G13 controls angiogenesis through regulation of VEGFR-2 expression

G12/13 signaling in asthma

Shortening of airway smooth muscle and bronchoconstriction are pathognomonic for asthma. Airway shortening occurs through calcium-dependent activation of myosin light chain kinase, and RhoA-dependent calcium sensitization, which inhibits myosin light chain phosphatase. The mechanism through which pro-contractile stimuli activate calcium sensitization is poorly understood. Our review of the literature suggests that pro-contractile G protein coupled receptors likely signal through G12/13 to activate RhoA and mediate calcium sensitization. This hypothesis is consistent with the effects of pro-contractile agonists on RhoA and Rho kinase activation, actin polymerization and myosin light chain phosphorylation. Recognizing the likely role of G12/13 signaling in the pathophysiology of asthma rationalizes the effects of pro-contractile stimuli on airway hyperresponsiveness, immune activation and airway remodeling, and suggests new approaches for asthma treatment.

GPCR-Gα13 Involvement in Mitochondrial Function, Oxidative Stress, and Prostate Cancer

Gα13 and Gα12, encoded by the GNA13 and GNA12 genes, respectively, are members of the G12 family of Gα proteins that, along with their associated Gβγ subunits, mediate signaling from specific G protein-coupled receptors (GPCRs). Advanced prostate cancers have increased expression of GPCRs such as CXC Motif Chemokine Receptor 4 (CXCR4), lysophosphatidic acid receptor (LPAR), and protease activated receptor 1 (PAR-1). These GPCRs signal through either the G12 family, or through Gα13 exclusively, often in addition to other G proteins. The effect of Gα13 can be distinct from that of Gα12, and the role of Gα13 in prostate cancer initiation and progression is largely unexplored. The oncogenic effect of Gα13 on cell migration and invasion in prostate cancer has been characterized, but little is known about other biological processes such as mitochondrial function and oxidative stress. Current knowledge on the link between Gα13 and oxidative stress is based on animal studies in which GPCR-Gα13 signaling decreased superoxide levels, and the overexpression of constitutively active Gα13 promoted antioxidant gene activation. In human samples, mitochondrial superoxide dismutase 2 (SOD2) correlates with prostate cancer risk and prognostic Gleason grade. However, overexpression of SOD2 in prostate cancer cells yielded conflicting results on cell growth and survival under basal versus oxidative stress conditions. Hence, it is necessary to explore the effect of Gα13 on prostate cancer tumorigenesis, as well as the effect of Gα13 on SOD2 in prostate cancer cell growth under oxidative stress conditions.

The lncRNA TRG-AS1 promotes the growth of colorectal cancer cells through the regulation of P2RY10/GNA13

BACKGROUND

The lncRNA TRG-AS1 and its co-expressed gene P2RY10 are important for colorectal cancer (CRC) occurrence and development. The purpose of our research was to explore the roles of TRG-AS1 and P2RY10 in CRC progression.

METHODS

The abundance of TRG-AS1 and P2RY10 in CRC cell lines (HT-29 and LoVo) and normal colon cells FHC was determined and difference between CRC cells and normal cells was compared. LoVo cells were transfected with si-TRG-AS1 and si-P2RY10 constructs. Subsequently, the viability, colony formation, and migration of the transfected cells were analyzed using cell counting kit-8, clonogenicity, and scratch-wound/Transwell® assays, respectively. Cells overexpressing GNA13 were used to further explore the relationship between TRG-AS1 and P2RY10 along with their downstream functions. Finally, nude mice were injected with different transfected cell types to observe tumor formation in vivo.

RESULTS

TRG-AS1 and P2RY10 were significantly upregulated in HT-29 and LoVo compared to FHC cells. TRG-AS1 knockdown and P2RY10 silencing suppressed the viability, colony formation, and migration of LoVo cells. TRG-AS1 knockdown downregulated the expression of P2RY10, GNA12, and GNA13, while P2RY10 silencing downregulated the expression of TRG-AS1, GNA12, and GNA13. Additionally, GNA13 overexpression reversed the cell growth and gene expression changes in LoVo cells induced by TRG-AS1 knockdown or P2RY10 silencing. In vivo experiments revealed that CRC tumor growth was suppressed by TRG-AS1 knockdown and P2RY10 silencing.

CONCLUSIONS

TRG-AS1 knockdown repressed the growth of HT-29 and LoVo by regulating P2RY10 and GNA13 expression.

Computer-assisted drug discovery (CADD) of an anti-cancer derivative of the theobromine alkaloid inhibiting VEGFR-2

VEGFR-2 is a significant target in cancer treatment, inhibiting angiogenesis and impeding tumor growth. Utilizing the essential pharmacophoric structural properties, a new semi-synthetic theobromine analogue (T-1-MBHEPA) was designed as VEGFR-2 inhibitor. Firstly, T-1-MBHEPA's stability and reactivity were indicated through several DFT computations. Additionally, molecular docking, MD simulations, MM-GPSA, PLIP, and essential dynamics (ED) experiments suggested T-1-MBHEPA's strong binding capabilities to VEGFR-2. Its computational ADMET profiles were also studied before the semi-synthesis and indicated a good degree of drug-likeness. T-1-MBHEPA was then semi-synthesized to evaluate the design and the in silico findings. It was found that, T-1-MBHEPA inhibited VEGFR-2 with an IC50 value of 0.121 ± 0.051 µM, as compared to sorafenib which had an IC50 value of 0.056 µM. Similarly, T-1-MBHEPA inhibited the proliferation of HepG2 and MCF7 cell lines with IC50 values of 4.61 and 4.85 µg/mL respectively - comparing sorafenib's IC50 values which were 2.24 µg/mL and 3.17 µg/mL respectively. Interestingly, T-1-MBHEPA revealed a noteworthy IC50 value of 80.0 µM against the normal cell lines exhibiting exceptionally high selectivity indexes (SI) of 17.4 and 16. 5 against the examined cell lines, respectively. T-1-MBHEPA increased the percentage of apoptotic MCF7 cells in early and late stages, respectively, from 0.71 % to 7.22 % and from 0.13 % to 2.72 %, while the necrosis percentage was increased to 11.41 %, in comparison to 2.22 % in control cells. Furthermore, T-1-MBHEPA reduced the production of pro-inflammatory cytokines TNF-α and IL-2 in the treated MCF7 cells by 33 % and 58 %, respectively indicating an additional anti-angiogenic mechanism. Also, T-1-MBHEPA decreased significantly the potentialities of MCF7 cells to heal and migrate from 65.9 % to 7.4 %. Finally, T-1-MBHEPA's oral treatment didn't show toxicity on the liver function (ALT and AST) and the kidney function (creatinine and urea) levels of mice.

CASZ1: Current Implications in Cardiovascular Diseases and Cancers

Castor zinc finger 1 (CASZ1) is a C2H2 zinc finger family protein that has two splicing variants, CASZ1a and CASZ1b. It is involved in multiple physiological processes, such as tissue differentiation and aldosterone antagonism. Genetic and epigenetic alternations of CASZ1 have been characterized in multiple cardiovascular disorders, such as congenital heart diseases, chronic venous diseases, and hypertension. However, little is known about how CASZ1 mechanically participates in the pathogenesis of these diseases. Over the past decades, at first glance, paradoxical influences on cell behaviors and progressions of different cancer types have been discovered for CASZ1, which may be explained by a "double-agent" role for CASZ1. In this review, we discuss the physiological function of CASZ1, and focus on the association of CASZ1 aberrations with the pathogenesis of cardiovascular diseases and cancers.

Endothelial FAT1 inhibits angiogenesis by controlling YAP/TAZ protein degradation via E3 ligase MIB2

Activation of endothelial YAP/TAZ signaling is crucial for physiological and pathological angiogenesis. The mechanisms of endothelial YAP/TAZ regulation are, however, incompletely understood. Here we report that the protocadherin FAT1 acts as a critical upstream regulator of endothelial YAP/TAZ which limits the activity of these transcriptional cofactors during developmental and tumor angiogenesis by promoting their degradation. We show that loss of endothelial FAT1 results in increased endothelial cell proliferation in vitro and in various angiogenesis models in vivo. This effect is due to perturbed YAP/TAZ protein degradation, leading to increased YAP/TAZ protein levels and expression of canonical YAP/TAZ target genes. We identify the E3 ubiquitin ligase Mind Bomb-2 (MIB2) as a FAT1-interacting protein mediating FAT1-induced YAP/TAZ ubiquitination and degradation. Loss of MIB2 expression in endothelial cells in vitro and in vivo recapitulates the effects of FAT1 depletion and causes decreased YAP/TAZ degradation and increased YAP/TAZ signaling. Our data identify a pivotal mechanism of YAP/TAZ regulation involving FAT1 and its associated E3 ligase MIB2, which is essential for YAP/TAZ-dependent angiogenesis.

Thromboxane A2 receptor activation via Gα13-RhoA/C-ROCK-LIMK2-dependent signal transduction inhibits angiogenic sprouting of human endothelial cells

We could previously show that thromboxane A₂ receptor (TP) activation inhibits the angiogenic capacity of human endothelial cells, but the underlying mechanisms remained unclear. Therefore, the aim of this study was to elucidate TP signal transduction pathways relevant to angiogenic sprouting of human endothelial cells. To clarify this matter, we used RNAi-mediated gene silencing as well as pharmacological inhibition of potential TP downstream targets in human umbilical vein endothelial cells (HUVEC) and VEGF-induced angiogenic sprouting of HUVEC spheroids in vitro as a functional read-out. In this experimental set-up, the TP agonist U-46619 completely blocked VEGF-induced angiogenic sprouting of HUVEC spheroids. Moreover, in live-cell analyses TP activation induced endothelial cell contraction, sprout retraction as well as endothelial cell tension and focal adhesion dysregulation of HUVEC. These effects were reversed by pharmacological TP inhibition or TP knockdown. Moreover, we identified a TP-G_α13-RhoA/C-ROCK-LIMK2-dependent signal transduction pathway to be relevant for U-46619-induced inhibition of VEGF-mediated HUVEC sprouting. In line with these results, U-46619-mediated TP activation potently induced RhoA and RhoC activity in live HUVEC as measured by FRET biosensors. Interestingly, pharmacological inhibition of ROCK and LIMK2 also normalized U-46619-induced endothelial cell tension and focal adhesion dysregulation of HUVEC. In summary, our work reveals mechanisms by which the TP may disturb angiogenic endothelial function in disease states associated with sustained endothelial TP activation.

New Therapeutic Approach for Intestinal Fibrosis Through Inhibition of pH-Sensing Receptor GPR4

BACKGROUND

Patients suffering from inflammatory bowel diseases (IBDs) express increased mucosal levels of pH-sensing receptors compared with non-IBD controls. Acidification leads to angiogenesis and extracellular matrix remodeling. We aimed to determine the expression of pH-sensing G protein-coupled receptor 4 (GPR4) in fibrotic lesions in Crohn's disease (CD) patients. We further evaluated the effect of deficiency in Gpr4 or its pharmacologic inhibition.

METHODS

Paired samples from fibrotic and nonfibrotic terminal ileum were obtained from CD patients undergoing ileocaecal resection. The effects of Gpr4 deficiency were assessed in the spontaneous Il-10-/- and the chronic dextran sodium sulfate (DSS) murine colitis model. The effects of Gpr4 deficiency and a GPR4 antagonist (39c) were assessed in the heterotopic intestinal transplantation model.

RESULTS

In human terminal ileum, increased expression of fibrosis markers was accompanied by an increase in GPR4 expression. A positive correlation between the expression of procollagens and GPR4 was observed. In murine disease models, Gpr4 deficiency was associated with a decrease in angiogenesis and fibrogenesis evidenced by decreased vessel length and expression of Edn, Vegfα, and procollagens. The heterotopic animal model for intestinal fibrosis, transplanted with terminal ileum from Gpr4-/- mice, revealed a decrease in mRNA expression of fibrosis markers and a decrease in collagen content and layer thickness compared with grafts from wild type mice. The GPR4 antagonist decreased collagen deposition. The GPR4 expression was also observed in human and murine intestinal fibroblasts. The GPR4 inhibition reduced markers of fibroblast activation stimulated by low pH, notably Acta2 and cTgf.

CONCLUSIONS

Expression of GPR4 positively correlates with the expression of profibrotic genes and collagen. Deficiency of Gpr4 is associated with a decrease in angiogenesis and fibrogenesis. The GPR4 antagonist decreases collagen deposition. Targeting GPR4 with specific inhibitors may constitute a new treatment option for IBD-associated fibrosis.

The emerging roles of Gα12/13 proteins on the hallmarks of cancer in solid tumors

G12 proteins comprise a subfamily of G-alpha subunits of heterotrimeric GTP-binding proteins (G proteins) that link specific cell surface G protein-coupled receptors (GPCRs) to downstream signaling molecules and play important roles in human physiology. The G12 subfamily contains two family members: Gα12 and Gα13 (encoded by the GNA12 and GNA13 genes, respectively) and, as with all G proteins, their activity is regulated by their ability to bind to guanine nucleotides. Increased expression of both Gα12 and Gα13, and their enhanced signaling, has been associated with tumorigenesis and tumor progression of multiple cancer types over the past decade. Despite these strong associations, Gα12/13 proteins are underappreciated in the field of cancer. As our understanding of G protein involvement in oncogenic signaling has evolved, it has become clear that Gα12/13 signaling is pleotropic and activates specific downstream effectors in different tumor types. Further, the expression of Gα12/13 proteins is regulated through a series of transcriptional and post-transcriptional mechanisms, several of which are frequently deregulated in cancer. With the ever-increasing understanding of tumorigenic processes driven by Gα12/13 proteins, it is becoming clear that targeting Gα12/13 signaling in a context-specific manner could provide a new strategy to improve therapeutic outcomes in a number of solid tumors. In this review, we detail how Gα12/13 proteins, which were first discovered as proto-oncogenes, are now known to drive several "classical" hallmarks, and also play important roles in the "emerging" hallmarks, of cancer.

G Protein-Coupled receptors and heterotrimeric G proteins as cancer drivers

G protein-coupled receptors (GPCRs) and heterotrimeric G proteins play central roles in a diverse array of cellular processes. As such, dysregulation of GPCRs and their coupled heterotrimeric G proteins can dramatically alter the signalling landscape and functional state of a cell. Consistent with their fundamental physiological functions, GPCRs and their effector heterotrimeric G proteins are implicated in some of the most prevalent human diseases, including a complex disease such as cancer that causes significant morbidity and mortality worldwide. GPCR/G protein-mediated signalling impacts oncogenesis at multiple levels by regulating tumour angiogenesis, immune evasion, metastasis, and drug resistance. Here, we summarize the growing body of research on GPCRs and their effector heterotrimeric G proteins as drivers of cancer initiation and progression, and as emerging antitumoural therapeutic targets.

GNA13 regulates BCL2 expression and the sensitivity of GCB-DLBCL cells to BCL2 inhibitors in a palmitoylation-dependent manner

GNA13, encoding one of the G protein alpha subunits of heterotrimeric G proteins that transduce signals of G protein-coupled receptors (GPCR), is frequently mutated in germinal center B-cell-like diffuse large B-cell lymphoma (GCB-DLBCL) with poor prognostic outcomes. Due to the "undruggable" nature of GNA13, targeted therapy for these patients is not available. In this study, we found that palmitoylation of GNA13 not only regulates its plasma membrane localization, but also regulates GNA13's stability. It is essential for the tumor suppressor function of GNA13 in GCB-DLBCL cells. Interestingly, GNA13 negatively regulates BCL2 expression in GCB-DLBCL cells in a palmitoylation-dependent manner. Consistently, BCL2 inhibitors were found to be effective in killing GNA13-deficient GCB-DLBCL cells in a cell-based chemical screen. Furthermore, we demonstrate that inactivating GNA13 by targeting its palmitoylation enhanced the sensitivity of GCB-DLBCL to the BCL2 inhibitor. These studies indicate that the loss-of-function mutation of GNA13 is a biomarker for BCL2 inhibitor therapy of GCB-DLBCL and that GNA13 palmitoylation is a potential target for combination therapy with BCL2 inhibitors to treat GCB-DLBCL with wild-type GNA13.

The role of Gα protein signaling in the membrane estrogen receptor-mediated signaling

Estrogens exert rapid, extranuclear effects by their action on the plasma membrane estrogen receptors (mERs). Gα protein associated with the cell membrane is involved in many important processes regulated by estrogens. However, the Gα's role in the mER-mediated signaling and the signaling pathways involved are poorly understood. This review aims to outline the Gα's role in the mER-mediated signaling. Immunoblotting, immunofluorescence, co-immunoprecipitation, and RNA interference were carried out using vascular endothelial cells (ECs) and human breast carcinoma cell lines as experimental models. Electrophysiology and immunocytochemistry were carried out using guinea pigs as animal models. Recent advances suggest that the signaling of mERα through Gα is required for vascular EC migration or endothelial H₂S release, while Gα₁₃ is involved in estrogen-induced breast cancer cell invasion. Besides, the Gα_q-coupled PLC-PKC-PKA pathway is critical for the neural regulation of energy homeostasis. This review summarizes the contributions of Gα to mER-mediated signaling, including cardiovascular protection, breast cancer metastasis, neural regulation of homeostatic functions, and osteogenesis.

YAP1 and TAZ negatively control bone angiogenesis by limiting hypoxia-inducible factor signaling in endothelial cells

Blood vessels are integrated into different organ environments with distinct properties and physiology (Augustin and Koh, 2017). A striking example of organ-specific specialization is the bone vasculature where certain molecular signals yield the opposite effect as in other tissues (Glomski et al., 2011; Kusumbe et al., 2014; Ramasamy et al., 2014). Here, we show that the transcriptional coregulators Yap1 and Taz, components of the Hippo pathway, suppress vascular growth in the hypoxic microenvironment of bone, in contrast to their pro-angiogenic role in other organs. Likewise, the kinase Lats2, which limits Yap1/Taz activity, is essential for bone angiogenesis but dispensable in organs with lower levels of hypoxia. With mouse genetics, RNA sequencing, biochemistry, and cell culture experiments, we show that Yap1/Taz constrain hypoxia-inducible factor 1α (HIF1α) target gene expression in vivo and in vitro. We propose that crosstalk between Yap1/Taz and HIF1α controls angiogenesis depending on the level of tissue hypoxia, resulting in organ-specific biological responses.

Gα-13 induces CXC motif chemokine ligand 5 expression in prostate cancer cells by transactivating NF-κB

GNA13, the α subunit of a heterotrimeric G protein, mediates signaling through G-protein-coupled receptors (GPCRs). GNA13 is up-regulated in many solid tumors, including prostate cancer, where it contributes to tumor initiation, drug resistance, and metastasis. To better understand how GNA13 contributes to tumorigenesis and tumor progression, we compared the entire transcriptome of PC3 prostate cancer cells with those cells in which GNA13 expression had been silenced. This analysis revealed that GNA13 levels affected multiple CXC-family chemokines. Further investigation in three different prostate cancer cell lines singled out pro-tumorigenic CXC motif chemokine ligand 5 (CXCL5) as a target of GNA13 signaling. Elevation of GNA13 levels consistently induced CXCL5 RNA and protein expression in all three cell lines. Analysis of the CXCL5 promoter revealed that the -505/+62 region was both highly active and influenced by GNA13, and a single NF-κB site within this region of the promoter was critical for GNA13-dependent promoter activity. ChIP experiments revealed that, upon induction of GNA13 expression, occupancy at the CXCL5 promoter was significantly enriched for the p65 component of NF-κB. GNA13 knockdown suppressed both p65 phosphorylation and the activity of a specific NF-κB reporter, and p65 silencing impaired the GNA13-enhanced expression of CXCL5. Finally, blockade of Rho GTPase activity eliminated the impact of GNA13 on NF-κB transcriptional activity and CXCL5 expression. Together, these findings suggest that GNA13 drives CXCL5 expression by transactivating NF-κB in a Rho-dependent manner in prostate cancer cells.

Myogenic vasoconstriction requires G12/G13 and LARG to maintain local and systemic vascular resistance

Myogenic vasoconstriction is an autoregulatory function of small arteries. Recently, G-protein-coupled receptors have been involved in myogenic vasoconstriction, but the downstream signalling mechanisms and the in-vivo-function of this myogenic autoregulation are poorly understood. Here, we show that small arteries from mice with smooth muscle-specific loss of G₁₂/G₁₃ or the Rho guanine nucleotide exchange factor ARHGEF12 have lost myogenic vasoconstriction. This defect was accompanied by loss of RhoA activation, while vessels showed normal increases in intracellular [Ca²⁺]. In the absence of myogenic vasoconstriction, perfusion of peripheral organs was increased, systemic vascular resistance was reduced and cardiac output and left ventricular mass were increased. In addition, animals with defective myogenic vasoconstriction showed aggravated hypotension in response to endotoxin. We conclude that G₁₂/G₁₃- and Rho-mediated signaling plays a key role in myogenic vasoconstriction and that myogenic tone is required to maintain local and systemic vascular resistance under physiological and pathological condition.

Illuminating the Onco-GPCRome: Novel G protein-coupled receptor-driven oncocrine networks and targets for cancer immunotherapy

G protein-coupled receptors (GPCRs) are the largest gene family of cell membrane-associated molecules mediating signal transmission, and their involvement in key physiological functions is well-established. The ability of GPCRs to regulate a vast array of fundamental biological processes, such as cardiovascular functions, immune responses, hormone and enzyme release from endocrine and exocrine glands, neurotransmission, and sensory perception (e.g. vision, odor, and taste), is largely due to the diversity of these receptors and the layers of their downstream signaling circuits. Dysregulated expression and aberrant functions of GPCRs have been linked to some of the most prevalent human diseases, which renders GPCRs one of the top targets for pharmaceutical drug development. However, the study of the role of GPCRs in tumor biology has only just begun to make headway. Recent studies have shown that GPCRs can contribute to the many facets of tumorigenesis, including proliferation, survival, angiogenesis, invasion, metastasis, therapy resistance, and immune evasion. Indeed, GPCRs are widely dysregulated in cancer and yet are underexploited in oncology. We present here a comprehensive analysis of GPCR gene expression, copy number variation, and mutational signatures in 33 cancer types. We also highlight the emerging role of GPCRs as part of oncocrine networks promoting tumor growth, dissemination, and immune evasion, and we stress the potential benefits of targeting GPCRs and their signaling circuits in the new era of precision medicine and cancer immunotherapies.

N-terminal syndecan-2 domain selectively enhances 6-O heparan sulfate chains sulfation and promotes VEGFA165-dependent neovascularization

The proteoglycan Syndecan-2 (Sdc2) has been implicated in regulation of cytoskeleton organization, integrin signaling and developmental angiogenesis in zebrafish. Here we report that mice with global and inducible endothelial-specific deletion of Sdc2 display marked angiogenic and arteriogenic defects and impaired VEGFA165 signaling. No such abnormalities are observed in mice with deletion of the closely related Syndecan-4 (Sdc4) gene. These differences are due to a significantly higher 6-O sulfation level in Sdc2 versus Sdc4 heparan sulfate (HS) chains, leading to an increase in VEGFA165 binding sites and formation of a ternary Sdc2-VEGFA165-VEGFR2 complex which enhances VEGFR2 activation. The increased Sdc2 HS chains 6-O sulfation is driven by a specific N-terminal domain sequence; the insertion of this sequence in Sdc4 N-terminal domain increases 6-O sulfation of its HS chains and promotes Sdc2-VEGFA165-VEGFR2 complex formation. This demonstrates the existence of core protein-determined HS sulfation patterns that regulate specific biological activities.

TAK1 regulates endothelial cell necroptosis and tumor metastasis

Formation of metastases is the major cause of death in patients diagnosed with cancer. It is a complex multistep process, including tumor cell migration, intravasation, survival in the circulation, and extravasation. Previously it was shown that tumor cell-induced endothelial necroptosis promotes tumor cell extravasation and metastasis. Here, we identified endothelial TGF-β-activated kinase 1 (TAK1) as a critical regulator of endothelial necroptosis and metastasis. Human and murine endothelial cells lacking TAK1 exhibit higher levels of necroptosis both in vitro and in vivo, and mice with endothelial cell-specific loss of TAK1 are more prone to form metastases. Endothelial RIPK3, a key component of the necroptotic machinery, was upregulated in mice with endothelial TAK1-deficiency, and endothelial knockout of RIPK3 reverted the effects of TAK1-deficiency. Moreover, altered expression levels of TAK1 and RIPK3 in pulmonary endothelial cells of mice bearing primary tumors correlated with increased endothelial necroptosis and metastasis. Together, our data suggest an important protective role for endothelial TAK1 in tumor progression by keeping endothelial necroptosis in check.

Signaling mechanisms and physiological functions of G-protein Gα13 in blood vessel formation, bone homeostasis, and cancer

Heterotrimeric G-proteins are cellular signal transducers. They mainly relay signals from G-protein-coupled receptors (GPCRs). GPCRs function as guanine nucleotide-exchange factors to active these G-proteins. Based on the sequence and functional similarities, these G-proteins are grouped into four subfamilies: G_s , G_i , G_q , and G_12/13 . The G_12/13 subfamily consists of two members: G₁₂ and G₁₃ . G_12/13 -mediated signaling pathways play pivotal roles in a variety of physiological processes, while aberrant regulation of this pathway has been identified in various human diseases. Here we summarize the signaling mechanisms and physiological functions of Gα₁₃ in blood vessel formation and bone homeostasis. We further discuss the expanding roles of Gα₁₃ in cancers, serving as oncogenes as well as tumor suppressors.

Vascular Endothelial (VE)-Cadherin, Endothelial Adherens Junctions, and Vascular Disease

Endothelial cell-cell adherens junctions (AJs) supervise fundamental vascular functions, such as the control of permeability and transmigration of circulating leukocytes, and the maintenance of existing vessels and formation of new ones. These processes are often dysregulated in pathologies. However, the evidence that links dysfunction of endothelial AJs to human pathologies is mostly correlative. In this review, we present an update of the molecular organization of AJ complexes in endothelial cells (ECs) that is mainly based on observations from experimental models. Furthermore, we report in detail on a human pathology, cerebral cavernous malformation (CCM), which is initiated by loss-of-function mutations in the genes that encode the three cytoplasmic components of AJs (CCM1, CCM2, and CCM3). At present, these represent a unique example of mutations in components of endothelial AJs that cause human disease. We describe also how studies into the defects of AJs in CCM are shedding light on the crucial regulatory mechanisms and signaling activities of these endothelial structures. Although these observations are specific for CCM, they support the concept that dysfunction of endothelial AJs can directly contribute to human pathologies.

Nogo-A inhibits vascular regeneration in ischemic retinopathy

Nogo-A is a potent glial-derived inhibitor of axon growth in the injured CNS and acts as a negative regulator of developmental angiogenesis by inhibiting vascular endothelial cell migration. However, its function in pathological angiogenesis has never been studied after ischemic injury in the CNS. Using the mouse model of oxygen-induced retinopathy (OIR) which yields defined zones of retinal ischemia, our goal was to investigate the role of Nogo-A in vascular regeneration. We demonstrate a marked upregulation of the Nogo-A receptor sphingosine 1-phosphate receptor 2 in blood vessels following OIR, while Nogo-A is abundantly expressed in surrounding glial cells. Acute inhibition of Nogo-A with function-blocking antibody 11C7 significantly improved vascular regeneration and consequently prevented pathological pre-retinal angiogenesis. Ultimately, inhibition of Nogo-A led to restoration of retinal function as determined by electrophysiological response of retinal cells to light stimulation. Our data suggest that anti-Nogo-A antibody may protect neuronal cells from ischemic damage by accelerating blood vessel repair in the CNS. Targeting Nogo-A by immunotherapy may improve CNS perfusion after vascular injuries.

HHEX is a transcriptional regulator of the VEGFC/FLT4/PROX1 signaling axis during vascular development

Formation of the lymphatic system requires the coordinated expression of several key regulators: vascular endothelial growth factor C (VEGFC), its receptor FLT4, and a key transcriptional effector, PROX1. Yet, how expression of these signaling components is regulated remains poorly understood. Here, using a combination of genetic and molecular approaches, we identify the transcription factor hematopoietically expressed homeobox (HHEX) as an upstream regulator of VEGFC, FLT4, and PROX1 during angiogenic sprouting and lymphatic formation in vertebrates. By analyzing zebrafish mutants, we found that hhex is necessary for sprouting angiogenesis from the posterior cardinal vein, a process required for lymphangiogenesis. Furthermore, studies of mammalian HHEX using tissue-specific genetic deletions in mouse and knockdowns in cultured human endothelial cells reveal its highly conserved function during vascular and lymphatic development. Our findings that HHEX is essential for the regulation of the VEGFC/FLT4/PROX1 axis provide insights into the molecular regulation of lymphangiogenesis.

VEGFC, its receptor FLT4, and transcriptional effector PROX1 control formation of the lymphatic system but how is unclear. Here, the authors show that the transcription factor hematopoietically expressed homeobox (HHEX) regulates VEGFC, FLT4 and PROX1 in fish and mammals during angiogenic sprouting and lymphatic formation.

Pseudopodium-enriched atypical kinase 1 mediates angiogenesis by modulating GATA2-dependent VEGFR2 transcription

PEAK1 is a newly described tyrosine kinase and scaffold protein that transmits integrin-mediated extracellular matrix (ECM) signals to facilitate cell movement and growth. While aberrant expression of PEAK1 has been linked to cancer progression, its normal physiological role in vertebrate biology is not known. Here we provide evidence that PEAK1 plays a central role in orchestrating new vessel formation in vertebrates. Deletion of the PEAK1 gene in zebrafish, mice, and human endothelial cells (ECs) induced severe defects in new blood vessel formation due to deficiencies in EC proliferation, survival, and migration. Gene transcriptional and proteomic analyses of PEAK1-deficient ECs revealed a significant loss of vascular endothelial growth factor receptor 2 (VEGFR2) mRNA and protein expression, as well as downstream signaling to its effectors, ERK, Akt, and Src kinase. PEAK1 regulates VEGFR2 expression by binding to and increasing the protein stability of the transcription factor GATA-binding protein 2 (GATA2), which controls VEGFR2 transcription. Importantly, PEAK1-GATA2-dependent VEGFR2 expression is mediated by EC adhesion to the ECM and is required for breast cancer-induced new vessel formation in mice. Also, elevated expression of PEAK1 and VEGFR2 mRNA are highly correlated in many human cancers including breast cancer. Together, our findings reveal a novel PEAK1-GATA2-VEGFR2 signaling axis that integrates cell adhesion and growth factor cues from the extracellular environment necessary for new vessel formation during vertebrate development and cancer.

CCL24 contributes to HCC malignancy via RhoB- VEGFA-VEGFR2 angiogenesis pathway and indicates poor prognosis

CCL24 is one chemotactic factor extensively studied in airway inflammation and colorectal cancer but less studied in hepatocellular carcinoma (HCC) retrospectively. So HCC tissue microarray (TMA) was used to estimate relationship between CCL24 and prognosis, cell experiments were conducted to study its influence for HCC cell biological behavior. CCL24 was injected to nude mice to monitor tumor formation and pulmonary metastasis; qRT-PCR, western blot and Immunohistochemistry were used to explore potential mechanism. CCL24 plays roles in target cells via its downstream CCR3, or it is regulated by Type 2 helper T cells (Th2 cell) factors, so immune related experiments were conducted. Meanwhile, Rho GTPase family have close relation not only with T cell priming, but with neovascularization; CCL24 contributes to neovascularization in age-related macular degeneration via CCR3, so Rho GTPase family, Th2 cell factors, Human Umbilical Vein Endothelial Cells were used to uncover their trafficking. Ultimate validation was confirmed by small interfering RNA. Results showed CCL24 expression was higher in caner tissues than adjacent normal tissues, it could contribute to proliferation, migration, and invasion in HCCs, could accelerate pulmonary metastasis, promote HUVECs tube formation. Th2 cell factors were irrelevant with CCL24 in HCCs; and RhoB, VEGFA, and VEGFR2 correlated with CCL24 in both mRNA and protein level. Downstream RhoB-VEGFA signaling pathway was validated by siRhoB and siVEGFA inhibition. In a word, CCL24 contributes to HCC malignancy via RhoB-VEGFA-VEGFR2 angiogenesis pathway and indicates poor prognosis, which urges us to study further CCL24 effects on diagnosis and potential therapy for HCC.

LW-215, a newly synthesized flavonoid, exhibits potent anti-angiogenic activity in vitro and in vivo

LW-215 is a newly synthesized flavonoid, which is the derivative of wogonin. Our group has previously confirmed that wogonin has an anti-angiogenic activity, while the anti-angiogenic effect of LW-215 is unclear. In this study, we explored whether LW-215 can inhibit angiogenesis and further probed the potential molecular mechanisms. We found that LW-215 inhibited migration and tube formation in human umbilical vein endothelial cells (HUVECs) and immortalized endothelial EA.hy926 cells without a significant decrease in cell viability. Microvessels sprouting from rat aortic ring and chicken chorioallantoic membrane (CAM) model also revealed that LW-215 could suppress angiogenesis in vivo. Western blot and ELISA analysis indicated that LW-215 could prevent VEGFR2 activation though reducing VEGF autocrine other than VEGFR1. Thus, its downstream kinases, such as Akt, ERK and p38 signaling, were inhibited. Taken together, these results fully showed that LW-215 might be a promising anti-angiogenesis agent.

G-Protein Gα13 Functions with Abl Kinase to Regulate Actin Cytoskeletal Reorganization

Heterotrimeric G-proteins are essential cellular signal transducers. One of the G-proteins, Gα₁₃, is critical for actin cytoskeletal reorganization, cell migration, cell proliferation, and apoptosis. Previously, we have shown that Gα₁₃ is essential for both G-protein-coupled receptor and receptor tyrosine kinase-induced actin cytoskeletal reorganization such as dynamic dorsal ruffle turnover and cell migration. However, the mechanism by which Gα₁₃ signals to actin cytoskeletal reorganization is not completely understood. Here we show that Gα₁₃ directly interacts with Abl tyrosine kinase, which is a critical regulator of actin cytoskeleton. This interaction is critical for Gα₁₃-induced dorsal ruffle turnover, endothelial cell remodeling, and cell migration. Our data uncover a new molecular signaling pathway by which Gα₁₃ controls actin cytoskeletal reorganization.

The Identification of Key Genes and Pathways in Glioma by Bioinformatics Analysis

Glioma is the most common malignant tumor in the central nervous system. This study aims to explore the potential mechanism and identify gene signatures of glioma. The glioma gene expression profile GSE4290 was analyzed for differentially expressed genes (DEGs). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were applied for the enriched pathways. A protein-protein interaction (PPI) network was constructed to find the hub genes. Survival analysis was conducted to screen and validate critical genes. In this study, 775 downregulated DEGs were identified. GO analysis demonstrated that the DEGs were enriched in cellular protein modification, regulation of cell communication, and regulation of signaling. KEGG analysis indicated that the DEGs were enriched in the MAPK signaling pathway, endocytosis, oxytocin signaling, and calcium signaling. PPI network and module analysis found 12 hub genes, which were enriched in synaptic vesicle cycling rheumatoid arthritis and collecting duct acid secretion. The four key genes CDK17, GNA13, PHF21A, and MTHFD2 were identified in both generation (GSE4412) and validation (GSE4271) dataset, respectively. Regression analysis showed that CDK13, PHF21A, and MTHFD2 were independent predictors. The results suggested that CDK17, GNA13, PHF21A, and MTHFD2 might play important roles and potentially be valuable in the prognosis and treatment of glioma.

Potentiation of receptor responses induced by prolonged binding of Gα13 and leukemia-associated RhoGEF

Diverse cellular functions are controlled by RhoA-GTPases, which are activated by trimeric G proteins via RhoGEFs, among others. In this study, we focused on the signaling from GPCRs to RhoA via Gα₁₃ and leukemia-associated RhoGEF (LARG). The activation of Gα₁₃ was elucidated in living cells with high temporal and spatial resolution by means of FRET. The inactivation after agonist withdrawal occurred in the same range (t_1/2 = 25.3 ± 2.2 s; mean ± sem; n = 22) as described for other Gα proteins. The interaction of Gα₁₃ and LARG and the thereby-induced LARG translocation to the plasma membrane were at least 1 order of magnitude more stable after agonist withdrawal, exceeding Gα₁₃ deactivation in the absence of LARG several fold. Consequently, we observed an almost 100-fold higher agonist sensitivity of the Gα₁₃ LARG interaction compared to the Gα₁₃ activation in the absence of LARG.-Bodmann, E.-L., Krett, A.-L., Bünemann, M. Potentiation of receptor responses induced by prolonged binding of Gα₁₃ and leukemia-associated RhoGEF.

FZD10-Gα13 signalling axis points to a role of FZD10 in CNS angiogenesis

Among the 10 Frizzled (FZD) isoforms belonging to the Class F of G protein-coupled receptors (GPCRs), FZD₁₀ remains the most enigmatic. FZD₁₀ shows homology to FZD₄ and FZD₉ and was previously implicated in both β-catenin-dependent and -independent signalling. In normal tissue, FZD₁₀ levels are generally very low; however, its upregulation in synovial carcinoma has attracted some attention for therapy. Our findings identify FZD₁₀ as a receptor interacting with and signalling through the heterotrimeric G protein Gα₁₃ but not Gα_12, Gα_i1, Gα_oA, Gα_s, or Gα_q. Stimulation with the FZD agonist WNT induced the dissociation of the Gα₁₃ protein from FZD₁₀, and led to global Gα_12/13-dependent cell changes assessed by dynamic mass redistribution measurements. Furthermore, we show that FZD₁₀ mediates Gα_12/13 activation-dependent induction of YAP/TAZ transcriptional activity. In addition, we show a distinct expression of FZD₁₀ in embryonic CNS endothelial cells at E11.5-E14.5. Given the well-known importance of Gα₁₃ signalling for the development of the vascular system, the selective expression of FZD₁₀ in brain vascular endothelial cells points at a potential role of FZD₁₀-Gα₁₃ signalling in CNS angiogenesis.

GNA13 as a prognostic factor and mediator of gastric cancer progression

Guanine nucleotide binding protein (G protein), alpha 13 (GNA13) has been implicated as an oncogenic protein in several human cancers. In this study, GNA13 was characterized for its role in gastric cancer (GC) progression and underlying molecular mechanisms. The expression dynamics of GNA13 were examined by immunohistochemistry (IHC) in two independent cohorts of GC samples. A series of in-vivo and in-vitro assays was performed to elucidate the function of GNA13 in GC and its underlying mechanisms. In both two cohorts of GC samples, we observed that GNA13 was markedly overexpressed in GC tissues and associated closely with aggressive magnitude of GC progression and poor patients' survival. Further study showed that upregulation of GNA13 expression increased the proliferation and tumorigenicity of GC cells in vitro and in vivo, by promoting cell growth rate, colony formation, and tumor formation in nude mice. By contrast, knockdown of GNA13 effectively suppressed the proliferation and tumorigenicity of GC cells in vitro and in vivo. Our results also demonstrated that the molecular mechanisms of the effect of GNA13 in GC included promotion of G1/S cell cycle transition through upregulation of c-Myc, activation of AKT and ERK activity, suppression of FOXO1 activity, upregulation of cyclin-dependent kinase (CDK) regulator cyclin D1 and downregulation of CDK inhibitor p21Cip1 and p27Kip1. Our present study illustrated that GNA13 has an important role in promoting proliferation and tumorigenicity of GC, and may represent a novel prognostic biomarker and therapeutic target for this disease.

Endothelial cation channel PIEZO1 controls blood pressure by mediating flow-induced ATP release

Arterial blood pressure is controlled by vasodilatory factors such as nitric oxide (NO) that are released from the endothelium under the influence of fluid shear stress exerted by flowing blood. Flow-induced endothelial release of ATP and subsequent activation of Gq/G11-coupled purinergic P2Y2 receptors have been shown to mediate fluid shear stress-induced stimulation of NO formation. However, the mechanism by which fluid shear stress initiates these processes is unclear. Here, we have shown that the endothelial mechanosensitive cation channel PIEZO1 is required for flow-induced ATP release and subsequent P2Y2/Gq/G11-mediated activation of downstream signaling that results in phosphorylation and activation of AKT and endothelial NOS. We also demonstrated that PIEZO1-dependent ATP release is mediated in part by pannexin channels. The PIEZO1 activator Yoda1 mimicked the effect of fluid shear stress on endothelial cells and induced vasorelaxation in a PIEZO1-dependent manner. Furthermore, mice with induced endothelium-specific PIEZO1 deficiency lost the ability to induce NO formation and vasodilation in response to flow and consequently developed hypertension. Together, our data demonstrate that PIEZO1 is required for the regulation of NO formation, vascular tone, and blood pressure.

Rho GTPases: Regulation and roles in cancer cell biology

Rho GTPases are well known for their roles in regulating cell migration, and also contribute to a variety of other cellular responses. They are subdivided into 2 groups: typical and atypical. The typical Rho family members, including RhoA, Rac1 and Cdc42, cycle between an active GTP-bound and inactive GDP-bound conformation, and are regulated by GEFs, GAPs and GDIs, whereas atypical Rho family members have amino acid substitutions that alter their ability to interact with GTP/GDP and hence are regulated by different mechanisms. Both typical and atypical Rho GTPases contribute to cancer progression. In a few cancers, RhoA or Rac1 are mutated, but in most cancers expression levels and/or activity of Rho GTPases is altered. Rho GTPase signaling could therefore be therapeutically targeted in cancer treatment.

WNT Stimulation Dissociates a Frizzled 4 Inactive-State Complex with Gα12/13

Frizzleds (FZDs) are unconventional G protein-coupled receptors that belong to the class Frizzled. They are bound and activated by the Wingless/Int-1 lipoglycoprotein (WNT) family of secreted lipoglycoproteins. To date, mechanisms of signal initiation and FZD-G protein coupling remain poorly understood. Previously, we showed that FZD6 assembles with Gαi1/Gαq (but not with Gαs, Gαo and Ga12/13), and that these inactive-state complexes are dissociated by WNTs and regulated by the phosphoprotein Dishevelled (DVL). Here, we investigated the inactive-state assembly of heterotrimeric G proteins with FZD4, a receptor important in retinal vascular development and frequently mutated in Norrie disease or familial exudative vitreoretinopathy. Live-cell imaging experiments using fluorescence recovery after photobleaching show that human FZD4 assembles-in a DVL-independent manner-with Gα12/13 but not representatives of other heterotrimeric G protein subfamilies, such as Gαi1, Gαo, Gαs, and Gαq The FZD4-G protein complex dissociates upon stimulation with WNT-3A, WNT-5A, WNT-7A, and WNT-10B. In addition, WNT-induced dynamic mass redistribution changes in untransfected and, even more so, in FZD4 green fluorescent protein-transfected cells depend on Gα12/13 Furthermore, expression of FZD4 and Gα12 or Gα13 in human embryonic kidney 293 cells induces WNT-dependent membrane recruitment of p115-RHOGEF (RHO guanine nucleotide exchange factor, molecular weight 115 kDa), a direct target of Gα12/13 signaling, underlining the functionality of an FZD4-Gα12/13-RHO signaling axis. In summary, Gα12/13-mediated WNT/FZD4 signaling through p115-RHOGEF offers an intriguing and previously unappreciated mechanistic link of FZD4 signaling to cytoskeletal rearrangements and RHO signaling with implications for the regulation of angiogenesis during embryonic and tumor development.

Reck enables cerebrovascular development by promoting canonical Wnt signaling

The cerebral vasculature provides the massive blood supply that the brain needs to grow and survive. By acquiring distinctive cellular and molecular characteristics it becomes the blood-brain barrier (BBB), a selectively permeable and protective interface between the brain and the peripheral circulation that maintains the extracellular milieu permissive for neuronal activity. Accordingly, there is great interest in uncovering the mechanisms that modulate the formation and differentiation of the brain vasculature. By performing a forward genetic screen in zebrafish we isolated no food for thought (nft (y72)), a recessive late-lethal mutant that lacks most of the intracerebral central arteries (CtAs), but not other brain blood vessels. We found that the cerebral vascularization deficit of nft (y72) mutants is caused by an inactivating lesion in reversion-inducing cysteine-rich protein with Kazal motifs [reck; also known as suppressor of tumorigenicity 15 protein (ST15)], which encodes a membrane-anchored tumor suppressor glycoprotein. Our findings highlight Reck as a novel and pivotal modulator of the canonical Wnt signaling pathway that acts in endothelial cells to enable intracerebral vascularization and proper expression of molecular markers associated with BBB formation. Additional studies with cultured endothelial cells suggest that, in other contexts, Reck impacts vascular biology via the vascular endothelial growth factor (VEGF) cascade. Together, our findings have broad implications for both vascular and cancer biology.

S1P2/G12/13 Signaling Negatively Regulates Macrophage Activation and Indirectly Shapes the Atheroprotective B1-Cell Population

OBJECTIVES

Monocyte/macrophage recruitment and activation at vascular predilection sites plays a central role in the pathogenesis of atherosclerosis. Heterotrimeric G proteins of the G12/13 family have been implicated in the control of migration and inflammatory gene expression, but their function in myeloid cells, especially during atherogenesis, is unknown.

APPROACH AND RESULTS

Mice with myeloid-specific deficiency for G12/13 show reduced atherosclerosis with a clear shift to anti-inflammatory gene expression in aortal macrophages. These changes are because of neither altered monocyte/macrophage migration nor reduced activation of inflammatory gene expression; on the contrary, G12/13-deficient macrophages show an increased nuclear factor-κB-dependent gene expression in the resting state. Chronically increased inflammatory gene expression in resident peritoneal macrophages results in myeloid-specific G12/13-deficient mice in an altered peritoneal micromilieu with secondary expansion of peritoneal B1 cells. Titers of B1-derived atheroprotective antibodies are increased, and adoptive transfer of peritoneal cells from mutant mice conveys atheroprotection to wild-type mice. With respect to the mechanism of G12/13-mediated transcriptional control, we identify an autocrine feedback loop that suppresses nuclear factor-κB-dependent gene expression through a signaling cascade involving sphingosine 1-phosphate receptor subtype 2, G12/13, and RhoA.

CONCLUSIONS

Together, these data show that selective inhibition of G12/13 signaling in macrophages can augment atheroprotective B-cell populations and ameliorate atherosclerosis.

YAP promotes proliferation, chemoresistance, and angiogenesis in human cholangiocarcinoma through TEAD transcription factors

The Yes-associated protein (YAP)/Hippo pathway has been implicated in tissue development, regeneration, and tumorigenesis. However, its role in cholangiocarcinoma (CC) is not established. We show that YAP activation is a common feature in CC patient biopsies and human CC cell lines. Using microarray expression profiling of CC cells with overexpressed or down-regulated YAP, we show that YAP regulates genes involved in proliferation, apoptosis, and angiogenesis. YAP activity promotes CC growth in vitro and in vivo by functionally interacting with TEAD transcription factors (TEADs). YAP activity together with TEADs prevents apoptosis induced by cytotoxic drugs, whereas YAP knockdown sensitizes CC cells to drug-induced apoptosis. We further show that the proangiogenic microfibrillar-associated protein 5 (MFAP5) is a direct transcriptional target of YAP/TEAD in CC cells and that secreted MFAP5 promotes tube formation of human microvascular endothelial cells. High YAP activity in human CC xenografts and clinical samples correlates with increased MFAP5 expression and CD31(+) vasculature.

CONCLUSIONS

These findings establish YAP as a key regulator of proliferation and antiapoptotic mechanisms in CC and provide first evidence that YAP promotes angiogenesis by regulating the expression of secreted proangiogenic proteins.

Endothelial Gαq/11 is required for VEGF-induced vascular permeability and angiogenesis

AIMS

VEGF A (VEGF-A) is a central regulator of pre- and postnatal vascular development. In vitro studies suggested that heterotrimeric G-proteins of the Gq/11 family contribute to VEGF receptor 2 (VEGFR2) signalling, but the mechanism and physiological relevance of this finding is unknown. The aim of this study is to understand the role of endothelial Gαq/11 in VEGF-dependent regulation of vascular permeability and angiogenesis.

METHODS AND RESULTS

We show here that VEGF-A-induced signalling events, such as VEGFR2 autophosphorylation, calcium mobilization, or phosphorylation of Src and Cdh5, were reduced in Gαq/11-deficient endothelial cells (ECs), resulting in impaired VEGF-dependent barrier opening, tube formation, and proliferation. Agonists at Gq/11-coupled receptors facilitated VEGF-A-induced VEGFR2 autophosphorylation in a Gαq/11-dependent manner, thereby enhancing downstream VEGFR2 signalling. In vivo, EC-specific Gαq/11- and Gαq-deficient mice showed reduced VEGF-induced fluid extravasation, and retinal angiogenesis was significantly impaired. Gαq-deficient ECs showed reduced proliferation, Cdh5 phosphorylation, and fluid extravasation, whereas apoptosis was increased.

CONCLUSION

Gαq/11 critically contributes to VEGF-A-dependent permeability control and angiogenic behaviour in vitro and in vivo.

Evaluation of spheroid head and neck squamous cell carcinoma cell models in comparison to monolayer cultures

Two-dimensional (2D) monolayer cell culture models are the most common method used to investigate tumor cells in vitro. In the few last decades, a multicellular spheroid model has gained attention due to its adjacency to tumors in vivo. The aim of the present study was to investigate immunohistochemical differences between these two cell culture systems. The FaDu, CAL27 and SCC25 head and neck squamous cell carcinoma (HNSCC) cell lines were seeded out in monolayer and multicellular spheroids. The FaDu and SCC25 cells were treated with increasing doses of cisplatin and irradiation. CAL27 cells were not used in theproliferation experiments, since the spheroids of CAL27 cells were not able to process the reagent in CCK-8 assays. Furthermore, they were stained to present alterations of the following antigens: Ki-67, vascular endothelial growth factor receptor, epithelial growth factor and survivin. Differences in growth rates and expression patterns were detected in certain HNSCC cell lines. The proliferation rates showed a significant divergence of cells grown in the three-dimensional model compared with cells grown in the 2D model. Overall, multicellular spheroids are a promising method to reproduce the immunohistochemical aspects and characteristics of tumor cells, and may show different response rates to therapeutic options.

P2Y₂ and Gq/G₁₁ control blood pressure by mediating endothelial mechanotransduction

Elevated blood pressure is a key risk factor for developing cardiovascular diseases. Blood pressure is largely determined by vasodilatory mediators, such as nitric oxide (NO), that are released from the endothelium in response to fluid shear stress exerted by the flowing blood. Previous work has identified several mechanotransduction signaling processes that are involved in fluid shear stress-induced endothelial effects, but how fluid shear stress initiates the response is poorly understood. Here, we evaluated human and bovine endothelial cells and found that the purinergic receptor P2Y2 and the G proteins Gq/G11 mediate fluid shear stress-induced endothelial responses, including [Ca2+]i transients, activation of the endothelial NO synthase (eNOS), phosphorylation of PECAM-1 and VEGFR-2, as well as activation of SRC and AKT. In response to fluid shear stress, endothelial cells released ATP, which activates the purinergic P2Y2 receptor. Mice with induced endothelium-specific P2Y2 or Gq/G11 deficiency lacked flow-induced vasodilation and developed hypertension that was accompanied by reduced eNOS activation. Together, our data identify P2Y2 and Gq/G11 as a critical endothelial mechanosignaling pathway that is upstream of previously described mechanotransduction processes and demonstrate that P2Y2 and Gq/G11 are required for basal endothelial NO formation, vascular tone, and blood pressure.

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

The low molecular weight G protein RhoA (rat sarcoma virus homolog family member A) serves as a node for transducing signals through G protein-coupled receptors (GPCRs). Activation of RhoA occurs through coupling of G proteins, most prominently, G12/13, to Rho guanine nucleotide exchange factors. The GPCR ligands that are most efficacious for RhoA activation include thrombin, lysophosphatidic acid, sphingosine-1-phosphate, and thromboxane A2. These ligands also stimulate proliferation, differentiation, and inflammation in a variety of cell and tissues types. The molecular events underlying these responses are the activation of transcription factors, transcriptional coactivators, and downstream gene programs. This review describes the pathways leading from GPCRs and RhoA to the regulation of activator protein-1, NFκB (nuclear factor κ-light-chain-enhancer of activated B cells), myocardin-related transcription factor A, and Yes-associated protein. We also focus on the importance of two prominent downstream transcriptional gene targets, the inflammatory mediator cyclooxygenase 2, and the matricellular protein cysteine-rich angiogenic inducer 61 (CCN1). Finally, we describe the importance of GPCR-induced activation of these pathways in the pathophysiology of cancer, fibrosis, and cardiovascular disease.

VEGFR3 does not sustain retinal angiogenesis without VEGFR2

Angiogenesis, the formation of new blood vessels, is regulated by vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs). VEGFR2 is abundant in the tip cells of angiogenic sprouts, where VEGF/VEGFR2 functions upstream of the delta-like ligand 4 (DLL4)/Notch signal transduction pathway. VEGFR3 is expressed in all endothelia and is indispensable for angiogenesis during early embryonic development. In adults, VEGFR3 is expressed in angiogenic blood vessels and some fenestrated endothelia. VEGFR3 is abundant in endothelial tip cells, where it activates Notch signaling, facilitating the conversion of tip cells to stalk cells during the stabilization of vascular branches. Subsequently, Notch activation suppresses VEGFR3 expression in a negative feedback loop. Here we used conditional deletions and a Notch pathway inhibitor to investigate the cross-talk between VEGFR2, VEGFR3, and Notch in vivo. We show that postnatal angiogenesis requires VEGFR2 signaling also in the absence of Notch or VEGFR3, and that even small amounts of VEGFR2 are able to sustain angiogenesis to some extent. We found that VEGFR2 is required independently of VEGFR3 for endothelial DLL4 up-regulation and angiogenic sprouting, and for VEGFR3 functions in angiogenesis. In contrast, VEGFR2 deletion had no effect, whereas VEGFR3 was essential for postnatal lymphangiogenesis, and even for lymphatic vessel maintenance in adult skin. Knowledge of these interactions and the signaling functions of VEGFRs in blood vessels and lymphatic vessels is essential for the therapeutic manipulation of the vascular system, especially when considering multitargeted antiangiogenic treatments.

Breast cancer cell invasion mediated by Gα12 signaling involves expression of interleukins-6 and -8, and matrix metalloproteinase-2

Background

Recent studies on the involvement of the G12 family of heterotrimeric G proteins (Gα12 and Gα13, the products of the GNA12 and GNA13 genes, respectively) in oncogenic pathways have uncovered a link between G12 signaling and cancer progression. However, despite a well characterized role of Rho GTPases, the potential role of secreted factors in the capacity of G12 signaling to promote invasion of cancer cells is just beginning to be addressed.

Methods

MDA-MB-231 and MCF10A breast cancer cell lines were employed as a model system to explore the involvement of secreted factors in G12-stimulated cell invasion. Factors secreted by cells expressing dominant-active Gα12 were identified by protein array, and their involvement in breast cancer cell invasion was assessed through both RNAi-mediated knockdown and antibody neutralization approaches. Bioinformatics analysis of the promoter elements of the identified factors suggested NF-κB elements played a role in their enhanced expression, which was tested by chromatin immunoprecipitation.

Results

We found that signaling through the Gα12 in MDA-MB-231 and MCF10A breast cancer cell lines enhances expression of interleukins (IL)-6 and −8, and matrix metalloproteinase (MMP)-2, and that these secreted factors play a role in G12-stimulated cell invasion. Furthermore, the enhanced expression of these secreted factors was found to be facilitated by the activation of their corresponding promoters, where NF-κB seems to be one of the major regulators. Inhibition of IL-6 and IL-8, or MMP-2 activity significantly decreased Gα12-mediated cell invasion.

Conclusions

These studies confirm and extend findings that secreted factors contribute to the oncogenic potential of G12 signaling, and suggest potential therapeutic targets to control this process.

Evidence of a common mechanism of disassembly of adherens junctions through Gα13 targeting of VE-cadherin

The heterotrimeric G protein Gα13 transduces signals from G protein-coupled receptors (GPCRs) to induce cell spreading, differentiation, migration, and cell polarity. Here, we describe a novel GPCR-independent function of Gα13 in regulating the stability of endothelial cell adherens junctions (AJs). We observed that the oxidant H2O2, which is released in response to multiple proinflammatory mediators, induced the interaction of Gα13 with VE-cadherin. Gα13 binding to VE-cadherin in turn induced Src activation and VE-cadherin phosphorylation at Tyr 658, the p120-catenin binding site thought to be responsible for VE-cadherin internalization. Inhibition of Gα13-VE-cadherin interaction using an interfering peptide derived from the Gα13 binding motif on VE-cadherin abrogated the disruption of AJs in response to inflammatory mediators. These studies identify a unique role of Gα13 binding to VE-cadherin in mediating VE-cadherin internalization and endothelial barrier disruption and inflammation.

The CASZ1/Egfl7 transcriptional pathway is required for RhoA expression in vascular endothelial cells

Vertebrate development depends on the formation of a closed circulatory loop consisting of intricate networks of veins, arteries, and lymphatic vessels. The coordinated participation of multiple molecules including growth factors, transcription factors, extracellular matrix proteins, and regulators of signaling such as small GTPases is essential for eliciting the desired cellular behaviors associated with vascular assembly and morphogenesis. We have recently demonstrated that a novel transcriptional pathway involving activation of the Epidermal Growth Factor-like Domain 7 (Egfl7) gene by the transcription factor CASTOR (CASZ1) is required for blood vessel assembly and lumen morphogenesis. Furthermore, this transcriptional network promotes RhoA expression and subsequent GTPase activity linking transcriptional regulation of endothelial gene expression to direct physiological outputs associated with Rho GTPase signaling, i.e., cell adhesion and cytoskeletal dynamics. Here we will discuss our studies with respect to our current understanding of the mechanisms underlying regulation of RhoA transcription, protein synthesis, and activity.

Different Raf protein kinases mediate different signaling pathways to stimulate E3 ligase RFFL gene expression in cell migration regulation

We previously characterized a Gα12-specific signaling pathway that stimulates the transcription of the E3 ligase RFFL via the protein kinase ARAF and ERK. This pathway leads to persistent PKC activation and is important for sustaining fibroblast migration. However, questions remain regarding how Gα12 specifically activates ARAF, which transcription factor is involved in Gα12-mediated RFFL expression, and whether RFFL is important for cell migration stimulated by other signaling mechanisms that can activate ERK. In this study, we show that replacement of the Gα12 residue Arg-264 with Gln, which is the corresponding Gα13 residue, abrogates the ability of Gα12 to interact with or activate ARAF. We also show that Gα12 can no longer interact with and activate an ARAF mutant with its C-terminal sequence downstream of the kinase domain being replaced with the corresponding CRAF sequence. These results explain why Gα12, but not Gα13, specifically activates ARAF but not CRAF. Together with our finding that recombinant Gα12 is sufficient for stimulating the kinase activity of ARAF, this study reveals an ARAF activation mechanism that is different from that of CRAF. In addition, we show that this Gα12-ARAF-ERK pathway stimulates RFFL transcription through the transcription factor c-Myc. We further demonstrate that EGF, which signals through CRAF, and an activated BRAF mutant also activate PKC and stimulate cell migration through up-regulating RFFL expression. Thus, RFFL-mediated PKC activation has a broad significance in cell migration regulation.