Role of G12 proteins in oncogenesis and metastasis

Allosteric Activation of RhoA Complexed with p115-RhoGEF Deciphered by Conformational Dynamics

The Ras homologue family member A (RhoA) is a member of the Rho family, a subgroup of the Ras superfamily. RhoA interacts with the 115 kDa guanine nucleotide exchange factor (p115-RhoGEF), which assists in activation and binding with downstream effectors. Here, we use molecular dynamics (MD) simulations and essential dynamics analysis of the inactive RhoA-GDP and active RhoA-GTP, when bound to p115-RhoGEF to decipher the mechanism of RhoA activation at the structural level. We observe that inactive RhoA-GDP maintains its position near the catalytic site on the Dbl homology (DH) domain of p115-RhoGEF through the interaction of its Switch I region with the DH domain. We further show that the active RhoA-GTP is engaged in more interactions with the p115-RhoGEF membrane-bound Pleckstrin homology (PH) domain as compared to RhoA-GDP. We hypothesize that the role of the interactions between the active RhoA-GTP and the PH domain is to help release it from the DH domain upon activation. Our results support this premise, and our simulations uncover the beginning of this process and provide structural details. They also point to allosteric communication pathways that take part in RhoA activation to promote and strengthen the interaction between the active RhoA-GTP and the PH domain. Allosteric regulation also occurs among other members of the Rho superfamily. Collectively, we suggest that in the activation process, the role of the RhoA-GTP interaction with the PH domain is to release RhoA-GTP from the DH domain after activation, making it available to downstream effectors.

Dual role of the adhesion G-protein coupled receptor ADRGE5/CD97 in glioblastoma invasion and proliferation

CD97, an adhesion G-protein coupled receptor highly expressed in glioblastoma (GBM), consists of two noncovalently bound domains: the N-terminal fragment (NTF) and C-terminal fragment. The C-terminal fragment contains a GPCR domain that couples to Gα12/13, while the NTF interacts with extracellular matrix components and other receptors. We investigated the effects of changing CD97 levels and its function on primary patient-derived GBM stem cells (pdGSCs) in vitro and in vivo. We created two functional mutants: a constitutively active ΔNTF and the noncleavable dominant-negative H436A mutant. The CD97 knockdown in pdGSCs decreased, while overexpression of CD97 increased tumor size. Unlike other constructs, the ΔNTF mutant promoted tumor cell proliferation, but the tumors were comparable in size to those with CD97 overexpression. As expected, the GBM tumors overexpressing CD97 were very invasive, but surprisingly, the knockdown did not inhibit invasiveness and even induced it in noninvasive U87 tumors. Importantly, our results indicate that NTF was present in the tumor core cells but absent in the pdGSCs invading the brain. Furthermore, the expression of noncleavable H436A mutant led to large tumors that invade by sending massive protrusions, but the invasion of individual tumor cells was substantially reduced. These data suggest that NTF association with CD97 GPCR domain inhibits individual cell dissemination but not overall tumor invasion. However, NTF dissociation facilitates pdGSCs brain infiltration and may promote tumor proliferation. Thus, the interplay between two functional domains regulates CD97 activity resulting in either enhanced cell adhesion or stimulation of tumor cell invasion and proliferation.

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.

Both age and social environment shape the phenotype of ant workers

Position within the social group has consequences on individual lifespans in diverse taxa. This is especially obvious in eusocial insects, where workers differ in both the tasks they perform and their aging rates. However, in eusocial wasps, bees and ants, the performed task usually depends strongly on age. As such, untangling the effects of social role and age on worker physiology is a key step towards understanding the coevolution of sociality and aging. We performed an experimental protocol that allowed a separate analysis of these two factors using four groups of black garden ant (Lasius niger) workers: young foragers, old foragers, young nest workers, and old nest workers. We highlighted age-related differences in the proteome and metabolome of workers that were primarily related to worker subcaste and only secondarily to age. The relative abundance of proteins and metabolites suggests an improved xenobiotic detoxification, and a fuel metabolism based more on lipid use than carbohydrate use in young ants, regardless of their social role. Regardless of age, proteins related to the digestive function were more abundant in nest workers than in foragers. Old foragers were mostly characterized by weak abundances of molecules with an antibiotic activity or involved in chemical communication. Finally, our results suggest that even in tiny insects, extended lifespan may require to mitigate cancer risks. This is consistent with results found in eusocial rodents and thus opens up the discussion of shared mechanisms among distant taxa and the influence of sociality on life history traits such as longevity.

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.

An Insight into GPCR and G-Proteins as Cancer Drivers

G-protein-coupled receptors (GPCRs) are the largest family of cell surface signaling receptors known to play a crucial role in various physiological functions, including tumor growth and metastasis. Various molecules such as hormones, lipids, peptides, and neurotransmitters activate GPCRs that enable the coupling of these receptors to highly specialized transducer proteins, called G-proteins, and initiate multiple signaling pathways. Integration of these intricate networks of signaling cascades leads to numerous biochemical responses involved in diverse pathophysiological activities, including cancer development. While several studies indicate the role of GPCRs in controlling various aspects of cancer progression such as tumor growth, invasion, migration, survival, and metastasis through its aberrant overexpression, mutations, or increased release of agonists, the explicit mechanisms of the involvement of GPCRs in cancer progression is still puzzling. This review provides an insight into the various responses mediated by GPCRs in the development of cancers, the molecular mechanisms involved and the novel pharmacological approaches currently preferred for the treatment of cancer. Thus, these findings extend the knowledge of GPCRs in cancer cells and help in the identification of therapeutics for cancer patients.

Overexpressed GNA13 induces temozolomide sensitization via down-regulating MGMT and p-RELA in glioma

Temozolomide (TMZ), one of the few effective drugs used during adjuvant therapy, could effectively prolong the overall survival (OS) of glioma patients. In our previous study, the mRNA level of G Protein Subunit Alpha 13 (GNA13) was found to be inversely correlated with OS and was therefore identified as a potential biomarker for the prognosis of glioma. Henceforth, this study aims to identify the molecular mechanism of GNA13 in enhancing TMZ sensitization through bioinformatic analyses of GSE80729 and GSE43452 and other experiments. In glioma, overexpression of GNA13 downregulated PRKACA, which is a subunit of PKA, hence reducing phosphorylated RELA and MGMT. Since p-RELA and MGMT were proven to be closely associated with TMZ resistance, we therefore investigated whether thetwo signaling pathways, "GNA13/PRKACA/p-RELA", and "GNA13/PRKACA/MGMT", were involved in the molecular mechanism of GNA13 in TMZ sensitization. Our conclusion was that, GNA13 overexpression in glioma cells were more sensitive in TMZ treatment.

Identification of GNA12-driven gene signatures and key signaling networks in ovarian cancer

With the focus on defining the oncogenic network stimulated by lysophosphatidic acid (LPA) in ovarian cancer, the present study sought to interrogate the oncotranscriptome regulated by the LPA-mediated signaling pathway. LPA, LPA-receptor (LPAR) and LPAR-activated G protein 12 α-subunit, encoded by G protein subunit α 12 (GNA12), all serve an important role in ovarian cancer progression. While the general signaling mechanism regulated by LPA/LPAR/GNA12 has previously been characterized, the global transcriptomic network regulated by GNA12 in ovarian cancer pathophysiology remains largely unknown. To define the LPA/LPAR/GNA12-orchestrated oncogenic networks in ovarian cancer, transcriptomic and bioinformatical analyses were conducted using SKOV3 cells, in which the expression of GNA12 was silenced. Array analysis was performed in Agilent SurePrint G3 Human Comparative Genomic Hybridization 8×60 microarray platform. The array results were validated using Kuramochi cells. Gene and functional enrichment analyses were performed using Database for Annotation, Visualization and Integrated Discovery, Search Tool for Retrieval of Interacting Genes and Cytoscape algorithms. The results indicated a paradigm in which GNA12 drove ovarian cancer progression by upregulating a pro-tumorigenic network with AKT1, VEGFA, TGFB1, BCL2L1, STAT3, insulin-like growth factor 1 and growth hormone releasing hormone as critical hub and/or bottleneck nodes. Moreover, GNA12 downregulated a growth-suppressive network involving proteasome 20S subunit (PSM) β6, PSM α6, PSM ATPase 5, ubiquitin conjugating enzyme E2 E1, PSM non-ATPase 10, NDUFA4 mitochondrial complex-associated, NADH:ubiquinone oxidoreductase subunit B8 and anaphase promoting complex subunit 1 as hub or bottleneck nodes. In addition to providing novel insights into the LPA/LPAR/GNA12-regulated oncogenic networks in ovarian cancer, the present study identified several potential nodes in this network that could be assessed for targeted therapy.

Gene Expression and Transcriptome Profiling of Changes in a Cancer Cell Line Post-Exposure to Cadmium Telluride Quantum Dots: Possible Implications in Oncogenesis

Cadmium telluride quantum dots (CdTe-QDs) are acquiring great interest in terms of their applications in biomedical sciences. Despite earlier sporadic studies on possible oncogenic roles and anticancer properties of CdTe-QDs, there is limited information regarding the oncogenic potential of CdTe-QDs in cancer progression. Here, we investigated the oncogenic effects of CdTe-QDs on the gene expression profiles of Chang cancer cells. Chang cancer cells were treated with 2 different doses of CdTe-QDs (10 and 25 μg/ml) at different time intervals (6, 12, and 24 h). Functional annotations helped identify the gene expression profile in terms of its biological process, canonical pathways, and gene interaction networks activated. It was found that the gene expression profiles varied in a time and dose-dependent manner. Validation of transcriptional changes of several genes through quantitative PCR showed that several genes upregulated by CdTe-QD exposure were somewhat linked with oncogenesis. CdTe-QD-triggered functional pathways that appear to associate with gene expression, cell proliferation, migration, adhesion, cell-cycle progression, signal transduction, and metabolism. Overall, CdTe-QD exposure led to changes in the gene expression profiles of the Chang cancer cells, highlighting that this nanoparticle can further drive oncogenesis and cancer progression, a finding that indicates the merit of immediate in vivo investigation.

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.

Genetic manipulation of adhesion GPCR CD97/ADGRE5 modulates invasion in patient-derived glioma stem cells

INTRODUCTION

Effective glioblastoma (GBM) treatment is limited by high invasiveness and heterogeneity. Current therapies target proliferating Glioma Stem Cell (GSC) subpopulations while sparing invading GSCs, which eventually engender tumor recurrence after treatment. Surface receptor CD97/ADRGE5 is associated with invasion and metastasis regulation in non-CNS cancers. Although CD97 expression level positively correlates with poor GBM patient prognosis, its role in this tumor is unclear.

METHODS

Here, we examined CD97 function in primary patient-derived GSCs (pdGSCs) obtained from five GBM tumors, belonging to three major genetic subtypes. We compared endogenous CD97 levels in pdGSCs to the corresponding patient MRI's radiographic invasion pattern aggressiveness. We manipulated CD97 levels in these pdGSCs by knockdown and overexpression and analyzed: (i) stem and subtype marker expression, (ii) in vitro invasive properties, and (iii) cell proliferation.

RESULTS

Endogenous CD97 levels in pdGSCs positively correlated with radiographic invasion pattern aggressiveness on patient MRIs, and in vitro invasion rate. CD97 knockdown decreased pdGSC invasion rates in vitro, most markedly in mesenchymal subtype pdGSCs, as well as classical subtype pdGSCs. Invasion rates in vitro increased after CD97 overexpression predominately in proneural subtype pdGSCs. In the pdGSC line with the lowest endogenous CD97 level, CD97 overexpression increased the proliferation rate almost threefold.

CONCLUSIONS

For the first time in pdGSCs, we have shown that CD97 knockdown decreases and overexpression increases invasion rate in vitro. The effect of CD97 on invasion is pdGSC subtype-dependent. Future in vivo and mechanistic studies are needed for validation. Pharmacologic CD97 inhibitors should be identified, as they may potentially therapeutically diminish GBM invasion.

Plant miR171 modulates mTOR pathway in HEK293 cells by targeting GNA12

Plant microRNAs have shown the capacity to regulate mammalian systems. The potential bioactivity of miR171vr, an isoform of the plant miR171, on human embryonic kidney 293 (HEK293) cells was investigated. Bioinformatics simulations revealed that human G protein subunit alpha 12 (GNA12) transcript could represent an excellent target for miR171vr. To confirm this prediction, in vitro experiments were performed using a synthetic microRNA designed on miR171vr sequence. MiR-treated cells showed a significant decrease of GNA12 mRNA and protein levels, confirming the putative cross-kingdom interaction. In addition, miR171vr determined the modulation of GNA12 downstream signaling factors, including mTOR, as expected. Finally, the effect of the plant miRNA on HEK293 cell growth and its stability in presence of several stressors, such as those miming digestive processes and procedures for preparing food, were evaluated. All this preliminary evidence would suggest that miR171vr, introduced by diet or as supplement in gene therapies, could potentially influence human gene expression, especially for treating disorders where GNA12 is over-expressed (i.e. oral cancer, breast and prostate adenocarcinoma) or mTOR kinase is down-regulated (e.g. obesity, type 2 diabetes, neurodegeneration).

Role of Nurr1 in Carcinogenesis and Tumor Immunology: A State of the Art Review

Simple Summary

Nuclear receptor related-1 protein (Nurr1) emerges as a therapeutic target in multiple malignancies and immunotherapies. Previous studies have highlighted its association with clinicopathological parameters, tumorigenesis and therapeutic resistance in cancers. In addition, recent studies unraveled its contribution to the suppression of antitumor immunity, suggesting that inhibition of Nurr1 is a potential method to repress cancer aggressiveness and disrupt tumor immune tolerance. In line with this evidence, the present review provides the roles of Nurr1 in tumor progression and the associated underlying molecular mechanisms. Moreover, the significance of Nurr1 in promoting immune tolerance and potential strategies for Nurr1 inhibition are highlighted.

Abstract

Nuclear receptor related-1 protein (Nurr1), coded by an early response gene, is involved in multiple cellular and physiological functions, including proliferation, survival, and self-renewal. Dysregulation of Nurr1 has been frequently observed in many cancers and is attributed to multiple transcriptional and post-transcriptional mechanisms. Besides, Nurr1 exhibits extensive crosstalk with many oncogenic and tumor suppressor molecules, which contribute to its potential pro-malignant behaviors. Furthermore, Nurr1 is a key player in attenuating antitumor immune responses. It not only potentiates immunosuppressive functions of regulatory T cells but also dampens the activity of cytotoxic T cells. The selective accessibility of chromatin by Nurr1 in T cells is closely associated with cell exhaustion and poor efficacy of cancer immunotherapy. In this review, we summarize the reported findings of Nurr1 in different malignancies, the mechanisms that regulate Nurr1 expression, and the downstream signaling pathways that Nurr1 employs to promote a wide range of malignant phenotypes. We also give an overview of the association between Nurr1 and antitumor immunity and discuss the inhibition of Nurr1 as a potential immunotherapeutic strategy.

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.

Heterotrimeric Gα12/13 proteins in kidney injury and disease

Gα₁₂ and Gα₁₃ are ubiquitous members of the heterotrimeric guanine nucleotide-binding protein (G protein) family that play central and integrative roles in the regulation of signal transduction cascades within various cell types in the kidney. Gα₁₂/Gα₁₃ proteins enable the kidney to adapt to an ever-changing environment by transducing stimuli from cell surface receptors and accessory proteins to effector systems. Therefore, perturbations in Gα₁₂/Gα₁₃ levels or their activity can contribute to the pathogenesis of various renal diseases, including renal cancer. This review will highlight and discuss the complex and expanding roles of Gα₁₂/Gα₁₃ proteins on distinct renal pathologies, with emphasis on more recently reported findings. Deciphering how the different Gα₁₂/Gα₁₃ interaction networks participate in the onset and development of renal diseases may lead to the discovery of new therapeutic strategies.

Reversion of tumor hepatocytes to normal hepatocytes during liver tumor regression in an oncogene-expressing transgenic zebrafish model

Tumors are frequently dependent on primary oncogenes to maintain their malignant properties (known as 'oncogene addiction'). We have previously established several inducible hepatocellular carcinoma (HCC) models in zebrafish by transgenic expression of an oncogene. These tumor models are strongly oncogene addicted, as the induced and histologically proven liver tumors regress after suppression of oncogene expression by removal of a chemical inducer. However, the question of whether the liver tumor cells are eliminated or revert to normal cells remains unanswered. In the present study, we generated a novel Cre/loxP transgenic zebrafish line, Tg(fabp10: loxP-EGFP-stop-loxP-DsRed; TRE: CreERT2) (abbreviated to CreER), in order to trace tumor cell lineage during tumor regression after crossing with the xmrk (activated EGFR homolog) oncogene transgenic line, Tg(fabp10: rtTA; TRE: xmrk; krt4: EGFP) We found that, during HCC regression, restored normal liver contained both reverted tumor hepatocytes (RFP+) and newly differentiated hepatocytes (GFP+). RNA sequencing (RNA-seq) analyses of the RFP+ and GFP+ hepatocyte populations after tumor regression confirmed the conversion of tumor cells to normal hepatocytes, as most of the genes and pathways that were deregulated in the tumor stages were found to have normal regulation in the tumor-reverted hepatocytes. Thus, our lineage-tracing studies demonstrated the potential for transformed tumor cells to revert to normal cells after suppression of expression of a primary oncogene. This observation may provide a basis for the development of a therapeutic approach targeting addicted oncogenes or oncogenic pathways.

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.

YAP and MRTF-A, transcriptional co-activators of RhoA-mediated gene expression, are critical for glioblastoma tumorigenicity

The role of YAP (Yes-associated protein 1) and MRTF-A (myocardin-related transcription factor A), two transcriptional co-activators regulated downstream of GPCRs (G protein-coupled receptors) and RhoA, in the growth of glioblastoma cells and in vivo glioblastoma multiforme (GBM) tumor development was explored using human glioblastoma cell lines and tumor-initiating cells derived from patient-derived xenografts (PDX). Knockdown of these co-activators in GSC-23 PDX cells using short hairpin RNA significantly attenuated in vitro self-renewal capability assessed by limiting dilution, oncogene expression, and neurosphere formation. Orthotopic xenografts of the MRTF-A and YAP knockdown PDX cells formed significantly smaller tumors and were of lower morbidity than wild-type cells. In vitro studies used PDX and 1321N1 glioblastoma cells to examine functional responses to sphingosine 1-phosphate (S1P), a GPCR agonist that activates RhoA signaling, demonstrated that YAP signaling was required for cell migration and invasion, whereas MRTF-A was required for cell adhesion; both YAP and MRTF-A were required for proliferation. Gene expression analysis by RNA-sequencing of S1P-treated MRTF-A or YAP knockout cells identified 44 genes that were induced through RhoA and highly dependent on YAP, MRTF-A, or both. Knockdown of F3 (tissue factor (TF)), a target gene regulated selectively through YAP, blocked cell invasion and migration, whereas knockdown of HBEGF (heparin-binding epidermal growth factor-like growth factor), a gene selectively induced through MRTF-A, prevented cell adhesion in response to S1P. Proliferation was sensitive to knockdown of target genes regulated through either or both YAP and MRTF-A. Expression of TF and HBEGF was also selectively decreased in tumors from PDX cells lacking YAP or MRTF-A, indicating that these transcriptional pathways are regulated in preclinical GBM models and suggesting that their activation through GPCRs and RhoA contributes to growth and maintenance of human GBM.

Interplay between YAP/TAZ and Metabolism

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are two homologous transcriptional coactivators that promote cell proliferation, stem cell maintenance, and tissue homeostasis. Under favorable conditions, YAP and TAZ are active to promote cell growth through a transcriptional program mediated by the TEAD family transcription factors. Given the indispensability of cellular energy and metabolites for survival and growth, YAP and TAZ are inhibited when energy level is low. Indeed, glucose, fatty acids, hormones, and other metabolic factors have been recently revealed to regulate YAP and TAZ. Conversely, YAP and TAZ are also involved in metabolism regulation, such as to promote glycolysis, lipogenesis, and glutaminolysis, suggesting YAP and TAZ as emerging nodes in coordinating nutrient availability with cell growth and tissue homeostasis. In this Review, we summarize recent findings and provide a current overview of YAP and TAZ in metabolism by focusing on the role of YAP and TAZ as integrators for metabolic cues and cell growth.

GNA13 expression promotes drug resistance and tumor-initiating phenotypes in squamous cell cancers

Treatment failure in solid tumors occurs due to the survival of specific subpopulations of cells that possess tumor-initiating (TIC) phenotypes. Studies have implicated G protein-coupled-receptors (GPCRs) in cancer progression and the acquisition of TIC phenotypes. Many of the implicated GPCRs signal through the G protein GNA13. In this study, we demonstrate that GNA13 is upregulated in many solid tumors and impacts survival and metastases in patients. GNA13 levels modulate drug resistance and TIC-like phenotypes in patient-derived head and neck squamous cell carcinoma (HNSCC) cells in vitro and in vivo. Blockade of GNA13 expression, or of select downstream pathways, using small-molecule inhibitors abrogates GNA13-induced TIC phenotypes, rendering cells vulnerable to standard-of-care cytotoxic therapies. Taken together, these data indicate that GNA13 expression is a potential prognostic biomarker for tumor progression, and that interfering with GNA13-induced signaling provides a novel strategy to block TICs and drug resistance in HNSCCs.

G protein-coupled receptor GPR55 promotes colorectal cancer and has opposing effects to cannabinoid receptor 1

The putative cannabinoid receptor GPR55 has been shown to play a tumor-promoting role in various cancers, and is involved in many physiological and pathological processes of the gastrointestinal (GI) tract. While the cannabinoid receptor 1 (CB₁ ) has been reported to suppress intestinal tumor growth, the role of GPR55 in the development of GI cancers is unclear. We, therefore, aimed at elucidating the role of GPR55 in colorectal cancer (CRC), the third most common cancer worldwide. Using azoxymethane (AOM)- and dextran sulfate sodium (DSS)-driven CRC mouse models, we found that GPR55 plays a tumor-promoting role that involves alterations of leukocyte populations, i.e. myeloid-derived suppressor cells and T lymphocytes, within the tumor tissues. Concomitantly, expression levels of COX-2 and STAT3 were reduced in tumor tissue of GPR55 knockout mice, indicating reduced presence of tumor-promoting factors. By employing the experimental CRC models to CB₁ knockout and CB₁ /GPR55 double knockout mice, we can further show that GPR55 plays an opposing role to CB₁ . We report that GPR55 and CB₁ mRNA expression are differentially regulated in the experimental models and in a cohort of 86 CRC patients. Epigenetic methylation of CNR1 and GPR55 was also differentially regulated in human CRC tissue compared to control samples. Collectively, our data suggest that GPR55 and CB₁ play differential roles in colon carcinogenesis where the former seems to act as oncogene and the latter as tumor suppressor.

c-Jun Contributes to Transcriptional Control of GNA12 Expression in Prostate Cancer Cells

GNA12 is the α subunit of a heterotrimeric G protein that possesses oncogenic potential. Activated GNA12 also promotes prostate and breast cancer cell invasion in vitro and in vivo, and its expression is up-regulated in many tumors, particularly metastatic tissues. In this study, we explored the control of expression of GNA12 in prostate cancer cells. Initial studies on LnCAP (low metastatic potential, containing low levels of GNA12) and PC3 (high metastatic potential, containing high GNA12 levels) cells revealed that GNA12 mRNA levels correlated with protein levels, suggesting control at the transcriptional level. To identify potential factors controlling GNA12 transcription, we cloned the upstream 5′ regulatory region of the human GNA12 gene and examined its activity using reporter assays. Deletion analysis revealed the highest level of promoter activity in a 784 bp region, and subsequent in silico analysis indicated the presence of transcription factor binding sites for C/EBP (CCAAT/enhancer binding protein), CREB1 (cAMP-response-element-binding protein 1), and c-Jun in this minimal element for transcriptional control. A small interfering RNA (siRNA) knockdown approach revealed that silencing of c-Jun expression significantly reduced GNA12 5′ regulatory region reporter activity. In addition, chromatin immunoprecipitation assays confirmed that c-Jun binds to the GNA12 5′ regulatory region in PC3 cells. Silencing of c-Jun expression reduced mRNA and protein levels of GNA12, but not the closely-related GNA13, in prostate cancer cells. Understanding the mechanisms by which GNA12 expression is controlled may aid in the development of therapies that target key elements responsible for GNA12-mediated tumor progression.

Pharmacological Inhibition of Myocardin-related Transcription Factor Pathway Blocks Lung Metastases of RhoC-Overexpressing Melanoma

Melanoma is the most dangerous form of skin cancer with the majority of deaths arising from metastatic disease. Evidence implicates Rho-activated gene transcription in melanoma metastasis mediated by the nuclear localization of the transcriptional coactivator, myocardin-related transcription factor (MRTF). Here, we highlight a role for Rho and MRTF signaling and its reversal by pharmacologic inhibition using in vitro and in vivo models of human melanoma growth and metastasis. Using two cellular models of melanoma, we clearly show that one cell type, SK-Mel-147, is highly metastatic, has high RhoC expression, and MRTF nuclear localization and activity. Conversely, SK-Mel-19 melanoma cells have low RhoC expression, and decreased levels of MRTF-regulated genes. To probe the dependence of melanoma aggressiveness to MRTF transcription, we use a previously developed small-molecule inhibitor, CCG-203971, which at low micromolar concentrations blocks nuclear localization and activity of MRTF-A. In SK-Mel-147 cells, CCG-203971 inhibits cellular migration and invasion, and decreases MRTF target gene expression. In addition, CCG-203971-mediated inhibition of the Rho/MRTF pathway significantly reduces cell growth and clonogenicity and causes G₁ cell-cycle arrest. In an experimental model of melanoma lung metastasis, the RhoC-overexpressing melanoma cells (SK-Mel-147) exhibited pronounced lung colonization compared with the low RhoC-expressing SK-Mel-19. Furthermore, pharmacologic inhibition of the MRTF pathway reduced both the number and size of lung metastasis resulting in a marked reduction of total lung tumor burden. These data link Rho and MRTF-mediated signaling with aggressive phenotypes and support targeting the MRTF transcriptional pathway as a novel approach to melanoma therapeutics. Mol Cancer Ther; 16(1); 193-204. ©2016 AACR.

A Gα12-specific Binding Domain in AKAP-Lbc and p114RhoGEF

AKAP-Lbc is a Rho-activating guanine nucleotide exchange factor (RhoGEF) important in heart development and pro-fibrotic signaling in cardiomyocytes. Heterotrimeric G proteins of the G12/13 subfamily, comprising Gα12 and Gα13, are well characterized as stimulating a specialized group of RhoGEFs through interaction with their RGS-homology (RH) domain. Despite lacking an RH domain, AKAP-Lbc is bound by Gα12 through an unknown mechanism to activate Rho signaling. We identified a Gα12-binding region near the C-terminus of AKAP-Lbc, closely homologous to a region of p114RhoGEF that we also discovered to interact with Gα12. This binding mechanism is distinct from the well-studied interface between RH-RhoGEFs and G12/13 α subunits, as demonstrated by Gα12 mutants selectively impaired in binding either this AKAP-Lbc/p114RhoGEF region or RH-RhoGEFs. AKAP-Lbc and p114RhoGEF showed high specificity for binding Gα12 in comparison to Gα13, and experiments using chimeric G12/13 α subunits mapped determinants of this selectivity to the N-terminal region of Gα12. In cultured cells expressing constitutively GDP-bound Gα12 or Gα13, the Gα12 construct was more potent in exerting a dominant-negative effect on serum-mediated signaling to p114RhoGEF, demonstrating coupling of these signaling proteins in a cellular pathway. In addition, charge-reversal of conserved residues in AKAP-Lbc and p114RhoGEF disrupted Gα12 binding for both proteins, suggesting they harbor a common structural mechanism for interaction with this α subunit. Our results provide the first evidence of p114RhoGEF as a Gα12 signaling effector, and define a novel region conserved between AKAP-Lbc and p114RhoGEF that allows Gα12 signaling input to these non-RH RhoGEFs.

Fatty acid extract from CLA-enriched egg yolks can mediate transcriptome reprogramming of MCF-7 cancer cells to prevent their growth and proliferation

Background

Our previous study showed that fatty acids extract obtained from CLA-enriched egg yolks (EFA-CLA) suppressed the viability of MCF-7 cancer cell line more effectively than extract from non-enriched egg yolks (EFA). In this study, we analysed the effect of EFA-CLA and EFA on transcriptome profile of MCF-7 cells by applying the whole Human Genome Microarray technology.

Results

We found that EFA-CLA and EFA treated cells differentially regulated genes involved in cancer development and progression. EFA-CLA, compared to EFA, positively increased the mRNA expression of TSC2 and PTEN tumor suppressors as well as decreased the expression of NOTCH1, AGPS, GNA12, STAT3, UCP2, HIGD2A, HIF1A, PPKAR1A oncogenes.

Conclusions

We show for the first time that EFA-CLA can regulate genes engaged in AKT/mTOR pathway and inhibiting cell cycle progression. The observed results are most likely achieved by the combined effect of both: incorporated CLA isomers and other fatty acids in eggs organically modified through hens’ diet. Our results suggest that CLA-enriched eggs could be easily available food products with a potential of a cancer chemopreventive agent.

Electronic supplementary material

The online version of this article (doi:10.1186/s12263-016-0537-z) contains supplementary material, which is available to authorized users.

Gα12/13 signaling promotes cervical cancer invasion through the RhoA/ROCK-JNK signaling axis

Several reports have indicated a role for the members of the G12 family of heterotrimeric G proteins (Gα12 and Gα13) in oncogenesis and tumor cell growth. The aims of the present study were to evaluate the role of G12 signaling in cervical cancer. We demonstrated that expression of the G12 proteins was highly upregulated in cervical cancer cells. Additionally, expression of the activated forms of Gα12/Gα13 but not expression of activated Gαq induced cell invasion through the activation of the RhoA family of G proteins, but had no effect on cell proliferation in the cervical cancer cells. Inhibition of G12 signaling by expression of the RGS domain of the p115-Rho-specific guanine nucleotide exchange factor (p115-RGS) blocked thrombin-stimulated cell invasion, but did not inhibit cell proliferation in cervical cells, whereas the inhibition of Gαq (RGS2) had no effect. Furthermore, G12 signaling was able to activate Rho proteins, and this stimulation was inhibited by p115-RGS, and Gα12-induced invasion was blocked by an inhibitor of RhoA/B/C (C3 toxin). Pharmacological inhibition of JNK remarkably decreased G12-induced JNK activation. Both a JNK inhibitor (SP600125) and a ROCK inhibitor (Y27632) reduced G12-induced JNK and c-Jun activation, and markedly inhibited G12-induced cellular invasion. Collectively, these findings demonstrate that stimulation of G12 proteins is capable of promoting invasion through RhoA/ROCK-JNK activation.

Inactivating mutations in GNA13 and RHOA in Burkitt's lymphoma and diffuse large B-cell lymphoma: a tumor suppressor function for the Gα13/RhoA axis in B cells

G proteins and their cognate G protein-coupled receptors (GPCRs) function as critical signal transduction molecules that regulate cell survival, proliferation, motility and differentiation. The aberrant expression and/or function of these molecules have been linked to the growth, progression and metastasis of various cancers. As such, the analysis of mutations in the genes encoding GPCRs, G proteins and their downstream targets provides important clues regarding how these signaling cascades contribute to malignancy. Recent genome-wide sequencing efforts have unveiled the presence of frequent mutations in GNA13, the gene encoding the G protein Gα13, in Burkitt's lymphoma and diffuse large B-cell lymphoma (DLBCL). We found that mutations in the downstream target of Gα13, RhoA, are also present in Burkitt's lymphoma and DLBCL. By multiple complementary approaches, we now show that that these cancer-specific GNA13 and RHOA mutations are inhibitory in nature, and that the expression of wild-type Gα13 in B-cell lymphoma cells with mutant GNA13 has limited impact in vitro but results in a remarkable growth inhibition in vivo. Thus, although Gα13 and RhoA activity has previously been linked to cellular transformation and metastatic potential of epithelial cancers, our findings support a tumor suppressive role for Gα13 and RhoA in Burkitt's lymphoma and DLBCL.

GPR55 promotes migration and adhesion of colon cancer cells indicating a role in metastasis

BACKGROUND AND PURPOSE

Tumour cell migration and adhesion constitute essential features of metastasis. G-protein coupled receptor 55 (GPR55), a lysophospholipid receptor, has been shown to play an important role in carcinogenesis. Here, we investigated the involvement of GPR55 in migration and metastasis of colon cancer cells.

EXPERIMENTAL APPROACH

Adhesion and migration assays using the highly metastatic colon cancer cell line HCT116 and an in vivo assay of liver metastasis were performed. The GPR55 antagonist CID16020046, cannabidiol, a putative GPR55 antagonist and GPR55 siRNA were used to block GPR55 activity in HCT116 colon cancer cells.

KEY RESULTS

HCT116 cells showed a significant decrease in adhesion to endothelial cells and in migration after blockade with CID16020046 or cannabidiol. The inhibitory effects of CID16020046 or cannabidiol were averted by GPR55 siRNA knock down in cancer cells. The integrity of endothelial cell monolayers was increased after pretreatment of HCT116 cells with the antagonists or after GPR55 siRNA knockdown while pretreatment with lysophosphatidylinositol (LPI), the endogenous ligand of GPR55, decreased integrity of the monolayers. LPI also induced migration in GPR55 overexpressing HCT116 cells that was blocked by GPR55 antagonists. In a mouse model of metastasis, the arrest of HCT116 cancer cells in the liver was reduced after treatment with CID16020046 or cannabidiol. Increased levels of LPI (18:0) were found in colon cancer patients when compared with healthy individuals.

CONCLUSIONS AND IMPLICATIONS

GPR55 is involved in the migratory behaviour of colon carcinoma cells and may serve as a pharmacological target for the prevention of metastasis. © 2015 The British Pharmacological Society.

Polycystin-1 and Gα12 regulate the cleavage of E-cadherin in kidney epithelial cells

Interaction of polycystin-1 (PC1) and Gα12 is important for development of kidney cysts in autosomal dominant polycystic kidney disease (ADPKD). The integrity of cell polarity and cell-cell adhesions (mainly E-cadherin-mediated adherens junction) is altered in the renal epithelial cells of ADPKD. However, the key signaling pathway for this alteration is not fully understood. Madin-Darby canine kidney (MDCK) cells maintain the normal integrity of epithelial cell polarity and adherens junctions. Here, we found that deletion of Pkd1 increased activation of Gα12, which then promoted the cystogenesis of MDCK cells. The morphology of these cells was altered after the activation of Gα12. By using liquid chromatography-mass spectrometry, we found several proteins that could be related this change in the extracellular milieu. E-cadherin was one of the most abundant peptides after active Gα12 was induced. Gα12 activation or Pkd1 deletion increased the shedding of E-cadherin, which was mediated via increased ADAM10 activity. The increased shedding of E-cadherin was blocked by knockdown of ADAM10 or specific ADAM10 inhibitor GI254023X. Pkd1 deletion or Gα12 activation also changed the distribution of E-cadherin in kidney epithelial cells and caused β-catenin to shift from cell membrane to nucleus. Finally, ADAM10 inhibitor, GI254023X, blocked the cystogenesis induced by PC1 knockdown or Gα12 activation in renal epithelial cells. Our results demonstrate that the E-cadherin/β-catenin signaling pathway is regulated by PC1 and Gα12 via ADAM10. Specific inhibition of this pathway, especially ADAM10 activity, could be a novel therapeutic regimen for ADPKD.

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.

VASP activation via the Gα13/RhoA/PKA pathway mediates cucurbitacin-B-induced actin aggregation and cofilin-actin rod formation

Cucurbitacin B (CuB), a potent antineoplastic agent of cucurbitacin triterpenoids, induces rapid disruption of actin cytoskeleton and aberrant cell cycle inhibiting carcinogenesis. However, the underlying molecular mechanism of such anticancer effects remains incompletely understood. In this study, we showed that CuB treatment rapidly induced vasodilator-stimulated phosphoprotein (VASP) phosphorylation (i.e. activation) at the Ser157 residue and generated VASP clumps which were co-localized with amorphous actin aggregates prior to the formation of highly-ordered cofilin-actin rods in melanoma cells. Knockdown of VASP or inhibition of VASP activation using PKA-specific inhibitor H89 suppressed CuB-induced VASP activation, actin aggregation and cofilin-actin rod formation. The VASP activation was mediated by cAMP-independent PKA activation as CuB decreased the levels of cAMP while MDL12330A, an inhibitor of adenylyl cyclase, had weak effect on VASP activation. Knockdown of either Gα13 or RhoA not only suppressed VASP activation, but also ameliorated CuB-induced actin aggregation and abrogated cofilin-actin rod formation. Collectively, our studies highlighted that the CuB-induced actin aggregation and cofilin-actin rod formation was mediated via the Gα13/RhoA/PKA/VASP pathway.

Gα12 structural determinants of Hsp90 interaction are necessary for serum response element-mediated transcriptional activation

The G12/13 class of heterotrimeric G proteins, comprising the α-subunits Gα12 and Gα13, regulates multiple aspects of cellular behavior, including proliferation and cytoskeletal rearrangements. Although guanine nucleotide exchange factors for the monomeric G protein Rho (RhoGEFs) are well characterized as effectors of this G protein class, a variety of other downstream targets has been reported. To identify Gα12 determinants that mediate specific protein interactions, we used a structural and evolutionary comparison between the G12/13, Gs, Gi, and Gq classes to identify "class-distinctive" residues in Gα12 and Gα13. Mutation of these residues in Gα12 to their deduced ancestral forms revealed a subset necessary for activation of serum response element (SRE)-mediated transcription, a G12/13-stimulated pathway implicated in cell proliferative signaling. Unexpectedly, this subset of Gα12 mutants showed impaired binding to heat-shock protein 90 (Hsp90) while retaining binding to RhoGEFs. Corresponding mutants of Gα13 exhibited robust SRE activation, suggesting a Gα12-specific mechanism, and inhibition of Hsp90 by geldanamycin or small interfering RNA-mediated lowering of Hsp90 levels resulted in greater downregulation of Gα12 than Gα13 signaling in SRE activation experiments. Furthermore, the Drosophila G12/13 homolog Concertina was unable to signal to SRE in mammalian cells, and Gα12:Concertina chimeras revealed Gα12-specific determinants of SRE activation within the switch regions and a C-terminal region. These findings identify Gα12 determinants of SRE activation, implicate Gα12:Hsp90 interaction in this signaling mechanism, and illuminate structural features that arose during evolution of Gα12 and Gα13 to allow bifurcated mechanisms of signaling to a common cell proliferative pathway.

Gα₁₂ drives invasion of oral squamous cell carcinoma through up-regulation of proinflammatory cytokines

Oral squamous cell carcinoma (OSCC) ranks among the top ten most prevalent cancers worldwide. Like most head and neck squamous cell carcinomas (HNSCCs), OSCC is highly inflammatory and aggressive. However, the signaling pathways triggering the activation of its inflammatory processes remain elusive. G protein-coupled receptor signaling regulates the inflammatory response and invasiveness of cancers, but it remains unclear whether Gα₁₂ is a critical player in the inflammatory cytokine pathway during the tumorigenesis of OSCC. This study was undertaken to determine the role of Gα₁₂ signaling in the regulation of proinflammatory cytokines in their mediation of OSCC invasion. We found that both the transcription and protein levels of Gα₁₂ are up-regulated in OSCC tumors. The elevated Gα₁₂ expressions in OSCC patients also correlated with extra-capsular spread, an indicator of tumor invasiveness in HNSCCs. This clinical finding was supported by the studies of overexpression and RNAi knockdown of Gα₁₂ in OSCC cells, which demonstrated that Gα₁₂ promoted tumor cell migration and invasion. To understand how Gα₁₂ modulates OSCC invasiveness, we analyzed key biological processes in microarray data upon depletion of Gα₁₂ and found that cytokine- and other immune-related pathways were severely impaired. Importantly, the mRNA levels of IL-6 and IL-8 proinflammatory cytokines in clinical samples were found to be significantly correlated with the increased Gα₁₂ levels, suggesting a potential role of Gα₁₂ in modulating the IL-6 and IL-8 expressions. Supporting this hypothesis, overexpression or RNAi knockdown of Gα₁₂ in OSCC cell lines both showed that Gα₁₂ positively regulated the mRNA and protein levels of IL-6 and IL-8. Finally, we demonstrated that the Gα₁₂ promotion of tumor cell invasiveness was suppressed by the neutralization of IL-6 and IL-8 in OSCC cells. Together, these findings suggest that Gα₁₂ drives OSCC invasion through the up-regulation of IL-6 and IL-8 cytokines.

Determinants at the N- and C-termini of Gα12 required for activation of Rho-mediated signaling

BACKGROUND

Heterotrimeric guanine nucleotide binding proteins of the G12/13 subfamily, which includes the α-subunits Gα12 and Gα13, stimulate the monomeric G protein RhoA through interaction with a distinct subset of Rho-specific guanine nucleotide exchange factors (RhoGEFs). The structural features that mediate interaction between Gα13 and RhoGEFs have been examined in crystallographic studies of the purified complex, whereas a Gα12:RhoGEF complex has not been reported. Several signaling responses and effector interactions appear unique to Gα12 or Gα13, despite their similarity in amino acid sequence.

METHODS

To comprehensively examine Gα12 for regions involved in RhoGEF interaction, we screened a panel of Gα12 cassette substitution mutants for binding to leukemia-associated RhoGEF (LARG) and for activation of serum response element mediated transcription.

RESULTS

We identified several cassette substitutions that disrupt Gα12 binding to LARG and the related p115RhoGEF. These Gα12 mutants also were impaired in activating serum response element mediated signaling, a Rho-dependent response. Most of these mutants matched corresponding regions of Gα13 reported to contact p115RhoGEF, but unexpectedly, several RhoGEF-uncoupling mutations were found within the N- and C-terminal regions of Gα12. Trypsin protection assays revealed several mutants in these regions as retaining conformational activation. In addition, charge substitutions near the Gα12 N-terminus selectively disrupted binding to LARG but not p115RhoGEF.

CONCLUSIONS

Several structural aspects of the Gα12:RhoGEF interface differ from the reported Gα13:RhoGEF complex, particularly determinants within the C-terminal α5 helix and structurally uncharacterized N-terminus of Gα12. Furthermore, key residues at the Gα12 N-terminus may confer selectivity for LARG as a downstream effector.

G protein-coupled receptors engage the mammalian Hippo pathway through F-actin: F-Actin, assembled in response to Galpha12/13 induced RhoA-GTP, promotes dephosphorylation and activation of the YAP oncogene

The Hippo pathway, a cascade of protein kinases that inhibits the oncogenic transcriptional coactivators YAP and TAZ, was discovered in Drosophila as a major determinant of organ size in development. Known modes of regulation involve surface proteins that mediate cell-cell contact or determine epithelial cell polarity which, in a tissue-specific manner, use intracellular complexes containing FERM domain and actin-binding proteins to modulate the kinase activities or directly sequester YAP. Unexpectedly, recent work demonstrates that GPCRs, especially those signaling through Galpha12/13 such as the protease activated receptor PAR1, cause potent YAP dephosphorylation and activation. This response requires active RhoA GTPase and increased assembly of filamentous (F-)actin. Morever, cell architectures that promote F-actin assembly per se also activate YAP by kinase-dependent and independent mechanisms. These findings unveil the ability of GPCRs to activate the YAP oncogene through a newly recognized signaling function of the actin cytoskeleton, likely to be especially important for normal and cancerous stem cells.

Prostanoid EP₁ receptors mediate up-regulation of the orphan nuclear receptor Nurr1 by cAMP-independent activation of protein kinase A, CREB and NF-κB

BACKGROUND AND PURPOSE

Prostaglandin E(2) (PGE(2)) stimulation of the G protein-coupled prostanoid EP(1) receptor was found to up-regulate the expression of Nur-related factor 1 (Nurr1) (NR4A2), a transcription factor in the NR4A subfamily of nuclear receptors. The present studies characterize the molecular mechanism of this up-regulation.

EXPERIMENTAL APPROACH

The expression of Nurr1 was examined by immunoblot analysis, the polymerase chain reaction and reporter gene assays in human embryonic kidney (HEK) cells stably expressing the recombinant EP(1) receptor and in SH-SY5Y neuroblastoma cells expressing endogenous EP(1) receptors. Signalling pathway inhibitors were used to examine the roles of Rho, PKA, the cAMP response element binding protein (CREB) and NF-κB on the PGE(2) stimulated up-regulation of Nurr1. CREB and NF-κB signalling were also examined by immunoblot analysis and reporter gene assays.

KEY RESULTS

The EP(1) receptor mediated up-regulation of Nurr1 was blocked with inhibitors of Rho, PKA, NF-κB and CREB; but PGE(2) failed to significantly stimulate intracellular cAMP formation. PGE(2) stimulation of the EP1 receptor induced the phosphorylation and activation of CREB and NF-κB, which could be blocked by inhibition of PKA.

CONCLUSIONS AND IMPLICATIONS

PGE(2) stimulation of the human EP(1) receptor up-regulates the expression of Nurr1 by a mechanism involving the sequential activation of the Rho, PKA, CREB and NF-κB signalling pathways. EP(1) receptors are implicated in tumorigenesis and the up-regulation of Nurr1 may underlie the anti-apoptotic effects of PGE(2) .

Tumor suppressor gene NGX6 induces changes in protein expression profiles in colon cancer HT-29 cells

Nasopharyngeal carcinoma-associated gene 6 (NGX6; syn. transmembrane protein 8B, TMEM8B) is a recently identified tumor suppressor gene. The underlying mechanisms by which the gene inhibits tumor development are not completely known. To further understand the function of the gene's protein product NGX6, in the present study, we employed two-dimensional difference gel electrophoresis to analyze the protein expression profiles of colon cancer HT-29 cells stably transfected with the gene NGX6. The differentially expressed proteins were selected and identified by matrix-assisted laser desorption/ionization coupled with time-of-flight tandem mass spectrometry. The results showed that 12 proteins were down-regulated and 4 were up-regulated in NGX6-transfected HT-29 cells, compared with vector-transfected HT-29 cells. The MS results were verified by western blot. Bioinformatic analysis showed that these proteins are involved in cell proliferation, metastasis, apoptosis, cytoskeletal structure, metabolism, and signal transduction, suggesting that NGX6 may inhibit colon cancer through the regulation of these biological processes.

A synthetic biology approach reveals a CXCR4-G13-Rho signaling axis driving transendothelial migration of metastatic breast cancer cells

Tumor cells can co-opt the promigratory activity of chemokines and their cognate G protein-coupled receptors (GPCRs) to metastasize to regional lymph nodes or distant organs. Indeed, the migration toward SDF-1 (stromal cell-derived factor 1) of tumor cells bearing CXCR4 [chemokine (C-X-C motif) receptor 4] has been implicated in the lymphatic and organ-specific metastasis of various human malignancies. Here, we used chimeric G proteins and GPCRs activated solely by artificial ligands to selectively activate the signaling pathways downstream of specific G proteins and showed that CXCR4-mediated chemotaxis and transendothelial migration of metastatic basal-like breast cancer cells required activation of Gα(13), a member of the Gα(12/13) G protein family, and of the small guanosine triphosphatase Rho. Multiple complementary experimental strategies, including synthetic biology approaches, indicated that signaling-selective inhibition of the CXCR4-Gα(13)-Rho axis prevents the metastatic spread of basal-like breast cancer cells.

A synthetic biology approach reveals a CXCR4-G13-Rho signaling axis driving transendothelial migration of metastatic breast cancer cells

Tumor cells can co-opt the promigratory activity of chemokines and their cognate G protein-coupled receptors (GPCRs) to metastasize to regional lymph nodes or distant organs. Indeed, the migration toward SDF-1 (stromal cell-derived factor 1) of tumor cells bearing CXCR4 [chemokine (C-X-C motif) receptor 4] has been implicated in the lymphatic and organ-specific metastasis of various human malignancies. Here, we used chimeric G proteins and GPCRs activated solely by artificial ligands to selectively activate the signaling pathways downstream of specific G proteins and showed that CXCR4-mediated chemotaxis and transendothelial migration of metastatic basal-like breast cancer cells required activation of Gα(13), a member of the Gα(12/13) G protein family, and of the small guanosine triphosphatase Rho. Multiple complementary experimental strategies, including synthetic biology approaches, indicated that signaling-selective inhibition of the CXCR4-Gα(13)-Rho axis prevents the metastatic spread of basal-like breast cancer cells.

Mitogenic Signaling by the gep Oncogene Involves the Upregulation of S-Phase Kinase-Associated Protein 2

The gep oncogene, defined by the activated mutant of the α-subunit of the G protein G(12) (Gα(12)Q229L or Gα(12)QL), potently stimulates the proliferation of many different cell types in addition to inducing neoplastic transformation of several fibroblast cell lines. While it has been demonstrated that Gα(12)QL accelerates G1- to S-phase cell cycle progression, the precise mechanism through which Gα(12) communicates to cell cycle machinery is largely unknown. In the present study, we report that the activated-mutational as well as receptor-mediated-Gα(12) transmits its proliferative signals to cell cycle machinery by modulating the levels of the S-phase kinase-associated protein 2 (Skp2), an E3 ubiquitin ligase, involved in the regulation of the cyclin-dependent kinase inhibitor (CKI), p27(Kip1). Our results show that the expression of Gα(12)QL leads to an increase in the levels of Skp2 with a correlatable decrease in p27(Kip1) levels and subsequent increase in the activities of specific CDKs. By demonstrating that the transient expression of Gα(12)QL induces an increase in Skp2 levels with resultant downregulation of p27(Kip1) in both NIH3T3 and human astrocytoma 1321N1 cells, we establish here that the effect of Gα(12) on Skp2/p27(Kip1) is cell type independent. In addition, we demonstrate that LPA-stimulated proliferation and changes in Skp2 and p27(Kip1) levels in 1321N1 cells could be inhibited by the expression of a dominant-negative mutant of Gα(12), thereby pointing to the critical role of Gα(12) in LPA-mediated mitogenic signaling. Our findings also indicate that LPA as well as Gα(12)-mediated upregulation of Skp2 requires a yet to be characterized mechanism involving JNK. Since Skp2 has been identified as an oncogene, and it is overexpressed in many cancers, our results presented here describe for the first time that Skp2 is a novel target in the cell cycle machinery through which Gα(12) and its cognate receptors transmit their oncogenic signals.

G12 signaling through c-Jun NH2-terminal kinase promotes breast cancer cell invasion

Signaling through the heterotrimeric G protein, G12, via Rho induces a striking increase in breast cancer cell invasion. In this study, evidence is provided that the c-Jun NH₂-terminal kinase (JNK) is a key downstream effector of G12 on this pathway. Expression of constitutively-active Gα12 or activation of G12 signaling by thrombin leads to increased JNK and c-Jun phosphorylation. Pharmacologic inhibition of JNK or knockdown of JNK expression by siRNA significantly decreases G12-induced JNK activation as well as the ability of breast cancer cells to invade a reconstituted basement membrane. Furthermore, expression of dominant-negative Rho or treatment of cells with an inhibitor of the Rho kinase, ROCK, reduces G12-induced JNK and c-Jun activation, and ROCK inhibitor treatment also inhibits G12-induced cellular invasion. JNK knockdown or ROCK inhibitor treatment has no effect on activation of Rho by G12. Taken together, our data indicate that JNK activation is required for G12-induced invasion of breast cancer cells and that JNK is downstream of Rho and ROCK on this pathway. This study implicates a G12-stimulated mitogen-activated protein kinase cascade in cancer cell invasion, and supports a role for JNK in cancer progression.

Novel somatic mutations in heterotrimeric G proteins in melanoma

Heterotrimeric guanine nucleotide-binding proteins (G proteins) mediate signals between G-protein coupled receptors and their downstream pathways, and have been shown to be mutated in cancer. In particular, GNAQ was found to be frequently mutated in blue nevi of the skin and uveal melanoma, acting as an oncogene in its mutated form. To further examine the role of heterotrimeric G proteins in malignant melanoma, we performed a comprehensive mutational analysis of the 35 genes in the heterotrimeric G protein gene family in a panel of 80 melanoma samples. Somatic alterations in a G protein subunit were detected in 17% of samples spanning 7 genes. The highest rates of somatic, non-synonymous mutations were found in GNG10 and GNAZ, neither of which has been previously reported to be mutated in melanoma. Our study is the first systematic analysis of the heterotrimeric G proteins in melanoma and indicates that multiple mutated heterotrimeric G proteins may be involved in melanoma progression.

L-α-lysophosphatidylinositol meets GPR55: a deadly relationship

Evidence points to a role of L-α-lysophosphatidylinositol (LPI) in cancer. First, clinical data identified LPI as a biomarker for poor prognosis in cancer patients. Second, in vitro studies demonstrated significantly elevated levels of LPI in highly proliferative cancer cells. Third, LPI displays mitogenic activity in cancer cell lines, in which the lipid significantly increased cell proliferation. However, a receptor target for LPI remained elusive until very recently. It has now been revealed that LPI activates GPR55, a G protein-coupled receptor that couples to G(12/13) and G(q) proteins, which direct oncogenic signalling. New evidence indicates that LPI and GPR55 are key partners in driving cancer cell proliferation and migration. GPR55 is expressed in human tumours and drives proliferation and its expression correlates with tumour aggressiveness. Overall patient survival is lower in patients whose glioblastomas express higher levels of GPR55. Thus, evidence suggests that interaction with GPR55 might underlie the pro-tumoural actions of LPI.

G protein-coupled receptors: novel targets for drug discovery in cancer

G protein-coupled receptors (GPCRs) belong to a superfamily of cell surface signalling proteins that have a pivotal role in many physiological functions and in multiple diseases, including the development of cancer and cancer metastasis. Current drugs that target GPCRs - many of which have excellent therapeutic benefits - are directed towards only a few GPCR members. Therefore, huge efforts are currently underway to develop new GPCR-based drugs, particularly for cancer. We review recent findings that present unexpected opportunities to interfere with major tumorigenic signals by manipulating GPCR-mediated pathways. We also discuss current data regarding novel GPCR targets that may provide promising opportunities for drug discovery in cancer prevention and treatment.

A role for L-alpha-lysophosphatidylinositol and GPR55 in the modulation of migration, orientation and polarization of human breast cancer cells

BACKGROUND AND PURPOSE

Increased circulating levels of L-alpha-lysophosphatidylinositol (LPI) are associated with cancer and LPI is a potent, ligand for the G-protein-coupled receptor GPR55. Here we have assessed the modulation of breast cancer cell migration, orientation and polarization by LPI and GPR55.

EXPERIMENTAL APPROACH

Quantitative RT-PCR was used to measure GPR55 expression in breast cancer cell lines. Cell migration and invasion were measured using a Boyden chamber chemotaxis assay and Cultrex invasion assay, respectively. Cell polarization and orientation in response to the microenvironment were measured using slides containing nanometric grooves.

KEY RESULTS

GPR55 expression was detected in the highly metastatic MDA-MB-231 breast cancer cell line. In these cells, LPI stimulated binding of [(35)S]GTPgammaS to cell membranes (pEC(50) 6.47 +/- 0.45) and significantly enhanced cell chemotaxis towards serum. MCF-7 cells expressed low levels of GPR55 and did not migrate or invade towards serum factors. When GPR55 was over-expressed in MCF-7 cells, serum induced a robust migratory and invasive response, which was further enhanced by LPI and prevented by siRNA to GPR55. The physical microenvironment has been identified as a key factor in determining breast tumour cell metastatic fate. LPI endowed MDA-MB-231 cells with the capacity to detect shallow (40 nm deep) grooved slides and induced marked cancer cell polarization on both flat and grooved surfaces.

CONCLUSIONS AND IMPLICATIONS

LPI and GPR55 play a role in the modulation of migration, orientation and polarization of breast cancer cells in response to the tumour microenvironment.

Oxytocin induces the migration of prostate cancer cells: involvement of the Gi-coupled signaling pathway

Expression of genes that encode oxytocin (OXT) and vasopressin (AVP) and their cognate receptors in normal and diseased prostates are only partially characterized. Reverse transcription and PCR were used to examine the expression of these genes in normal prostate epithelial and stromal cell lines, k-ras-transformed prostate epithelial cell lines, and in four prostate cancer cell lines. Secreted and cell-associated OXT peptide was measured by an enzyme immunoassay. OXT and its receptor (OXTR) were expressed in all eight prostate cell lines. Cell-associated OXT peptide was also found in all prostate epithelial cell lines except in DU145 cells. Neither AVP nor its cognate receptors (V1a receptor and V2 receptor) were expressed in any prostate cell line examined. These data point to the OXTR as the primary target of OXT and AVP, and suggest that OXT might be an autocrine/paracrine regulator in human prostate. We found that OXT induces the migration of PC3 and PC3M, but not DU145 prostate cancer cells. The effect of OXT is distinct from the epidermal growth factor (EGF)-induced migration of prostate cancer cells, in which ERK1/2 and EGF receptor kinase activities were required. When cells were pretreated with pertussis toxin, the effect of OXT, but not EGF, on cell migration was abolished. Pretreatment with the cyclic AMP analogue, 8-Br-cAMP, did not affect OXT-induced cell migration, which eliminated the nonspecific effect of pertussis toxin. We conclude that a Gi-dependent mechanism is involved in OXTR-mediated migration of prostate cancer cells, and indicates a role for OXTR in prostate cancer metastasis.

GPCR theme editorial

This themed section of BJP includes 11 reviews on the biology of G-protein coupled receptors (GPCRs) and the drug targets that these present, 21 research papers on the pharmacology of a range of GPCRs and Commentaries on four of the papers. Areas reviewed include molecular interactions, particular in respect of hetero-dimerisation between receptors and other membrane-located proteins and other key signalling molecules including cAMP and G12/13 proteins and recently de-orphanised receptors including the Neuromedins U & S and the Free Fatty Acid receptors FFA2 & FFA3. The research papers cover the pharmacology of a range of agents acting at GPCRs, including adrenoceptors, purinoceptors, 5HT, opioid, cannabinoid & PAR-2 receptors. A group of papers is concerned with the interesting and rapidly developing pharmacology of drugs acting at beta(2)-adrenoceptors. The reach of GPCRs is illustrated by the range of physiological systems and therapeutic applications involved, including pain, cancer, cardiovascular, gastrointestinal, visual and respiratory and central nervous systems.

Critical role of G(alpha)12 and G(alpha)13 for human small cell lung cancer cell proliferation in vitro and tumor growth in vivo

PURPOSE

In small cell lung cancer cells (SCLC), various autocrine stimuli lead to the parallel activation of G(q/11) and G(12/13) proteins. Although the contribution of the G(q/11)-phospholipase C-beta cascade to mitogenic effects in SCLC cells is well established, the relevance of G(12/13) signaling is still elusive. In other tumor entities, G(12/13) activation promotes invasiveness without affecting cellular proliferation. Here, we investigate the role of G(12/13)-dependent signaling in SCLC.

EXPERIMENTAL DESIGN

We used small hairpin RNA-mediated targeting of G(alpha)(12), G(alpha)(13), or both in H69 and H209 cells and analyzed the effects of G(alpha)(12) and/or G(alpha)(13) knockdown on tumor cells in vitro, tumor growth in vivo, and mitogen-activated protein kinase (MAPK) activation.

RESULTS

Lentiviral expression of small hairpin RNAs resulted in robust and specific G(alpha)(12) and G(alpha)(13) knockdown as well as markedly inhibited proliferation, colony formation, and bradykinin-promoted stimulation of cell growth. Analyzing the activation status of all three major MAPK families revealed nonredundant functions of G(alpha)(12) and G(alpha)(13) in SCLC and a marked p42/p44 activation upon G(alpha)(12)/G(alpha)(13) knockdown. In a s.c. tumor xenograft mouse model, G(alpha)(12) or G(alpha)(13) downregulation led to decreased tumor growth due to reduced tumor cell proliferation. More importantly, G(alpha)(12)/G(alpha)(13) double knockdown completely abolished H69 tumorigenicity in mice.

CONCLUSIONS

G(alpha)(12) and G(alpha)13) exert a complex pattern of nonredundant effects in SCLC, and in contrast to other tumor types, SCLC cell proliferation in vitro and tumorigenicity in vivo critically depend on G(12/13) signaling. Due to the complete abolishment of tumorgenicity in our study, RNAi-mediated double knockdown may provide a promising new avenue in SCLC treatment.