of ARHGAP29 on the Invasion of Mesenchymal-Transformed Breast Cancer Cells

Aggressive and mesenchymal-transformed breast cancer cells show high expression levels of Rho GTPase activating protein 29 (ARHGAP29), a negative regulator of RhoA. ARHGAP29 was the only one of 32 GTPase-activating enzymes whose expression significantly increased after the induction of mesenchymal transformation in breast cancer cells. Therefore, we investigated the influence of ARHGAP29 on the invasiveness of aggressive and mesenchymal-transformed breast cancer cells. After knock-down of ARHGAP29 using siRNA, invasion of HCC1806, MCF-7-EMT, and T-47D-EMT breast cancer cells was significantly reduced. This could be explained by reduced inhibition of RhoA and a consequent increase in stress fiber formation. Proliferation of the breast cancer cell line T-47D-EMT was slightly increased by reduced expression of ARHGAP29, whereas that of HCC1806 and MCF-7-EMT significantly increased. Using interaction analyses we found that AKT1 is a possible interaction partner of ARHGAP29. Therefore, the expression of AKT1 after siRNA knock-down of ARHGAP29 was tested. Reduced ARHGAP29 expression was accompanied by significantly reduced AKT1 expression. However, the ratio of active pAKT1 to total AKT1 remained unchanged or was significantly increased after ARHGAP29 knock-down. Our results show that ARHGAP29 could be an important factor in the invasion of aggressive and mesenchymal-transformed breast cancer cells. Further research is required to fully understand the underlying mechanisms.

Calmodulin downregulation in conditional knockout HeLa cells inhibits cell migration

The study of calmodulin (CaM) functions in living cells has been tackled up to date using cell-permeant CaM inhibitors or interference-RNA methods. CaM inhibitors may lack specificity and the siRNA interference approach is challenging, as all three CaM genes expressing an identical protein in mammals have to be blocked. Therefore, we recently introduced a novel genetic system using CRISPR/Cas9-mediated gene deletion and conditional CaM expression to study the function of CaM in HeLa cells. Here, we describe the effect of CaM downregulation on the basal and epidermal growth factor (EGF)-dependent 2D- and 3D-migration in HeLa cells. CaM downregulation inhibited cell migration on a 2D-surface in the absence but not in the presence of EGF. In contrast, CaM downregulation led to inhibition of 3D-migration across a porous membrane both in the absence and presence of EGF. CaM downregulation decreased the expression of Rac1, Cdc42 and RhoA, all known to play crucial roles in cell migration. These results show that EGF-dependent 2D- and 3D-migration utilize distinct CaM-regulated systems and identify several essential migratory proteins directly or indirectly regulated by CaM.

Histamine-induced biphasic activation of RhoA allows for persistent RhoA signaling

The small GTPase RhoA is a central signaling enzyme that is involved in various cellular processes such as cytoskeletal dynamics, transcription, and cell cycle progression. Many signal transduction pathways activate RhoA—for instance, Gα_q-coupled Histamine 1 Receptor signaling via Gα_q-dependent activation of RhoGEFs such as p63. Although multiple upstream regulators of RhoA have been identified, the temporal regulation of RhoA and the coordination of different upstream components in its regulation have not been well characterized. In this study, live-cell measurement of RhoA activation revealed a biphasic increase of RhoA activity upon histamine stimulation. We showed that the first and second phase of RhoA activity are dependent on p63 and Ca²⁺/PKC, respectively, and further identified phosphorylation of serine 240 on p115 RhoGEF by PKC to be the mechanistic link between PKC and RhoA. Combined approaches of computational modeling and quantitative measurement revealed that the second phase of RhoA activation is insensitive to rapid turning off of the receptor and is required for maintaining RhoA-mediated transcription after the termination of the receptor signaling. Thus, two divergent pathways enable both rapid activation and persistent signaling in receptor-mediated RhoA signaling via intricate temporal regulation.

The small GTPase RhoA is a central signaling enzyme that is involved in various cellular processes such as cytoskeletal dynamics, transcription, and cell cycle progression. This study shows that histamine induces biphasic activation of RhoA via two divergent signaling pathways, allowing for intricate regulation of cellular processes.

Ran GTPase: A Key Player in Tumor Progression and Metastasis

Ran (Ras-related nuclear protein) GTPase is a member of the Ras superfamily. Like all the GTPases, Ran cycles between an active (GTP-bound) and inactive (GDP-bound) state. However, Ran lacks the CAAX motif at its C-terminus, a feature of other small GTPases that ensures a plasma membrane localization, and largely traffics between the nucleus and the cytoplasm. Ran regulates nucleo-cytoplasmic transport of molecules through the nuclear pore complex and controls cell cycle progression through the regulation of microtubule polymerization and mitotic spindle formation. The disruption of Ran expression has been linked to cancer at different levels - from cancer initiation to metastasis. In the present review, we discuss the contribution of Ran in the acquisition of three hallmarks of cancer, namely, proliferative signaling, resistance to apoptosis, and invasion/metastasis, and highlight its prognostic value in cancer patients. In addition, we discuss the use of this GTPase as a therapeutic target in cancer.

Divergent C-terminal motifs in Gα12 and Gα13 provide distinct mechanisms of effector binding and SRF activation

The G12/13 subfamily of heterotrimeric guanine nucleotide binding proteins comprises the α subunits Gα12 and Gα13, which transduce signals for cell growth, cytoskeletal rearrangements, and oncogenic transformation. In an increasing range of cancers, overexpressed Gα12 or Gα13 are implicated in aberrant cell proliferation and/or metastatic invasion. Although Gα12 and Gα13 bind non-redundant sets of effector proteins and participate in unique signalling pathways, the structural features responsible for functional differences between these α subunits are largely unknown. Invertebrates encode a single G12/13 homolog that participates in cytoskeletal changes yet appears to lack signalling to SRF (serum response factor), a transcriptional activator stimulated by mammalian Gα12 and Gα13 to promote growth and tumorigenesis. Our previous studies identified an evolutionarily divergent region in Gα12 for which replacement by homologous sequence from Drosophila melanogaster abolished SRF signalling, whereas the same invertebrate substitution was fully tolerated in Gα13 [Montgomery et al. (2014) Mol. Pharmacol. 85: 586]. These findings prompted our current approach of evolution-guided mutagenesis to identify fine structural features of Gα12 and Gα13 that underlie their respective SRF activation mechanisms. Our results identified two motifs flanking the α4 helix that play a key role in Gα12 signalling to SRF. We found the region encompassing these motifs to provide an interacting surface for multiple Gα12-specific target proteins that fail to bind Gα13. Adjacent to this divergent region, a highly-conserved domain was vital for SRF activation by both Gα12 and Gα13. However, dissection of this domain using invertebrate substitutions revealed different signalling mechanisms in these α subunits and identified Gα13-specific determinants of binding Rho-specific guanine nucleotide exchange factors. Furthermore, invertebrate substitutions in the C-terminal, α5 helical region were selectively disruptive to Gα12 signalling. Taken together, our results identify key structural features near the C-terminus that evolved after the divergence of Gα12 and Gα13, and should aid the development of agents to selectively manipulate signalling by individual α subunits of the G12/13 subfamily.

Haploinsufficient Rock1+/- and Rock2+/- Mice Are Not Protected from Cardiac Inflammation and Postinflammatory Fibrosis in Experimental Autoimmune Myocarditis

Progressive cardiac fibrosis is a common cause of heart failure. Rho-associated, coiled-coil-containing protein kinases (ROCKs) have been shown to enhance fibrotic processes in the heart and in other organs. In this study, using wild-type, Rock1^+/− and Rock2^+/− haploinsufficient mice and mouse model of experimental autoimmune myocarditis (EAM) we addressed the role of ROCK1 and ROCK2 in development of myocarditis and postinflammatory fibrosis. We found that myocarditis severity was comparable in wild-type, Rock1^+/− and Rock2^+/− mice at day 21 of EAM. During the acute stage of the disease, hearts of Rock1^+/− mice showed unaffected numbers of CD11b⁺CD36⁺ macrophages, CD11b⁺CD36^–Ly6G^hiLy6c^hi neutrophils, CD11b⁺CD36^–Ly6G^–Ly6c^hi inflammatory monocytes, CD11b⁺CD36^–Ly6G^–Ly6c^– monocytes, CD11b⁺SiglecF⁺ eosinophils, CD11b⁺CD11c⁺ inflammatory dendritic cells and type I collagen-producing fibroblasts. Isolated Rock1^+/− cardiac fibroblasts treated with transforming growth factor-beta (TGF-β) showed attenuated Smad2 and extracellular signal-regulated kinase (Erk) phosphorylations that were associated with impaired upregulation of smooth muscle actin alpha (αSMA) protein. In contrast to cardiac fibroblasts, expanded Rock1^+/− heart inflammatory myeloid cells showed unaffected Smad2 activation but enhanced Erk phosphorylation following TGF-β treatment. Rock1^+/− inflammatory cells responded to TGF-β by a reduced transcriptional profibrotic response and failed to upregulate αSMA and fibronectin at the protein levels. Unexpectedly, in the EAM model wild-type, Rock1^+/− and Rock2^+/− mice developed a similar extent of cardiac fibrosis at day 40. In addition, hearts of the wild-type and Rock1^+/− mice showed comparable levels of cardiac vimentin, periostin and αSMA. In conclusion, despite the fact that ROCK1 regulates TGF-β-dependent profibrotic response, neither ROCK1 nor ROCK2 is critically involved in the development of postinflammatory fibrosis in the EAM model.

Modulation of sphingosine-1-phosphate in ulcerative colitis

Introduction: Sphingosine-1-phosphate (S1P) is a membrane-derived lysophospholipid signaling molecule implicated in various physiological and pathological processes, such as regulation of the immune, cardiovascular, pulmonary, and nervous systems and theoretical cancer-related risks, through extracellular activation of S1P1-5 receptors.Areas covered: S1P receptor agonism is a novel strategy for the treatment of UC targeting lymphocyte recirculation, through blockade of lymphocyte egress from lymph nodes. We conducted an extensive literature review on PUBMED on currently available data on molecular aspects of S1P modulation, the mechanisms of action of S1PR agonists (fingolimod, ozanimod, etrasimod, and KRP-203), and their potential efficacy and safety for the treatment of patients with ulcerative colitis.Expert opinion: Selective S1P modulators have emerged to enlarge the efficacy and safety profile of this class of agents. Phase 3 programs should add the potential body of evidence to prove their benefit for the management of UC patients.

Characterizing how probiotic Lactobacillus reuteri 6475 and lactobacillic acid mediate suppression of osteoclast differentiation

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Osteoporosis is a disease that impacts over 200 million people worldwide.

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The probiotic bacterium Lactobacillus reuteri (L. reuteri) has been shown to prevent bone loss during estrogen deficiency.

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Lactobacillic acid is important for L. reuteri-induced suppression of in vitro osteoclastogenesis.

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Osteoclastogenesis was inhibited by L. reuteri and lactobacillic acid via GPR120 signaling.

Osteoporosis is a disease that impacts over 200 million people worldwide. Taking into consideration the side effects stemming from medications used to treat this illness, investigators have increased their efforts to develop novel therapeutics for osteoporosis. In a previous study, we demonstrated that ovariectomy-induced bone loss in mice was prevented by treatment with the probiotic bacterium Lactobacillus reuteri 6475 (L. reuteri), an effect that correlated with reduced osteoclastogenesis in the bone marrow of L. reuteri treated mice. We also demonstrated that L. reuteri directly inhibited osteoclastogenesis in vitro. To better understand how L. reuteri impacts osteoclast formation, we used additional in vitro analyses to identify that conditioned supernatant from L. reuteri inhibited osteoclastogenesis at the intermediate stage of fused polykaryons. To elucidate the effect of L. reuteri treatment on host cell physiology, we performed RNAseq at multiple time points during in vitro osteoclastogenesis and established that L. reuteri downregulated several KEGG pathways including osteoclast differentiation as well as TNF-α, NF-κB, and MAP kinase signaling. These results were consistent with Western Blot data demonstrating that NF-κB and p38 activation were decreased by L. reuteri treatment. We further identified that lactobacillic acid (LA), a cyclopropane fatty acid produced by L. reuteri, contributed significantly to the suppression of osteoclastogenesis. Additionally, we demonstrated that L. reuteri is signaling through the long chain fatty acid receptor, GPR120, to impact osteoclastogenesis. Overall, these studies provide both bacterial and host mechanisms by which L. reuteri impacts osteoclastogenesis and suggest that long chain fatty acid receptors could be targets for preventing osteoclastogenesis.

Protein Kinase N Promotes Stress-Induced Cardiac Dysfunction Through Phosphorylation of Myocardin-Related Transcription Factor A and Disruption of Its Interaction With Actin

BACKGROUND

Heart failure is a complex syndrome that results from structural or functional impairment of ventricular filling or blood ejection. Protein phosphorylation is a major and essential intracellular mechanism that mediates various cellular processes in cardiomyocytes in response to extracellular and intracellular signals. The RHOA-associated protein kinase (ROCK/Rho-kinase), an effector regulated by the small GTPase RHOA, causes pathological phosphorylation of proteins, resulting in cardiovascular diseases. RHOA also activates protein kinase N (PKN); however, the role of PKN in cardiovascular diseases remains unclear.

METHODS

To explore the role of PKNs in heart failure, we generated tamoxifen-inducible, cardiomyocyte-specific PKN1- and PKN2-knockout mice by intercrossing the αMHC-CreERT2 line with Pkn1^flox/flox and Pkn2^flox/flox mice and applied a mouse model of transverse aortic constriction- and angiotensin II-induced heart failure. To identify a novel substrate of PKNs, we incubated GST-tagged myocardin-related transcription factor A (MRTFA) with recombinant GST-PKN-catalytic domain or GST-ROCK-catalytic domain in the presence of radiolabeled ATP and detected radioactive GST-MRTFA as phosphorylated MRTFA.

RESULTS

We demonstrated that RHOA activates 2 members of the PKN family of proteins, PKN1 and PKN2, in cardiomyocytes of mice with cardiac dysfunction. Cardiomyocyte-specific deletion of the genes encoding Pkn1 and Pkn2 (cmc-PKN1/2 DKO) did not affect basal heart function but protected mice from pressure overload- and angiotensin II-induced cardiac dysfunction. Furthermore, we identified MRTFA as a novel substrate of PKN1 and PKN2 and found that MRTFA phosphorylation by PKN was considerably more effective than that by ROCK in vitro. We confirmed that endogenous MRTFA phosphorylation in the heart was induced by pressure overload- and angiotensin II-induced cardiac dysfunction in wild-type mice, whereas cmc-PKN1/2 DKO mice suppressed transverse aortic constriction- and angiotensin II-induced phosphorylation of MRTFA. Although RHOA-mediated actin polymerization accelerated MRTFA-induced gene transcription, PKN1 and PKN2 inhibited the interaction of MRTFA with globular actin by phosphorylating MRTFA, causing increased serum response factor-mediated expression of cardiac hypertrophy- and fibrosis-associated genes.

CONCLUSIONS

Our results indicate that PKN1 and PKN2 activation causes cardiac dysfunction and is involved in the transition to heart failure, thus providing unique targets for therapeutic intervention for heart failure.

Dietary protein sources and tumoral overexpression of RhoA, VEGF-A and VEGFR2 genes among breast cancer patients

BACKGROUND

High protein intake may promote angiogenesis giving support to the development of metastasis according to the experimental data. However, nutritional epidemiologic evidence is inconsistent with metastasis. Therefore, we aimed to study the association between dietary intake of protein and tumoral expression levels of Ras homologous gene family member A (RhoA), vascular endothelial growth factor-A (VEGF-A), and VEGF receptor-2 (VEGFR2) in primary breast cancer (BC) patients.

METHODS

Over this consecutive case series, 177 women primary diagnosed with histopathologically confirmed BC in Tabriz (Iran) were enrolled between May 2011 and November 2016. A validated food frequency questionnaire was completed for eligible participants. Fold change in gene expression was measured using quantitative real-time PCR. Principal component factor analysis (PCA) was used to express dietary groups of proteins.

RESULTS

Total protein intake was associated with the expression level of VEGF-A in progesterone receptor-positive (PR+: β = 0.296, p < 0.01) and VEGFR2 in patients with involvement of axillary lymph node metastasis (ALNM+: β = 0.295, p < 0.01) when covariates were adjusted. High animal protein intake was correlated with overexpression of RhoA in tumors with estrogen receptor-positive (ER+: β = 0.230, p < 0.05), ALNM+ (β = 0.238, p < 0.05), and vascular invasion (VI+: β = 0.313, p < 0.01). Animal protein intake was correlated with the overexpression of VEGFR2 when tumors were positive for hormonal receptors (ER+: β = 0.299, p < 0.01; PR+: β = 0.296, p < 0.01). Based on the PCA outputs, protein provided by whole meat (white and red meat) was associated inversely with RhoA expression in ALNM+ (β = - 0.253, p < 0.05) and premenopausal women (β = - 0.285, p < 0.01) in adjusted models. Whole meat was correlated with VEGFR2 overexpression in VI+ (β = 0.288, p < 0.05) and premenopausal status (β = 0.300, p < 0.05) in adjusted models. A group composed of dairy products and legumes was correlated with the overexpression of RhoA (β = 0.249, p < 0.05) and VEGF-A (β = 0.297, p < 0.05) in VI+.

CONCLUSIONS

Based on the multivariate findings, the dietary protein could associate with the overexpression of RhoA and VEGF-VEGFR2 in favor of lymphatic and vascular metastasis in BC patients.

Rho GTPases in the Physiology and Pathophysiology of Peripheral Sensory Neurons

Numerous experimental studies demonstrate that the Ras homolog family of guanosine triphosphate hydrolases (Rho GTPases) Ras homolog family member A (RhoA), Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division cycle 42 (Cdc42) are important regulators in somatosensory neurons, where they elicit changes in the cellular cytoskeleton and are involved in diverse biological processes during development, differentiation, survival and regeneration. This review summarizes the status of research regarding the expression and the role of the Rho GTPases in peripheral sensory neurons and how these small proteins are involved in development and outgrowth of sensory neurons, as well as in neuronal regeneration after injury, inflammation and pain perception. In sensory neurons, Rho GTPases are activated by various extracellular signals through membrane receptors and elicit their action through a wide range of downstream effectors, such as Rho-associated protein kinase (ROCK), phosphoinositide 3-kinase (PI3K) or mixed-lineage kinase (MLK). While RhoA is implicated in the assembly of stress fibres and focal adhesions and inhibits neuronal outgrowth through growth cone collapse, Rac1 and Cdc42 promote neuronal development, differentiation and neuroregeneration. The functions of Rho GTPases are critically important in the peripheral somatosensory system; however, their signalling interconnections and partially antagonistic actions are not yet fully understood.

RhoGTPase in Vascular Disease

Ras-homologous (Rho)A/Rho-kinase pathway plays an essential role in many cellular functions, including contraction, motility, proliferation, and apoptosis, inflammation, and its excessive activity induces oxidative stress and promotes the development of cardiovascular diseases. Given its role in many physiological and pathological functions, targeting can result in adverse effects and limit its use for therapy. In this review, we have summarized the role of RhoGTPases with an emphasis on RhoA in vascular disease and its impact on endothelial, smooth muscle, and heart and lung fibroblasts. It is clear from the various studies that understanding the regulation of RhoGTPases and their regulators in physiology and pathological conditions is required for effective targeting of Rho.