Identification of novel GRM1 mutations and single nucleotide polymorphisms in prostate cancer cell lines and tissues

Metabotropic Glutamate Receptors Type 3 and 5 Feature the "NeuroTransmitter-type" of Glioblastoma: A Bioinformatic Approach

BACKGROUND

Glioblastoma (GBM) represents an aggressive and common tumor of the central nervous system. The prognosis of GBM is poor, and despite a refined genetic and molecular characterization, pharmacological treatment is largely suboptimal.

OBJECTIVE

Contribute to defining a therapeutic line in GBM targeting the mGlu3 receptor in line with the principles of precision medicine.

METHODS

Here, we performed a computational analysis focused on the expression of type 3 and 5 metabotropic glutamate receptor subtypes (mGlu3 and mGlu5, respectively) in high- and low-grade gliomas.

RESULTS

The analysis allowed the identification of a particular high-grade glioma type, characterized by a high expression level of both receptor subtypes and by other markers of excitatory and inhibitory neurotransmission. This so-called neurotransmitter-GBM (NT-GBM) also shows a distinct immunological, metabolic, and vascularization gene signature.

CONCLUSION

Our findings might lay the groundwork for a targeted therapy to be specifically applied to this putative novel type of GBM.

Genetic Variant in GRM1 Underlies Congenital Cerebellar Ataxia with No Obvious Intellectual Disability

Metabotropic glutamate receptor 1 (mGluR1) plays a crucial role in slow excitatory postsynaptic conductance, synapse formation, synaptic plasticity, and motor control. The GRM1 gene is expressed mainly in the brain, with the highest expression in the cerebellum. Mutations in the GRM1 gene have previously been known to cause autosomal recessive and autosomal dominant spinocerebellar ataxias. In this study, whole-exome sequencing of a patient from a family of Azerbaijani origin with a diagnosis of congenital cerebellar ataxia was performed, and a new homozygous missense mutation in the GRM1 gene was identified. The mutation leads to the homozygous amino acid substitution of p.Thr824Arg in an evolutionarily highly conserved region encoding the transmembrane domain 7, which is critical for ligand binding and modulating of receptor activity. This is the first report in which a mutation has been identified in the last transmembrane domain of the mGluR1, causing a congenital autosomal recessive form of cerebellar ataxia with no obvious intellectual disability. Additionally, we summarized all known presumable pathogenic genetic variants in the GRM1 gene to date. We demonstrated that multiple rare variants in the GRM1 underlie a broad diversity of clinical neurological and behavioral phenotypes depending on the nature and protein topology of the mutation.

Implications of a Neuronal Receptor Family, Metabotropic Glutamate Receptors, in Cancer Development and Progression

Cancer is the second leading cause of death, and incidences are increasing globally. Simply defined, cancer is the uncontrolled proliferation of a cell, and depending on the tissue of origin, the cancer etiology, biology, progression, prognosis, and treatment will differ. Carcinogenesis and its progression are associated with genetic factors that can either be inherited and/or acquired and are classified as an oncogene or tumor suppressor. Many of these genetic factors converge on common signaling pathway(s), such as the MAPK and PI3K/AKT pathways. In this review, we will focus on the metabotropic glutamate receptor (mGluR) family, an upstream protein that transmits extracellular signals into the cell and has been shown to regulate many aspects of tumor development and progression. We explore the involvement of members of this receptor family in various cancers that include breast cancer, colorectal cancer, glioma, kidney cancer, melanoma, oral cancer, osteosarcoma, pancreatic cancer, prostate cancer, and T-cell cancers. Intriguingly, depending on the member, mGluRs can either be classified as oncogenes or tumor suppressors, although in general most act as an oncogene. The extensive work done to elucidate the role of mGluRs in various cancers suggests that it might be a viable strategy to therapeutically target glutamatergic signaling.

Therapeutic and prognostic potential of GPCRs in prostate cancer from multi-omics landscape

Prostate cancer (PRAD) is a common and fatal malignancy. It is difficult to manage clinically due to drug resistance and poor prognosis, thus creating an urgent need for novel therapeutic targets and prognostic biomarkers. Although G protein-coupled receptors (GPCRs) have been most attractive for drug development, there have been lack of an exhaustive assessment on GPCRs in PRAD like their molecular features, prognostic and therapeutic values. To close this gap, we herein systematically investigate multi-omics profiling for GPCRs in the primary PRAD by analyzing somatic mutations, somatic copy-number alterations (SCNAs), DNA methylation and mRNA expression. GPCRs exhibit low expression levels and mutation frequencies while SCNAs are more prevalent. 46 and 255 disease-related GPCRs are identified by the mRNA expression and DNA methylation analysis, respectively, complementing information lack in the genome analysis. In addition, the genomic alterations do not exhibit an observable correlation with the GPCR expression, reflecting the complex regulatory processes from DNA to RNA. Conversely, a tight association is observed between the DNA methylation and mRNA expression. The virtual screening and molecular dynamics simulation further identify four potential drugs in repositioning to PRAD. The combination of 3 clinical characteristics and 26 GPCR molecular features revealed by the transcriptome and genome exhibit good performance in predicting progression-free survival in patients with the primary PRAD, providing candidates as new biomarkers. These observations from the multi-omics analysis on GPCRs provide new insights into the underlying mechanism of primary PRAD and potential of GPCRs in developing therapeutic strategies on PRAD.

Glutamatergic system components as potential biomarkers and therapeutic targets in cancer in non-neural organs

Glutamate is one of the most abundant amino acids in the blood. Besides its role as a neurotransmitter in the brain, it is a key substrate in several metabolic pathways and a primary messenger that acts through its receptors outside the central nervous system (CNS). The two main types of glutamate receptors, ionotropic and metabotropic, are well characterized in CNS and have been recently analyzed for their roles in non-neural organs. Glutamate receptor expression may be particularly important for tumor growth in organs with high concentrations of glutamate and might also influence the propensity of such tumors to set metastases in glutamate-rich organs, such as the liver. The study of glutamate transporters has also acquired relevance in the physiology and pathologies outside the CNS, especially in the field of cancer research. In this review, we address the recent findings about the expression of glutamatergic system components, such as receptors and transporters, their role in the physiology and pathology of cancer in non-neural organs, and their possible use as biomarkers and therapeutic targets.

circ‑Grm1 promotes pulmonary artery smooth muscle cell proliferation and migration via suppression of GRM1 expression by FUS

Pulmonary arterial hypertension is a progressive and fatal disease. Recent studies suggest that circular RNA (circRNAs/circs) can regulate various biological processes, including cell proliferation. Therefore, it is possible that circRNA may have important roles in pulmonary artery smooth muscle cell proliferation in hypoxic pulmonary hypertension (HPH). The aim of the present study was to determine the role and mechanism of circRNA‑glutamate metabotropic receptor 1 (circ‑Grm1; mmu_circ_0001907) in pulmonary artery smooth muscle cell (PASMC) proliferation and migration in HPH. High‑throughput transcriptome sequencing was used to screen circRNAs and targeted genes involved in HPH. Cell Counting Kit‑8 (CCK‑8), 5‑ethynyl‑2‑deoxyuridine and wound healing assays were employed to assess cell viability and migration. Reverse transcription‑quantitative PCR and western blotting were used to detect target gene expression in different groups. Bioinformatical approaches were used to predict the interaction probabilities of circ‑Grm1 and Grm1 with FUS RNA binding protein (FUS). The interactions of circ‑Grm1, Grm1 and FUS were evaluated using RNA silencing and RNA immunoprecipitation assays. The results demonstrated that circ‑Grm1 was upregulated in hypoxic PASMCs. Further experiments revealed that the knockdown of circ‑Grm1 could suppress the proliferation and migration of hypoxic PASMCs. Transcriptome sequencing revealed that Grm1 could be the target gene of circ‑Grm1. It was found that circ‑Grm1 could competitively bind to FUS and consequently downregulate Grm1. Moreover, Grm1 could inhibit the function of circ‑Grm1 by promoting the proliferative and migratory abilities of hypoxic PASMCs. The results also demonstrated that circ‑Grm1 influenced the biological functions of PASMCs via the Rap1/ERK pathway by regulating Grm1. Overall, the current results suggested that circ‑Grm1 was associated with HPH and promoted the proliferation and migration of PASMCs via suppression of Grm1 expression through FUS.

Nonhomologous end-joining repair is likely involved in the repair of double-stranded DNA breaks induced by riluzole in melanoma cells

Our group described the oncogenic potential of a normal neuronal receptor, metabotropic glutamate receptor 1 (GRM1/mGluR1, gene/protein), when aberrantly expressed in melanocytes led to cell transformation in vitro and spontaneous metastatic tumors in vivo. Earlier, we demonstrated the accumulation of phosphorylated histone H2AX (γH2AX), a marker for DNA damage when mGluR1-expressing melanoma cells were treated with a functional inhibitor, riluzole. The precise mechanisms on how riluzole induces DNA damage in these cells are unknown. In an attempt to begin to identify possible DNA repair pathways that may be involved in riluzole-induced DNA damage, we took advantage of specific inhibitors to two well-known DNA repair pathways, homologous recombination and nonhomologous end joining (NHEJ) repair pathways. Using flow cytometry and a fluorescent antibody to γH2AX, our results demonstrate that NHEJ is likely to be the preferred DNA repair pathway to restore DNA double-stranded breaks induced by riluzole in mGluR1-expressing melanoma cells.

Riluzole induces AR degradation via endoplasmic reticulum stress pathway in androgen-dependent and castration-resistant prostate cancer cells

BACKGROUND

Prostate cancer (PCa) is diagnosed at the highest rate of all non-cutaneous male cancers in the United States. The androgen-dependent (AD) transcription factor, androgen receptor (AR), drives PCa-but inhibiting AR or androgen biosynthesis induces remission for only a short time. At which point, patients acquire more aggressive castration-resistant (CR) disease with re-activated AR-dependent signaling. To combat treatment resistance, down-regulating AR protein expression has been considered as a potential treatment strategy for CR-PCa.

METHODS

AD- and CR-PCa cell lines were treated with the well-tolerated FDA-approved oral medicine, riluzole. Expression of full-length or wild-type AR (AR-FL) and constitutively active AR-splice variant 7 (AR-V7) was assessed by immunoblotting. AR-FL/AR-V7 activity was measured using qRT-PCR of AR-target genes. Cytoplasmic [Ca²⁺ ] levels were measured using a fluorescent Ca²⁺ indicator microplate assay. Markers of the endoplasmic reticulum stress (ERS) pathway and autophagy were assessed by immunoblotting. Direct interaction between AR and selective autophagy receptor p62 was demonstrated by co-immunoprecipitation.

RESULTS

We demonstrate that riluzole downregulates AR-FL, mutant ARs, and AR-V7 proteins expression by protein degradation through ERS pathway and selective autophagy. Riluzole also significantly inhibited AR transcription activity by decreasing its target genes expression (PSA, TMPRSS2, and KLK2).

CONCLUSIONS

We provide key mechanistic insights by which riluzole exerts its anti-tumorigenic effects and induces AR protein degradation via ERS pathways. Our findings support the potential utility of riluzole for treatment of PCa.

Inhibition of metabotropic glutamate receptor 5 facilitates hypoxia-induced glioma cell death

Glioma is a primary brain tumor with high frequency and dismal prognosis. As there is no permanent cure available, identifying new therapy or mediator to augment the effectiveness of existing therapy is urgently needed. In the current study we tested the effect of group I metabotropic glutamate receptors (mGluRs): mGluR1 and mGluR5 on the viability of glioma cell lines. We analyzed cell viability using lactate dehydrogenase (LDH) release assay and evaluated apoptosis by propidium iodide (PI) staining. We used qPCR to evaluate change in mitochondrial gene expression and Western blot to evaluate the phosphorylation of Akt and ERK. Inhibition of mGluR5 by a selective antagonist MPEP under hypoxia promoted cell death, and induced expression of mitochondrial oxidative function related genes, with concurrent lowering of AKT phosphorylation level in glioma cell lines. Akt activation reversed mGluR5 inhibition on hypoxia-induced glioma cell death. These results suggest mGluR5 as a potential therapeutic target for hypoxic tumors such as malignant glioma.

Metabotropic glutamate receptors as a new therapeutic target for malignant gliomas

Metabotropic glutamate receptors (mGluR) are predominantly involved in maintenance of cellular homeostasis of central nervous system. However, evidences have suggested other roles of mGluR in human tumors. Aberrant mGluR signaling has been shown to participate in transformation and maintenance of various cancer types, including malignant brain tumors. This review intends to summarize recent findings regarding the involvement of mGluR-mediated intracellular signaling pathways in progression, aggressiveness, and recurrence of malignant gliomas, mainly glioblastomas (GBM), highlighting the potential therapeutic applications of mGluR ligands. In addition to the growing number of studies reporting mGluR gene or protein expression in glioma samples (resections, lineages, and primary cultures), pharmacological blockade in vitro of mGluR1 and mGluR3 by selective ligands has been shown to be anti-proliferative and anti-migratory, decreasing activation of MAPK and PI3K pathways. In addition, mGluR3 antagonists promoted astroglial differentiation of GBM cells and also enabled cytotoxic action of temozolomide (TMZ). mGluR3-dependent TMZ toxicity was supported by increasing levels of MGMT transcripts through an intracellular signaling pathway that sequentially involves PI3K and NF-κB. Further, continuous pharmacological blockade of mGluR1 and mGluR3 have been shown to reduced growth of GBM tumor in two independent in vivo xenograft models. In parallel, low levels of mGluR3 mRNA in GBM resections may be a predictor for long survival rate of patients. Since several Phase I, II and III clinical trials are being performed using group I and II mGluR modulators, there is a strong scientifically-based rationale for testing mGluR antagonists as an adjuvant therapy for malignant brain tumors.

Computational Identification of Novel Stage-Specific Biomarkers in Colorectal Cancer Progression

It is well-known that the conversion of normal colon epithelium to adenoma and then to carcinoma stems from acquired molecular changes in the genome. The genetic basis of colorectal cancer has been elucidated to a certain extent, and much remains to be known about the identity of specific cancer genes that are associated with the advancement of colorectal cancer from one stage to the next. Here in this study we attempted to identify novel cancer genes that could underlie the stage-specific progression and metastasis of colorectal cancer. We conducted a stage-based meta-analysis of the voluminous tumor genome-sequencing data and mined using multiple approaches for novel genes driving the progression to stage-II, stage-III and stage-IV colorectal cancer. The consensus of these driver genes seeded the construction of stage-specific networks, which were then analyzed for the centrality of genes, clustering of subnetworks, and enrichment of gene-ontology processes. Our study identified three novel driver genes as hubs for stage-II progression: DYNC1H1, GRIN2A, GRM1. Four novel driver genes were identified as hubs for stage-III progression: IGF1R, CPS1, SPTA1, DSP. Three novel driver genes were identified as hubs for stage-IV progression: GSK3B, GGT1, EIF2B5. We also identified several non-driver genes that appeared to underscore the progression of colorectal cancer. Our study yielded potential diagnostic biomarkers for colorectal cancer as well as novel stage-specific drug targets for rational intervention. Our methodology is extendable to the analysis of other types of cancer to fill the gaps in our knowledge.

Metabotropic glutamate receptors in cancer

Metabotropic glutamate receptors (mGluRs) are widely known for their roles in synaptic signaling. However, accumulating evidence suggests roles of mGluRs in human malignancies in addition to synaptic transmission. Somatic cell homeostasis presents intriguing possibilities of mGluRs and glutamate signaling as novel targets for human cancers. More recently, aberrant glutamate signaling has been shown to participate in the transformation and maintenance of various cancer types, including glioma, melanoma skin cancer, breast cancer, and prostate cancer, indicating that genes encoding mGluRs, GRMs, can function as oncogenes. Here, we provide a review on the interactions of mGluRs and their ligand, glutamate, in processes that promote the growth of tumors of neuronal and non-neuronal origins. Further, we discuss the evolution of riluzole, a glutamate release inhibitor approved for amyotrophic lateral sclerosis (ALS), but now fashioned as an mGluR1 inhibitor for melanoma therapy and as a radio-sensitizer for tumors that have metastasized to the brain. With the success of riluzole, it is not far-fetched to believe that other drugs that may act directly or indirectly on other mGluRs can be beneficial for multiple applications. This article is part of the Special Issue entitled 'Metabotropic Glutamate Receptors, 5 years on'.

[The cancer paradigm in pulmonary arterial hypertension: towards anti-remodeling therapies targeting metabolic dysfunction?]

Pulmonary arterial hypertension (PAH) is a rare, complex and multifactorial disease in which pulmonary vascular remodeling plays a major role ending in right heart failure and death. Current specific therapies of PAH that mainly target the vasoconstriction/vasodilatation imbalance are not curative. Bi-pulmonary transplantation remains the only option in patients resistant to current therapies. It is thus crucial to identify novel vascular anti-remodeling therapeutic targets. This remodeling displays several properties of cancer cells, especially overproliferation and apoptosis resistance of pulmonary vascular cells, hallmarks of cancer related to the metabolic shift known as the "Warburg effect". The latter is characterized by a shift of ATP production, from oxidative phosphorylation to low rate aerobic glycolysis. In compensation, the cancer cells exhibit exacerbated glutaminolysis thus resulting in glutamine addiction, necessary to their overproliferation. Glutamine intake results in glutamate production, a molecule at the crossroads of energy metabolism and cancer cell communication, thus contributing to cell proliferation. Accordingly, therapeutic strategies targeting glutamate production, its release into the extracellular space and its membrane receptors have been suggested to treat different types of cancers, not only in the central nervous system but also in the periphery. We propose that similar strategies targeting glutamatergic signaling may be considered in PAH, especially as they could affect not only the vascular remodeling but also the right heart hypertrophy known to involve the glutaminolysis pathway. Ongoing studies aim to characterize the involvement of the glutamate pathway and its receptors in vascular remodeling, and the therapeutic potential of specific molecules targeting this pathway.