G-protein coupled receptor family C, group 5, member A (GPRC5A) expression is decreased in the adjacent field and normal bronchial epithelia of patients with chronic obstructive pulmonary disease and non-small-cell lung cancer. J Thorac Oncol. 2012;7:1747-1754. [PMID: 23154545 DOI: 10.1097/jto.0b013e31826bb1ff]

GPRC5A is a potential prognostic biomarker and correlates with immune cell infiltration in non-small cell lung cancer

Background

The tumor microenvironment (TME) plays an important role in tumor progression and immunotherapy responses in non-small cell lung cancer (NSCLC). The programmed cell death 1 (PD-1)/ programmed cell death-ligand 1 (PD-L1) checkpoint is a central mediator of immunosuppression in the TME. However, there is still a need to identify additional biomarkers that could reflect the difference in TME and PD-L1 expression in NSCLC patients. To this end, we focused on the expression of G-protein-coupled receptor family C group 5 type A (GPRC5A) in NSCLC. GPRC5A, is a retinoic acid-inducible gene that plays multiple roles in NSCLC. However, little is known about the role of GPRC5A in regulating the TME and PD-L1. Our objective was to describe the critical role of GPRC5A expression in NSCLC in the setting of immune cell infiltration.

Methods

We identified the relationship between GPRC5A expression and the clinicopathologic characteristics of NSCLC patients in the Fudan University Shanghai Cancer Center (FUSCC) cohort. Furthermore, we validated GPRC5A as a predictive biomarker by using public databases to reveal the relationship between GPRC5A expression and immune cell infiltration. To correlate the expression of GPRC5A with the spatial distribution of PD-L1 in NSCLC samples, we performed multiplex immunohistochemistry (mIHC).

Results

Low GPRC5A expression is associated with earlier pathological stage (pStage). Analysis of immune cell infiltration indicates there is a relationship between low GPRC5A expression and increased infiltration of CD8+ T cells, activated CD4+ T cells, and M1 macrophages within the TME. Furthermore, low GPRC5A expression is associated with an increased immunophenotype score (IPS) in NSCLC. Additionally, analysis of mIHC reveals there is a correlation between low GPRC5A expression and spatial distribution of tumoral PD-L1 expression.

Conclusions

Our study revealed the relationship between low expression of GPRC5A and earlier pStage in NSCLC. Furthermore, we observed that low expression of GPRC5A is associated with increased infiltration of immune cells, higher IPS, and spatial distribution of PD-L1-positive tumor cells. Therefore, we speculate that low expression of GPRC5A is associated with immunotherapy, but further validation is still required.

Deciphering the molecular regulatory of RAB32/GPRC5A axis in chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a significant public health problem characterized by persistent airflow limitation. Despite previous research into the pathogenesis of COPD, a comprehensive understanding of the cell-type-specific mechanisms in COPD remains lacking. Recent studies have implicated Rab GTPases in regulating chronic immune response and inflammation via multiple pathways. In this study, the molecular regulating mechanism of RAB32 in COPD was investigated by multiple bioinformatics mining and experimental verification.

METHODS

We collected lung tissue surgical specimens from Zhongshan Hospital, Fudan University, and RT-qPCR and western blotting were used to detect the expression of Rabs in COPD lung tissues. Four COPD microarray datasets from the Gene Expression Omnibus (GEO) were analyzed. COPD-related epithelial cell scRNA-seq data was obtained from the GSE173896 dataset. Weighted gene co-expression network analysis (WGCNA), mfuzz cluster, and Spearman correlation analysis were combined to obtain the regulatory network of RAB32 in COPD. The slingshot algorithm was used to identify the regulatory molecule, and the co-localization of RAB32 and GPRC5A was observed with immunofluorescence.

RESULTS

WGCNA identified 771 key module genes significantly associated with the occurrence of COPD, including five Rab genes. RAB32 was up-regulated in lung tissues from subjects with COPD as contrast to those without COPD on both mRNA and protein levels. Integrating the results of WGCNA, Mfuzz clusters, and Spearman analysis, nine potential interacting genes with RAB32 were identified. Among these genes, GPRC5A exhibited a similar molecular expression pattern to RAB32. Co-expression density analysis at the cell level demonstrated that the co-expression density of RAB32 and GPRC5A was higher in type I alveolar epithelial cells (AT1s) than in type II alveolar epithelial cells (AT2s). The immunofluorescence also confirmed the co-localization of RAB32 and GPRC5A, and the Pearson correlation analysis found the relationship between RAB32 and GPRC5A was significantly stronger in the COPD lungs (r = 0.65) compared to the non-COPD lungs (r = 0.33).

CONCLUSIONS

Our study marked endeavor to delineate the molecular regulatory axis of RAB32 in COPD by employing diverse methods and identifying GPRC5A as a potential interacting molecule with RAB32. These findings offered novel perspectives on the mechanism of COPD.

Multi-omics identification of GPCR gene features in lung adenocarcinoma based on multiple machine learning combinations

Background: Lung adenocarcinoma is a common malignant tumor that ranks second in the world and has a high mortality rate. G protein-coupled receptors (GPCRs) have been reported to play an important role in cancer; however, G protein-coupled receptor-associated features have not been adequately investigated. Methods: In this study, GPCR-related genes were screened at single-cell and bulk transcriptome levels based on AUcell, single-sample gene set enrichment analysis (ssGSEA) and weighted gene co-expression network (WGCNA) analysis. And a new machine learning framework containing 10 machine learning algorithms and their multiple combinations was used to construct a consensus G protein-coupled receptor-related signature (GPCRRS). GPCRRS was validated in the training set and external validation set. We constructed GPCRRS-integrated nomogram clinical prognosis prediction tools. Multi-omics analyses included genomics, single-cell transcriptomics, and bulk transcriptomics to gain a more comprehensive understanding of prognostic features. We assessed the response of risk subgroups to immunotherapy and screened for personalized drugs targeting specific risk subgroups. Finally, the expression of key GPCRRS genes was verified by RT-qPCR. Results: In this study, we identified 10 GPCR-associated genes that were significantly associated with the prognosis of lung adenocarcinoma by single-cell transcriptome and bulk transcriptome. Univariate and multivariate showed that the survival rate was higher in low risk than in high risk, which also suggested that the model was an independent prognostic factor for LUAD. In addition, we observed significant differences in biological function, mutational landscape, and immune cell infiltration in the tumor microenvironment between high and low risk groups. Notably, immunotherapy was also relevant in the high and low risk groups. In addition, potential drugs targeting specific risk subgroups were identified. Conclusion: In this study, we constructed and validated a lung adenocarcinoma G protein-coupled receptor-related signature, which has an important role in predicting the prognosis of lung adenocarcinoma and the effect of immunotherapy. It is hypothesized that LDHA, GPX3 and DOCK4 are new potential targets for lung adenocarcinoma, which can achieve breakthroughs in prognosis prediction, targeted prevention and treatment of lung adenocarcinoma and provide important guidance for anti-tumor.

Adapting Nanopore Sequencing Basecalling Models for Modification Detection via Incremental Learning and Anomaly Detection

We leverage machine learning approaches to adapt nanopore sequencing basecallers for nucleotide modification detection. We first apply the incremental learning technique to improve the basecalling of modification-rich sequences, which are usually of high biological interests. With sequence backbones resolved, we further run anomaly detection on individual nucleotides to determine their modification status. By this means, our pipeline promises the single-molecule, single-nucleotide and sequence context-free detection of modifications. We benchmark the pipeline using control oligos, further apply it in the basecalling of densely-modified yeast tRNAs and E.coli genomic DNAs, the cross-species detection of N6-methyladenosine (m6A) in mammalian mRNAs, and the simultaneous detection of N1-methyladenosine (m1A) and m6A in human mRNAs. Our IL-AD workflow is available at: https://github.com/wangziyuan66/IL-AD.

The G protein-coupled receptor GPRC5A-a phorbol ester and retinoic acid-induced orphan receptor with roles in cancer, inflammation, and immunity

GPRC5A is the first member of a new class of orphan receptors coupled to G proteins, which also includes GPRC5B, GPRC5C, and GPRC5D. Since its cloning and identification in the 1990s, substantial progress has been made in understanding the possible functions of this receptor. GPRC5A has been implicated in a variety of cellular events, such as cytoskeleton reorganization, cell proliferation, cell cycle regulation, migration, and survival. It appears to be a central player in different pathological processes, including tumorigenesis, inflammation, immune response, and tissue damage. The levels of GPRC5A expression differ depending on the type of cancer, with increased expression in colon, pancreas, and prostate cancers; decreased expression in lung cancer; and varied results in breast cancer. In this review, we discuss the early discovery of GPRC5A as a phorbol ester-induced gene and later as a retinoic acid-induced gene, its regulation, and its participation in important canonical pathways related to numerous types of tumors and inflammatory processes. GPRC5A represents a potential new target for cancer, inflammation, and immunity therapies.

RAI3 expression is not associated with clinical outcomes of patients with non-small cell lung cancer

PURPOSE

Retinoic acid inducible protein 3 (RAI3) has been suggested as prognostic biomarker in several cancer types. The present study aimed to examine the role of RAI3 expression in non-small cell lung cancers (NSCLCs).

METHODS

RAI3 protein expression was evaluated by immunohistochemistry in tissue microarray (TMA) sections from a retrospective cohort of more than 600 surgically resected NSCLCs and results were compared with clinicopathological features and follow-up data.

RESULTS

While membranous RAI3 immunostaining was always strong in benign lung, strong RAI3 staining was only detectable in 14.7% of 530 interpretable NSCLCs. Within NSCLC subtypes, immunostaining intensity for RAI3 was significantly decreased in large cell lung cancers (LCLCs) and squamous cell carcinomas (SQCCs) relative to lung adenocarcinomas (LUACs) (P < 0.0001 each). However, RAI3 staining was neither associated with pathological features of NSCLCs nor with survival of patients (P = 0.6915).

CONCLUSION

Our study shows that RAI3 expression was not associated with clinical outcomes of NSCLC patients and cannot be considered as prognostic marker in lung cancer patients.

NF-κB represses retinoic acid receptor-mediated GPRC5A transactivation in lung epithelial cells to promote neoplasia

Chronic inflammation is associated with lung tumorigenesis, in which NF-κB-mediated epigenetic regulation plays a critical role. Lung tumor suppressor G protein-coupled receptor, family C, member 5A (GPRC5A), is repressed in most non-small cell lung cancer (NSCLC); however, the mechanisms remain unclear. Here, we show that NF-κB acts as a transcriptional repressor in suppression of GPRC5A. NF-κB induced GPRC5A repression both in vitro and in vivo. Intriguingly, transactivation of NF-κB downstream targets was not required, but the transactivation domain of RelA/p65 was required for GPRC5A repression. NF-κB did not bind to any potential cis-element in the GPRC5A promoter. Instead, p65 was complexed with retinoic acid receptor α/β (RARα/β) and recruited to the RA response element site at the GPRC5A promoter, resulting in disrupted RNA polymerase II complexing and suppressed transcription. Notably, phosphorylation on serine 276 of p65 was required for interaction with RARα/β and repression of GPRC5A. Moreover, NF-κB-mediated epigenetic repression was through suppression of acetylated histone H3K9 (H3K9ac), but not DNA methylation of the CpG islands, at the GPRC5A promoter. Consistently, a histone deacetylase inhibitor, but not DNA methylation inhibitor, restored GPRC5A expression in NSCLC cells. Thus, NF-κB induces transcriptional repression of GPRC5A via a complex with RARα/β and mediates epigenetic repression via suppression of H3K9ac.

Lung Cancer Cell of Origin: Controversy and Clinical Translational Implications

Identifying the cell(s) of origin for lung cancer including detecting their expansion during "field cancerization" and understanding how to therapeutically target them for beneficial chemoprevention is an urgent need. In this issue of Cancer Research, Yin and colleagues provide new and potentially controversial information to this question using Gprc5a knockout genetically engineered mouse models of lung adenocarcinoma. Prior research identified several different cell types including resident lung stem/progenitor such as alveolar type II cells as well as terminally differentiated cells as candidates for the cancer-initiating cell. Yin and colleagues provide new information that the cancer-initiating cell in this model is the bronchioalveolar stem cell. See related article by Yin et al., p. 1025.

Lung proteomic biomarkers associated with chronic obstructive pulmonary disease

Identifying protein biomarkers for chronic obstructive pulmonary disease (COPD) has been challenging. Most previous studies have used individual proteins or preselected protein panels measured in blood samples. Mass spectrometry proteomic studies of lung tissue have been based on small sample sizes. We used mass spectrometry proteomic approaches to discover protein biomarkers from 150 lung tissue samples representing COPD cases and controls. Top COPD-associated proteins were identified based on multiple linear regression analysis with false discovery rate (FDR) < 0.05. Correlations between pairs of COPD-associated proteins were examined. Machine learning models were also evaluated to identify potential combinations of protein biomarkers related to COPD. We identified 4,407 proteins passing quality controls. Twenty-five proteins were significantly associated with COPD at FDR < 0.05, including interleukin 33, ferritin (light chain and heavy chain), and two proteins related to caveolae (CAV1 and CAVIN1). Multiple previously reported plasma protein biomarkers for COPD were not significantly associated with proteomic analysis of COPD in lung tissue, although RAGE was borderline significant. Eleven pairs of top significant proteins were highly correlated (r > 0.8), including several strongly correlated with RAGE (EHD2 and CAVIN1). Machine learning models using Random Forests with the top 5% of protein biomarkers demonstrated reasonable accuracy (0.707) and area under the curve (0.714) for COPD prediction. Mass spectrometry-based proteomic analysis of lung tissue is a promising approach for the identification of biomarkers for COPD.

Dysbiosis of gut microbiota in inflammatory bowel disease: Current therapies and potential for microbiota-modulating therapeutic approaches

There is a growing body of evidence reinforcing the unique connections between the host microbiome, health, and diseases. Due to the extreme importance of the symbiotic relationship between the intestinal microbiome and the host, it is not surprising that any alteration in the gut microbiota would result in various diseases, including inflammatory bowel disease (IBD), Crohn's disease, (CD) and ulcerative colitis (UC). IBD is a chronic, relapsing-remitting condition that is associated with significant morbidity, mortality, compromised quality of life, and costly medical care. Dysbiosis is believed to exacerbate the progression of IBD. One of the currently used treatments for IBD are anti-tumor necrosis factor (TNF) drugs, representing a biologic therapy that is reported to have an impact on the gut microbiota composition. The efficacy of anti-TNF agents is hindered by the possibility of non-response, which occurs in 10-20% of treated patients, and secondary loss of response, which occurs in up to 30% of treated patients. This underscores the need for novel therapies and studies that evaluate the role of the gut microbiota in these conditions. The success of any therapeutic strategy for IBD depends on our understanding of the interactions that occur between the gut microbiota and the host. In this review, the health and disease IBD-associated microbiota patterns will be discussed, in addition to the effect of currently used therapies for IBD on the gut microbiota composition, as well as new therapeutic approaches that can be used to overcome the current treatment constraints.

Prognostic and clinicopathological significance of GPRC5A in various cancers: A systematic review and meta-analysis

Background

GPRC5A is associated with various cancer initiation and progression. Controversial findings have been reported about GPRC5A prognostic characteristics, and no meta-analysis has been conducted to assess the relationship between GPRC5A and cancer prognosis. Therefore, the objective of this meta-analysis is to evaluate the overall prognostic effectiveness of GPRC5A.

Methods

We first conducted a systematic search in the PubMed, Embase, Web of Science, CNKI, Cochrane, and WangFang databases. The hazard ratio (HR) and odds ratios (OR) with 95% CI were then pooled to assess the associations between GPRC5A expression and overall survival (OS), disease-free survival (DFS), event-free survival (EFS), and clinicopathological characteristics. Chi-squared test and I² statistics were completed to evaluate the heterogeneity in our study. A random‐effects model was used when significant heterogeneity existed (I²>50% and p<0.05); otherwise, we chose the fixed-effect model. Subgroup analysis was stratified by tumor type, region, HR obtained measurements, and sample capacity to explore the source of heterogeneity.

Results

In total, 15 studies with 624 patients met inclusion criteria of this study. Our results showed that higher expression of GPRC5A is associated with worse OS (HR:1.69 95%CI: 1.20–2.38 I² = 75.6% p = 0.000), as well as worse EFS (HR:1.45 95%CI: 1.02–1.95 I² = 0.0% p = 0.354). Subgroup analysis indicated that tumor type might be the source of high heterogeneity. Additionally, cancer patients with enhanced GPRC5A expression were more likely to lymph node metastasis (OR:1.95, 95%CI 1.33–2.86, I² = 43.9%, p = 0.129) and advanced tumor stage (OR: 1.83, 95%CI 1.15–2.92, I² = 61.3%, p = 0.035), but not associated with age, sex, differentiation, and distant metastasis.

Conclusion

GPRC5A can be a promising candidate for predicting medical outcomes and used for accurate diagnosis, prognosis prediction for patients with cancer; however, the predictive value of GPRC5A varies significantly according to cancer type. Further studies for this mechanism will be necessary to reveal novel insights into application of GPRC5A in cancers.

Cell-autonomous immune gene expression is repressed in pulmonary neuroendocrine cells and small cell lung cancer

Small cell lung cancer (SCLC) is classified as a high-grade neuroendocrine (NE) tumor, but a subset of SCLC has been termed “variant” due to the loss of NE characteristics. In this study, we computed NE scores for patient-derived SCLC cell lines and xenografts, as well as human tumors. We aligned NE properties with transcription factor-defined molecular subtypes. Then we investigated the different immune phenotypes associated with high and low NE scores. We found repression of immune response genes as a shared feature between classic SCLC and pulmonary neuroendocrine cells of the healthy lung. With loss of NE fate, variant SCLC tumors regain cell-autonomous immune gene expression and exhibit higher tumor-immune interactions. Pan-cancer analysis revealed this NE lineage-specific immune phenotype in other cancers. Additionally, we observed MHC I re-expression in SCLC upon development of chemoresistance. These findings may help guide the design of treatment regimens in SCLC.

Ling Cai et al. used transcriptomic profiling data of healthy lung, patient-derived small cell lung cancer cell lines, xenografts, and primary tumors to examine a link between neuroendocrine (NE) signatures and immune gene expression. Their findings suggest that cell-autonomous immune gene repression is a shared feature between healthy and tumor cells of NE lineage and may influence tumor-immune cell interaction and response to immunotherapy.

Dysregulated Glutamate Transporter SLC1A1 Propels Cystine Uptake via Xc- for Glutathione Synthesis in Lung Cancer

Cancer cells need to generate large amounts of glutathione (GSH) to buffer oxidative stress during tumor development. A rate-limiting step for GSH biosynthesis is cystine uptake via a cystine/glutamate antiporter Xc^-. Xc^- is a sodium-independent antiporter passively driven by concentration gradients from extracellular cystine and intracellular glutamate across the cell membrane. Increased uptake of cystine via Xc^- in cancer cells increases the level of extracellular glutamate, which would subsequently restrain cystine uptake via Xc^-. Cancer cells must therefore evolve a mechanism to overcome this negative feedback regulation. In this study, we report that glutamate transporters, in particular SLC1A1, are tightly intertwined with cystine uptake and GSH biosynthesis in lung cancer cells. Dysregulated SLC1A1, a sodium-dependent glutamate carrier, actively recycled extracellular glutamate into cells, which enhanced the efficiency of cystine uptake via Xc^- and GSH biosynthesis as measured by stable isotope-assisted metabolomics. Conversely, depletion of glutamate transporter SLC1A1 increased extracellular glutamate, which inhibited cystine uptake, blocked GSH synthesis, and induced oxidative stress-mediated cell death or growth inhibition. Moreover, glutamate transporters were frequently upregulated in tissue samples of patients with non-small cell lung cancer. Taken together, active uptake of glutamate via SLC1A1 propels cystine uptake via Xc^- for GSH biosynthesis in lung tumorigenesis. SIGNIFICANCE: Cellular GSH in cancer cells is not only determined by upregulated Xc^- but also by dysregulated glutamate transporters, which provide additional targets for therapeutic intervention.

Integrated Single-Cell RNA-Sequencing Analysis of Aquaporin 5-Expressing Mouse Lung Epithelial Cells Identifies GPRC5A as a Novel Validated Type I Cell Surface Marker

Molecular and functional characterization of alveolar epithelial type I (AT1) cells has been challenging due to difficulty in isolating sufficient numbers of viable cells. Here we performed single-cell RNA-sequencing (scRNA-seq) of tdTomato⁺ cells from lungs of AT1 cell-specific Aqp5-Cre-IRES-DsRed (ACID);R26tdTomato reporter mice. Following enzymatic digestion, CD31^-CD45^-E-cadherin⁺tdTomato⁺ cells were subjected to fluorescence-activated cell sorting (FACS) followed by scRNA-seq. Cell identity was confirmed by immunofluorescence using cell type-specific antibodies. After quality control, 92 cells were analyzed. Most cells expressed ‘conventional’ AT1 cell markers (Aqp5, Pdpn, Hopx, Ager), with heterogeneous expression within this population. The remaining cells expressed AT2, club, basal or ciliated cell markers. Integration with public datasets identified three robust AT1 cell- and lung-enriched genes, Ager, Rtkn2 and Gprc5a, that were conserved across species. GPRC5A co-localized with HOPX and was not expressed in AT2 or airway cells in mouse, rat and human lung. GPRC5A co-localized with AQP5 but not pro-SPC or CC10 in mouse lung epithelial cell cytospins. We enriched mouse AT1 cells to perform molecular phenotyping using scRNA-seq. Further characterization of putative AT1 cell-enriched genes revealed GPRC5A as a conserved AT1 cell surface marker that may be useful for AT1 cell isolation.

RhoA/C inhibits proliferation by inducing the synthesis of GPRC5A

Rho GTPases are important regulators of many cellular functions like cell migration, adhesion and polarity. The molecular switches are often dysregulated in cancer. We detected Rho-dependent upregulation of the orphan seven-transmembrane receptor G-protein-coupled receptor family C group 5 member A (GPRC5A). GPRC5A is highly expressed in breast cancer whereas in lung cancer, it is often downregulated. Here, we analyzed the function of GPRC5A in breast epithelial and breast cancer cells. Activation or expression of RhoA/C led to GPRC5A-dependent inhibition of proliferation and reduction of the colony forming capacity of benign breast epithelial cells. This effect is based on an inhibition of EGFR signalling. Knockout of retinoic acid induced 3 (RAI3, the gene for GPRC5A) in breast cancer cells increased cell division, whereas Rho activation had no effect on proliferation. Knockout of RAI3 in benign breast epithelial cells led to decrease of EGFR expression and diminished proliferation.

GPRC5a suppresses the proliferation of non-small cell lung cancer under wild type p53 background

Introduction: GPRC5a plays an important role in many types of cancers with intriguing dual functions. GPRC5a acts as oncogene or tumor suppressor in different types of cancer. It is interesting to illustrate why GPRC5a functions differently.Methods: Data mining method were used to analyze the potential prognostic value of GPRC5a expression for Non-Small Cell Lung Cancer (NSCLC) lung cancer patients. Then we used cell models to further investigate the effect of p53 mutation on GPRC5a expression and the thereafter cell biological behaviors.Results: Our results present here showed High mRNA-level expression of GPRC5a was associated with worse overall survival about lung cancer patients; mutation of p53 gene could result in up regulation of GPRC5a expression and promotion of cell proliferation in lung cancer cells. Our results not only demonstrate the role of GPRC5a as a tumor suppressor in lung cancer, but also revealed the tumor suppressive factor p53 regulated tightly on GPRC5a and cell growth of NSCLC cancer.Conclusions: Our results demonstrated that p53 upregulated GPRC5a expression in NSCLC cells, and the loss of p53 expression in NSCLC may be one of the mechanisms leading to the decreased GPRC5a expression in NSCLC.

Identification of Sca-1+Abcg1+ bronchioalveolar epithelial cells as the origin of lung adenocarcinoma in Gprc5a-knockout mouse model through the interaction between lung progenitor AT2 and Lgr5 cells

The reason for the reduced efficacy of lung cancer therapy is the existence of lung cancer stem cells (CSCs). Targeting CSCs results in evolved phenotypes with increased malignancy, leading to therapy failure. Here, we propose a new therapeutic strategy: investigating the “transitional” cells that represent the stage between normal lung stem cells and lung CSCs. Identifying and targeting the key molecule that drives carcinogenesis to inhibit or reverse this process would thus provide new perspectives for early diagnosis and intervention in lung cancer. We used Gprc5a-knockout (KO) mice, the first animal model of spontaneous lung adenocarcinoma established by the deletion of a single lung tumor suppressor gene. We investigated the interaction of lung progenitor cells AT2 with Lgr5 cells in the generation of CSCs and related signaling mechanism. In the present study, using Gprc5a-KO mice, we found the initiator Sca-1⁺Abcg1⁺ subset with a CSC-like phenotype within the lung progenitor AT2 cell population in mice that had not yet developed tumors. We confirmed the self-renewal and tumor initiation capacities of this subset in vitro, in vivo, and clinical samples. Mechanistically, we found that the generation of Sca-1⁺Abcg1⁺ cells was associated with an interaction between AT2 and Lgr5 cells and the subsequent activation of the ECM1-α6β4-ABCG1 axis. Importantly, Sca-1⁺Abcg1⁺ and SPA⁺ABCG1⁺ cells specifically existed in the small bronchioles of Gprc5a-KO mice and patients with pneumonia, respectively. Thus, the present study unveiled a new kind of lung cancer-initiating cells (LCICs) and provided potential markers for the early diagnosis of lung cancer.

Gprc5a depletion enhances the risk of smoking-induced lung tumorigenesis and mortality

AIMS

Lung cancer remains the leading cause of cancer incidence and mortality. Although cigarette smoke is regarded as a high risk factor for lung tumor initiation, the role of the lung tumor suppressor GPRC5A in smoking-induced lung cancer is unclear.

MAIN METHODS

We obtained two lung cancer cohorts from the TCGA and GEO databases. Bioinformatics analysis showed differential gene expression in the cohorts. Quantitative real-time PCR, Western Blot and Gprc5a^-/- mice uncovered the relationship between cigarette smoke and lung cancer in the GPRC5A deletion system in vitro and in vivo.

KEY FINDINGS

Bioinformatics analysis showed that the smoking lung cancer patients with low expression of GPRC5A had poor overall survival compared to the patients with high GPRC5A expression. Further analysis revealed that cancer-related stemness pathways such as the Hippo signaling pathway were induced in smoking patients with low GPRC5A expression. Additionally, we detected enriched expression of WNT5A and DLX5 in normal human lung epithelial 16HBE cells and human lung cancer H1299 cells in vitro. A relationship between cigarette smoke extract (NNK) and lung tumor initiation was observed in Gprc5a^-/- mice.

SIGNIFICANCE

The lung tumor suppressor gene GPRC5A played a protective role in cigarette smoke-induced lung tumor initiation, providing a target for the prevention of lung cancer development and monitoring of prognosis.

High levels of RAI3 expression is linked to shortened survival in esophageal cancer patients

Expression of the retinoic acid-induced protein 3 (RAI3) has been suggested to predict clinical outcome in a variety of malignancies. However, its role in esophageal cancers remains unclear. Immunohistochemical RAI3 staining was analyzed on tissue microarrays containing 359 esophageal adenocarcinomas (EAC) and 254 esophageal squamous cell carcinomas (ESCC). RAI3 immunostaining was typically absent or weakly detectable in the membranes in benign esophageal tissues. RAI3 staining was higher in malignant than in benign esophagus epithelium. High-levels of RAI3 staining were found in 79.2% of interpretable EACs and 55.9% of ESCCs. In EACs, strong RAI3 staining was associated with advanced pathological tumor stage (p < .0001), high UICC stage (p < .0001), high tumor grade (p = .0133), and positive lymph nodal status (p = .0002). Additionally, high RAI3 staining predicted shortened overall survival of EAC and ESCC patients (p = .0298 and p = .0227). RAI3 overexpression is associated with poor prognosis in esophageal cancers. We propose that RAI3 overexpression might play a biologically relevant role of RAI3 in esophageal cancers.

GPRC5A deficiency leads to dysregulated MDM2 via activated EGFR signaling for lung tumor development

GPRC5A, a retinoic acid induced gene, is preferentially expressed in lung tissue. Gprc5a gene deletion leads to spontaneous lung tumor development. However, the mechanism of Gprc5a-mediated lung tumor suppression is not fully understood. Here we showed that MDM2, a p53-negative regulator, was dysregulated in Gprc5a-knockout (ko) mouse tracheal epithelial cells (KO-MTEC) compared to wild type ones. Targeting MDM2 in 1601-a Gprc5a-ko mouse derived lung tumor cell line-and A549-human lung cancer cells, by MDM2 inhibitor Nutlin-3a or small hairpin RNA (sh-RNA)-restored p53 signaling pathway, reduced cancer stem cell markers, and inhibited tumorigenicity. This suggests that dysregulated MDM2 pathway is essential for the oncogenic activities of these cells. MDM2 was found to be stabilized mainly by activated EGFR signaling as targeting EGFR by Erlotinib or sh-RNA repressed MDM2 in a transcription-independent manner. Importantly, overexpression of MDM2 and reduced GPRC5A expression at both protein and mRNA levels were frequently found in clinical human lung cancer tissues. Taken together, GPRC5A deficiency contributes to dysregulated MDM2 via activated EGFR signaling, which promotes lung tumor development.

GPRC5A: An Emerging Biomarker in Human Cancer

Aberrant expression of G protein-coupled receptors (GPCRs) is frequently associated with tumorigenesis. G Protein-coupled receptor class C group 5 member A (GPRC5A) is a member of the GPCR superfamily, is expressed preferentially in lung tissues, and is regulated by various entities at multiple levels. GPRC5A exerts a tumor suppressive role in lung cancer and GPRC5A deletion promotes lung tumor initiation and progression. Recent advances have highlighted that GPRC5A dysregulation is found in various human cancers and is related to many tumor-associated signaling pathways, including the cyclic adenosine monophosphate (cAMP), nuclear factor (NF)-κB, signal transducer and activator of transcription (STAT) 3, and focal adhesion kinase (FAK)/Src signaling. This review aimed to summarize our updated view on the biology and regulation of GPRC5A, its expression in human cancers, and the linked signaling pathways. A better comprehension of the underlying cellular and molecular mechanisms of GPRC5A will provide novel insights into its potential diagnostic and therapeutic value.

Clinical significance of reduced GPRC5A expression in surgically resected non-small cell lung cancer

G protein-coupled receptor, family C, group 5 member A (GPRC5A) is a retinoid-inducible protein, which has been characterized as a tumor-suppressor gene in lung cancer. The present study further examined GPRC5A expression in non-small cell lung cancer (NSCLC) for any association with the clinical features and treatment outcomes of patients with NSCLC. A total of 30 paired NSCLC tumor and adjacent normal tissues were analyzed for the detection of GPRC5A mRNA and protein using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis, respectively. Immunohistochemistry was performed to determine the GPRC5A expression levels in 110 NSCLC and 60 para-tumor tissues. The results confirmed significantly lower expression levels of GPRC5A in NSCLC tumors compared with the corresponding noncancerous tissues (P<0.001). Lost GPRC5A expression was significantly associated with the tumor histological type (P=0.008), poor tumor differentiation (P<0.001) and tumor-node-metastasis (TNM) stage (P<0.001). Kaplan-Meier curve analysis revealed that patients with NSCLC with low GPRC5A expression tumors had a worse prognosis compared with those with high GPRC5A expression tumors (P=0.010). The results of multivariate Cox analysis further suggested that low GPRC5A expression was an independent prognostic factor for patients with NSCLC (P<0.001). The results of this study suggest GPRC5A expression has clinical potential as a prognostic biomarker for patients with NSCLC.

Genome-Wide Gene Expression Changes in the Normal-Appearing Airway during the Evolution of Smoking-Associated Lung Adenocarcinoma

Smoking perpetuates in cytologically normal airways a molecular "field of injury" that is pertinent to lung cancer and early detection. The evolution of airway field changes prior to lung oncogenesis is poorly understood largely due to the long latency of lung cancer in smokers. Here, we studied airway expression changes prior to lung cancer onset in mice with knockout of the Gprc5a gene (Gprc5a^-/-) and tobacco carcinogen (NNK) exposure and that develop the most common type of lung cancer, lung adenocarcinoma, within 6 months following exposure. Airway epithelial brushings were collected from Gprc5a^-/- mice before exposure and at multiple times post-NNK until time of lung adenocarcinoma development and then analyzed by RNA sequencing. Temporal airway profiles were identified by linear models and analyzed by comparative genomics in normal airways of human smokers with and without lung cancer. We identified significantly altered profiles (n = 926) in the NNK-exposed mouse normal airways relative to baseline epithelia, a subset of which were concordantly modulated with smoking status in the human airway. Among airway profiles that were significantly modulated following NNK, we found that expression changes (n = 22) occurring as early as 2 months following exposure were significantly associated with lung cancer status when examined in airways of human smokers. Furthermore, a subset of a recently reported human bronchial gene classifier (Percepta; n = 56) was enriched in the temporal mouse airway profiles. We underscore evolutionarily conserved profiles in the normal-appearing airway that develop prior to lung oncogenesis and that comprise viable markers for early lung cancer detection in suspect smokers. Cancer Prev Res; 11(4); 237-48. ©2018 AACR.

Development of Kras mutant lung adenocarcinoma in mice with knockout of the airway lineage-specific gene Gprc5a

Despite the urgency for prevention and treatment of lung adenocarcinoma (LUAD), we still do not know drivers in pathogenesis of the disease. Earlier work revealed that mice with knockout of the G-protein coupled receptor Gprc5a develop late onset lung tumors including LUADs. Here, we sought to further probe the impact of Gprc5a expression on LUAD pathogenesis. We first surveyed GPRC5A expression in human tissues and found that GPRC5A was markedly elevated in human normal lung relative to other normal tissues and was consistently downregulated in LUADs. In sharp contrast to wild-type littermates, Gprc5a-/- mice treated chronically with the nicotine-specific carcinogen NNK developed LUADs by 6 months following NNK exposure. Immunofluorescence analysis revealed that the LUADs exhibited abundant expression of surfactant protein C and lacked the clara cell marker Ccsp, suggesting that these LUADs originated from alveolar type II cells. Next, we sought to survey genome-wide alterations in the pathogenesis of Gprc5a-/- LUADs. Using whole exome sequencing, we found that carcinogen-induced LUADs exhibited markedly higher somatic mutation burdens relative to spontaneous tumors. All LUADs were found to harbor somatic mutations in the Kras oncogene (p. G12D or p. Q61R). In contrast to spontaneous lesions, carcinogen-induced Gprc5a-/- LUADs exhibited mutations (variants and copy number gains) in additional drivers (Atm, Kmt2d, Nf1, Trp53, Met, Ezh2). Our study underscores genomic alterations that represent early events in the development of Kras mutant LUAD following Gprc5a loss and tobacco carcinogen exposure and that may constitute targets for prevention and early treatment of this disease.

Gprc5a-knockout mouse lung epithelial cells predicts ceruloplasmin, lipocalin 2 and periostin as potential biomarkers at early stages of lung tumorigenesis

Lung cancer is the leading cause of cancer death. As most of lung cancer patients were diagnosed with the advanced stage, early detection is considered as the most effective strategy to reduce high mortality. Thus, it is desirable to identify specific biomarkers at early stages of lung tumorigenesis. GPRC5A is a lung tumor suppressor gene. GPRC5A deficiency is linked to lung cancer development. We hyposthesized that, dysregulated gene expression that results from Gprc5a deficiency may provide potential biomarkers at early stages of lung tumorigenesis. By analysis of top 20 upregulated genes in mouse tracheal epithelial cells (MTEC) of Gprc5a knockout (KO) vs wild-type (WT), we found that ceruloplasmin, lipocalin-2, and periostin are not only upregulated in lung epithelial cells of Gprc5a-ko mice, but also expressed at high levels in lung tumor tissues of Gprc5a-ko mice. This suggests that increased expression of these genes is associated with lung tumorigenesis. Importantly, expression of ceruloplasmin, lipocalin-2, and periostin has also been found to be significantly increased, both at mRNA and protein levels, in the lung tissues from NSCLC patients, which is correlated with repressed GPRC5A. Thus, dysregulated ceruloplasmin, lipocalin-2, and periostin may be used as potential biomarkers at early stages of lung tumorigenesis.

Dextran sodium sulfate colitis murine model: An indispensable tool for advancing our understanding of inflammatory bowel diseases pathogenesis

Inflammatory bowel diseases (IBD), including Crohn’s disease and ulcerative colitis, are complex diseases that result from the chronic dysregulated immune response in the gastrointestinal tract. The exact etiology is not fully understood, but it is accepted that it occurs when an inappropriate aggressive inflammatory response in a genetically susceptible host due to inciting environmental factors occurs. To investigate the pathogenesis and etiology of human IBD, various animal models of IBD have been developed that provided indispensable insights into the histopathological and morphological changes as well as factors associated with the pathogenesis of IBD and evaluation of therapeutic options in the last few decades. The most widely used experimental model employs dextran sodium sulfate (DSS) to induce epithelial damage. The DSS colitis model in IBD research has advantages over other various chemically induced experimental models due to its rapidity, simplicity, reproducibility and controllability. In this manuscript, we review the newer publicized advances of research in murine colitis models that focus upon the disruption of the barrier function of the intestine, effects of mucin on the development of colitis, alterations found in microbial balance and resultant changes in the metabolome specifically in the DSS colitis murine model and its relation to the pathogenesis of IBD.

RAI3 knockdown promotes adipogenic differentiation of human adipose-derived stem cells by decreasing β-catenin levels

Retinoic acid-induced protein 3 (RAI3) has been found to play significant roles in embryonic development, cellular proliferation and differentiation, but its role in adipogenesis has not been explored. In this study, we discovered RAI3 was downregulated during the adipogenic differentiation of human adipose derived stem cells (hASCs). Moreover, we demonstrated that knockdown of RAI3 promoted adipogenic differentiation of hASCs both in vitro and in vivo. Mechanistically, our findings showed that inhibition of RAI3 in hASCs reduced the expression of β-catenin, and lithium chloride which can activate the β-catenin pathway abolished the effect of RAI3 knockdown on the adipogenesis. These results suggest RAI3 plays an important role in adipogenesis of hASCs and may have a potential use in the future application.

Lung cancer suppressor gene GPRC5A mediates p53 activity in non‑small cell lung cancer cells in vitro

Cellular tumor antigen p53 (p53) functions to maintain genomic stability and regulate cell apoptosis, while G protein‑coupled receptor class C group 5 member A (GPCR5A) is a lung cancer suppressor gene whose expression is induced by retinoids. The present in vitro study assessed the effects of p53 on the regulation of GPRC5A expression and on non‑small cell lung cancer (NSCLC) cells. Human NSCLC H1299 (p53‑null) and A549 (wild‑type p53) cell lines were subjected to p53 cDNA and small interfering (si)RNA transfection, respectively. GPRC5A expression was analyzed by reverse transcription‑quantitative polymerase chain reaction and western blotting, and cell behavior was analyzed using cell viability and apoptosis assays. The results of the present study demonstrated that knockdown of GPRC5A expression markedly upregulated tumor cell viability and reduced tumor cell apoptosis, while p53 overexpression in H1299 cells significantly increased the expression level of GPRC5A. p53 overexpression and GPRC5A induction markedly inhibited tumor cell viability and induced apoptosis, while knockdown of p53 resulted in a decrease in GPRC5A expression, inhibited tumor cell apoptosis and increased tumor cell viability. In serum‑free culture conditions, GPRC5A expression was decreased in the two cell lines; this decrease was less marked in p53 cDNA‑transfected H1299 cells and more marked in p53 siRNA‑transfected A549 cells. The results of the present study indicated that p53 antitumor activity may be mediated by GPRC5A in NSCLC cells.

Orphan G protein-coupled receptor GPRC5A modulates integrin β1-mediated epithelial cell adhesion

G-Protein Coupled Receptor (GPCR), Class C, Group 5, Member A (GPRC5A) has been implicated in several malignancies. The underlying mechanisms, however, remain poorly understood. Using a panel of human cell lines, we demonstrate that CRISPR/Cas9-mediated knockout and RNAi-mediated depletion of GPRC5A impairs cell adhesion to integrin substrates: collagens I and IV, fibronectin, as well as to extracellular matrix proteins derived from the Engelbreth-Holm-Swarm (EHS) mouse sarcoma (Matrigel). Consistent with the phenotype, knock-out of GPRC5A correlated with a reduced integrin β1 (ITGB1) protein expression, impaired phosphorylation of the focal adhesion kinase (FAK), and lower activity of small GTPases RhoA and Rac1. Furthermore, we provide the first evidence for a direct interaction between GPRC5A and a receptor tyrosine kinase EphA2, an upstream regulator of FAK, although its contribution to the observed adhesion phenotype is unclear. Our findings reveal an unprecedented role for GPRC5A in regulation of the ITGB1-mediated cell adhesion and it's downstream signaling, thus indicating a potential novel role for GPRC5A in human epithelial cancers.

The G Protein-Coupled Receptor RAI3 Is an Independent Prognostic Factor for Pancreatic Cancer Survival and Regulates Proliferation via STAT3 Phosphorylation

Pancreatic Ductal Adenocarcinoma (PDAC) is one of the deadliest tumors worldwide. Understanding the function of gene expression alterations is a prerequisite for developing new strategies in diagnostic and therapy. GPRC5A (RAI3), coding for a seven transmembrane G protein-coupled receptor is known to be overexpressed in pancreatic cancer and might be an interesting candidate for therapeutic intervention. Expression levels of RAI3 were compared using a tissue microarray of 435 resected patients with pancreatic cancer as well as 209 samples from chronic pancreatitis (CP), intra-ductal papillary mucinous neoplasm (IPMN) and normal pancreatic tissue. To elucidate the function of RAI3 overexpression, siRNA based knock-down was used and transfected cells were analyzed using proliferation and migration assays. Pancreatic cancer patients showed a statistically significant overexpression of RAI3 in comparison to normal and chronic pancreatitis tissue. Especially the loss of apical RAI3 expression represents an independent prognostic parameter for overall survival of patients with pancreatic cancer. Suppression of GPRC5a results in decreased cell growth, proliferation and migration in pancreatic cancer cell lines via a STAT3 modulated pathway, independent from ERK activation.

GPRC5A is a potential oncogene in pancreatic ductal adenocarcinoma cells that is upregulated by gemcitabine with help from HuR

GPRC5A is an orphan G-protein coupled receptor with an intriguing dual behavior, acting as an oncogene in some cancers and as a tumor suppressor in other cancers. In the pancreatic cancer context, very little is known about GPRC5A. By analyzing messenger RNA (mRNA) expression data from 675 human cancer cell lines and 10 609 samples from The Cancer Genome Atlas (TCGA) we found that GPRC5A's abundance in pancreatic cancer is highest (cell lines) or second highest (TCGA) among all tissues and cancer types. Further analyses of an independent set of 252 pancreatic normal and cancer samples showed GPRC5A mRNA to be more than twofold upregulated in primary tumor samples compared with normal pancreas (P-value<10⁻⁵), and even further upregulated in pancreatic cancer metastases to various organs (P-value=0.0021). Immunostaining of 208 cores (103 samples) of a tissue microarray showed generally low expression of GPRC5A protein in normal pancreatic ductal cells; on the other hand, in primary and metastatic samples, GPRC5A protein levels were dramatically increased in pancreatic ductal cells. In vitro studies of multiple pancreatic cancer cell lines showed that an increase in GPRC5A protein levels promoted pancreatic cancer cell growth and migration. Unexpectedly, when we treated pancreatic cancer cell lines with gemcitabine (2′,2′-difluorodeoxycytidine), we observed an increase in GPRC5A protein abundance. On the other hand, when we knocked down GPRC5A we sensitized pancreatic cancer cells to gemcitabine. Through further experimentation we showed that the monotonic increase in GPRC5A protein levels that we observe for the first 18 h following gemcitabine treatment results from interactions between GPRC5A's mRNA and the RNA-binding protein HuR, which is an established key mediator of gemcitabine's efficacy in cancer cells. As we discovered, the interaction between GPRC5A and HuR is mediated by at least one HuR-binding site in GPRC5A's mRNA. Our findings indicate that GPRC5A is part of a complex molecular axis that involves gemcitabine and HuR, and, possibly, other genes. Further work is warranted before it can be established unequivocally that GPRC5A is an oncogene in the pancreatic cancer context.

Folic Acid Supplementation in Postpolypectomy Patients in a Randomized Controlled Trial Increases Tissue Folate Concentrations and Reduces Aberrant DNA Biomarkers in Colonic Tissues Adjacent to the Former Polyp Site

BACKGROUND

Low folate status is associated with an increased risk of colorectal carcinogenesis. Optimal folate status may be genoprotective by preventing uracil misincorporation into DNA and DNA hypomethylation. Adenomatous polyps have low folate status compared with normal colonic mucosa, and they are surrounded by histologically normal mucosa that also is of low folate status.

OBJECTIVE

In a randomized controlled trial conducted at a single Dublin hospital between April 2002 and March 2004, we assessed the effect of folic acid supplementation on tissue folate, uracil misincorporation into DNA, and global DNA hypomethylation in colonocytes isolated from sites of adenomatous polyps and from histologically normal tissue adjacent and 10-15 cm distal to them.

METHODS

Twenty patients with adenomatous polyps on initial colonoscopy and polypectomy were randomly assigned to receive either 600 μg folic acid/d [n = 12, 38% men, mean age 64.3 y, and body mass index (BMI, in kg/m(2)) 26.6] or placebo (n = 8, 50% men, mean age 68.4 y, and BMI 27.2) for 6 mo, and then repeat the colonoscopy. Blood and colonocyte tissue folate concentrations were measured with the use of a microbiological assay. Uracil misincorporation and global DNA hypomethylation were measured in colonocytes with the use of modified comet assays.

RESULTS

Over time, folic acid supplementation, compared with placebo, increased tissue folate (mean ± SEM) from 15.6 ± 2.62 pg/10(5) cells to 18.1 ± 2.12 pg/10(5) cells (P < 0.001) and decreased the global DNA hypomethylation ratio from 1.7 ± 0.1 to 1.0 ± 0.1 (P < 0.001). The uracil misincorporation ratio decreased by 0.5 ± 0.1 for the site adjacent to the polyp over time (P = 0.05).

CONCLUSION

A response to folic acid supplementation, which increased colonocyte folate and improved folate-related DNA biomarkers of cancer risk, was seen in the participants studied. Exploratory analysis points toward the area formerly adjacent to polyps as possibly driving the response. That these areas persist after polypectomy in the absence of folate supplementation is consistent with a potentially carcinogenic field's causing the appearance of the polyp.

Large-scale RNA-Seq Transcriptome Analysis of 4043 Cancers and 548 Normal Tissue Controls across 12 TCGA Cancer Types

The Cancer Genome Atlas (TCGA) has accrued RNA-Seq-based transcriptome data for more than 4000 cancer tissue samples across 12 cancer types, translating these data into biological insights remains a major challenge. We analyzed and compared the transcriptomes of 4043 cancer and 548 normal tissue samples from 21 TCGA cancer types, and created a comprehensive catalog of gene expression alterations for each cancer type. By clustering genes into co-regulated gene sets, we identified seven cross-cancer gene signatures altered across a diverse panel of primary human cancer samples. A 14-gene signature extracted from these seven cross-cancer gene signatures precisely differentiated between cancerous and normal samples, the predictive accuracy of leave-one-out cross-validation (LOOCV) were 92.04%, 96.23%, 91.76%, 90.05%, 88.17%, 94.29%, and 99.10% for BLCA, BRCA, COAD, HNSC, LIHC, LUAD, and LUSC, respectively. A lung cancer-specific gene signature, containing SFTPA1 and SFTPA2 genes, accurately distinguished lung cancer from other cancer samples, the predictive accuracy of LOOCV for TCGA and GSE5364 data were 95.68% and 100%, respectively. These gene signatures provide rich insights into the transcriptional programs that trigger tumorigenesis and metastasis, and many genes in the signature gene panels may be of significant value to the diagnosis and treatment of cancer.

Lung Tumor Suppressor GPRC5A Binds EGFR and Restrains Its Effector Signaling

GPRC5A is a G-protein-coupled receptor expressed in lung tissue but repressed in most human lung cancers. Studies in Gprc5a(-/-) mice have established its role as a tumor-suppressor function in this setting, but the basis for its role has been obscure. Here, we report that GPRC5A functions as a negative modulator of EGFR signaling. Mouse tracheal epithelial cells (MTEC) from Gprc5a(-/-) mice exhibited a relative increase in EGFR and downstream STAT3 signaling, whereas GPRC5A expression inhibited EGFR and STAT3 signaling. GPRC5A physically interacted with EGFR through its transmembrane domain, which was required for its EGFR inhibitory activity. Gprc5a(-/-) MTEC were much more susceptible to EGFR inhibitors than wild-type MTEC, suggesting their dependence on EGFR signaling for proliferation and survival. Dysregulated EGFR and STAT3 were identified in the normal epithelia of small and terminal bronchioles as well as tumors of Gprc5a(-/-) mouse lungs. Moreover, in these lungs EGFR inhibitor treatment inhibited EGFR and STAT3 activation along with cell proliferation. Finally, overexpression of ectopic GPRC5A in human non-small cell lung carcinoma cells inhibited both EGF-induced and constitutively activated EGFR signaling. Taken together, our results show how GPRC5A deficiency leads to dysregulated EGFR and STAT3 signaling and lung tumorigenesis. Cancer Res; 75(9); 1801-14. ©2015 AACR.

The emerging roles of GPRC5A in diseases

The ‘Retinoic Acid-Inducible G-protein-coupled receptors’ or RAIG are a group comprising the four orphan receptors GPRC5A, GPRC5B, GPRC5C and GPRC5D. As the name implies, their expression is induced by retinoic acid but beyond that very little is known about their function. In recent years, one member, GPRC5A, has been receiving increasing attention as it was shown to play important roles in human cancers. As a matter of fact, dysregulation of GPRC5A has been associated with several cancers including lung cancer, breast cancer, colorectal cancer, and pancreatic cancer. Here we review the current state of knowledge about the heterogeneity and evolution of GPRC5A, its regulation, its molecular functions, and its involvement in human disease.

EGFR phosphorylates and inhibits lung tumor suppressor GPRC5A in lung cancer

Background

GPRC5A is a retinoic acid inducible gene that is preferentially expressed in lung tissue. Gprc5a– knockout mice develop spontaneous lung cancer, indicating Gprc5a is a lung tumor suppressor gene. GPRC5A expression is frequently suppressed in majority of non-small cell lung cancers (NSCLCs), however, elevated GPRC5A is still observed in a small portion of NSCLC cell lines and tumors, suggesting that the tumor suppressive function of GPRC5A is inhibited in these tumors by an unknown mechanism.

Methods

In this study, we examined EGF receptor (EGFR)-mediated interaction and tyrosine phosphorylation of GPRC5A by immunoprecipitation (IP)-Westernblot. Tyrosine phosphorylation of GPRC5A by EGFR was systematically identified by site-directed mutagenesis. Cell proliferation, migration, and anchorage-independent growth of NSCLC cell lines stably transfected with wild-type GPRC5A and mutants defective in tyrosine phosphorylation were assayed. Immunohistochemical (IHC) staining analysis with specific antibodies was performed to measure the total and phosphorylated GPRC5A in both normal lung and lung tumor tissues.

Result

We found that EGFR interacted with GPRC5A and phosphorylated it in two conserved double-tyrosine motifs, Y317/Y320 and Y347/ Y350, at the C-terminal tail of GPRC5A. EGF induced phosphorylation of GPRC5A, which disrupted GPRC5A-mediated suppression on anchorage-independent growth of NSCLC cells. On contrary, GPRC5A-4 F, in which the four tyrosine residues have been replaced with phenylalanine, was resistant to EGF-induced phosphorylation and maintained tumor suppressive activities. Importantly, IHC analysis with anti-Y317/Y320-P sites showed that GPRC5A was non-phosphorylated in normal lung tissue whereas it was highly tyrosine-phosphorylated in NSCLC tissues.

Conclusion

GPRC5A can be inactivated by receptor tyrosine kinase via tyrosine phosphorylation. Thus, targeting EGFR can restore the tumor suppressive functions of GPRC5A in lung cancer.

Genome-wide association study for wool production traits in a Chinese Merino sheep population

Genome-wide association studies (GWAS) provide a powerful approach for identifying quantitative trait loci without prior knowledge of location or function. To identify loci associated with wool production traits, we performed a genome-wide association study on a total of 765 Chinese Merino sheep (JunKen type) genotyped with 50 K single nucleotide polymorphisms (SNPs). In the present study, five wool production traits were examined: fiber diameter, fiber diameter coefficient of variation, fineness dispersion, staple length and crimp. We detected 28 genome-wide significant SNPs for fiber diameter, fiber diameter coefficient of variation, fineness dispersion, and crimp trait in the Chinese Merino sheep. About 43% of the significant SNP markers were located within known or predicted genes, including YWHAZ, KRTCAP3, TSPEAR, PIK3R4, KIF16B, PTPN3, GPRC5A, DDX47, TCF9, TPTE2, EPHA5 and NBEA genes. Our results not only confirm the results of previous reports, but also provide a suite of novel SNP markers and candidate genes associated with wool traits. Our findings will be useful for exploring the genetic control of wool traits in sheep.

DNA methylation is globally disrupted and associated with expression changes in chronic obstructive pulmonary disease small airways

DNA methylation is an epigenetic modification that is highly disrupted in response to cigarette smoke and involved in a wide spectrum of malignant and nonmalignant diseases, but surprisingly not previously assessed in small airways of patients with chronic obstructive pulmonary disease (COPD). Small airways are the primary sites of airflow obstruction in COPD. We sought to determine whether DNA methylation patterns are disrupted in small airway epithelia of patients with COPD, and evaluate whether changes in gene expression are associated with these disruptions. Genome-wide methylation and gene expression analysis were performed on small airway epithelial DNA and RNA obtained from the same patient during bronchoscopy, using Illumina's Infinium HM27 and Affymetrix's Genechip Human Gene 1.0 ST arrays. To control for known effects of cigarette smoking on DNA methylation, methylation and gene expression profiles were compared between former smokers with and without COPD matched for age, pack-years, and years of smoking cessation. Our results indicate that aberrant DNA methylation is (1) a genome-wide phenomenon in small airways of patients with COPD, and (2) associated with altered expression of genes and pathways important to COPD, such as the NF-E2-related factor 2 oxidative response pathway. DNA methylation is likely an important mechanism contributing to modulation of genes important to COPD pathology. Because these methylation events may underlie disease-specific gene expression changes, their characterization is a critical first step toward the development of epigenetic markers and an opportunity for developing novel epigenetic therapeutic interventions for COPD.

Overexpression of retinoic acid-induced protein 3 predicts poor prognosis for hepatocellular carcinoma

AIM

To investigate clinical significance of retinoic acid-induced protein 3 (RAI3) in hepatocellular carcinoma (HCC).

METHODS

Expression of RAI3 at both mRNA and protein levels in tumor, para-tumor and normal liver tissues was detected in 106 HCC patients by real-time quantitative RT-PCR, Western blot and immunohistochemistry. Then, the correlation of RAI3 expression with clinicopathological characteristics and survivals of HCC patients was analyzed.

RESULTS

Our data first found that RAI3 mRNA and protein expression were both significantly higher in HCC than in para-tumor (both P < 0.001) and normal liver tissues (both P < 0.001). The correlation analysis showed a positive correlation between RAI3 mRNA level and RAI3 protein level in HCC tissues (r = 0.8, P < 0.001). Immunohistochemistry data also revealed that overexpression of RAI3 was present in 73.6 % (78/106) of HCC tissues. In addition, high RAI3 protein expression was correlated with advanced TNM stage (P = 0.001), high serum AFP (P = 0.008), vascular invasion (P = 0.01) and tumor recurrence (P = 0.008). Moreover, HCC patients with overexpression of RAI3 had significantly shorter overall (P = 0.01) and disease-free survival (P = 0.01). Furthermore, multivariate analysis showed that overexpression of RAI3 was an independent prognostic factor for both overall (P = 0.02) and disease-free survival (P = 0.03) in HCC.

CONCLUSION

Our data for the first time provide a basis for the concept that overexpression of RAI3 may contribute to the malignant progression of HCC and predict poor prognosis for patients with this deadly disease after curative hepatectomy. RAI3 might be an important marker for tumor progression and prognosis, as well as a potential therapeutic target of HCC.