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

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.

Functional Assessment of Cancer-Linked Mutations in Sensitive Regions of Regulators of G Protein Signaling Predicted by Three-Dimensional Missense Tolerance Ratio Analysis

Regulators of G protein signaling (RGS) proteins modulate G protein-coupled receptor (GPCR) signaling by acting as negative regulators of G proteins. Genetic variants in RGS proteins are associated with many diseases, including cancers, although the impact of these mutations on protein function is uncertain. Here we analyze the RGS domains of 15 RGS protein family members using a novel bioinformatic tool that measures the missense tolerance ratio (MTR) using a three-dimensional (3D) structure (3DMTR). Subsequent permutation analysis can define the protein regions that are most significantly intolerant (P < 0.05) in each dataset. We further focused on RGS14, RGS10, and RGS4. RGS14 exhibited seven significantly tolerant and seven significantly intolerant residues, RGS10 had six intolerant residues, and RGS4 had eight tolerant and six intolerant residues. Intolerant and tolerant-control residues that overlap with pathogenic cancer mutations reported in the COSMIC cancer database were selected to define the functional phenotype. Using complimentary cellular and biochemical approaches, proteins were tested for effects on GPCR-Gα activation, Gα binding properties, and downstream cAMP levels. Identified intolerant residues with reported cancer-linked mutations RGS14-R173C/H and RGS4-K125Q/E126K, and tolerant RGS14-S127P and RGS10-S64T resulted in a loss-of-function phenotype in GPCR-G protein signaling activity. In downstream cAMP measurement, tolerant RGS14-D137Y and RGS10-S64T and intolerant RGS10-K89M resulted in change of function phenotypes. These findings show that 3DMTR identified intolerant residues that overlap with cancer-linked mutations cause phenotypic changes that negatively impact GPCR-G protein signaling and suggests that 3DMTR is a potentially useful bioinformatics tool for predicting functionally important protein residues. SIGNIFICANCE STATEMENT: Human genetic variant/mutation information has expanded rapidly in recent years, including cancer-linked mutations in regulator of G protein signaling (RGS) proteins. However, experimental testing of the impact of this vast catalogue of mutations on protein function is not feasible. We used the novel bioinformatics tool three-dimensional missense tolerance ratio (3DMTR) to define regions of genetic intolerance in RGS proteins and prioritize which cancer-linked mutants to test. We found that 3DMTR more accurately classifies loss-of-function mutations in RGS proteins than other databases thereby offering a valuable new research tool.

Polyphenon E Effects on Gene Expression in PC-3 Prostate Cancer Cells

Polyphenon E (Poly E) is a standardized, caffeine-free green tea extract with defined polyphenol content. Poly E is reported to confer chemoprotective activity against prostate cancer (PCa) progression in the TRAMP model of human PCa, and has shown limited activity against human PCa in human trials. The molecular mechanisms of the observed Poly E chemopreventive activity against PCa are not fully understood. We hypothesized that Poly E treatment of PCa cells induces gene expression changes, which could underpin the molecular mechanisms of the limited Poly E chemoprevention activity against PCa. PC-3 cells were cultured in complete growth media supplemented with varied Poly E concentrations for 24 h, then RNA was isolated for comparative DNA microarray (0 vs. 200 mg/L Poly E) and subsequent TaqMan qRT-PCR analyses. Microarray data for 54,613 genes were filtered for >2-fold expression level changes, with 8319 genes increased and 6176 genes decreased. Eight genes involved in key signaling or regulatory pathways were selected for qRT-PCR. Two genes increased expression significantly, MXD1 (13.98-fold; p = 0.0003) and RGS4 (21.98-fold; p = 0.0011), by qRT-PCR. MXD1 and RGS4 significantly increased gene expression in Poly E-treated PC-3 cells, and the MXD1 gene expression increases were Poly E dose-dependent.

Identification of Novel Imatinib-Resistant Genes in Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are common ICC precursor sarcomas, which are considered to be a potential malignant mesenchymal tumor driven by specific KIT or PDGFRA signals in the gastrointestinal tract. The standard treatment for GIST without metastasis is surgical resection. GIST with metastasis is usually treated with tyrosine kinase inhibitors (TKIs) only but cannot be cured. The TKI imatinib is the main drug of GIST drug therapy. In adjuvant therapy, the duration of imatinib adjuvant therapy is 3 years. It has been proved that imatinib can improve the overall survival time (OS). However, many GIST patients develop drug resistance due to the long-term use of imatinib. We were forced to look for new strategies to treat GIST. The purpose of the current academic work is to study the drug-resistant genes of imatinib and their potential mechanisms. A total of 897 differentially expressed genes (DEGs) were found between imatinib-sensitive cell line GIST882 and imatinib-resistant cell line GIST430 by RNA sequencing (RNA-seq). After analyzing the DEGs, 10 top genes were selected (NDN, FABP4, COL4A1, COLEC11, MEG3, EPHA3, EDN3, LMO3, RGS4, and CRISP2). These genes were analyzed by RT-PCR, and it was confirmed that the expression trend of FABP4, COL4A1, and RGS4 in different imatinib-resistant cell lines was in accord with the GEO database. It is suggested that these genes may play a potential role in the clinical diagnosis and treatment of imatinib resistance in GIST.

Oxidative Stress in Intestinal Ischemia-Reperfusion

Ischemia-reperfusion (I/R) injury is a manifestation of tissue or organ damage that is followed by ischemia and exacerbated by the return of blood flow to a previously damaged tissue or organ. The intestines are one of the most sensitive tissues and organs to I/R injury. Moreover, the adverse consequences of intestinal I/R (II/R) injury are not limited to the intestine itself and can also lead to damage of the distant tissues and organs. The mechanism of II/R is extremely complex and oxidative stress is the key link in the pathogenesis of II/R injury. This study summarizes the roles of oxidative stress and its signaling pathways involved in II/R. The signaling pathways that mitigate II/R injury include the nuclear factor erythroid-related factor 2 (Nrf2)-mediated signaling pathway, Wnt/β-catenin pathway, and phosphatidylinositol kinase 3 (PI3K)/Akt pathway; those that aggravate II/R injury include the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, Toll-like receptor (TLR) receptor-mediated signaling pathway, protein kinase CβII (PKCβII)/p66shc pathway, and microRNA (miRNA)/p66shc pathway; the effect of miRNA on related pathways and mitochondrial DNA translocation. The aforementioned pathways provide new ideas for further exploring the occurrence and development of II/R and more effective treatments for II/R injury.

NKX2-1 re-expression induces cell death through apoptosis and necrosis in dedifferentiated thyroid carcinoma cells

NK2 homeobox 1 (NKX2-1) is a thyroid transcription factor essential for proper thyroid formation and maintaining its physiological function. In thyroid cancer, NKX2-1 expression decreases in parallel with declined differentiation. However, the molecular pathways and mechanisms connecting NKX2-1 to thyroid cancer phenotypes are largely unknown. This study aimed to examine the effects of NKX2-1 re-expression on dedifferentiated thyroid cancer cell death and explore the underlying mechanisms. A human papillary thyroid carcinoma cell line lacking NKX2-1 expression was infected with an adenoviral vector containing Nkx2-1. Cell viability decreased after Nkx2-1 transduction and apoptosis and necrosis were detected. Arginase 2 (ARG2), regulator of G protein signaling 4 (RGS4), and RGS5 mRNA expression was greatly increased in Nkx2-1-transducted cells. After suppressing these genes by siRNA, cell death, apoptosis, and necrosis decreased in RGS4 knockdown cells. These findings demonstrated that cell death was induced via apoptosis and necrosis by NKX2-1 re-expression and involves RGS4.

Adenomatous Polyposis Coli loss controls cell cycle regulators and response to paclitaxel in MDA-MB-157 metaplastic breast cancer cells

Adenomatous Polyposis Coli (APC) is lost in approximately 70% of sporadic breast cancers, with an inclination towards triple negative breast cancer (TNBC). TNBC is treated with traditional chemotherapy, such as paclitaxel (PTX); however, tumors often develop drug resistance. We previously created APC knockdown cells (APC shRNA1) using the human TNBC cells, MDA-MB-157, and showed that APC loss induces PTX resistance. To understand the mechanisms behind APC-mediated PTX response, we performed cell cycle analysis and analyzed cell cycle related proteins. Cell cycle analysis indicated increased G2/M population in both PTX-treated APC shRNA1 and parental cells, suggesting that APC expression does not alter PTX-induced G2/M arrest. We further studied the subcellular localization of the G2/M transition proteins, cyclin B1 and CDK1. The APC shRNA1 cells had increased CDK1, which was preferentially localized to the cytoplasm, and increased baseline CDK6. RNA-sequencing was performed to gain a global understanding of changes downstream of APC loss and identified a broad mis-regulation of cell cycle-related genes in APC shRNA1 cells. Our studies are the first to show an interaction between APC and taxane response in breast cancer. The implications include designing combination therapy to re-sensitize APC-mutant breast cancers to taxanes using the specific cell cycle alterations.

Rgs4 is a regulator of mTOR activity required for motoneuron axon outgrowth and neuronal development in zebrafish

The Regulator of G protein signaling 4 (Rgs4) is a member of the RGS proteins superfamily that modulates the activity of G-protein coupled receptors. It is mainly expressed in the nervous system and is linked to several neuronal signaling pathways; however, its role in neural development in vivo remains inconclusive. Here, we generated and characterized a rgs4 loss of function model (MZrgs4) in zebrafish. MZrgs4 embryos showed motility defects and presented reduced head and eye sizes, reflecting defective motoneurons axon outgrowth and a significant decrease in the number of neurons in the central and peripheral nervous system. Forcing the expression of Rgs4 specifically within motoneurons rescued their early defective outgrowth in MZrgs4 embryos, indicating an autonomous role for Rgs4 in motoneurons. We also analyzed the role of Akt, Erk and mechanistic target of rapamycin (mTOR) signaling cascades and showed a requirement for these pathways in motoneurons axon outgrowth and neuronal development. Drawing on pharmacological and rescue experiments in MZrgs4, we provide evidence that Rgs4 facilitates signaling mediated by Akt, Erk and mTOR in order to drive axon outgrowth in motoneurons and regulate neuronal numbers.

Targeting RGS4 Ablates Glioblastoma Proliferation

Glioblastoma (GBM) is the most common type of adult primary brain tumor with a median survival rate of less than 15 months, regardless of the current standard of care. Cellular heterogeneity, self-renewal ability and tumorigenic glioma cancer stem cell (GSC) populations contribute to the difficulty in treating GBM. G-protein-coupled receptors (GPCRs) are the largest group of membrane proteins and mediate many cellular responses. Regulators of G-protein signaling 4 (RGS4) are negative regulators of G-protein signaling, and elevated levels of RGS4 are reportedly linked with several human diseases, including cancer. This study investigates the effect of silencing RGS4, resulting in inhibition of GSC growth, invasion and migration. Data obtained from The Cancer Genome Atlas (TCGA) demonstrated poor patient survival with high expression of RGS4. Immunohistochemistry and immunoblot analysis conducted on GBM patient biopsy specimens demonstrated increased RGS4 expression correlative with the TCGA data. RNA sequencing confirmed a significant decrease in the expression of markers involved in GSC invasion and migration, particularly matrix metalloproteinase-2 (MMP2) in knockout of RGS4 using CRISPR plasmid (ko-RGS4)-treated samples compared to parental controls. Gelatin zymography confirmed the reduced activity of MMP2 in ko-RGS4-treated samples. Silencing RGS4 further reduced the invasive and migratory abilities and induction of apoptosis of GSCs as evidenced by Matrigel plug assay, wound healing assay and human apoptosis array. Collectively, our results showed that the silencing of RGS4 plays an important role in regulating multiple cellular functions, and is an important therapeutic target in GBM.

RGS4 promotes allergen- and aspirin-associated airway hyperresponsiveness by inhibiting PGE2 biosynthesis

BACKGROUND

Allergens elicit host production of mediators acting on G-protein-coupled receptors to regulate airway tone. Among these is prostaglandin E2 (PGE2), which, in addition to its role as a bronchodilator, has anti-inflammatory actions. Some patients with asthma develop bronchospasm after the ingestion of aspirin and other nonsteroidal anti-inflammatory drugs, a disorder termed aspirin-exacerbated respiratory disease. This condition may result in part from abnormal dependence on the bronchoprotective actions of PGE2.

OBJECTIVE

We sought to understand the functions of regulator of G protein signaling 4 (RGS4), a cytoplasmic protein expressed in airway smooth muscle and bronchial epithelium that regulates the activity of G-protein-coupled receptors, in asthma.

METHODS

We examined RGS4 expression in human lung biopsies by immunohistochemistry. We assessed airways hyperresponsiveness (AHR) and lung inflammation in germline and airway smooth muscle-specific Rgs4^-/- mice and in mice treated with an RGS4 antagonist after challenge with Aspergillus fumigatus. We examined the role of RGS4 in nonsteroidal anti-inflammatory drug-associated bronchoconstriction by challenging aspirin-exacerbated respiratory disease-like (ptges1^-/-) mice with aspirin.

RESULTS

RGS4 expression in respiratory epithelium is increased in subjects with severe asthma. Allergen-induced AHR was unexpectedly diminished in Rgs4^-/- mice, a finding associated with increased airway PGE2 levels. RGS4 modulated allergen-induced PGE2 secretion in human bronchial epithelial cells and prostanoid-dependent bronchodilation. The RGS4 antagonist CCG203769 attenuated AHR induced by allergen or aspirin challenge of wild-type or ptges1^-/- mice, respectively, in association with increased airway PGE2 levels.

CONCLUSIONS

RGS4 may contribute to the development of AHR by reducing airway PGE2 biosynthesis in allergen- and aspirin-induced asthma.

MiR-21-3p modulates lipopolysaccharide-induced inflammation and apoptosis via targeting TGS4 in retinal pigment epithelial cells

Age-related macular degeneration (AMD) is a major reason of blindness in the elderly. MicroRNAs are implicated in various pathological processes, including inflammation and apoptosis. In this study, we aim to investigate the biological functions of miR-21-3p in inflammation and apoptosis caused by lipopolysaccharide (LPS) in human retinal pigment epithelial (ARPE-19) cells. The miR-21-3p inhibitor and mimic were transfected into ARPE-19 cells for 48 hours, followed by exposed to LPS (10 μg/mL) for 24 hours. The mRNA and protein expression of IL-6 and MCP-1 were measured using real-time PCR (RT-PCR) and enzyme-linked immunosorbent assays. Cell viability, apoptosis, caspase 3 activity, cleaved caspase-3 and cleaved-PARP protein levels were detected to evaluate the effects of miR-21-3p on apoptosis. Additionally, the target relationship between miR-21-3p and regulator of G-protein signalling 4 (RGS4) was verified by dual luciferase reporter assay. RT-PCR analysis demonstrated that LPS induced miR-21-3p expression. Inhibition of miR-21-3p reduced the mRNA and protein levels of IL-6 and MCP-1. Apoptosis, caspase-3 activity, and cleaved-caspase 3 and cleaved PARP protein levels were repressed by the miR-21-3p inhibitor. However, overexpression of miR-21-3p showed the opposite results. Furthermore, we identified that miR-21-3p directly targeted the 3' untranslated region of RGS4. MiR-21-3p negatively regulated the expression of RGS4 both in mRNA and protein levels. Silencing RGS4 reduced the anti-inflammatory and anti-apoptotic effects of miR-21-3p inhibitor. Our results revealed that miR-21-3p inhibition targeted RGS4 to attenuate inflammatory responses and apoptosis caused by LPS in ARPE-19 cells.

Ginsenoside Rb1 attenuates intestinal ischemia/reperfusion‑induced inflammation and oxidative stress via activation of the PI3K/Akt/Nrf2 signaling pathway

Ginsenoside Rb1 (GRb1), one of the major active saponins isolated from ginseng, has recently been reported to protect various organs against ischemia/reperfusion (IR) injury; however, the mechanisms underlying these protective effects following intestinal IR (IIR) remain unclear. The present study aimed to evaluate the effects of GRb1 on IIR injury and determine the mechanisms involved in these effects. Sprague Dawley rats were subjected to 75 min of superior mesenteric artery occlusion, followed by 3 h of reperfusion. GRb1 (15 mg/kg) was administered intraperitoneally 1 h prior to the induction of IIR, with or without intravenous administration of Wortmannin [WM; a phosphoinositide 3-kinase (PI3K) inhibitor, 0.6 mg/kg]. The degree of intestinal injury and oxidative stress-induced damage was determined by histopathologic evaluation and measurement of the serum activity levels of D-lactate, diamine oxidase and endotoxin, and the levels of malondialdehyde (MDA), superoxide dismutase (SOD) and 8-iso-prostaglandin F_2α (8-iso-PGF_2α). The protein expression levels of p85, phosphorylated (p)-p85, protein kinase B (Akt), p-Akt and nuclear factor erythroid 2-related factor 2 (Nrf2) were determined via western blotting, and the concentrations of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-6 were measured via ELISA. It was revealed that IIR led to severe intestinal injury (as determined by significant increases in intestinal Chiu scores), which was accompanied with disruptions in the integrity of the intestinal mucosal barrier. IIR also increased the expression levels of TNF-α, IL-1β, IL-6, MDA and 8-iso-PGF_2α in the intestine, and decreased those of SOD. GRb1 reduced intestinal histological injury, and suppressed inflammatory responses and oxidative stress. Additionally, the protective effects of GRb1 were eliminated by WM. These findings indicated that GRb1 may ameliorate IIR injury by activating the PI3K/protein kinase B/Nrf2 pathway.

Helix aspersa maxima mucus exhibits antimelanogenic and antitumoral effects against melanoma cells

Snail secretion is currently revolutionizing the world of cosmetics and human skin care. The efficacy of snail secretion in wounds healing has been proven both in vitro and by clinical studies. However, the potential anti-tumor effect of snail secretion was poorly investigated. In this report, our in vitro study showed that Helix aspersa maxima species snail slime (SS) could not only treat melanogenesis but also endowed with anti-tumoral activity against human melanoma cells. Indeed, SS reduced melanin content and tyrosinase activity on B16F10 cells with IC₅₀ values of 288 μg/mL and 286 μg/mL, respectively, without altering cell viability. This effect was also observed, at a lesser extent, on human melanoma IGR-39 and SK-MEL-28 cell lines. On another hand, SS specifically inhibited the viability of IGR-39 and SK-MEL-28 cells associated to an apoptotic effect highlighted by PARP cleavage. It is worth to note that SS did not affect the viability of B16F10 cells and non tumorigenic HaCaT cells. Interestingly, this extract was found to inhibit migration and invasion of both human melanoma cells through reducing the expression of Matrix metalloproteinase MMP2. Snail slime also exerted a high inhibitory effect on IGR-39 cell adhesion through blocking the function of α₂β₁ (45%), α_vβ₃ (38%) integrins and by reducing the expression levels of α_v and β₁ integrins. The presented results shed light on the potential anti-melanoma effect of SS and support its use against skin diseases.