RGS17, an overexpressed gene in human lung and prostate cancer, induces tumor cell proliferation through the cyclic AMP-PKA-CREB pathway

The PDE4DIP-AKAP9 axis promotes lung cancer growth through modulation of PKA signalling

Phosphodiesterase 4D interacting protein (PDE4DIP) is a Golgi/centrosome-associated protein that plays critical roles in the regulation of microtubule dynamics and maintenance of the Golgi structure. However, its biological role in human cancer remains largely unknown. In this study, we showed that PDE4DIP is overexpressed in human non-small cell lung cancer (NSCLC) tissues and that upregulated PDE4DIP expression is associated with poor prognosis in patients with lung cancer. We demonstrated that PDE4DIP knockdown inhibits NSCLC cell proliferation in vitro and tumorigenicity in vivo. We further demonstrated that PDE4DIP knockdown triggers apoptosis and cell cycle arrest in NSCLC cells by activating the Protein kinase A (PKA) /CREB signalling pathway. PDE4DIP coordinates with A-kinase anchoring proteins 9 (AKAP9) to enhance the Golgi localization and stability of PKA RIIα. Depletion of PDE4DIP mislocalizes PKA RIIα from the Golgi and leads to its degradation, thereby compromising its negative regulatory effect on PKA signalling. Overall, our findings provide novel insights into the roles of the PDE4DIP-AKAP9 complex in regulating PKA signalling and NSCLC growth and highlight PDE4DIP as a promising therapeutic target for NSCLC.

Advances in targeting Phosphodiesterase 1: From mechanisms to potential therapeutics

Phosphodiesterase 1 (PDE1) is an enzyme entrusted with the hydrolysis of the second messengers cAMP and cGMP, thereby governing a plethora of metabolic processes, encompassing ion channel modulation and cellular apoptosis. Recent advancements in the realm of small molecule structural variations have greatly facilitated the exploration of innovative applications for PDE1. Remarkably, a recent series of PDE1 inhibitors (PDE1i) have been meticulously formulated and devised, showcasing enhanced selectivity and potency. Among them, ITI-214 has entered Phase II clinical trials, holding promise for the treatment of Parkinson's disease and heart failure. Nevertheless, the majority of current PDE1 inhibitors have encountered substantial side effects in clinical trials attributable to their limited selectivity, this predicament presents a formidable obstacle in the development of specific small molecule inhibitors targeting PDE1. This Perspective endeavors to illuminate the potential design approaches, structure-activity relationships, and biological activities of current PDE1i, aiming to offer support and insights for clinical practice and the development of novel PDE1i.

Inhibition of PKA/CREB1 pathway confers sensitivity to ferroptosis in non-small cell lung cancer

Ferroptosis is a type of regulated cell death characterized by iron accumulation and lipid peroxidation. The molecular mechanisms underlying ferroptosis regulation in non-small cell lung cancer (NSCLC) are poorly understood. In this study, we found that protein kinase A (PKA) inhibition enhanced ferroptosis susceptibility in NSCLC cells, as evidenced by reduced cell viability and increased lipid peroxidation. We further identified cAMP-responsive element protein 1 (CREB1), a transcription factor and a substrate of PKA, as a key regulator of ferroptosis. Knockdown of CREB1 sensitized NSCLC cells to ferroptosis inducers (FINs) and abolished the effects of PKA inhibitor and agonist, revealing the pivotal role of CREB1 in ferroptosis regulation. Using a high-throughput screening approach and subsequent validation by chromatin immunoprecipitation (ChIP) and dual-luciferase assays, we discovered that CREB1 transcriptionally activated stearoyl-CoA desaturase (SCD), an enzyme that catalyzes the conversion of saturated fatty acids to monounsaturated fatty acids. SCD conferred ferroptosis resistance by decreasing the availability of polyunsaturated fatty acids for lipid peroxidation, and its overexpression rescued the effect of CREB1 knockdown on ferroptosis in vitro. Besides, CREB1 knockdown suppressed xenograft tumor growth in the presence of Imidazole Ketone Erastin (IKE), a potent FIN, and this effect was reversed by SCD. Finally, we showed that high expression of CREB1 was associated with poor prognosis in NSCLC patients from public datasets and our institution. Collectively, this study illustrates the effect of PKA/CREB1/SCD axis in regulating ferroptosis of NSCLC, targeting this pathway may provide new strategies for treating NSCLC patients.

Function and regulation of RGS family members in solid tumours: a comprehensive review

G protein-coupled receptors (GPCRs) play a key role in regulating the homeostasis of the internal environment and are closely associated with tumour progression as major mediators of cellular signalling. As a diverse and multifunctional group of proteins, the G protein signalling regulator (RGS) family was proven to be involved in the cellular transduction of GPCRs. Growing evidence has revealed dysregulation of RGS proteins as a common phenomenon and highlighted the key roles of these proteins in human cancers. Furthermore, their differential expression may be a potential biomarker for tumour diagnosis, treatment and prognosis. Most importantly, there are few systematic reviews on the functional/mechanistic characteristics and clinical application of RGS family members at present. In this review, we focus on the G-protein signalling regulator (RGS) family, which includes more than 20 family members. We analysed the classification, basic structure, and major functions of the RGS family members. Moreover, we summarize the expression changes of each RGS family member in various human cancers and their important roles in regulating cancer cell proliferation, stem cell maintenance, tumorigenesis and cancer metastasis. On this basis, we outline the molecular signalling pathways in which some RGS family members are involved in tumour progression. Finally, their potential application in the precise diagnosis, prognosis and treatment of different types of cancers and the main possible problems for clinical application at present are discussed. Our review provides a comprehensive understanding of the role and potential mechanisms of RGS in regulating tumour progression. Video Abstract.

RGS proteins and their roles in cancer: friend or foe?

As negative modulators of G-protein-coupled receptors (GPCRs) signaling, regulators of G protein signaling (RGS) proteins facilitate various downstream cellular signalings through regulating kinds of heterotrimeric G proteins by stimulating the guanosine triphosphatase (GTPase) activity of G-protein α (Gα) subunits. The expression of RGS proteins is dynamically and precisely mediated by several different mechanisms including epigenetic regulation, transcriptional regulation -and post-translational regulation. Emerging evidence has shown that RGS proteins act as important mediators in controlling essential cellular processes including cell proliferation, survival -and death via regulating downstream cellular signaling activities, indicating that RGS proteins are fundamentally involved in sustaining normal physiological functions and dysregulation of RGS proteins (such as aberrant expression of RGS proteins) is closely associated with pathologies of many diseases such as cancer. In this review, we summarize the molecular mechanisms governing the expression of RGS proteins, and further discuss the relationship of RGS proteins and cancer.

The Role of Genetic, Metabolic, Inflammatory, and Immunologic Mediators in the Progression of Intraductal Papillary Mucinous Neoplasms to Pancreatic Adenocarcinoma

Intraductal papillary mucinous neoplasms (IPMN) have the potential to progress to pancreatic ductal adenocarcinoma (PDAC). As with any progression to malignancy, there are a variety of genetic and metabolic changes, as well as other disruptions to the cellular microenvironment including immune alterations and inflammation, that can contribute to tumorigenesis. Previous studies further characterized these alterations, revealing changes in lipid and glucose metabolism, and signaling pathways that mediate the progression of IPMN to PDAC. With the increased diagnosis of IPMNs and pancreatic cysts on imaging, the opportunity to attenuate risk with the removal of high-risk lesions is possible with the understanding of what factors accelerate malignant progression and how they can be clinically utilized to determine the level of dysplasia and stratify the risk of progression. Here, we reviewed the genetic, metabolic, inflammatory, and immunologic pathways regulating the progression of IPMN to PDAC.

Ensemble learning based assessment of the role of transcription factors in gene expression

Cancer cells are formed when the associated, active genes fail to function the way they are meant to function. Multiple genes collectively control cell growth by activating a proper set of genes. Regulation of gene expression is controlled through the combined effort of multiple regulatory elements. Transcription of each gene is affected differently according to the combinatorial patterns of regulatory elements bound in the nearby regions. Identifying and analysing such patterns will give a better insight into the cell function. The main focus of this study is on developing a computational model to predict the functional role of transcriptional factors residing between divergent gene pairs. Acute Myeloid Leukaemia (AML) gene expression data from GEO and the two TFs EP300 and CTCF binding data calibrated in k562 cell line from ENCODE consortium are taken as a case study.

MHY4571, a novel diarylcyclohexanone derivative, exerts anti-cancer activity by regulating the PKA-cAMP-response element-binding protein pathway in squamous cell lung cancer

Background

The protein kinase A (PKA)/cAMP response element-binding protein (CREB) has been suggested to be related to the inhibition of the proliferation of non-small cell lung cancer (NSCLC) cells. This study aimed to investigate the efficacy of a novel diarylcyclohexanone derivative, MHY4571, in regulating the PKA-CREB pathway and to study its anti-tumor role in squamous NSCLC.

Methods

We designed MHY4571 as a novel PKA inhibitor with acceptable in silico ADME properties and tested it in vitro in lung cancer cell lines and in vivo in xenograft and orthotopic mouse models of squamous cell lung carcinoma.

Results

MHY4571 inhibited PKA activity (> 70% inhibition) and suppressed the expression of p-PKA and p-CREB dose-dependently. MHY4571 treatment reduced lung cancer cell viability and promoted caspase 3-dependent apoptotic cell death. Orally administered MHY4571 significantly suppressed lung tumor growth in xenograft and orthotopic mouse models. PKA catalytic subunit alpha-silencing by siRNA (siPKA) strongly attenuated CREB phosphorylation; siCREB did not alter PKA protein levels or its phosphorylation, suggesting that PKA is an upstream regulator of CREB activity. MHY4571 acted synergistically with cisplatin (on co-treatment) to induce apoptotic cell death in lung cancer cells.

Conclusions

Our results imply that MHY4571 may be a potential drug candidate for squamous cell lung cancer treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40164-022-00324-8.

Regulator of G Protein Signaling 20 Correlates with Long Intergenic Non-Coding RNA (lincRNAs) Harboring Oncogenic Potential and Is Markedly Upregulated in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is at the forefront of the global cancer burden, and biomarkers for HCC are constantly being sought. Interestingly, RGS (Regulators of G protein signaling) proteins, which negatively regulate GPCR signaling, have been associated with various cancers, with some members of the RGS family being associated with liver cancer as well. Considering this, we investigated the role of RGS20 as a potential prognostic marker in 28 different cancer types with special emphasis on HCC. By using the Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) data, our analysis revealed that (a) RGS20 was strongly upregulated in tumor tissue compared with adjacent normal tissue of HCC patients; (b) RGS20 was strongly associated with some important clinical parameters such as alpha-fetoprotein and tumor grade in the HCC patients; (c) besides HCC (p < 0.001), RGS20 was found to be an important factor for survival in four other cancers (clear renal cell carcinoma: p < 0.001, lung adenocarcinoma: p = 0.004, mesothelioma: p = 0.039, ovarian serous cystadenocarcinoma: p = 0.048); (d) RGS20 was found to be significantly associated with some tumor-related signaling pathways and long intergenic non-coding RNAs (lincRNAs: LINC00511, PVT1, MIR4435-2HG, BCYRN1, and MAPKAPK5-AS1) that exhibit oncogenic potential. Taken together, we showed that RGS20 correlates with a few HCC-associated lincRNAs harboring oncogenic potential and is markedly upregulated in HCC patients. Our analysis further supports the putative function of RGS proteins, particularly RGS20, in cancer.

CREB1 contributes colorectal cancer cell plasticity by regulating lncRNA CCAT1 and NF-κB pathways

The CREB1 gene encodes an exceptionally pleiotropic transcription factor that frequently dysregulated in human cancers. CREB1 can regulate tumor cell status of proliferation and/or migration; however, the molecular basis for this switch involvement in cell plasticity has not fully been understood yet. Here, we first show that knocking out CREB1 triggers a remarkable effect of epithelial-mesenchymal transition (EMT) and leads to the occurrence of inhibited proliferation and enhanced motility in HCT116 colorectal cancer cells. By monitoring 45 cellular signaling pathway activities, we find that multiple growth-related pathways decline significantly while inflammatory pathways including NF-κB are largely upregulated in comparing between the CREB1 wild-type and knocked out cells. Mechanistically, cells with CREB1 knocked out show downregulation of MYC as a result of impaired CREB1-dependent transcription of the oncogenic lncRNA CCAT1. Interestingly, the unbalanced competition between the coactivator CBP/p300 for CREB1 and p65 leads to the activation of the NF-κB pathway in cells with CREB1 disrupted, which induces an obvious EMT phenotype of the cancer cells. Taken together, these studies identify previously unknown mechanisms of CREB1 in CRC cell plasticity via regulating lncRNA CCAT1 and NF-κB pathways, providing a critical insight into a combined strategy for CREB1-targeted tumor therapies.

cAMP Signaling in Cancer: A PKA-CREB and EPAC-Centric Approach

Cancer is one of the most common causes of death globally. Despite extensive research and considerable advances in cancer therapy, the fundamentals of the disease remain unclear. Understanding the key signaling mechanisms that cause cancer cell malignancy may help to uncover new pharmaco-targets. Cyclic adenosine monophosphate (cAMP) regulates various biological functions, including those in malignant cells. Understanding intracellular second messenger pathways is crucial for identifying downstream proteins involved in cancer growth and development. cAMP regulates cell signaling and a variety of physiological and pathological activities. There may be an impact on gene transcription from protein kinase A (PKA) as well as its downstream effectors, such as cAMP response element-binding protein (CREB). The position of CREB downstream of numerous growth signaling pathways implies its oncogenic potential in tumor cells. Tumor growth is associated with increased CREB expression and activation. PKA can be used as both an onco-drug target and a biomarker to find, identify, and stage tumors. Exploring cAMP effectors and their downstream pathways in cancer has become easier using exchange protein directly activated by cAMP (EPAC) modulators. This signaling system may inhibit or accelerate tumor growth depending on the tumor and its environment. As cAMP and its effectors are critical for cancer development, targeting them may be a useful cancer treatment strategy. Moreover, by reviewing the material from a distinct viewpoint, this review aims to give a knowledge of the impact of the cAMP signaling pathway and the related effectors on cancer incidence and development. These innovative insights seek to encourage the development of novel treatment techniques and new approaches.

Allele-specific aberration of imprinted domain chromosome architecture associates with large offspring syndrome

Large offspring syndrome (LOS) and Beckwith-Wiedemann syndrome are similar epigenetic congenital overgrowth conditions in ruminants and humans, respectively. We have reported global loss-of-imprinting, methylome epimutations, and gene misregulation in LOS. However, less than 4% of gene misregulation can be explained with short range (<20kb) alterations in DNA methylation. Therefore, we hypothesized that methylome epimutations in LOS affect chromosome architecture which results in misregulation of genes located at distances >20kb in cis and in trans (other chromosomes). Our analyses focused on two imprinted domains that frequently reveal misregulation in these syndromes, namely KvDMR1 and IGF2R. Using bovine fetal fibroblasts, we identified CTCF binding at IGF2R imprinting control region but not KvDMR1, and allele-specific chromosome architecture of these domains in controls. In LOS, analyses identified erroneous long-range contacts and clustering tendency in the direction of expression of misregulated genes. In conclusion, altered chromosome architecture is associated with LOS.

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IGF2R imprinted domain has allele-specific chromosome architecture in bovines

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In bovines, CTCF binds at IGF2R imprinting control region but not at KvDMR1

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Bovine large offspring syndrome (LOS) shows altered chromosome architecture at IGF2R

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Misregulated genes in LOS exhibit genomic location-based clustering tendency

Gab2 promotes acute myeloid leukemia growth and migration through the SHP2-Erk-CREB signaling pathway

Acute myeloid leukemia (AML) is a hematologic malignant disease largely affecting older adults with poor outcomes. Lack of effective targeted treatment is a major challenge in managing the disease in the clinic. Scaffolding adaptor Gab2 is amplified in a subset of AML. However, the causative role of Gab2 in AML remains to be explored. In this study, it was found that Gab2 was expressed at high levels in AML patient samples and AML cell lines. Experiments by knocking down Gab2 expression using shRNA showed that Gab2 promoted AML cell growth and migration in vitro and in vivo. Further studies using Gab2 mutants and pharmacological inhibitors revealed that Gab2 increased CREB phosphorylation via the SHP-2/Erk signaling pathway. CREB phosphorylation contributed to Gab2-induced cell migration by increasing MMP2 and MMP9 expression. This research indicates that high Gab2 expression promotes AML progression through the SHP2-Erk-CREB signaling pathway. CREB suppression may help treat AML with high Gab2 expression.

Circ_0006220 promotes non-small cell lung cancer progression via sponging miR-203-3p and regulating RGS17 expression

BACKGROUND

Lung cancer is the most common malignancy, and its mortality ranks first among malignancies. Non-small cell lung carcinoma (NSCLC) is the most common pathological subtype of lung cancer. It is reported that circular RNAs (circRNAs) feature prominently in the occurrence and metastasis of NSCLC.

PURPOSE

This study aims to decipher the biological functions of circ_0006220 in NSCLC and the underlying mechanism.

METHODS

The microarray data (GSE101586) were downloaded from the Gene Expression Omnibus database, and differentially expressed circRNAs in NSCLC tissues were screened using the GEO2R tool. Quantitative real-time polymerase chain reaction was used for detecting the expression of circ_0006220, miR-203-3p, and regulator of G-protein signaling 17 (RGS17) mRNA in NSCLC tissues and cells. The connection between circ_0006220 expression and clinicopathological indicators was analyzed through the chi-square test. EdU and cell counting kit-8 assays were carried out to detect cell growth. Cell migration and invasion were detected by transwell assays. Bioinformatics was used to predict, and RNA immunoprecipitation assay and dual-luciferase reporter gene assay were conducted for verifying, the targeted relationship among circ_0006220, miR-203-3p, and RGS17.

RESULTS

The expression of circ_0006220 was elevated in NSCLC cells and tissues, and high circ_0006220 expression was significantly associated with unfavorable clinicopathological indicators. In addition, it was revealed that circ_0006220 overexpression facilitated NSCLC cell growth, migration, and invasion, whereas knocking down circ_0006220 had contrary effects. Furthermore, miR-203-3p was identified as a downstream target of circ_0006220, and circ_0006220 could sponge miR-203-3p; RGS17 was identified as a downstream target of miR-203-3p and was positively modulated by circ_0006220.

CONCLUSIONS

Circ_0006220 up-regulates RGS17 expression by adsorbing miR-203-3p to promote NSCLC development.

Association of RGS20 expression with the progression and prognosis of renal cell carcinoma

Regulator of G protein signaling 20 (RGS20) has been shown to be highly expressed in various types of cancer. The present study aimed to investigate the effects of RGS20 in patients with renal cell carcinoma (RCC) and in RCC cells. Bioinformatics analysis was performed to analyze the role of RGS20 in RCC. Quantitative PCR and western blotting were used to determine the mRNA and protein expression levels of RGS20 in cells, respectively. After RGS20 inhibition, the proliferation, apoptosis, migration and invasiveness of A-498 cells were tested using MTT assay, EdU assay, propidium iodide staining, Annexin V-FITC/PI kit, wound healing assay and Transwell assay. High RGS20 expression was closely associated with the progression and immune infiltration of RCC, and may be considered as an independent indicator of poor prognosis in RCC. After knocking down RGS20, the proliferation, migration and invasiveness of cells were impaired, the cell cycle was arrested at the G₀/G₁ phase, and the level of apoptosis was increased. In addition, the mRNA expression levels of securin, CDC20 and cyclin B1 were decreased in RGS20-knockdown cells. RGS20 expression was significantly associated with the infiltration level of activated CD4 T cells, type 1 T helper cells and activated dendritic cells. In summary, RGS20 expression was associated with RCC progression and poor prognosis; thus, it may be used to estimate the prognosis of RCC and may serve as a new potential treatment strategy for RCC.

Genomic Landscapes of Noncoding RNAs Regulating VEGFA and VEGFC Expression in Endothelial Cells

Vascular endothelial growth factors (VEGFs) are best known as key regulators of angiogenesis and lymphangiogenesis. Although VEGFs have been promising therapeutic targets for various cardiovascular diseases, their regulatory landscape in endothelial cells remains elusive. Several studies have highlighted the involvement of noncoding RNAs (ncRNAs) in the modulation of VEGF expression. In this study, we investigated the role of two classes of ncRNAs, long ncRNAs (lncRNAs) and enhancer RNAs (eRNAs), in the transcriptional regulation of VEGFA and VEGFC. By integrating genome-wide global run-on sequencing (GRO-Seq) and chromosome conformation capture (Hi-C) data, we identified putative lncRNAs and eRNAs associated with VEGFA and VEGFC genes in endothelial cells. A subset of the identified putative enhancers demonstrated regulatory activity in a reporter assay. Importantly, we demonstrate that deletion of enhancers and lncRNAs by CRISPR/Cas9 promoted significant changes in VEGFA and VEGFC expression. Transcriptome sequencing (RNA-Seq) data from lncRNA deletions showed downstream factors implicated in VEGFA- and VEGFC-linked pathways, such as angiogenesis and lymphangiogenesis, suggesting functional roles for these lncRNAs. Our study uncovers novel lncRNAs and eRNAs regulating VEGFA and VEGFC that can be targeted to modulate the expression of these important molecules in endothelial cells.

Role of phosphodiesterase 1 in the pathophysiology of diseases and potential therapeutic opportunities

Cyclic nucleotide phosphodiesterases (PDEs) are superfamily of enzymes that regulate the spatial and temporal relationship of second messenger signaling in the cellular system. Among the 11 different families of PDEs, phosphodiesterase 1 (PDE1) sub-family of enzymes hydrolyze both 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) in a mutually competitive manner. The catalytic activity of PDE1 is stimulated by their binding to Ca²⁺/calmodulin (CaM), resulting in the integration of Ca²⁺ and cyclic nucleotide-mediated signaling in various diseases. The PDE1 family includes three subtypes, PDE1A, PDE1B and PDE1C, which differ for their relative affinities for cAMP and cGMP. These isoforms are differentially expressed throughout the body, including the cardiovascular, central nervous system and other organs. Thus, PDE1 enzymes play a critical role in the pathophysiology of diseases through the fundamental regulation of cAMP and cGMP signaling. This comprehensive review provides the current research on PDE1 and its potential utility as a therapeutic target in diseases including the cardiovascular, pulmonary, metabolic, neurocognitive, renal, cancers and possibly others.

Regulator of G protein signaling 17 represents a novel target for treating cisplatin induced hearing loss

Regulators of G protein signaling (RGS) accelerate the GTPase activity of G proteins to enable rapid termination of the signals triggered by G protein-coupled receptors (GPCRs). Activation of several GPCRs, including cannabinoid receptor 2 (CB2R) and adenosine A1 receptor (A1AR), protects against noise and drug-induced ototoxicity. One such drug, cisplatin, an anticancer agent used to treat various solid tumors, produces permanent hearing loss in experimental animals and in a high percentage of cancer patients who undergo treatments. In this study we show that cisplatin induces the expression of the RGS17 gene and increases the levels of RGS17 protein which contributes to a significant proportion of the hearing loss. Knockdown of RGS17 suppressed cisplatin-induced hearing loss in male Wistar rats, while overexpression of RGS17 alone produced hearing loss in vivo. Furthermore, RGS17 and CB2R negatively regulate the expression of each other. These data suggest that RGS17 mediates cisplatin ototoxicity by uncoupling cytoprotective GPCRs from their normal G protein interactions, thereby mitigating the otoprotective contributions of endogenous ligands of these receptors. Thus, RGS17 represents a novel mediator of cisplatin ototoxicity and a potential therapeutic target for treating hearing loss.

Hsa-miR-149-5p Suppresses Prostate Carcinoma Malignancy by Suppressing RGS17

Background

MicroRNAs (miRNAs) are key players in the progression of human cancers. While several miRNAs have been reported to regulate the development of tumors, the molecular mechanisms and roles of miR-149-5p in prostate carcinoma (PCa) remain unclear. Our aim was to investigate the interaction and functions of miR-149-5p and RGS17 in PCa.

Methods

Microarray analysis was performed to identify the key miRNA and gene involved in PCa progression. The expression levels of miRNA and mRNA in PCa tissues and cells were verified by qRT-PCR. MTT assay, BrdU proliferation assay and wound-healing assay were applied to assess the effect of miR-149-5p and RGS17 on PCa cells’ viability, proliferation, and migration ability. The association between RGS17 and miR-149-5p was identify using dual-luciferase reporter assay and Western blot assay.

Results

Data analysis indicated the reduction of miR-149-5p expression in PCa tissues and cells. Experimental investigations also showed that this miRNA suppressed the viability, proliferation and migration ability of PCa cells. RGS17 was found to be the target of miR-149-5p, and the low expression of miR-149-5p upregulated RGS17 in PCa tissues and cells. The results of the cell-function assays showed that RGS17 acted as an oncogene in PCa even though its promotive effect could be reversed by miR-149-5p.

Conclusion

This research confirmed that by targeting and inhibiting RGS17, miR-149-5p could suppress PCa development.

Fragment-Based Nuclear Magnetic Resonance Screen against a Regulator of G Protein Signaling Identifies a Binding "Hot Spot"

Regulator of G protein signaling (RGS) proteins have attracted attention as a result of their primary role in directing the specificity as well as the temporal and spatial aspects of G protein-coupled receptor signaling. In addition, alterations in RGS protein expression have been observed in a number of disease states, including certain cancers. In this area, RGS17 is of particular interest. It has been demonstrated that, while RGS17 is expressed primarily in the central nervous system, it has been found to be inappropriately expressed in lung, prostate, breast, cervical, and hepatocellular carcinomas. Overexpression of RGS17 leads to dysfunction in inhibitory G protein signaling and an overproduction of the intracellular second messenger cAMP, which in turn alters the transcription patterns of proteins known to promote various cancer types. Suppressing RGS17 expression with RNA interference (RNAi) has been found to decrease tumorigenesis and sufficiently prevents cancer cell migration, leading to the hypothesis that pharmacological blocking of RGS17 function could be useful in anticancer therapies. We have identified small-molecule fragments capable of binding the RGS homology (RH) domain of RGS17 by using a nuclear magnetic resonance fragment-based screening approach. By chemical shift mapping of the two-dimensional ¹⁵ N,¹ H heteronuclear single quantum coherence (HSQC) spectra of the backbone-assigned ¹⁵ N-labeled RGS17-RH, we determined the fragment binding sites to be distant from the Gα interface. Thus, our study identifies a putative fragment binding site on RGS17 that was previously unknown.

Targeting lung cancer screening to individuals at greatest risk: the role of genetic factors

Lung cancer (LC) is the most common global cancer. An individual’s risk of developing LC is mediated by an array of factors, including family history of the disease. Considerable research into genetic risk factors for LC has taken place in recent years, with both low-penetrance and high-penetrance variants implicated in increasing or decreasing a person’s risk of the disease. LC is the leading cause of cancer death worldwide; poor survival is driven by late onset of non-specific symptoms, resulting in late-stage diagnoses. Evidence for the efficacy of screening in detecting cancer earlier, thereby reducing lung-cancer specific mortality, is now well established. To ensure the cost-effectiveness of a screening programme and to limit the potential harms to participants, a risk threshold for screening eligibility is required. Risk prediction models (RPMs), which provide an individual’s personal risk of LC over a particular period based on a large number of risk factors, may improve the selection of high-risk individuals for LC screening when compared with generalised eligibility criteria that only consider smoking history and age. No currently used RPM integrates genetic risk factors into its calculation of risk. This review provides an overview of the evidence for LC screening, screening related harms and the use of RPMs in screening cohort selection. It gives a synopsis of the known genetic risk factors for lung cancer and discusses the evidence for including them in RPMs, focusing in particular on the use of polygenic risk scores to increase the accuracy of targeted lung cancer screening.

Complex roles of cAMP-PKA-CREB signaling in cancer

Cyclic adenosine monophosphate (cAMP) is the first discovered second messenger, which plays pivotal roles in cell signaling, and regulates many physiological and pathological processes. cAMP can regulate the transcription of various target genes, mainly through protein kinase A (PKA) and its downstream effectors such as cAMP-responsive element binding protein (CREB). In addition, PKA can phosphorylate many kinases such as Raf, GSK3 and FAK. Aberrant cAMP-PKA signaling is involved in various types of human tumors. Especially, cAMP signaling may have both tumor-suppressive and tumor-promoting roles depending on the tumor types and context. cAMP-PKA signaling can regulate cancer cell growth, migration, invasion and metabolism. This review highlights the important roles of cAMP-PKA-CREB signaling in tumorigenesis. The potential strategies to target this pathway for cancer therapy are also discussed.

Arginine vasopressin receptor 1a is a therapeutic target for castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) recurs after androgen deprivation therapy (ADT) and is incurable. Reactivation of androgen receptor (AR) signaling in the low androgen environment of ADT drives CRPC. This AR activity occurs through a variety of mechanisms, including up-regulation of AR coactivators such as VAV3 and expression of constitutively active AR variants such as the clinically relevant AR-V7. AR-V7 lacks a ligand-binding domain and is linked to poor prognosis. We previously showed that VAV3 enhances AR-V7 activity to drive CRPC progression. Gene expression profiling after depletion of either VAV3 or AR-V7 in CRPC cells revealed arginine vasopressin receptor 1a (AVPR1A) as the most commonly down-regulated gene, indicating that this G protein-coupled receptor may be critical for CRPC. Analysis of publicly available human PC datasets showed that AVPR1A has a higher copy number and increased amounts of mRNA in advanced PC. Depletion of AVPR1A in CRPC cells resulted in decreased cell proliferation and reduced cyclin A. In contrast, androgen-dependent PC, AR-negative PC, or nontumorigenic prostate epithelial cells, which have undetectable AVPR1A mRNA, were minimally affected by AVPR1A depletion. Ectopic expression of AVPR1A in androgen-dependent PC cells conferred castration resistance in vitro and in vivo. Furthermore, treatment of CRPC cells with the AVPR1A ligand, arginine vasopressin (AVP), activated ERK and CREB, known promoters of PC progression. A clinically safe and selective AVPR1A antagonist, relcovaptan, prevented CRPC emergence and decreased CRPC orthotopic and bone metastatic growth in mouse models. Based on these preclinical findings, repurposing AVPR1A antagonists is a promising therapeutic approach for CRPC.

Progesterone/Org inhibits lung adenocarcinoma cell growth via membrane progesterone receptor alpha

BACKGROUND

The aim of this study was to determine whether progesterone could inhibit the growth of lung adenocarcinoma cells via membrane progesterone receptor alpha (mPRα) and elucidate its potential mechanism. The relationship between mPRα expression and the survival prognosis of lung adenocarcinoma patients was studied.

METHODS

A mPRα knockdown lung adenocarcinoma cell line was constructed and treated with P4 and Org (a derivative of P4 and specific agonist of mPRα). Cell proliferation was assessed using CCK-8 and plate colony formation assays. Protein expression was detected by western blotting. A nude mouse model of lung adenocarcinoma was established to assess the antitumor effect of P4/Org in vivo.

RESULTS

We initially determined that mPRα could promote the development of lung adenocarcinoma through the following lines of evidence. High expression of mPRα both at the mRNA and protein level was significantly associated with the poor prognosis of lung adenocarcinoma patients. The downregulation of mPRα inhibited the proliferation of lung adenocarcinoma cells. We further showed that mPRα mediates the ability of P4 to inhibit the growth of lung adenocarcinoma cells through the following lines of evidence: P4/Org inhibited the proliferation of lung adenocarcinoma cells; mPRα mediated the ability of P4/Org to inhibit lung adenocarcinoma cell proliferation; mPRα mediated the ability of P4/Org to inhibit the PKA (cAMP-dependent protein kinase)/CREB (cAMP responsive element binding protein) and PKA/β-catenin signaling pathways; and P4/Org inhibited the growth of a lung adenocarcinoma tumor model in vivo.

CONCLUSIONS

In summary, the results of our study show that progesterone can inhibit lung adenocarcinoma cell growth via mPRα.

DNA methylation and cis-regulation of gene expression by prostate cancer risk SNPs

Genome-wide association studies have identified more than 100 SNPs that increase the risk of prostate cancer (PrCa). We identify and compare expression quantitative trait loci (eQTLs) and CpG methylation quantitative trait loci (meQTLs) among 147 established PrCa risk SNPs in primary prostate tumors (n = 355 from a Seattle-based study and n = 495 from The Cancer Genome Atlas, TCGA) and tumor-adjacent, histologically benign samples (n = 471 from a Mayo Clinic study). The role of DNA methylation in eQTL regulation of gene expression was investigated by data triangulation using several causal inference approaches, including a proposed adaptation of the Causal Inference Test (CIT) for causal direction. Comparing eQTLs between tumors and benign samples, we show that 98 of the 147 risk SNPs were identified as eQTLs in the tumor-adjacent benign samples, and almost all 34 eQTL identified in tumor sets were also eQTLs in the benign samples. Three lines of results support the causal role of DNA methylation. First, nearly 100 of the 147 risk SNPs were identified as meQTLs in one tumor set, and almost all eQTLs in tumors were meQTLs. Second, the loss of eQTLs in tumors relative to benign samples was associated with altered DNA methylation. Third, among risk SNPs identified as both eQTLs and meQTLs, mediation analyses suggest that over two-thirds have evidence of a causal role for DNA methylation, mostly mediating genetic influence on gene expression. In summary, we provide a comprehensive catalog of eQTLs, meQTLs and putative cancer genes for known PrCa risk SNPs. We observe that a substantial portion of germline eQTL regulatory mechanisms are maintained in the tumor development, despite somatic alterations in tumor genome. Finally, our mediation analyses illuminate the likely intermediary role of CpG methylation in eQTL regulation of gene expression.

Probing the mutational landscape of regulators of G protein signaling proteins in cancer

The advent of deep-sequencing techniques has revealed that mutations in G protein-coupled receptor (GPCR) signaling pathways in cancer are more prominent than was previously appreciated. An emergent theme is that cancer-associated mutations tend to cause enhanced GPCR pathway activation to favor oncogenicity. Regulators of G protein signaling (RGS) proteins are critical modulators of GPCR signaling that dampen the activity of heterotrimeric G proteins through their GTPase-accelerating protein (GAP) activity, which is conferred by a conserved domain dubbed the "RGS-box." Here, we developed an experimental pipeline to systematically assess the mutational landscape of RGS GAPs in cancer. A pan-cancer bioinformatics analysis of the 20 RGS domains with GAP activity revealed hundreds of low-frequency mutations spread throughout the conserved RGS domain structure with a slight enrichment at positions that interface with G proteins. We empirically tested multiple mutations representing all RGS GAP subfamilies and sampling both G protein interface and noninterface positions with a scalable, yeast-based assay. Last, a subset of mutants was validated using G protein activity biosensors in mammalian cells. Our findings reveal that a sizable fraction of RGS protein mutations leads to a loss of function through various mechanisms, including disruption of the G protein-binding interface, loss of protein stability, or allosteric effects on G protein coupling. Moreover, our results also validate a scalable pipeline for the rapid characterization of cancer-associated mutations in RGS proteins.

Regulator of G-protein signaling (RGS) proteins as drug targets: Progress and future potentials

G protein-coupled receptors (GPCRs) play critical roles in regulating processes such as cellular homeostasis, responses to stimuli, and cell signaling. Accordingly, GPCRs have long served as extraordinarily successful drug targets. It is therefore not surprising that the discovery in the mid-1990s of a family of proteins that regulate processes downstream of GPCRs generated great excitement in the field. This finding enhanced the understanding of these critical signaling pathways and provided potentially new targets for pharmacological intervention. These regulators of G-protein signaling (RGS) proteins were viewed by many as nodes downstream of GPCRs that could be targeted with small molecules to tune signaling processes. In this review, we provide a brief overview of the discovery of RGS proteins and of the gradual and continuing discovery of their roles in disease states, focusing particularly on cancer and neurological disorders. We also discuss high-throughput screening efforts that have led to the discovery first of peptide-based and then of small-molecule inhibitors targeting a subset of the RGS proteins. We explore the unique mechanisms of RGS inhibition these chemical tools have revealed and highlight the most up-to-date studies using these tools in animal experiments. Finally, we discuss the future opportunities in the field, as there are clearly more avenues left to be explored and potentials to be realized.

An Interhelical Salt Bridge Controls Flexibility and Inhibitor Potency for Regulators of G-protein Signaling Proteins 4, 8, and 19

Regulators of G-protein signaling (RGS) proteins modulate receptor signaling by binding to activated G-protein α-subunits, accelerating GTP hydrolysis. Selective inhibition of RGS proteins increases G-protein activity and may provide unique tissue specificity. Thiadiazolidinones (TDZDs) are covalent inhibitors that act on cysteine residues to inhibit RGS4, RGS8, and RGS19. There is a correlation between protein flexibility and potency of inhibition by the TDZD 4-[(4- fluorophenyl)methyl]-2-(4-methylphenyl)-1,2,4-thiadiazolidine-3,5-dione (CCG-50014). In the context of a single conserved cysteine residue on the α 4 helix, RGS19 is the most flexible and most potently inhibited by CCG-50014, followed by RGS4 and RGS8. In this work, we identify residues responsible for differences in both flexibility and potency of inhibition among RGS isoforms. RGS19 lacks a charged residue on the α 4 helix that is present in RGS4 and RGS8. Introducing a negative charge at this position (L118D) increased the thermal stability of RGS19 and decreased the potency of inhibition of CCG-50014 by 8-fold. Mutations eliminating salt bridge formation in RGS8 and RGS4 decreased thermal stability in RGS8 and increased potency of inhibition of both RGS4 and RGS8 by 4- and 2-fold, respectively. Molecular dynamics simulations with an added salt bridge in RGS19 (L118D) showed reduced RGS19 flexibility. Hydrogen-deuterium exchange studies showed striking differences in flexibility in the α 4 helix of RGS4, 8, and 19 with salt bridge-modifying mutations. These results show that the α 4 salt bridge-forming residue controls flexibility in several RGS isoforms and supports a causal relationship between RGS flexibility and the potency of TDZD inhibitors. SIGNIFICANCE STATEMENT: Inhibitor potency is often viewed in relation to the static structure of a target protein binding pocket. Using both experimental and computation studies we assess determinants of dynamics and inhibitor potency for three different RGS proteins. A single salt bridge-forming residue determines differences in flexibility between RGS isoforms; mutations either increase or decrease protein motion with correlated alterations in inhibitor potency. This strongly suggests a causal relationship between RGS protein flexibility and covalent inhibitor potency.

Mechanism of miR-107-targeting of regulator of G-protein signaling 4 in hepatocellular carcinoma

The aim of the present study was to investigate the mechanism of microRNA (miR)-107 in targeting regulator of G-protein signaling 4 (RGS4) in hepatic carcinoma. SK-HEP-1 cells were transfected with miR-107 mimics and control mimics. Reverse transcription-quantitative PCR was performed to determine the miR-107 expression levels, and following miR-107 upregulation, MTT, colony formation, transwell and wound-healing assays were performed to assess cell proliferation, colony-forming ability, invasion and migration, respectively. In addition, the effect of miR-107 upregulation on the cell cycle and apoptosis in SK-HEP-1 cells was evaluated using flow cytometry. Western blot analysis was performed to measure the protein expression levels of RGS4, epidermal growth factor receptor (EGFR), CXC chemokine receptor type 4 (CXCR4) and matrix metalloproteinase (MMP)-2 and −9. Expression level changes and the association between miR-107 and RGS4 in HCC cells were assessed using dual luciferase analysis. The results indicated that the overexpression of miR-107 in HCC cells suppressed cellular proliferation, invasion, migration and colony-forming ability, but promoted apoptosis and G₁ phase arrest. Furthermore, miR-107 mimics notably increased the protein expression level of RGS4, but significantly downregulated that of EGFR, CXCR4 and MMP-2 and −9. Together, these findings suggest that targeting this potential mechanism of miR-107 may be beneficial in the treatment of patients with HCC.

Bioinformatics Analysis of Stromal Molecular Signatures Associated with Breast and Prostate Cancer

This study aimed to identify stromal molecular signatures associated with breast and prostate cancer. The microarray data GSE26910 was downloaded from Gene Expression Omnibus database, including six invasive breast tumor stroma, six matched normal controls, six invasive prostate tumor stroma, and six matched controls. The differentially expressed genes (DEGs) in invasive breast and prostate tumors stroma were, respectively, identified. Then common stromal genes (B_P.DEGs) were further screened. Protein-protein interaction (PPI) network was constructed and Gene Ontology analysis was performed. Besides, gene-chemical interactions were mapped in Comparative Toxicogenomics Database to screen the chemicals related to feature genes. The results showed that, in total, 16 B_P.DEGs were identified. Thereinto, only seven B_P.DEGs were mapped into PPI, and only four functional modules (adenylate cyclase activating polypeptide 1 (pituitary) receptor type I (ADCYAP1R1) module, aspartoacylase (ASPA) module, glutathione S-transferase mu 5 (GSTM5) module, and periplakin (PPL) module) were involved in important biological processes associated with cancer progression. In addition, the chemicals, such as dihydrotestosterone, apocarotenal, testosterone, and progesterone, were screened for the roles of feature genes in the progression of breast and prostate cancer. In conclusion, ADCYAP1R1, GSTM5, and PPL were stromal molecular signatures and might play a key role in the progression of breast and prostate cancer.

High-resolution structure of RGS17 suggests a role for Ca2+ in promoting the GTPase-activating protein activity by RZ subfamily members

Regulator of G protein signaling (RGS) proteins are negative regulators of G protein-coupled receptor (GPCR) signaling through their ability to act as GTPase-activating proteins (GAPs) for activated Gα subunits. Members of the RZ subfamily of RGS proteins bind to activated Gα_o, Gα_z, and Gα_i1-3 proteins in the nervous system and thereby inhibit downstream pathways, including those involved in Ca²⁺-dependent signaling. In contrast to other RGS proteins, little is known about RZ subfamily structure and regulation. Herein, we present the 1.5-Å crystal structure of RGS17, the most complete and highest-resolution structure of an RZ subfamily member to date. RGS17 cocrystallized with Ca²⁺ bound to conserved positions on the predicted Gα-binding surface of the protein. Using NMR chemical shift perturbations, we confirmed that Ca²⁺ binds in solution to the same site. Furthermore, RGS17 had greater than 55-fold higher affinity for Ca²⁺ than for Mg²⁺ Finally, we found that Ca²⁺ promotes interactions between RGS17 and activated Gα and decreases the K_m for GTP hydrolysis, potentially by altering the binding mechanism between these proteins. Taken together, these findings suggest that Ca²⁺ positively regulates RGS17, which may represent a general mechanism by which increased Ca²⁺ concentration promotes the GAP activity of the RZ subfamily, leading to RZ-mediated inhibition of Ca²⁺ signaling.

Genetic Analysis of Rare Human Variants of Regulators of G Protein Signaling Proteins and Their Role in Human Physiology and Disease

Regulators of G protein signaling (RGS) proteins modulate the physiologic actions of many neurotransmitters, hormones, and other signaling molecules. Human RGS proteins comprise a family of 20 canonical proteins that bind directly to G protein-coupled receptors/G protein complexes to limit the lifetime of their signaling events, which regulate all aspects of cell and organ physiology. Genetic variations account for diverse human traits and individual predispositions to disease. RGS proteins contribute to many complex polygenic human traits and pathologies such as hypertension, atherosclerosis, schizophrenia, depression, addiction, cancers, and many others. Recent analysis indicates that most human diseases are due to extremely rare genetic variants. In this study, we summarize physiologic roles for RGS proteins and links to human diseases/traits and report rare variants found within each human RGS protein exome sequence derived from global population studies. Each RGS sequence is analyzed using recently described bioinformatics and proteomic tools for measures of missense tolerance ratio paired with combined annotation-dependent depletion scores, and protein post-translational modification (PTM) alignment cluster analysis. We highlight selected variants within the well-studied RGS domain that likely disrupt RGS protein functions and provide comprehensive variant and PTM data for each RGS protein for future study. We propose that rare variants in functionally sensitive regions of RGS proteins confer profound change-of-function phenotypes that may contribute, in newly appreciated ways, to complex human diseases and/or traits. This information provides investigators with a valuable database to explore variation in RGS protein function, and for targeting RGS proteins as future therapeutic targets.

High-throughput screening of prostate cancer risk loci by single nucleotide polymorphisms sequencing

Functional characterization of disease-causing variants at risk loci has been a significant challenge. Here we report a high-throughput single-nucleotide polymorphisms sequencing (SNPs-seq) technology to simultaneously screen hundreds to thousands of SNPs for their allele-dependent protein-binding differences. This technology takes advantage of higher retention rate of protein-bound DNA oligos in protein purification column to quantitatively sequence these SNP-containing oligos. We apply this technology to test prostate cancer-risk loci and observe differential allelic protein binding in a significant number of selected SNPs. We also test a unique application of self-transcribing active regulatory region sequencing (STARR-seq) in characterizing allele-dependent transcriptional regulation and provide detailed functional analysis at two risk loci (RGS17 and ASCL2). Together, we introduce a powerful high-throughput pipeline for large-scale screening of functional SNPs at disease risk loci.

Functional characterization of disease-causing variants at risk loci in cancer is challenging. Here, in prostate cancer the authors report a pipeline for high-throughput single-nucleotide polymorphisms sequencing (SNPs-seq) for large scale screening of functional SNPs at disease risk loci.

CREB1 directly activates the transcription of ribonucleotide reductase small subunit M2 and promotes the aggressiveness of human colorectal cancer

As the small subunit of Ribonucleotide reductase (RR), RRM2 displays a very important role in various critical cellular processes such as cell proliferation, DNA repair, and senescence, etc. Importantly, RRM2 functions like a tumor driver in most types of cancer but little is known about the regulatory mechanism of RRM2 in cancer development. In this study, we found that the cAMP responsive element binding protein 1 (CREB1) acted as a transcription factor of RRM2 gene in human colorectal cancer (CRC). CREB1 directly bound to the promoter of RRM2 gene and induced its transcriptional activation. Knockdown of CREB1 decreased the expression of RRM2 at both mRNA and protein levels. Moreover, knockdown of RRM2 attenuated CREB1-induced aggressive phenotypes of CRC cells in vitro and in vivo. Analysis of the data from TCGA database and clinical CRC specimens with immunohistochemical staining also demonstrated a strong correlation between the co-expression of CREB1 and RRM2. Decreased disease survivals were observed in CRC patients with high expression levels of CREB1 or RRM2. Our results indicate CREB1 as a critical transcription factor of RRM2 which promotes tumor aggressiveness, and imply a significant correlation between CREB1 and RRM2 in CRC specimens. These may provide the possibility that CREB1 and RRM2 could be used as biomarkers or targets for CRC diagnosis and treatment.

Differentially expressed microRNAs in lung adenocarcinoma invert effects of copy number aberrations of prognostic genes

In many cancers, significantly down- or upregulated genes are found within chromosomal regions with DNA copy number alteration opposite to the expression changes. Generally, this paradox has been overlooked as noise, but can potentially be a consequence of interference of epigenetic regulatory mechanisms, including microRNA-mediated control of mRNA levels.

To explore potential associations between microRNAs and paradoxes in non-small-cell lung cancer (NSCLC) we curated and analyzed lung adenocarcinoma (LUAD) data, comprising gene expressions, copy number aberrations (CNAs) and microRNA expressions. We integrated data from 1,062 tumor samples and 241 normal lung samples, including newly-generated array comparative genomic hybridization (aCGH) data from 63 LUAD samples.

We identified 85 “paradoxical” genes whose differential expression consistently contrasted with aberrations of their copy numbers. Paradoxical status of 70 out of 85 genes was validated on sample-wise basis using The Cancer Genome Atlas (TCGA) LUAD data. Of these, 41 genes are prognostic and form a clinically relevant signature, which we validated on three independent datasets. By meta-analysis of results from 9 LUAD microRNA expression studies we identified 24 consistently-deregulated microRNAs. Using TCGA-LUAD data we showed that deregulation of 19 of these microRNAs explains differential expression of the paradoxical genes.

Our results show that deregulation of paradoxical genes is crucial in LUAD and their expression pattern is maintained epigenetically, defying gene copy number status.

Regulating the regulators: Epigenetic, transcriptional, and post-translational regulation of RGS proteins

Regulators of G protein signaling (RGS) are a family of proteins classically known to accelerate the intrinsic GTPase activity of G proteins, which results in accelerated inactivation of heterotrimeric G proteins and inhibition of G protein coupled receptor signaling. RGS proteins play major roles in essential cellular processes, and dysregulation of RGS protein expression is implicated in multiple diseases, including cancer, cardiovascular and neurodegenerative diseases. The expression of RGS proteins is highly dynamic and is regulated by epigenetic, transcriptional and post-translational mechanisms. This review summarizes studies that report dysregulation of RGS protein expression in disease states, and presents examples of drugs that regulate RGS protein expression. Additionally, this review discusses, in detail, the transcriptional and post-transcriptional mechanisms regulating RGS protein expression, and further assesses the therapeutic potential of targeting these mechanisms. Understanding the molecular mechanisms controlling the expression of RGS proteins is essential for the development of therapeutics that indirectly modulate G protein signaling by regulating expression of RGS proteins.

miR-203 inhibits cell proliferation, invasion, and migration of non-small-cell lung cancer by downregulating RGS17

Involvement of the RGS17 oncogene in the promotion of non‐small‐cell lung cancer (NSCLC) has been reported, but the regulation mechanism in NSCLC remains unclear. MicroRNAs (miRNAs) negatively regulate gene expression, and their dysregulation has been implicated in tumorigenesis. To understand the role of miRNAs in Regulator of G Protein Signaling 17 (RGS17)‐induced NSCLC, we showed that miR‐203 was downregulated during tumorigenesis, and inhibited the proliferation and invasion of lung cancer cells. We then determined whether miR‐203 regulated NSCLC by targeting RGS17. To characterize the regulatory effect of miR‐203 on RGS17, we used lung cancer cell lines, A549 and Calu‐1, and the constructed miR‐203 and RGS17 overexpression vectors. The CCK8 kit was used to determine cell proliferation, and the Transwell® assay was used to measure cell invasion and migration. RT‐PCR, western blots, and immunofluorescence were used to analyze expression of miR‐203 and RGS17, and the luciferase reporter assay was used to examine the interaction between miR‐203 and RGS17. Nude mice were used to characterize in vivo tumor growth regulation. Expression of miR‐203 inhibited proliferation, invasion, and migration of lung cancer cell lines A549 and Calu‐1 by targeting RGS17. The regulatory effect of miR‐203 was inhibited after overexpression of RGS17. The luciferase reporter assay showed that miR‐203 downregulated RGS17 by direct integration into the 3′‐UTR of RGS17 mRNA. In vivo studies showed that expression of miR‐203 significantly inhibited growth of tumors. Taken together, the results suggested that expression of miR‐203 inhibited tumor growth and metastasis by targeting RGS17.

Regulator of G protein signaling 4 inhibits human melanoma cells proliferation and invasion through the PI3K/AKT signaling pathway

Melanoma is a tumor produced by skin melanocytes, which has a high metastatic rate and poor prognosis. So far, plenty of work has been done on melanoma, but mechanisms underlying melanoma development have not been fully elucidated. Here we identified regulator of G protein signaling 4(RGS4) as novel therapeutic target for malignant melanoma and its regulating effect on melanoma. We found that endogenous RGS4 expression was much lower in melanoma tissues and cells. In A375 cell line with low endogenous RGS4 expression, the function of RGS4 was detected by up-regulation its expression with pcDNA3.1-RGS4 and knockdown its expression with siRNA. Our results showed that RGS4 could significantly reduce the proliferation, migration and invasion of melanoma cells. RGS4 is an important regulator for the apoptosis of melanocyte, and the apoptosis rate is significantly decreased in low RGS4 enviroment. RGS4 induced non-activation of PI3K/AKT pathway, resulting in decreased expression of E2F1 and Cyclin D1, thus constraining cell proliferation and invasion. These results were further confirmed in M14 cell lines. Collectively, our findings show that RGS4 plays an important role in multiple cellular functions of melanoma development and is valuable to be a therapeutic target.

Natural Products Discovered in a High-Throughput Screen Identified as Inhibitors of RGS17 and as Cytostatic and Cytotoxic Agents for Lung and Prostate Cancer Cell Lines

Regulator of G Protein Signaling (RGS) 17 is an overexpressed promoter of cancer survival in lung and prostate tumors, the knockdown of which results in decreased tumor cell proliferation in vitro. Identification of drug-like molecules inhibiting this protein could ameliorate the RGS17's pro-tumorigenic effect. Using high-throughput screening, a chemical library containing natural products was interrogated for inhibition of the RGS17-Gα_o interaction. Initial hits were verified in control and counter screens. Leads were characterized via biochemical, mass spectrometric, Western blot, microscopic, and cytotoxicity measures. Four known compounds (1-4) were identified with IC₅₀ values ranging from high nanomolar to low micromolar. Three compounds were extensively characterized biologically, demonstrating cellular activity determined by confocal microscopy, and two compounds were assessed via ITC exhibiting high nanomolar to low micromolar dissociation constants. The compounds were found to have a cysteine-dependent mechanism of binding, verified through site-directed mutagenesis and cysteine reactivity assessment. Two compounds, sanguinarine (1) and celastrol (2), were found to be cytostatic against lung and prostate cancer cell lines and cytotoxic against prostate cancer cell lines in vitro, although the dependence of RGS17 on these phenomena remains elusive, a result that is perhaps not surprising given the multimodal cytostatic and cytotoxic activities of many natural products.

RGS19 upregulates Nm23-H1/2 metastasis suppressors by transcriptional activation via the cAMP/PKA/CREB pathway

The Nm23 metastasis suppressor family is involved in physiological and pathological processes including tumorigenesis and metastasis. Although the inverse correlation of Nm23 level with tumor metastasis potential has been widely observed, the mechanisms that regulate the expression of Nm23 remain poorly understood. Our previous studies have revealed that Nm23-H1/2 isoforms are upregulated by RGS19, a regulator of G protein signaling (RGS) protein which accelerates the termination of G_i signals. Here, we examined the ability of RGS19 to stimulate transcriptional regulation of Nm23 by screening a panel of luciferase reporter genes. Transient and stable overexpression of RGS19 upregulated the Nm23-H1/2 protein levels and activated several transcription factors including CREB, AP-1 and SRE in HEK293 cells. Interestingly, agents that increase the intracellular cAMP level and the phosphorylation of CREB (e.g., adrenergic receptor agonist, forskolin, and cAMP analogues) upregulated the expression of Nm23-H1/2 in HEK293 cells and several cancer cell lines including A549, HeLa, MDA-MB-231, and MDA-MB-435s cells. Conversely, inhibition of protein kinase A (PKA) by H-89 suppressed the phosphorylation of CREB and reduced the expression of Nm23-H1/2. Furthermore, activation of PKA attenuated cancer cell migration in wound healing and transwell assays. Collectively, these results revealed a PKA-dependent mechanism for controlling Nm23-H1/2 expression.

Lithium and an EPAC-specific inhibitor ESI-09 synergistically suppress pancreatic cancer cell proliferation and survival

Our previous studies showed that while lithium suppresses proliferation and induces apoptosis in pancreatic cancer cells, the inhibition of exchange proteins directly activated by cyclic adenosine monophosphate (cAMP) (EPAC)1 blocks pancreatic cancer cell migration and invasion. In this study, we further investigated the combinatory effects of lithium and EPAC-specific inhibitor (ESI)-09, an EPAC-specific inhibitor, on pancreatic cancer cell proliferation and viability, and explored whether lithium synergistically cooperates with EPAC inhibition in suppressing pancreatic cancer cell tumorigenicity. The cell viability of pancreatic cancer cell lines PANC-1 and MiaPaCa-2 was measured after 48 h of incubation with different dose combination of lithium and ESI-09. Flow cytometric analysis was carried out to further verify the impact of lithium and ESI-09 upon PANC-1 cell proliferation and apoptosis. To investigate the mechanism that the effects generated by lithium and ESI-09 on PANC-1 cells, the intracellular cAMP level was measured by an ELISA-based cAMP immunoassay. Our data showed that lithium and ESI-09 synergistically inhibit pancreatic cancer cell growth and survival. Furthermore, our results revealed a novel mechanism in which the synergism between lithium and ESI-09 is not mediated by the inhibitory effect of lithium toward GSK3β, but by lithium's ability to suppress cAMP/protein kinase A signaling.

G-Protein Signaling Protein-17 (RGS17) Is Upregulated and Promotes Tumor Growth and Migration in Human Colorectal Carcinoma

Colorectal carcinoma is one of the leading causes of cancer-related deaths and has a high tendency for metastasis, which makes it a priority to find novel methods to diagnose and treat colorectal carcinoma at a very early stage. We studied the role of the regulator of G-protein signaling (RGS) family of proteins RGS17 in colorectal carcinoma growth and metastasis. We found that RGS17 was upregulated in both clinical colorectal carcinoma tissues and cultured colorectal carcinoma cells. Knockdown of RGS17 by specific siRNA decreased the cell proliferation rate, whereas overexpression of RGS17 with expression plasmid increased the rate in cultured cells. Consistently, a mouse model for colorectal carcinoma also showed that depletion of RGS17 significantly inhibited tumor growth in vivo. Moreover, a Transwell assay showed that RGS17 promoted the ability of colorectal carcinoma cells to migrate and invade. These data suggest that RGS17 is overexpressed in colorectal carcinoma and promotes cell proliferation, migration, and invasion.

Regulator of G protein signaling 20 correlates with clinicopathological features and prognosis in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a highly aggressive tumor subtype lacking effective prognostic indicators or therapeutic targets. Therefore, finding a novel molecular biomarker for TNBC to achieve target therapy and predict its prognosis is crucial in preventing inappropriate treatment. Regulator of G-protein signaling (RGS) families of protein can negatively regulate signaling of heterotrimeric G proteins and are known to be upregulated in various tumors. In this study, we demonstrated that RGS20 was more highly expressed in TNBC tumor tissue than in adjacent normal tissue by analyzing the cancer genome atlas (TCGA) database. However, RGS20 expression was low in all breast cancer and luminal breast cancer patients. Validated by the TCGA cohort, RGS20 was upregulated in lymph node-positive TNBC compared with that in lymph node-negative breast cancer. High expression of RGS20 had a risk of lymph node metastasis, ki-67 > 14%, poor N stage, and poor clinical stage in the immunohistochemistry of tissue microarrays. Moreover, K-M plot analysis showed that TNBC patients with high RGS20 expression had poor relapse-free survival. In summary, the findings revealed that RGS20 was a special TNBC oncogene that promoted tumor progression and influenced TNBC prognosis. This study is the first to show that RGS20 was a special oncogene, and its high expression was significantly associated with the progression and prognosis of TNBC. RGS20 may be a novel molecular biomarker for the targeted therapy and prognosis of TNBC.

The evolution of regulators of G protein signalling proteins as drug targets - 20 years in the making: IUPHAR Review 21

Regulators of G protein signalling (RGS) proteins are celebrating the 20th anniversary of their discovery. The unveiling of this new family of negative regulators of G protein signalling in the mid-1990s solved a persistent conundrum in the G protein signalling field, in which the rate of deactivation of signalling cascades in vivo could not be replicated in exogenous systems. Since then, there has been tremendous advancement in the knowledge of RGS protein structure, function, regulation and their role as novel drug targets. RGS proteins play an important modulatory role through their GTPase-activating protein (GAP) activity at active, GTP-bound Gα subunits of heterotrimeric G proteins. They also possess many non-canonical functions not related to G protein signalling. Here, an update on the status of RGS proteins as drug targets is provided, highlighting advances that have led to the inclusion of RGS proteins in the IUPHAR/BPS Guide to PHARMACOLOGY database of drug targets.

Development of a bimolecular luminescence complementation assay for RGS: G protein interactions in cells

Cell based assessment tools and screening platforms are the preferred paradigm for small molecule identification and validation due to selectively identifying molecules with cellular activity and validation of compound activity against target proteins in their native environment. With respect to Regulator of G Protein Signaling (RGS) proteins, current cell based methodologies are either low throughput or monitor downstream signaling consequences. The increasing number of reports indicating RGS function in various disease pathogeneses highlights the need for a robust RGS inhibitor discovery and characterization paradigm. Promega's NanoBit Protein Complementation Assay utilizes NanoLuc, an engineered luciferase with enhanced luminescence characteristics which allow for both robust and kinetic assessment of protein interaction formation and disruption. Here we characterized 15 separate RGS: G protein interactions using this system. The binding profile of RGS: Gα interactions correlates to prior published biochemical binding profiles of these proteins. Additionally, we demonstrated this system is suitable for high throughput screening efforts via calculation of Z-factors for three of the interactions and demonstrated that a known small molecule inhibitor of RGS4 disrupts the RGS4: Gα_i1 protein-protein interaction. In conclusion, the NanoBit Protein Complementation Assay holds promise as a robust platform for discovery and characterization of RGS inhibitors.

Regulator of G protein signaling 20 enhances cancer cell aggregation, migration, invasion and adhesion

Several RGS (regulator of G protein signaling) proteins are known to be upregulated in a variety of tumors but their roles in modulating tumorigenesis remain undefined. Since the expression of RGS20 is elevated in metastatic melanoma and breast tumors, we examined the effects of RGS20 overexpression and knockdown on the cell mobility and adhesive properties of different human cancer cell lines, including cervical cancer HeLa, breast adenocarcinoma MDA-MB-231, and non-small cell lung carcinoma H1299 and A549 cells. Expression of RGS20 enhanced cell aggregation, migration, invasion and adhesion as determined by hanging drop aggregation, wound healing, transwell chamber migration and invasion assays. Conversely, shRNA-mediated knockdown of endogenous RGS20 impaired these responses. In addition, RGS20 elevated the expression of vimentin (a mesenchymal cell marker) but down-regulated the expression of E-cadherin, two indicators commonly associated with metastasis. These results suggest that the expression of RGS20 may promote metastasis of tumor cells.

Regulator of G Protein Signaling 17 as a Negative Modulator of GPCR Signaling in Multiple Human Cancers

Regulators of G protein signaling (RGS) proteins modulate G protein-coupled receptor (GPCR) signaling networks by terminating signals produced by active Gα subunits. RGS17, a member of the RZ subfamily of RGS proteins, is typically only expressed in appreciable amounts in the human central nervous system, but previous works have shown that RGS17 expression is selectively upregulated in a number of malignancies, including lung, breast, prostate, and hepatocellular carcinoma. In addition, this upregulation of RGS17 is associated with a more aggressive cancer phenotype, as increased proliferation, migration, and invasion are observed. Conversely, decreased RGS17 expression diminishes the response of ovarian cancer cells to agents commonly used during chemotherapy. These somewhat contradictory roles of RGS17 in cancer highlight the need for selective, high-affinity inhibitors of RGS17 to use as chemical probes to further the understanding of RGS17 biology. Based on current evidence, these compounds could potentially have clinical utility as novel chemotherapeutics in the treatment of lung, prostate, breast, and liver cancers. Recent advances in screening technologies to identify potential inhibitors coupled with increasing knowledge of the structural requirements of RGS-Gα protein-protein interaction inhibitors make the future of drug discovery efforts targeting RGS17 promising. This review highlights recent findings related to RGS17 as both a canonical and atypical RGS protein, its role in various human disease states, and offers insights on small molecule inhibition of RGS17.