Lung Tumor Suppressor GPRC5A Binds EGFR and Restrains Its Effector Signaling

NF-κB-mediated EAAT3 upregulation in antioxidant defense and ferroptosis sensitivity in lung cancer

Cellular glutathione (GSH) in lung cancer cells represents the most abundant antioxidant. GSH production is regulated not only by upregulated cystine/glutamate exchanger (xCT) but also by the involvement of glutamate transporters, specifically excitatory amino acid transporter 3 (EAAT3). Our prior research established that the uptake of glutamate via EAAT3 plays a pivotal role in driving cystine uptake through xCT, contributing to GSH biosynthesis during lung tumorigenesis. Nevertheless, the underlying mechanism governing the upregulation of EAAT3 remains enigmatic. In this study, we conducted a comprehensive reanalysis of publicly available data and employed the Gprc5a-/-/SR-IκB mouse model alongside in vitro cell experiments to elucidate the correlations between NF-κB and EAAT3 in lung cancer. We observed that EAAT3 knockdown, similar to NF-κB inhibition, led to the accumulation of reactive oxygen species (ROS) and increased sensitivity to ferroptosis induction by RAS-selective lethal 3 (RSL3). Mechanistic insights were obtained through chromatin immunoprecipitation and luciferase reporter assays, revealing that NF-κB induces EAAT3 expression via two putative cis-elements within its promoter. Furthermore, our investigation unveiled the upregulation of EAAT3 in a subset of clinical non-small cell lung cancer (NSCLC) tissues, exhibiting a positive correlation with the P65 protein. In addition, the inflammatory factor of smoking was found to augment EAAT3 expression in both human and murine experimental models. These findings collectively emphasize the pivotal role of the NF-κB/EAAT3 axis in managing antioxidant stress and influencing lung cancer development. Moreover, this research offers insights into the potential for a combined ferroptosis therapy strategy in lung cancer treatment.

Immunogenic dying cells elicit potent anti-tumor T cell immunity against lung metastasis and tumorigenesis

PURPOSE

Immune checkpoint blockades (ICBs) are promising, however they do not fit all types of tumor, such as those lack of tumor antigens. Induction of potent anti-tumor T cell immunity is critical for cancer therapy. In this study, we investigated the efficacy of immunotherapy via the immunogenic cell death (ICD) dying tumor cells in mouse models of lung metastasis and tumorigenesis.

METHODS

ICD was induced by short exposure to lethal dose of chemotherapeutic drug doxorubicin (Dox), which initiated an irreversible ICD program in tumor cells. We immunized mice with ICD dying tumor cells in prevention, therapy in lung metastasis models, and Gprc5a-knockout (ko) model of lung tumorigenesis. T cells and macrophages isolated from lymph nodes or tumor tissues were analyzed by flow cytometry. Cytokines were analyzed by ELISA or Q-PCR analysis.

RESULTS

Immunization with these live but ICD dying tumor cells induced potent tumor-specific anti-tumor T cell immunity, which not only protected host from challenge by these tumor cells in prevention and therapy in mouse model of lung metastasis, but also prevented tumors development in Gprc5a-ko mouse model of lung tumorigenesis. The lymphocytes from lymph nodes and tumor tissues exhibited greatly enhanced activities of Th1 cells and M1 macrophages.

CONCLUSION

Immunization with the ICD dying tumor cells evokes potent tumor-specific T cell immunity, which provides a novel approach for cancer immunotherapy.

GPRC5A promotes lung colonization of esophageal squamous cell carcinoma

Emerging evidence suggests that cancer cells may disseminate early, prior to the formation of traditional macro-metastases. However, the mechanisms underlying the seeding and transition of early disseminated cancer cells (DCCs) into metastatic tumors remain poorly understood. Through single-cell RNA sequencing, we show that early lung DCCs from esophageal squamous cell carcinoma (ESCC) exhibit a trophoblast-like 'tumor implantation' phenotype, which enhances their dissemination and supports metastatic growth. Notably, ESCC cells overexpressing GPRC5A demonstrate improved implantation and persistence, resulting in macro-metastases in the lungs. Clinically, elevated GPRC5A level is associated with poorer outcomes in a cohort of 148 ESCC patients. Mechanistically, GPRC5A is found to potentially interact with WWP1, facilitating the polyubiquitination and degradation of LATS1, thereby activating YAP1 signaling pathways essential for metastasis. Importantly, targeting YAP1 axis with CA3 or TED-347 significantly diminishes early implantation and macro-metastases. Thus, the GPRC5A/WWP1/LATS1/YAP1 pathway represents a crucial target for therapeutic intervention in ESCC lung metastases.

GPRC5A promotes gallbladder cancer metastasis by upregulating TNS4 via the JAK2-STAT3 pathway

Aberrant expression of G protein-coupled receptor class C group 5 member A (GPRC5A) has been reported in multiple cancers and is closely related to patient prognosis. However, the mechanistic role of GPRC5A in gallbladder cancer (GBC) remains unclear. Here, we determined tumor expression levels of GPRC5A and the molecular mechanisms by which GPRC5A regulates gallbladder cancer metastasis. We found that GPRC5A was significantly upregulated in GBC, correlating with poorer patient survival. Knocking down GPRC5A inhibited GBC cell metastasis both in vitro and in vivo. GRPRC5A knockdown resulted in downregulation of TNS4 expression through the JAK2-STAT3 axis. Clinically, GPRC5A expression positively correlated with TNS4. Finally, STAT3 bound to TNS4's promoter region, inducing its expression. Overall, GPRC5A showed high expression in GBC tissues, associated with poor patient prognosis. Our findings first demonstrate that the GPRC5A-JAK2-STAT3-TNS4 pathway promotes GBC cell metastasis, suggesting potential therapy targets.

GPRC5A promotes paclitaxel resistance and glucose content in NSCLC

Lung cancer is one of the most common and malignant cancers worldwide. Chemotherapy has been widely used in the clinical setting, and paclitaxel is the first-line therapy for lung cancer patients but paclitaxel resistance is the main problem. First, we successfully established paclitaxel-resistant lung cancer cells treated with elevated doses of paclitaxel for 3 months, as confirmed by the CCK-8 assay. Paclitaxel-resistant cancer cells increased glucose content. Second, Gtex, Oncomine, and gene expression omnibus database data mining identified GPRC5A, G protein-coupled receptor, as the most prominent differentially expressed gene in drug-resistant datasets including gemcitabine, paclitaxel, and gefitinib overlapped with the microarray data from cancer cell metabolism. Third, qPCR analysis and western blot technique showed that GPRC5A mRNA and protein levels were significantly enhanced in paclitaxel-resistant lung cancer cells. Fourth, functional analysis was conducted by siRNA-mediated transient knockdown of GPRC5A. Silencing GPRC5A significantly decreased paclitaxel resistance and glucose content. In the end, retinoic acid substantially upregulated GPRC5A proteins and promoted glucose content in two lung cancer cells. Kaplan-Meier plot also confirmed that lung cancer patients with high expression of GPRC5A had a relatively lower survival rate. Our study provided a potential drug target GPRC5A, which may benefit lung cancer patients with acquired paclitaxel resistance in the future and a theoretical basis for future preclinical trials.

Gprc5a is a novel parathyroid hormone-inducible gene and negatively regulates osteoblast proliferation and differentiation

Teriparatide is a peptide derived from a parathyroid hormone (PTH) and an osteoporosis therapeutic drug with potent bone formation-promoting activity. To identify novel druggable genes that act downstream of PTH signaling and are potentially involved in bone formation, we screened PTH target genes in mouse osteoblast-like MC3T3-E1 cells. Here we show that Gprc5a, encoding an orphan G protein-coupled receptor, is a novel PTH-inducible gene and negatively regulates osteoblast proliferation and differentiation. PTH treatment induced Gprc5a expression in MC3T3-E1 cells, rat osteosarcoma ROS17/2.8 cells, and mouse femurs. Induction of Gprc5a expression by PTH occurred in the absence of protein synthesis and was mediated primarily via the cAMP pathway, suggesting that Gprc5a is a direct target of PTH signaling. Interestingly, Gprc5a expression was induced additively by co-treatment with PTH and 1α, 25-dihydroxyvitamin D3 (calcitriol), or retinoic acid in MC3T3-E1 cells. Reporter analysis of a 1 kb fragment of human GPRC5A promoter revealed that the promoter fragment showed responsiveness to PTH via the cAMP response element, suggesting that GPRC5A is also a PTH-inducible gene in humans. Gprc5a knockdown promoted cell viability and proliferation, as demonstrated by MTT and BrdU assays. Gprc5a knockdown also promoted osteoblast differentiation, as indicated by gene expression analysis and mineralization assay. Mechanistic studies showed that Gprc5a interacted with BMPR1A and suppressed BMP signaling induced by BMP-2 and constitutively active BMP receptors, ALK2 (ACVR1) Q207D and ALK3 (BMPR1A) Q233D. Thus, our results suggest that Gprc5a is a novel gene induced by PTH that acts in an inhibitory manner on both cell proliferation and osteoblast differentiation and is a candidate for drug targets for osteoporosis.

Myeloid-derived suppressor cells in cancer: therapeutic targets to overcome tumor immune evasion

Paradoxically, tumor development and progression can be inhibited and promoted by the immune system. After three stages of immune editing, namely, elimination, homeostasis and escape, tumor cells are no longer restricted by immune surveillance and thus develop into clinical tumors. The mechanisms of immune escape include abnormalities in antitumor-associated immune cells, selection for immune resistance to tumor cells, impaired transport of T cells, and the formation of an immunosuppressive tumor microenvironment. A population of distinct immature myeloid cells, myeloid-derived suppressor cells (MDSCs), mediate immune escape primarily by exerting immunosuppressive effects and participating in the constitution of an immunosuppressive microtumor environment. Clinical trials have found that the levels of MDSCs in the peripheral blood of cancer patients are strongly correlated with tumor stage, metastasis and prognosis. Moreover, animal experiments have confirmed that elimination of MDSCs inhibits tumor growth and metastasis to some extent. Therefore, MDSCs may become the target of immunotherapy for many cancers, and eliminating MDSCs can help improve the response rate to cancer treatment and patient survival. However, a clear definition of MDSCs and the specific mechanism involved in immune escape are lacking. In this paper, we review the role of the MDSCs population in tumor development and the mechanisms involved in immune escape in different tumor contexts. In addition, we discuss the use of these cells as targets for tumor immunotherapy. This review not only contributes to a systematic and comprehensive understanding of the essential role of MDSCs in immune system reactions against tumors but also provides information to guide the development of cancer therapies targeting MDSCs.

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.

Chemoproteomics reveals microbiota-derived aromatic monoamine agonists for GPRC5A

The microbiota generates diverse metabolites to modulate host physiology and disease, but their protein targets and mechanisms of action have not been fully elucidated. To address this challenge, we explored microbiota-derived indole metabolites and developed photoaffinity chemical reporters for proteomic studies. We identified many potential indole metabolite-interacting proteins, including metabolic enzymes, transporters, immune sensors and G protein-coupled receptors. Notably, we discovered that aromatic monoamines can bind the orphan receptor GPRC5A and stimulate β-arrestin recruitment. Metabolomic and functional profiling also revealed specific amino acid decarboxylase-expressing microbiota species that produce aromatic monoamine agonists for GPRC5A-β-arrestin recruitment. Our analysis of synthetic aromatic monoamine derivatives identified 7-fluorotryptamine as a more potent agonist of GPRC5A. These results highlight the utility of chemoproteomics to identify microbiota metabolite-interacting proteins and the development of small-molecule agonists for orphan receptors.

Upregulated GPRC5A disrupting the Hippo pathway promotes the proliferation and migration of pancreatic cancer cells via the cAMP-CREB axis

BACKGROUND

Pancreatic cancer has a high mortality rate worldwide, and is predicted to be third leading cause of death in the near future. However, the regulatory mechanisms that inhibit the progression of pancreatic cancer remain elusive. Currently, exploring the function and mechanisms of GPCRs (G-protein coupled receptors) is an important way to discover promising therapeutic targets for cancer.

METHODS

GPRC5A expression was measured using real-time quantitative PCR, immunohistochemistry and western blot assays. Cell proliferation and migration were assessed using CCK-8, clone formation, wound-healing and transwell assays. A cytosolic/nuclear distribution experiment was used to detect the protein location transfer. A xenograft model of pancreatic cancer was established to explore the role of GPRC5A in vivo.

RESULTS

GPRC5A expression was increased in pancreatic cancer, and disruption of GPRC5A expression inhibited tumor growth in vivo. Mechanistically, GPRC5A positively regulated the transcription of YAP1 through cAMP-CREB signaling. Moreover, we show that the proliferation and migration induced by GPRC5A in pancreatic cancer could be rescued by inhibiting YAP1 expression.

CONCLUSIONS

GPRC5A interacts with the Hippo pathway to promote the progression of pancreatic cancer. These findings reveal an important crosstalk model and provide potential targets for pancreatic cancer therapy.

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.

GPCR-mediated EGFR transactivation ameliorates skin toxicities induced by afatinib

Many G-protein-coupled receptor (GPCR) agonists have been studied for transactivating epidermal growth factor receptor (EGFR) signaling through extracellular or intracellular pathways. Accumulated evidence has confirmed that GPCR transactivation participates in various diseases. However, the clinical application of GPCR transactivation has not been explored, and more translational studies are needed to develop therapies to target GPCR-mediated EGFR transactivation. In cancer patients treated with EGFR inhibitors (EGFRi), especially afatinib, a unique acneiform rash is frequently developed. In this study, we first established the connection between GPCR transactivation and EGFRi-induced skin disease. We examined the ability of three different GPCR agonists to reverse signaling inhibition and ameliorate rash induced by EGFRi. The activation of different agonists follows unique time and kinase patterns. Rats treated with EGFRi show a similar skin phenotype, with rash occurring in the clinic; correspondingly, treatment with GPCR agonists reduced keratinocyte apoptosis, growth retardation and infiltration of inflammatory cytokines by transactivation. This phenomenon demonstrates that EGFR inhibition in keratinocytes regulates key factors associated with rash. Our findings indicate that maintaining EGFR signaling by GPCR agonists might provide a possible therapy for EGFR inhibitor-induced skin toxicities. Our study provides the first example of the translational application of GPCR transactivation in treating diseases.

EGFR signaling pathway as therapeutic target in human cancers

Epidermal Growth Factor Receptor (EGFR) enacts major roles in the maintenance of epithelial tissues. However, when EGFR signaling is altered, it becomes the grand orchestrator of epithelial transformation, and hence one of the most world-wide studied tyrosine kinase receptors involved in neoplasia, in several tissues. In the last decades, EGFR-targeted therapies shaped the new era of precision-oncology. Despite major advances, the dream of converting solid tumors into a chronic disease is still unfulfilled, and long-term remission eludes us. Studies investigating the function of this protein in solid malignancies have revealed numerous ways how tumor cells dysregulate EGFR function. Starting from preclinical models (cell lines, organoids, murine models) and validating in clinical specimens, EGFR-related oncogenic pathways, mechanisms of resistance, and novel avenues to inhibit tumor growth and metastatic spread enriching the therapeutic portfolios, were identified. Focusing on non-small cell lung cancer (NSCLC), where EGFR mutations are major players in the adenocarcinoma subtype, we will go over the most relevant discoveries that led us to understand EGFR and beyond, and highlight how they revolutionized cancer treatment by expanding the therapeutic arsenal at our disposal.

Endogenous and Exogenous Regulatory Signaling in the Secretory Pathway: Role of Golgi Signaling Molecules in Cancer

The biosynthetic transport route that constitutes the secretory pathway plays a fundamental role in the cell, providing to the synthesis and transport of around one third of human proteins and most lipids. Signaling molecules within autoregulatory circuits on the intracellular membranes of the secretory pathway regulate these processes, especially at the level of the Golgi complex. Indeed, cancer cells can hijack several of these signaling molecules, and therefore also the underlying regulated processes, to bolster their growth or gain more aggressive phenotypes. Here, we review the most important autoregulatory circuits acting on the Golgi, emphasizing the role of specific signaling molecules in cancer. In fact, we propose to draw awareness to highlight the Golgi-localized regulatory systems as potential targets in cancer therapy.

GPRC5A: An emerging prognostic biomarker for predicting malignancy of Pancreatic Cancer based on bioinformatics analysis

Background: Pancreatic cancer (PaCa) is a highly lethal malignancy. The treatment options for PaCa lack efficacy. The study aimed to explore the molecular biomarkers for predicting survival of PaCa and identify the potential carcinogenic mechanisms of the selected gene. Methods: Based on public databases of PaCa, differentially expressed genes (DEGs) were identified using Networkanalyst. Survival analyses were exerted on GEPIA. Oncomine and The Human Protein Atlas were used for verifying the expression on mRNA and protein levels. Enrichment analyses were generated on Metascape and gene set enrichment analysis (GSEA). Univariate analyses were performed to determine the clinical factors associated with the expression of GPRC5A. Results: GPRC5A was identified as the most valuable gene in predicting survival of PaCa patients. Patients with high expression of GPRC5A showed larger tumor size, higher TNM stages, higher tumor grade, and more positive resection margin. In mutant KRAS, TP53, CDKN2A and SMAD4 group, the expression of GPRC5A was higher than non-mutant group. Mechanistically, GPRC5A may promote metastasis of PaCa mainly via regulating epithelial-mesenchymal transition (EMT) and neuroactive ligand-receptor interaction. Conclusion: GPRC5A may act as an oncogene in the progression of PaCa and could be a prognostic biomarker in predicting survival of PaCa.

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.

Crystalline silica particles cause rapid NLRP3-dependent mitochondrial depolarization and DNA damage in airway epithelial cells

BACKGROUND

Respirable crystalline silica causes lung carcinomas and many thousand future cancer cases are expected in e.g. Europe. Critical questions are how silica causes genotoxicity in the respiratory epithelium and if new cases can be avoided by lowered permissible exposure levels. In this study we investigate early DNA damaging effects of low doses of silica particles in respiratory epithelial cells in vitro and in vivo in an effort to understand low-dose carcinogenic effects of silica particles.

RESULTS

We find DNA damage accumulation already after 5-10 min exposure to low doses (5 μg/cm²) of silica particles (Min-U-Sil 5) in vitro. DNA damage was documented as increased levels of γH2AX, pCHK2, by Comet assay, AIM2 induction, and by increased DNA repair (non-homologous end joining) signaling. The DNA damage response (DDR) was not related to increased ROS levels, but to a NLRP3-dependent mitochondrial depolarization. Particles in contact with the plasma membrane elicited a Ser198 phosphorylation of NLRP3, co-localization of NLRP3 to mitochondria and depolarization. FCCP, a mitochondrial uncoupler, as well as overexpressed NLRP3 mimicked the silica-induced depolarization and the DNA damage response. A single inhalation of 25 μg silica particles gave a similar rapid DDR in mouse lung. Biomarkers (CC10 and GPRC5A) indicated an involvement of respiratory epithelial cells.

CONCLUSIONS

Our findings demonstrate a novel mode of action (MOA) for silica-induced DNA damage and mutagenic double strand breaks in airway epithelial cells. This MOA seems independent of particle uptake and of an involvement of macrophages. Our study might help defining models for estimating exposure levels without DNA damaging effects.

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.

Identification and characterization of human PEIG-1/GPRC5A as a 12-O-tetradecanoyl phorbol-13-acetate (TPA) and PKC-induced gene

Homo sapiens orphan G protein-coupling receptor PEIG-1 was first cloned and characterized by applying differential display to T84 colonic carcinoma cells incubated in the presence of phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) (GenBank AF506289.1). Later, Lotan's laboratory found the same gene product in response to retinoic acid analogues, naming it with the symbol RAIG1. Now the official HGNC symbol is GPRC5A. Here, we report the extension of its original cDNA fragment towards the 5' and 3' end. In addition, we show that TPA (100 ng/ml, 162 nM) strongly stimulated GPRC5A mRNA in T84 colonic carcinoma cells, with maximal expression at 4 h and 100 ng/ml (162 nM). Western blots showed several bands between 35 and 50 kDa, responding to TPA stimulation. Confocal microscopy confirmed its TPA upregulation and the location in the plasma membrane. The PKC inhibitor Gö 6983 (10 μM), and the Ca²⁺ chelator BAPTA-AM (150 μM), strongly inhibited its TPA induced upregulation. The PKA inhibitor H-89 (10 μM), and the MEK1/2 inhibitor U0126 (10 μM), also produced a significant reduction in the TPA response (~50%). The SGK1 inhibitor GSK650394 stimulated GPRC5A basal levels at low doses and inhibit its TPA-induced expression at concentrations ≥10 μM. The IL-1β autocrine loop and downstream signalling did not affect its expression. In conclusion, RAIG1/RAI3/GPRC5A corresponds to the originally reported PEIG-1/TIG1; the inhibition observed in the presence of Gö 6983, BAPTA and U0126, suggests that its TPA-induced upregulation is mediated through a PKC/Ca²⁺ →MEK1/2 signalling axis. PKA and SGK1 kinases are also involved in its TPA-induced upregulation.

Cucurbitacin B inhibits gastric cancer progression by suppressing STAT3 activity

Signal transducer and activator of transcription 3 (STAT3) is expressed aberrantly in multiple tumors, including gastric cancer (GC). STAT3 overexpression and excessive activation have been confirmed to play vital roles in tumorigenesis. Cucurbitacin B (CuB) is a natural product with potent anti-cancer activities in solid tumors. Here, we systematically studied the underlying molecular mechanisms of CuB inhibition of GC both in vitro and in vivo. In GC cell lines, nanomolar concentrations of CuB decreased the phosphorylation of TYR-705 in STAT3 and suppressed STAT3 target gene expression, including c-Myc and Bcl-xL. Computational docking analysis showed that CuB interacts with the DNA-binding domain of STAT3 at several hydrophobic residues. In addition, pull-down experiments showed that CuB is a direct inhibitor of STAT3. CuB in combination with the conventional chemotherapy drug cisplatin exerted enhanced cytotoxicity in GC cells, possibly due to the potentiated inhibition of STAT3 activation. Moreover, a xenograft mouse model confirmed the therapeutic effect of CuB in vivo. These characteristics render CuB a promising candidate drug for further development in the design of new effective STAT3 inhibitors for treating GC.

PTGES/PGE2 signaling links immunosuppression and lung metastasis in Gprc5a-knockout mouse model

Chronic inflammation has been linked to promotion of tumorigenesis and metastasis in lung. However, due to lack of a relevant animal model for characterization, the underlying mechanism remains elusive. Lung tumor suppressor gene Gprc5a-knockout (ko) mice are susceptible to lung inflammation, tumorigenesis and metastasis, which resembles the pathological features in human patients. Here, we showed that PTGES/PGE2 signaling was highly associated with lung tumorigenesis and metastasis in Gprc5a-ko mice. Interestingly, Ptges-knockout in mouse lung tumor cells, although reduced their stemness and EMT-like features, still formed tumors and lung metastasis in immune-deficient nude mice, but not in immune-competent mice. This suggests that the major role of PTGES/PGE2 signaling in tumorigenicity and lung metastasis is through immunosuppression. Mechanistically, PTGES/PGE2 signaling intrinsically endows tumor cells resistant to T-cell cytotoxicity, and induces cytokines extrinsically for MDSC recruitment, which is crucial for suppression of T-cell immunity. Importantly, targeting PGE2 signaling in Gprc5a-ko mice by PTGES inhibitor suppressed MDSC recruitment, restored T cells, and significantly repressed lung metastasis. Thus, PTGES/PGE2 signaling links immunosuppression and metastasis in an inflammatory lung microenvironment of Gprc5a-ko mouse model.

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.

LNRRIL6, a novel long noncoding RNA, protects colorectal cancer cells by activating the IL-6-STAT3 pathway

Long noncoding RNAs (lncRNAs) are emerging as critical regulators of cancer. There is a comparable number of lncRNAs to protein‐coding genes, but the expression patterns, functions, and molecular mechanisms of most lncRNAs in colorectal cancer (CRC) remain unclear. In this study, we report the identification of a novel lncRNA, named long noncoding RNA regulating IL‐6 transcription (LNRRIL6), which is upregulated in CRC tissues and cell lines. Increased LNRRIL6 expression is associated with aggressive clinicopathological characteristics and poor prognosis of CRC patients. Functional experiments showed that enhanced expression of LNRRIL6 promotes CRC cell proliferation and survival in vitro and CRC tumor growth in vivo. Conversely, depletion of LNRRIL6 inhibits CRC cell proliferation and survival in vitro and CRC tumor growth in vivo. Mechanistically, we revealed that LNRRIL6 physically binds to the IL‐6 promoter, thereby increasing IL‐6 transcription, inducing IL‐6 autocrine signaling, and activating the IL‐6/STAT3 pathway. The expression of IL‐6 is positively associated with that of LNRRIL6 in CRC tissues. Blocking the IL‐6/STAT3 pathway using the FDA‐approved IL‐6‐receptor antagonist antibody, tocilizumab, abolished the oncogenic role of LNRRIL6 in CRC. Taken together, these findings identify a novel lncRNA, LNRRIL6, that promotes CRC cell survival through activation of the IL‐6/STAT3 pathway and suggest that LNRRIL6 may be a potential prognostic biomarker and therapeutic target for CRC.

GPRC5A facilitates cell proliferation through cell cycle regulation and correlates with bone metastasis in prostate cancer

The prognosis of patients with progressive prostate cancers that are hormone refractory and/or have bone metastasis is poor. Multiple therapeutic targets to improve prostate cancer patient survival have been investigated, including orphan GPCRs. In our study, we identified G Protein-Coupled Receptor Class C Group 5 Member A (GPRC5A) as a candidate therapeutic molecule using integrative gene expression analyses of registered data sets for prostate cancer cell lines. Kaplan-Meier analysis of TCGA data sets revealed that patients who have high GPRC5A expression had significantly shorter overall survival. PC3 prostate cancer cells with CRISPR/Cas9-mediated GPRC5A knockout exhibited significantly reduced cell proliferation both in vitro and in vivo. RNA-seq revealed that GPRC5A KO PC3 cells had dysregulated expression of cell cycle-related genes, leading to cell cycle arrest at the G2/M phase. Furthermore, the registered gene expression profile data set showed that the expression level of GPRC5A in original lesions of prostate cancer patients with bone metastasis was higher than that without bone metastasis. In fact, GPRC5A KO PC3 cells failed to establish bone metastasis in xenograft mice models. In addition, our clinical study revealed that GPRC5A expression levels in prostate cancer patient samples were significantly correlated with bone metastasis as well as the patient's Gleason score (GS). Combined assessment with the immunoreactivity of GPRC5A and GS displayed higher specificity for predicting the occurrence of bone metastasis. Together, our findings indicate that GPRC5A can be a possible therapeutic target and prognostic marker molecule for progressive prostate cancer.

Elevated levels of hsa_circ_006100 in gastric cancer promote cell growth and metastasis via miR-195/GPRC5A signalling

Objectives

Circular RNAs (circRNAs) are non‐coding RNAs, some of which are thought to be involved in gastric cancer development. Here, we examined the functions of circRNA hsa_circ_006100 in gastric cancer cells and an animal model of gastric cancer.

Materials and Methods

The expression of hsa_circ_006100, miR‐195 and various functional genes was determined by quantitative RT‐PCR. Cell viability, clone formation, apoptosis and cell migration/invasion abilities were analysed by the CCK‐8 assay, crystal violet staining, Hoechst staining and Transwell assay, respectively. A tumour model was established by subcutaneously injecting tumour cells into nude mice. Levels of protein expression were analysed by Western blotting and immunohistochemistry.

Results

A bioinformatics analysis showed that miR‐195 was negatively co‐expressed with hsa_circ_006100. Patients with a high hsa_circ_006100 level or low miR‐195 level had tumours with a high TNM stage, poor cellular differentiation and lymph node metastasis. miR‐195 was targeted and inhibited by hsa_circ_006100. Overexpression of hsa_circ_006100 enhanced cellular viability and proliferation, while miR‐195 suppressed hsa_circ_006100‐enhanced cell growth and induced apoptosis in MGC‐803 and AGS cells. Forced hsa_circ_006100 expression promoted the migration and invasion of MGC‐803 and AGS cells, while those activities were inhibited by miR‐195. Mechanistically, GPRC5A was predicted as a target of miR‐195 and was upregulated in gastric cancer. A miR‐195 inhibitor restored cell viability, proliferation, migration and invasion, and repressed apoptosis via GPRC5A. In vivo studies showed that knockdown of hsa_circ_006100 delayed tumour growth, reduced PCNA expression and upregulated miR‐195 and BCL‐2 expression which was restored by miR‐195 inhibition due to GPRC5A/EGFR signalling, and changed the EMT phenotype in vivo.

Conclusions

Hsa_circ_006100 functions as an oncogene in gastric cancer and exerts its effects via miR‐195/GPRC5A signalling.

The potential of retinoids for combination therapy of lung cancer: Updates and future directions

Lung cancer is the most common cancer-related death worldwide. Natural compounds have shown high biological and pharmaceutical relevance as anticancer agents. Retinoids are natural derivatives of vitamin A having many regulatory functions in the human body, including vision, cellular proliferation and differentiation, and activation of tumour suppressor genes. Retinoic acid (RA) is a highly active retinoid isoform with promising anti-lung cancer activity. The abnormal expression of retinoid receptors is associated with loss of anticancer activities and acquired resistance to RA in lung cancer. The preclinical promise has not translated to the general clinical utility of retinoids for lung cancer patients, especially those with a history of smoking. Newer retinoid nano-formulations and the combinatorial use of retinoids has been associated with lower toxicity and more favorably efficacy in both the preclinical and clinical settings. Here, we highlight epidemiological and clinical therapeutic studies involving retinoids and lung cancer. We also discuss the biological actions of retinoids in lung cancer, which include effects on cancer stem cell differentiation, angiogenesis, metastasis, and proliferative. We suggest that the use of retinoids in combination with conventional and targeted anticancer agents will broaden the utility of these potent anticancer compounds in the lung cancer clinic.

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.

Current Trends in Cancer Nanotheranostics: Metallic, Polymeric, and Lipid-Based Systems

Theranostics has emerged in recent years to provide an efficient and safer alternative in cancer management. This review presents an updated description of nanotheranostic formulations under development for skin cancer (including melanoma), head and neck, thyroid, breast, gynecologic, prostate, and colon cancers, brain-related cancer, and hepatocellular carcinoma. With this focus, we appraised the clinical advantages and drawbacks of metallic, polymeric, and lipid-based nanosystems, such as low invasiveness, low toxicity to the surrounding healthy tissues, high precision, deeper tissue penetration, and dosage adjustment in a real-time setting. Particularly recognizing the increased complexity and multimodality in this area, multifunctional hybrid nanoparticles, comprising different nanomaterials and functionalized with targeting moieties and/or anticancer drugs, present the best characteristics for theranostics. Several examples, focusing on their design, composition, imaging and treatment modalities, and in vitro and in vivo characterization, are detailed herein. Briefly, all studies followed a common trend in the design of these theranostics modalities, such as the use of materials and/or drugs that share both inherent imaging (e.g., contrast agents) and therapeutic properties (e.g., heating or production reactive oxygen species). This rationale allows one to apparently overcome the heterogeneity, complexity, and harsh conditions of tumor microenvironments, leading to the development of successful targeted therapies.

Cholinergic Signaling via Muscarinic Receptors Directly and Indirectly Suppresses Pancreatic Tumorigenesis and Cancer Stemness

In many solid tumors, parasympathetic input is provided by the vagus nerve, which has been shown to modulate tumor growth. However, whether cholinergic signaling directly regulates progression of pancreatic ductal adenocarcinoma (PDAC) has not been defined. Here, we found that subdiaphragmatic vagotomy in LSL-Kras +/G12D;Pdx1-Cre (KC) mice accelerated PDAC development, whereas treatment with the systemic muscarinic agonist bethanechol restored the normal KC phenotype, thereby suppressing the accelerated tumorigenesis caused by vagotomy. In LSL-Kras +/G12D;LSL-Trp53 +/R172H;Pdx1-Cre mice with established PDAC, bethanechol significantly extended survival. These effects were mediated in part through CHRM1, which inhibited downstream MAPK/EGFR and PI3K/AKT pathways in PDAC cells. Enhanced cholinergic signaling led to a suppression of the cancer stem cell (CSC) compartment, CD11b+ myeloid cells, TNFα levels, and metastatic growth in the liver. Therefore, these data suggest that cholinergic signaling directly and indirectly suppresses growth of PDAC cells, and therapies that stimulate muscarinic receptors may be useful in the treatment of PDAC.Significance: Subdiaphragmatic vagotomy or Chrm1 knockout accelerates pancreatic tumorigenesis, in part via expansion of the CSC compartment. Systemic administration of a muscarinic agonist suppresses tumorigenesis through MAPK and PI3K/AKT signaling, in early stages of tumor growth and in more advanced, metastatic disease. Therefore, CHRM1 may represent a potentially attractive therapeutic target. Cancer Discov; 8(11); 1458-73. ©2018 AACR. This article is highlighted in the In This Issue feature, p. 1333.

Long-chain acyl-CoA synthetase 1 interacts with key proteins that activate and direct fatty acids into niche hepatic pathways

Fatty acid channeling into oxidation or storage modes depends on physiological conditions and hormonal signaling. However, the directionality of this channeling may also depend on the association of each of the five acyl-CoA synthetase isoforms with specific protein partners. Long-chain acyl-CoA synthetases (ACSLs) catalyze the conversion of long-chain fatty acids to fatty acyl-CoAs, which are then either oxidized or used in esterification reactions. In highly oxidative tissues, ACSL1 is located on the outer mitochondrial membrane (OMM) and directs fatty acids into mitochondria for β-oxidation. In the liver, however, about 50% of ACSL1 is located on the endoplasmic reticulum (ER) where its metabolic function is unclear. Because hepatic fatty acid partitioning is likely to require the interaction of ACSL1 with other specific proteins, we used an unbiased protein interaction technique, BioID, to discover ACSL1-binding partners in hepatocytes. We targeted ACSL1 either to the ER or to the OMM of Hepa 1-6 cells as a fusion protein with the Escherichia coli biotin ligase, BirA*. Proteomic analysis identified 98 proteins that specifically interacted with ACSL1 at the ER, 55 at the OMM, and 43 common to both subcellular locations. We found subsets of peroxisomal and lipid droplet proteins, tethering proteins, and vesicle proteins, uncovering a dynamic role for ACSL1 in organelle and lipid droplet interactions. Proteins involved in lipid metabolism were also identified, including acyl-CoA-binding proteins and ceramide synthase isoforms 2 and 5. Our results provide fundamental and detailed insights into protein interaction networks that control fatty acid metabolism.

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.

Depletion of Gprc5a Promotes Development of Diabetic Nephropathy

Background Renal glomeruli are the primary target of injury in diabetic nephropathy (DN), and the glomerular podocyte has a key role in disease progression.Methods To identify potential novel therapeutic targets for DN, we performed high-throughput molecular profiling of G protein-coupled receptors (GPCRs) using human glomeruli.Results We identified an orphan GPCR, Gprc5a, as a highly podocyte-specific gene, the expression of which was significantly downregulated in glomeruli of patients with DN compared with those without DN. Inactivation of Gprc5a in mice resulted in thickening of the glomerular basement membrane and activation of mesangial cells, which are two hallmark features of DN in humans. Compared with wild-type mice, Gprc5a-deficient animals demonstrated increased albuminuria and more severe histologic changes after induction of diabetes with streptozotocin. Mechanistically, Gprc5a modulated TGF-β signaling and activation of the EGF receptor in cultured podocytes.Conclusions Gprc5a has an important role in the pathogenesis of DN, and further study of the podocyte-specific signaling activity of this protein is warranted.

Arctigenin inhibits STAT3 and exhibits anticancer potential in human triple-negative breast cancer therapy

Triple-negative breast cancers (TNBCs) are the most aggressive and hard-to-treat breast tumors with poor prognosis, and exploration for novel therapeutic drugs is impending. Arctigenin (Atn), a bioactive lignan isolated from seeds of Arctium lappa L, has been reported to inhibit many cancer types; however, the effect of Atn on TNBC remains unclear. In this study, we demonstrated that Atn decreased proliferation, and induced apoptosis in TNBC cells. Furthermore, we explored the underlying mechanism of Atn inhibition on TNBC cells. Computational docking and affinity assay showed that Atn bound to the SH2 domain of STAT3. Atn inhibited STAT3 binding to genomic DNA by disrupting hydrogen bond linking between DNA and STAT3. In addition, Atn augmented Taxotere^®-induced TNBC cell cytotoxicity. TNBC xenograft tests also confirmed the antitumor effect of Atn in vivo. These characteristics render Atn as a promising candidate drug for further development and for designing new effective STAT3 inhibitors.

S100A4 promotes lung tumor development through β-catenin pathway-mediated autophagy inhibition

Autophagy has emerged as a critical pathway in tumor development. S100A4 plays important roles in tumor metastasis, but its role in regulating autophagy has not been well characterized. In this study, we found that S100A4 was significantly upregulated in lung adenocarcinoma tissues. Clinical investigation demonstrated that high expression level of S100A4 was associated with tumor size and advanced tumor grades of lung adenocarcinoma patients. Moreover, our results revealed that extracellular S100A4 or overexpression of S100A4 inhibited starvation-induced autophagy and promoted cell proliferation in lung cancer cells in vitro; whereas small interfering RNA (siRNA)-mediated suppression of S100A4 increased autophagy and reduced cell viability in both A549 and LLC cells. Additionally, S100A4 inhibited starvation-induced autophagy to promote tumor cell viability via the Wnt pathway. Increased expression of β-catenin consistently led to a decreased LC3-II protein abundance. Further, the inhibitory effect of S100A4 on autophagy and its promotion role in cell proliferation was abolished in A549 and LLC cells using the receptor for advanced glycation end products (RAGE)-specific inhibitor (FPS-ZM1). S100A4-deficient mice showed retarded tumor development. This effect was well correlated with increased expression of autophagy markers. Our findings demonstrate that S100A4 promotes lung tumor development through inhibiting autophagy in a β-catenin signaling and S100A4 receptor RAGE-dependent manner, which provides a novel mechanism of S100A4-associated promotion of tumor development.

The role and gene expression profile of SOCS3 in colorectal carcinoma

SOCS3 has been postulated to play a role in the occurrence and progression of malignancies. However, the relationship of SOCS3 with colorectal carcinoma remains poorly understood. The purpose of the study was to explore the role of SOCS3 in colorectal carcinoma and its underlying mechanisms. Protein and mRNA expression of SOCS3 in colorectal carcinoma and normal colorectal mucosa was detected using immunohistochemistry and real-time quantitative PCR. SOCS3 expression was significantly lower in colorectal carcinoma tissue than in normal colorectal mucosa, and was negatively correlated with tumor invasion depth, lymph node metastasis, differentiation degree, and TNM stage. A stably transfected colorectal carcinoma cell line (8348SOCS3) with high expression of SOCS3 was established. The effects of SOCS3 overexpression on the growth, proliferation, invasion and tumor formation of colorectal carcinoma cells were examined by CCK-8 assay, transwell method and tumorigenicity assays in nude mice. Then we found SOCS3 overexpression significantly decreased proliferation and invasion capability of 8348 cells in vitro and in vivo. Furthermore, the effect of SOCS3 overexpression on the gene expression profile of colorectal carcinoma cells was analyzed using human genome arrays. The results revealed 369 genes that were differentially expressed in 8348SOCS3 cells. 193 genes was significantly increased and 176 genes was significantly decreased. Bioinformatics analysis demonstrated that high SOCS3 expression affected multiple signaling pathways in colorectal carcinoma including TGF-β/Smads, NF-κB, and HIF-MAPK pathways. Especially for the TGF-β/Smads pathways, high SOCS3 expression could inhibit TGF-β1 expression and activate Smad4 expression. These data suggested that low expression of SOCS3 was associated with the occurrence and progression of colorectal carcinoma. SOCS3 protein may be a useful indicator for malignancy and prognosis of colorectal carcinoma and also a new target for gene therapy.

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.

Nuclear survivin promoted by acetylation is associated with the aggressive phenotype of oral squamous cell carcinoma

Defects in apoptotic pathway contribute to development and progression of oral cancer. Survivin, a member of the inhibitors of apoptosis protein (IAP) family, is increased in many types of cancers. However, it is unclear whether increased survivin is associated with oral squamous cell carcinomas (OSCC), and what mechanisms may involve in. In this study, we examined survivin expression in OSCC compared with normal oral tissues via immunohistochemical staining. The results showed that, not only total survivin is increased in OSCCs, but also the subcellular location of survivin is changed in OSCCs compared with normal oral tissues. In most of normal oral tissues, survivin staining was either negative, or cytoplasmic positive/nuclear negative; whereas in most of OSCC tissues, survivin staining was nuclear positive. Statistic analysis indicates that nuclear survivin, rather than total or cytoplasmic one, correlates with tumor TNM stage and differentiation grade. Consistently, in vitro analysis showed that survivin is in cytoplasm in normal human oral kinotinocyte (HOK) cells; whereas it is in nucleus in OSCC HN6 cells. Importantly, treatment of HOK cells with HDAC inhibitor Trichostatin A (TSA) induces survivin acetylation and promotes its nuclear localization. Moreover, nuclear survivin in OSCC cells was acetylated at K129 in its C-terminal, suggesting that the acetylation is important for nuclear location of survivin. Our study demonstrates that it is nuclear survivin, rather than total or cytoplasmic one, associates with TNM stage and tumor grade of OSCC. Thus, we propose nuclear survivin as a prognostic marker for the progression of OSCC.

Elevation of GPRC5A expression in colorectal cancer promotes tumor progression through VNN-1 induced oxidative stress

The clearance of oxidative stress compounds is critical for the protection of the organism from malignancy, but how this key physiological process is regulated is not fully understood. Here, we found that the expression of GPRC5A, a well-characterized tumor suppressor in lung cancer, was elevated in colorectal cancer tissues in patients. In both cancer cell lines and a colitis-associated cancer model in mice, we found that GPRC5A deficiency reduced cell proliferation and increased cell apoptosis as well as inhibited tumorigenesis in vivo. Through RNA-Seq transcriptome analysis, we identified oxidative stress associated pathways were dysregulated. Moreover, in GPRC5A deficient cells and mouse tissues, the oxidative agents were reduced partially due to increased glutathione (GSH) level. Mechanistically, GPRC5A regulates NF-κB mediated Vanin-1 expression which is the predominant enzyme for cysteamine generation. Administration of cystamine (the disulfide form of cysteamine) in GPRC5A deficient cell lines inhibited γ-GCS activity, leading to reduction of GSH level and increase of cell growth. Taken together, our studies suggest that GPRC5a is a potential biomarker for colon cancer and promotes tumorigenesis through stimulation of Vanin-1 expression and oxidative stress in colitis associated cancer. This study revealed an unexpected oncogenic role of GPRC5A in colorectal cancer suggesting there are complicated functional and molecular mechanism differences of this gene in distinct tissues.

Repression of GPRC5A is associated with activated STAT3, which contributes to tumor progression of head and neck squamous cell carcinoma

Background

G protein–coupled receptor family C group 5 member A (GPRC5A), a retinoic acid-inducible gene, is a lung tumor suppressor. Previously, we showed that repression of GPRC5A expression was associated with pathologic differentiation grade of oral squamous cell carcinomas (OSCC) and overexpression of GPRC5A gene inhibited the malignant phenotype in OSCC cells, suggesting that GPRC5A also functions as a tumor suppressor in oral cancer. However, the molecular mechanisms underlying GPRC5A deficiency in head and neck squamous cell carcinoma (HNSCC) are still unclear.

Methods

In this study, we used Western blot analysis and immunohistochemical (IHC) staining to investigate the expression of GPRC5A in both HNSCC cell lines and clinical samples. GPRC5A stable transfectants and their parental HNSCC cells were characterized for their biological activities in anchorage-independent growth.

Results

IHC analysis showed that, GPRC5A expression was high in normal tissue, but gradually decreased in oral leukoplakia, a precancerous stage, and greatly suppressed in primary cancer. Repression of GPRC5A was correlated with activated STAT3, which associates with aggressive clinicopathological features in HNSCC patients. Moreover, overexpression of GPRC5A suppressed IL-6-induced-STAT3 activation and inhibited anchorage-independent growth in HNSCC cells.

Conclusions

Repressed GPRC5A associates with increased tumor grade and activated STAT3, which may be used as a prognostic marker for tumor progression of HNSCC.

Defining stem cell dynamics and migration during wound healing in mouse skin epidermis

Wound healing is essential to repair the skin after injury. In the epidermis, distinct stem cells (SCs) populations contribute to wound healing. However, how SCs balance proliferation, differentiation and migration to repair a wound remains poorly understood. Here, we show the cellular and molecular mechanisms that regulate wound healing in mouse tail epidermis. Using a combination of proliferation kinetics experiments and molecular profiling, we identify the gene signatures associated with proliferation, differentiation and migration in different regions surrounding the wound. Functional experiments show that SC proliferation, migration and differentiation can be uncoupled during wound healing. Lineage tracing and quantitative clonal analysis reveal that, following wounding, progenitors divide more rapidly, but conserve their homoeostatic mode of division, leading to their rapid depletion, whereas SCs become active, giving rise to new progenitors that expand and repair the wound. These results have important implications for tissue regeneration, acute and chronic wound disorders.

Wound healing is essential to repair the skin after injury and distinct stem cells in the epidermis are known to contribute to the process. Here the authors perform molecular, functional and clonal analysis and reveal the individual contribution of stem cells coming from different epidermal compartments to the wound-healing process in mice.

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.

ACTL6A Is Co-Amplified with p63 in Squamous Cell Carcinoma to Drive YAP Activation, Regenerative Proliferation, and Poor Prognosis

Loss-of-function mutations in SWI/SNF chromatin-remodeling subunit genes are observed in many cancers, but an oncogenic role for SWI/SNF is not well established. Here, we reveal that ACTL6A, encoding an SWI/SNF subunit linked to stem cell and progenitor cell function, is frequently co-amplified and highly expressed together with the p53 family member p63 in head and neck squamous cell carcinoma (HNSCC). ACTL6A and p63 physically interact, cooperatively controlling a transcriptional program that promotes proliferation and suppresses differentiation, in part through activation of the Hippo-YAP pathway via regulators including WWC1. Ectopic ACTL6A/p63 expression promotes tumorigenesis, while ACTL6A expression and YAP activation are highly correlated in primary HNSCC and predict poor patient survival. Thus, ACTL6A and p63 collaborate as oncogenic drivers in HNSCC.

Epithelial neoplasia coincides with exacerbated injury and fibrotic response in the lungs of Gprc5a-knockout mice following silica exposure

Exposure to crystalline silica is suggested to increase the risk for a variety of lung diseases, including fibrosis and lung cancer. However, epidemiological evidences for the exposure-risk relationship are ambiguous and conflicting, and experimental study from a reliable animal model to explore the relationship is lacking. We reasoned that a mouse model that is sensitive to both lung injury and tumorigenesis would be appropriate to evaluate the exposure-risk relationship. Previously, we showed that, Gprc5a^−/− mice are susceptible to both lung tumorigenesis and endotoxin-induced acute lung injury. In this study, we investigated the biological consequences in Gprc5a^−/− mouse model following silica exposure. Intra-tracheal administration of fine silica particles in Gprc5a^−/− mice resulted in more severe lung injury and pulmonary inflammation than in wild-type mice. Moreover, an enhanced fibrogenic response, including EMT-like characteristics, was induced in the lungs of Gprc5a^−/− mice compared to those from wild-type ones. Importantly, increased hyperplasia or neoplasia coincided with silica-induced tissue injury and fibrogenic response in lungs from Gprc5a^−/− mice. Consistently, expression of MMP9, TGFβ1 and EGFR was significantly increased in lungs from silica-treated Gprc5a^−/− mice compared to those untreated or wild-type ones. These results suggest that, the process of tissue repair coincides with tissue damages; whereas persistent tissue damages leads to abnormal repair or neoplasia. Thus, silica-induced pulmonary inflammation and injury contribute to increased neoplasia development in lungs from Gprc5a^−/− mouse model.