Regulator of G-protein signalling expression and function in ovarian cancer cell lines

Modelling genetic and clinical heterogeneity in epithelial ovarian cancers

The biology underlying early-stage epithelial ovarian cancer (EOC) development is poorly understood. Identifying biomarkers associated with early-stage disease could have a significant impact on reducing mortality. Here, we describe establishment of a three-dimensional (3D) in vitro genetic model of EOC initiation and early-stage neoplastic progression. Normal primary ovarian epithelial (POE) cells, immortalized using hTERT (immortalised ovarian epithelial [IOE] cells), were partially transformed by overexpressing the CMYC oncogene (IOE(CMYC) cells). Subsequent expression of mutant alleles of KRAS (KRAS(G12V)) or BRAF (BRAF(V600E)) created double-mutant lines (IOE(CMYC.KRAS) and IOE(CMYC.BRAF)). The transformed phenotype of IOE(CMYC) cells was further enhanced in concert with KRAS(G12V)/BRAF(V600E) expression, as in vitro analyses indicated that IOE(CMYC) cells had undergone morphological and phenotypic changes characteristic of neoplastic progression. When cultured as 3D spheroids, IOE cells underwent growth arrest, reminiscent of nonproliferative, unstimulated POE in vivo. In contrast, IOSE(CMYC+BRAF/KRAS) cells formed highly proliferative, poly-aggregate spheroid structures, showing increased expression of the Wilms tumour 1 tumourigenic marker and MIB1 proliferation marker. Transcriptomic analyses identified different gene expression profiles between the different cell lines and novel candidate genes (e.g. RGS4, CTGF and THBS1) that are somatically altered in EOCs. Gene expression signatures were compared with signatures from primary EOCs; tumours with IOE(CMYC) 'like' signatures were more likely to be high grade (P = 0.018); tumours with BRAF signatures were associated with improved relapse-free survival (P = 0.003). In conclusion, we have established in vitro 3D models of early-stage EOCs, which reflect genetic and phenotypic heterogeneity of the disease. Molecular genetic characteristics of these models correlated with molecular and clinical features of primary EOCs.

RGS6 variants are associated with dietary fat intake in Hispanics: the IRAS Family Study

Recently, a genome-wide association scan was completed in the IRAS (Insulin Resistance Atherosclerosis Study) Family Study (IRASFS) Hispanic-American cohort. Multiple single-nucleotide polymorphisms (SNPs) in the G-protein signaling 6 (RGS6) gene were found to be associated with adiposity phenotypes. RGS6 has shown downstream antagonistic interplay with opioid receptors, targets of fatty/sugary food agonists. The possibility that RGS6 promotes tolerance and tachyphylaxis among the opioid receptor is a plausible pathway for overconsuming fat/sugar-laden food. Therefore, we hypothesized that RGS6 variants are associated with intake of fatty/sugary foods. In 932 Hispanics from San Antonio and San Luis Valley, CO, the following dietary intake variables were assessed using the Block Brief 2000 food frequency questionnaire: total calories, total fat, % calories from fat, % calories from saturated fat, protein, % calories from protein, carbohydrates, % calories from carbohydrates, and daily frequency of servings of fats/oils/sweets. We tested for association between 23 SNPs in RGS6 and dietary intake using a variance components measured genotype approach. All models were adjusted for gender, recruitment site, admixture, BMI, and age. Using an additive genetic model, rs1402064 was associated with higher intake of fats/oils/sweets, total calories, total fat and saturated fat (P = 0.0007, 0.026, 0.023, and 0.024). SNPs rs847330 and rs847354 were associated with higher intake of fats/oils/sweets (P = 0.002 and 0.018), total fat (P = 0.040 and 0.048) and saturated fat (P = 0.044 and 0.041). Finally, rs769148 was associated with higher intake of fats/oils/sweets (P = 0.002). RGS6 is a new candidate gene for adiposity traits that may be associated with a behavioral tendency toward fat-laden food intake.

Genetic variations in the regulator of G-protein signaling genes are associated with survival in late-stage non-small cell lung cancer

The regulator of G-protein signaling (RGS) pathway plays an important role in signaling transduction, cellular activities, and carcinogenesis. We hypothesized that genetic variations in RGS gene family may be associated with the response of late-stage non-small cell lung cancer (NSCLC) patients to chemotherapy or chemoradiotherapy. We selected 95 tagging single nucleotide polymorphisms (SNPs) in 17 RGS genes and genotyped them in 598 late-stage NSCLC patients. Thirteen SNPs were significantly associated with overall survival. Among them, rs2749786 of RGS12 was most significant. Stratified analysis by chemotherapy or chemoradiation further identified SNPs that were associated with overall survival in subgroups. Rs2816312 of RGS1 and rs6689169 of RGS7 were most significant in chemotherapy group and chemoradiotherapy group, respectively. A significant cumulative effect was observed when these SNPs were combined. Survival tree analyses identified potential interactions between rs944343, rs2816312, and rs1122794 in affecting survival time in patients treated with chemotherapy, while the genotype of rs6429264 affected survival in chemoradiation-treated patients. To our knowledge, this is the first study to reveal the importance of RGS gene family in the survival of late-stage NSCLC patients.

Development of a novel high-throughput screen and identification of small-molecule inhibitors of the Gα-RGS17 protein-protein interaction using AlphaScreen

In this study, the authors used AlphaScreen technology to develop a high-throughput screening method for interrogating small-molecule libraries for inhibitors of the Gα(o)-RGS17 interaction. RGS17 is implicated in the growth, proliferation, metastasis, and the migration of prostate and lung cancers. RGS17 is upregulated in lung and prostate tumors up to a 13-fold increase over patient-matched normal tissues. Studies show RGS17 knockdown inhibits colony formation and decreases tumorigenesis in nude mice. The screen in this study uses a measurement of the Gα(o)-RGS17 protein-protein interaction, with an excellent Z score exceeding 0.73, a signal-to-noise ratio >70, and a screening time of 1100 compounds per hour. The authors screened the NCI Diversity Set II and determined 35 initial hits, of which 16 were confirmed after screening against controls. The 16 compounds exhibited IC(50) <10 µM in dose-response experiments. Four exhibited IC(50) values <6 µM while inhibiting the Gα(o)-RGS17 interaction >50% when compared to a biotinylated glutathione-S-transferase control. This report describes the first high-throughput screen for RGS17 inhibitors, as well as a novel paradigm adaptable to many other RGS proteins, which are emerging as attractive drug targets for modulating G-protein-coupled receptor signaling.

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

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

Regulators of G-Protein signaling RGS10 and RGS17 regulate chemoresistance in ovarian cancer cells

BACKGROUND

A critical therapeutic challenge in epithelial ovarian carcinoma is the development of chemoresistance among tumor cells following exposure to first line chemotherapeutics. The molecular and genetic changes that drive the development of chemoresistance are unknown, and this lack of mechanistic insight is a major obstacle in preventing and predicting the occurrence of refractory disease. We have recently shown that Regulators of G-protein Signaling (RGS) proteins negatively regulate signaling by lysophosphatidic acid (LPA), a growth factor elevated in malignant ascites fluid that triggers oncogenic growth and survival signaling in ovarian cancer cells. The goal of this study was to determine the role of RGS protein expression in ovarian cancer chemoresistance.

RESULTS

In this study, we find that RGS2, RGS5, RGS10 and RGS17 transcripts are expressed at significantly lower levels in cells resistant to chemotherapy compared with parental, chemo-sensitive cells in gene expression datasets of multiple models of chemoresistance. Further, exposure of SKOV-3 cells to cytotoxic chemotherapy causes acute, persistent downregulation of RGS10 and RGS17 transcript expression. Direct inhibition of RGS10 or RGS17 expression using siRNA knock-down significantly reduces chemotherapy-induced cell toxicity. The effects of cisplatin, vincristine, and docetaxel are inhibited following RGS10 and RGS17 knock-down in cell viability assays and phosphatidyl serine externalization assays in SKOV-3 cells and MDR-HeyA8 cells. We further show that AKT activation is higher following RGS10 knock-down and RGS 10 and RGS17 overexpression blocked LPA mediated activation of AKT, suggesting that RGS proteins may blunt AKT survival pathways.

CONCLUSIONS

Taken together, our data suggest that chemotherapy exposure triggers loss of RGS10 and RGS17 expression in ovarian cancer cells, and that loss of expression contributes to the development of chemoresistance, possibly through amplification of endogenous AKT signals. Our results establish RGS10 and RGS17 as novel regulators of cell survival and chemoresistance in ovarian cancer cells and suggest that their reduced expression may be diagnostic of chemoresistance.

RNA-binding protein HuR regulates RGS4 mRNA stability in rabbit colonic smooth muscle cells

Regulator of G protein signaling 4 (RGS4) regulates the strength and duration of G protein signaling and plays an important role in smooth muscle contraction, cardiac development, and psychiatric disorders. Little is known about the posttranscriptional regulation of RGS4 expression. We cloned the full-length cDNA of rabbit RGS4, which contains a long 3'-untranslated region (UTR) with several AU-rich elements (AREs). We determined whether RGS4 mRNA stability is mediated by the RNA-binding protein human antigen R (HuR) and contributes to IL-1β-induced upregulation of RGS4 expression. We show that IL-1β treatment in colonic smooth muscle cells doubled the half-life of RGS4 mRNA. Addition of RGS4 3'-UTR to the downstream of Renilla luciferase reporter induced dramatic reduction in the enzyme activity and mRNA expression of luciferase, which was attenuated by the site-directed mutation of the two 3'-most ARE sites. IL-1β increased luciferase mRNA stability in a UTR-dependent manner. Knockdown of HuR significantly aggravated UTR-mediated instability of luciferase and inhibited IL-1β-induced upregulation of RGS4 mRNA. In addition, IL-1β increased cytosolic translocation and RGS4 mRNA binding of HuR. These findings suggest that 3'-most ARE sites within RGS4 3'-UTR are essential for the instability of RGS4 mRNA and IL-1β promotes the stability of RGS4 mRNA through HuR.

Analysis of RGS2 expression and prognostic significance in stage II and III colorectal cancer

The role of RGS2 (regulator of G-protein signalling 2) has been studied in several tumours. The purpose of the present study is to investigate the correlations between clinicopathological factors and patients' survival time and RGS2 expression in stage II and III CRC (colorectal cancer) patients. Real-time quantitative PCR was performed in 36 CRC tissues with recurrence and 28 without recurrence, and in three CRC-metastasis-derived cell lines (SW620, LoVo and Colo205) and 3 primary-CRC-derived ones (SW480, Caco-2 and HCT116) to examine RGS2 mRNA expression. In addition, to provide visualized evidence for RGS2 mRNA expression, random CRC samples were also performed with RT–PCR (reverse transcription–PCR). RGS2 protein was detected by immunostaining in 118 paraffin-embedded specimens, and the correlations between clinicopathological factors and survival time and RGS2 expression were analysed. We found that RGS2 mRNA was down-regulated both in CRC tissues with recurrence and metastasis-derived cell lines, and the expression level of RGS2 was unrelated to gender, age, tumour grade, or lymphovascular or perineural invasion. However, it was positively related to disease-free survival time (P<0.05). Furthermore, low RGS2 expression indicated a poorer survival rate (P<0.05, log-rank test). Multivariate analysis also showed that weak RGS2 protein expression was an independent adverse prognosticator in CRC (P<0.05). Taken together, we suggested that down-regulation of RGS2 might play an important role in CRC metastasis and predict poor prognosis in stage II and III CRC patients.

Genetic variations in regulator of G-protein signaling genes as susceptibility loci for second primary tumor/recurrence in head and neck squamous cell carcinoma

Curatively treated patients with early-stage head and neck squamous cell carcinoma (HNSCC) are at high risks for second primary tumor (SPT) and recurrence. The regulator of G-protein signaling (RGS) is important in essential signaling transduction and cellular activities. We hypothesize that genetic variations of RGS may modulate the risk of SPT/recurrence in patients with early-stage HNSCC. In a nested case-control study, we evaluated 98 single-nucleotide polymorphisms (SNPs) in 17 RGS genes for the risk of SPT/recurrence among 450 HNSCC patients. Eight SNPs showed significant associations with the risk of SPT/recurrence, with the most significant one of rs2179653, which is located in the 5'-flanking region of RGS2 gene. Under a recessive genetic model, the homozygous variant genotype of this SNP was associated with 2.95-fold [95% confidence interval (CI): 1.52-5.74] increased risk of SPT/recurrence. This association remained significant after the adjustment for multiple comparisons. Cumulative effects analysis revealed that the risk increased significantly with the increasing numbers of unfavorable genotypes. Compared with subjects carrying 0-2 unfavorable genotypes, the hazard ratios (95% CIs) for those carrying 3 or 4+ were 1.73 (1.10-2.70) and 3.05 (1.92-4.83), respectively. Furthermore, survival tree analysis revealed potential higher order gene-gene interactions and indicated different outcomes based on distinct genotype profiles. Genetic variations of RGS genes may modulate the susceptibility to SPT/recurrence in early-stage HNSCC patients individually and cumulatively. Our results stressed the importance of taking a polygenic approach to evaluate the cumulative and interaction effects of genetic variations in the prediction of cancer risk and prognosis.

RGS19 enhances cell proliferation through its C-terminal PDZ motif

Regulator of G protein signaling 19 (RGS19), also known as Galpha-interacting protein (GAIP), is a GTPase activating protein (GAP) for Galpha(i) subunits. Apart from its GAP function, RGS19 has been implicated in growth factor signaling through binding to GAIP-interacting protein C-terminus (GIPC) via its C-terminal PDZ-binding motif. To gain additional insight on its function, we have stably expressed RGS19 in a number of mammalian cell lines and examined its effect on cell proliferation. Interestingly, overexpression of RGS19 stimulated the growth of HEK293, PC12, Caco2, and NIH3T3 cells. This growth promoting effect was not shared by other RGS proteins including RGS4, RGS10 and RGS20. Despite its ability to stimulate cell proliferation, RGS19 failed to induce neoplastic transformation in NIH3T3 cells as determined by focus formation and soft-agar assays, and it did not induce tumor growth in athymic nude mice. Deletion mutants of RGS19 lacking the PDZ-binding motif failed to complex with GIPC and did not exhibit any growth promoting effect. Overexpression of GIPC alone in HEK293 cells stimulated cell proliferation whereas its knockdown in H1299 non-small cell lung carcinomas suppressed cell proliferation. This study demonstrates that RGS19, in addition to acting as a GAP, is able to stimulate cell proliferation in a GIPC-dependent manner.

Cloning and characterization of rabbit Rgs4 promoter in gut smooth muscle

Regulator of G-protein signaling 4 (Rgs4) regulates the strength and duration of G-protein signaling, and plays an important role in cardiac development, smooth muscle contraction and psychiatric disorders. Rgs4 expression is regulated at both mRNA and protein levels. In order to examine the transcriptional mechanism of Rgs4 expression, we have cloned and characterized rabbit Rgs4 promoter. The coding sequence of rabbit Rgs4 was obtained by degenerative RT-PCR and used for Northern blot and 5'-RACE analysis. A single transcript was identified in rabbit colonic smooth muscle cells. The 5'-untranslated region (UTR) extended 120 bp nucleotides upstream of the Rgs4 start codon. A putative promoter sequence (1389 bp) showed a consensus TATA box and cis-acting binding sites for several potential transcriptional factors. Reporter gene assay identified strong promoter activity in various cell types. Further analysis by deletion mutagenesis suggested that the proximal region had a highest core promoter activity while the distal region is suppressive. IL-1beta significantly increased the promoter activity. The in vitro and in vivo binding activities for NF-kappaB transcription factor were validated by electrophoretic mobility shift assay and chromatin immunoprecipitation assay respectively. Mutation of NF-kappaB site reduced the promoter activity. These data suggest that the cloned rabbit Rgs4 promoter is functionally active and NF-kappaB binding site possesses enhancer activity in regulating Rgs4 transcription. Our studies provide an important basis for further understanding of Rgs4 regulation and function in different diseases.

Structure, function, and localization of Gβ5-RGS complexes

Members of the R7 subfamily of regulator of G protein signaling (RGS) proteins (RGS6, 7, 9, and 11) exist as heterodimers with the G protein beta subunit Gβ5. These protein complexes are only found in neurons and are defined by the presence of three domains: DEP/DHEX, Gβ5/GGL, and RGS. This article summarizes published work in the following areas: (1) the functional significance of structural organization of Gβ5-R7 complexes, (2) regional distribution of Gβ5-R7 in the nervous system and regulation of R7 family expression, (3) subcellular localization of Gβ5-R7 complexes, and (4) novel binding partners of Gβ5-R7 proteins. The review points out some contradictions between observations made by different research groups and highlights the importance of using alternative experimental approaches to obtain conclusive information about Gβ5-R7 function in vivo.