Linking γ-aminobutyric acid A receptor to epidermal growth factor receptor pathways activation in human prostate cancer

Remimazolam induced cytotoxicity mediated through multiple stress pathways and acted synergistically with tyrosine kinase inhibitors in hepatocellular carcinoma

The primary treatment for hepatocellular carcinoma (HCC) involves surgical removal of the primary tumor, but this creates a favorable environment for the proliferation and spread of residual and circulating cancer cells. The development of remimazolam-based balanced anesthesia is crucial for future antitumor applications. It is important to understand the mechanisms of cytotoxicity for HCC in detail.

We performed cell viability analysis, western blotting analysis, reverse transcription-polymerase chain reaction analysis, and flow cytometry analysis in two HCC cell lines, HepG2 and Hep3B cells.

Our data demonstrated that remimazolam induced cytotoxicity by suppressing cell proliferation, inhibiting G1 phase progression, and affecting mitochondrial reactive oxygen species (ROS) levels, leading to apoptosis, DNA damage, cytosolic ROS elevation, lipid peroxidation, autophagy, mitochondrial depolarization, and endoplasmic reticulum stress. Inhibitors of apoptosis, autophagic cell death, and ferroptosis and a ROS scavenger failed to rescue cell death caused by remimazolam besylate. Our combination index revealed that remimazolam besylate has the potential to act as a sensitizer for targeted tyrosine kinase inhibitor therapy for HCC.

Our findings open up new possibilities for combinatory HCC therapy using remimazolam, leveraging its dual functional roles in surgery and drug therapy for liver cancers.

Ligand-gated ion channels as potential biomarkers for ADT-mediated cognitive decline in prostate cancer patients

Men with prostate cancer are at increased risk of developing cognitive decline by the use of second-generation androgen signaling inhibitors. To date, reliable and sensitive biomarkers that could distinguish men at high risk of cognitive dysfunction under androgen deprivation therapy (ADT) have not been characterized. We used high-throughput transcriptional profiling utilizing human prostate cancer cell culture models mimicking ADT, biomarker selection using minimal common oncology data elements-cytoscape, and bioinformatic analyses employing Advaita® iPathwayGuide and DisGeNET for identification of disease-related gene associations. Validation analysis of genes was performed on brain neuronal and glial cells by quantitative real-time polymerase chain reaction assay. Our systematic analysis of androgen deprivation-associated genes involved multiple biological processes, including neuroactive ligand-receptor interaction, axon guidance, cytokine-cytokine receptor interaction, and metabolic and cancer signaling pathways. Genes associated with neuroreceptor ligand interaction, including gamma-aminobutyric acid (GABA) A and B receptors and nuclear core proteins, were identified as top upstream regulators. Functional enrichment and protein-protein interaction network analysis highlighted the role of ligand-gated ion channels (LGICs) and their receptors in cognitive dysfunction. Gene-disease association assigned forgetfulness, intellectual disability, visuospatial deficit, bipolar disorder, and other neurocognitive impairment with upregulation of type-1 angiotensin II receptor, brain-derived neurotrophic factor, GABA type B receptor subunit 2 (GABBR2), GABRA3, GABRA5, GABRB1, glycine receptor beta, glutamate ionotropic receptor N-methyl-D-aspartate receptor (NMDA) type subunit 1, glutamate ionotropic receptor NMDA type subunit 2D, 5-hydroxytryptamine receptor 1D, interferon beta 1, and nuclear receptor subfamily 3 group C member 1 as top differentially expressed genes. Validation studies of brain glial cells, neurons, and patients on ADT demonstrated the association of these genes with cognitive decline. Our findings highlight LGICs as potential biomarkers for ADT-mediated cognitive decline. Further validation of these biomarkers may lead to future practical clinical use.

Phytochemical Modulation of Ion Channels in Oncologic Symptomatology and Treatment

Modern chemotherapies offer a broad approach to cancer treatment but eliminate both cancer and non-cancer cells indiscriminately and, thus, are associated with a host of side effects. Advances in precision oncology have brought about new targeted therapeutics, albeit mostly limited to a subset of patients with an actionable mutation. They too come with side effects and, ultimately, 'self-resistance' to the treatment. There is recent interest in the modulation of ion channels, transmembrane proteins that regulate the flow of electrically charged molecules in and out of cells, as an approach to aid treatment of cancer. Phytochemicals have been shown to act on ion channels with high specificity regardless of the tumor's genetic profile. This paper explores the use of phytochemicals in cancer symptom management and treatment.

Integrated analysis identifies GABRB3 as a biomarker in prostate cancer

BACKGROUND

Treatment failure following androgen deprivation therapy (ADT) presents a significant challenge in the management of advanced prostate cancer. Thus, understanding the genetic factors influencing this process could facilitate the development of personalized treatments and innovative therapeutic strategies. The phosphoinositide 3-kinase (PI3K)/AKT signaling pathway plays a pivotal role in controlling cell growth and tumorigenesis. We hypothesized that genetic variants within this pathway may affect the clinical outcomes of patients undergoing ADT for prostate cancer.

METHODS

We genotyped 399 single-nucleotide polymorphisms (SNPs) across 28 core PI3K/AKT pathway genes in a cohort of 630 patients with prostate cancer undergoing ADT. We assessed the potential association of the SNPs with patient survival. Functional analyses of the implicated genes were also performed to evaluate their effects on prostate cancer.

RESULTS

After multivariate Cox regression analysis and multiple testing correction, GABRB3 rs12591845 exhibited the most significant association with both overall and cancer-specific survivals (P < 0.003). A comprehensive pooled analysis of 16 independent gene expression datasets revealed elevated expression of GABRB3 in prostate cancer tissues compared to that in normal tissues (P < 0.001). Furthermore, gene set enrichment analysis unveiled differential enrichment of pathways such as myogenesis, interferon γ and α responses, and the MYC proto-oncogene pathway in tumors with elevated GABRB3 expression, implying a role for GABRB3 in prostate cancer.

CONCLUSION

Our results suggest that rs12591845 could potentially serve as a valuable prognostic indicator for patients undergoing ADT. The potential role of GABRB3 in promoting prostate tumorigenesis is also highlighted.

GABAergic signaling beyond synapses: an emerging target for cancer therapy

Traditionally, γ-aminobutyric acid (GABA) is best known for its role as a primary inhibitory neurotransmitter reducing neuronal excitability in the mammalian central nervous system (CNS), thereby producing calming effects. However, an emerging body of data now supports a function for GABA beyond neurotransmission as a potent factor regulating cancer cell growth and metastasis, as well as the antitumor immune response, by shaping the tumor microenvironment (TME). Here, we review the current knowledge on GABA's effects on the function of tumor cells, tumor-immune interactions, and the underlying molecular mechanisms. Since altered GABAergic signaling is now recognized as a feature of certain types of solid tumors, we also discuss the potential of repurposing existing GABAergic agents as a new class of anticancer therapy.

miR-31-3p functions as a tumor suppressor by directly targeting GABBR2 in prostate cancer

MicroRNAs are key regulators of gene expression in tumorigenesis. In this study, we investigated the tumor-suppressive function of miR-31-3p. Analysis of the Gene Expression Omnibus database revealed that the expression of miR-31-3p in prostate cancer tissues is lower than that in adjacent normal tissues from patients with prostate cancer. Moreover, miR-31-3p induces apoptosis in DU145, PC-3, and LNCap prostate cancer cells, while those transfected with miR-31-3p exhibit significantly decreased cell proliferation, migration, invasiveness, and tumor sphere-forming ability, as determined using the cell counting kit-8, transwell, and sphere-forming assays. Further analysis revealed that GABBR2 is a direct target of miR-31-3p. Within a DU145 xenograft murine model, intratumoral injection of a miR-31-3p mimic suppresses tumor growth. Taken together, the findings of this study suggest that miR-31-3p performs a novel tumor-suppressive function in prostate cancer and may represent a novel target for anti-prostate cancer miRNA therapeutics.

Propofol enhances stem-like properties of glioma via GABAAR-dependent Src modulation of ZDHHC5-EZH2 palmitoylation mechanism

Background

Propofol is a commonly used anesthetic. However, its effects on glioma growth and recurrence remain largely unknown.

Methods

The effect of propofol on glioma growth was demonstrated by a series of in vitro and in vivo experiments (spheroidal formation assay, western blotting, and xenograft model). The acyl-biotin exchange method and liquid chromatography-mass spectrometry assays identified palmitoylation proteins mediated by the domain containing the Asp-His-His-Cys family. Western blotting, co-immunoprecipitation, quantitative real-time polymerase chain reaction, co-immunoprecipitation, chromatin immunoprecipitation, and luciferase reporter assays were used to explore the mechanisms of the γ-aminobutyric acid receptor (GABA_AR)/Src/ZDHHC5/EZH2 signaling axis in the effects of propofol on glioma stem cells (GSCs).

Results

We found that treatment with a standard dose of propofol promoted glioma growth in nude mice compared with control or low-dose propofol. Propofol-treated GSCs also led to larger tumor growth in nude mice than did vector-treated tumors. Mechanistically, propofol enhances the stem-like properties of gliomas through GABA_AR to increase Src expression, thereby enhancing the palmitoylation of ZDHHC5-mediated EZH2 and Oct4 expression.

Conclusion

These results demonstrate that propofol may promote glioma growth through the GABA_AR-Src-ZDHHC5-EZH2 mechanism and are helpful in guiding the clinical use of propofol to obtain a better patient prognosis after the surgical resection of tumors.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03087-5.

KIF15 Promotes Progression of Castration Resistant Prostate Cancer by Activating EGFR Signaling Pathway

Castration-resistant prostate cancer (CRPC) continues to be a major clinical problem and its underlying mechanisms are still not fully understood. The epidermal growth factor receptor (EGFR) activation is an important event that regulates mitogenic signaling. EGFR signaling plays an important role in the transition from androgen dependence to castration-resistant state in prostate cancer (PCa). Kinesin family member 15 (KIF15) has been suggested to be overexpressed in multiple malignancies. Here, we demonstrate that KIF15 expression is elevated in CRPC. We show that KIF15 contributes to CRPC progression by enhancing the EGFR signaling pathway, which includes complex network intermediates such as mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/AKT pathways. In CRPC tumors, increased expression of KIF15 is positively correlated with EGFR protein level. KIF15 binds to EGFR, and prevents EGFR proteins from degradation in a Cdc42-dependent manner. These findings highlight the key role of KIF15 in the development of CRPC and rationalize KIF15 as a potential therapeutic target.

Therapeutically leveraging GABAA receptors in cancer

γ-aminobutyric acid or GABA is an amino acid that functionally acts as a neurotransmitter and is critical to neurotransmission. GABA is also a metabolite in the Krebs cycle. It is therefore unsurprising that GABA and its receptors are also present outside of the central nervous system, including in immune cells. This observation suggests that GABAergic signaling impacts events beyond brain function and possibly human health beyond neurological disorders. Indeed, GABA receptor subunits are expressed in pathological disease states, including in disparate cancers. The role that GABA and its receptors may play in cancer development and progression remains unclear. If, however, those cancers have functional GABA receptors that participate in GABAergic signaling, it raises an important question whether these signaling pathways might be targetable for therapeutic benefit. Herein we summarize the effects of modulating Type-A GABA receptor signaling in various cancers and highlight how Type-A GABA receptors could emerge as a novel therapeutic target in cancer.

Interplay of Epidermal Growth Factor Receptor and Signal Transducer and Activator of Transcription 3 in Prostate Cancer: Beyond Androgen Receptor Transactivation

Prostate cancer (PCa) is one of the most common cancers in the world and causes thousands of deaths every year. Conventional therapy for PCa includes surgery and androgen deprivation therapy (ADT). However, about 10-20% of all PCa cases relapse; there is also the further development of castration resistant adenocarcinoma (CRPC-Adeno) or neuroendocrine (NE) PCa (CRPC-NE). Due to their androgen-insensitive properties, both CRPC-Adeno and CRPC-NE have limited therapeutic options. Accordingly, this study reveals the inductive mechanisms of CRPC (for both CRPC-Adeno and CRPC-NE) and fulfils an urgent need for the treatment of PCa patients. Although previous studies have illustrated the emerging roles of epidermal growth factor receptors (EGFR), signal transducer, and activator of transcription 3 (STAT3) signaling in the development of CRPC, the regulatory mechanisms of this interaction between EGFR and STAT3 is still unclear. Our recent studies have shown that crosstalk between EGFR and STAT3 is critical for NE differentiation of PCa. In this review, we have collected recent findings with regard to the involvement of EGFR and STAT3 in malignancy progression and discussed their interactions during the development of therapeutic resistance for PCa.

GABAergic signaling by cells of the immune system: more the rule than the exception

Gamma-aminobutyric acid (GABA) is best known as an essential neurotransmitter in the evolved central nervous system (CNS) of vertebrates. However, GABA antedates the development of the CNS as a bioactive molecule in metabolism and stress-coupled responses of prokaryotes, invertebrates and plants. Here, we focus on the emerging findings of GABA signaling in the mammalian immune system. Recent reports show that mononuclear phagocytes and lymphocytes, for instance dendritic cells, microglia, T cells and NK cells, express a GABAergic signaling machinery. Mounting evidence shows that GABA receptor signaling impacts central immune functions, such as cell migration, cytokine secretion, immune cell activation and cytotoxic responses. Furthermore, the GABAergic signaling machinery of leukocytes is implicated in responses to microbial infection and is co-opted by protozoan parasites for colonization of the host. Peripheral GABA signaling is also implicated in inflammatory conditions and diseases, such as type 1 diabetes, rheumatoid arthritis and cancer cell metastasis. Adding to its role in neurotransmission, growing evidence shows that the non-proteinogenic amino acid GABA acts as an intercellular signaling molecule in the immune system and, as an interspecies signaling molecule in host–microbe interactions. Altogether, the data raise the assumption of conserved GABA signaling in a broad range of mammalian cells and diversification of function in the immune system.

A motogenic GABAergic system of mononuclear phagocytes facilitates dissemination of coccidian parasites

Gamma-aminobutyric acid (GABA) serves diverse biological functions in prokaryotes and eukaryotes, including neurotransmission in vertebrates. Yet, the role of GABA in the immune system has remained elusive. Here, a comprehensive characterization of human and murine myeloid mononuclear phagocytes revealed the presence of a conserved and tightly regulated GABAergic machinery with expression of GABA metabolic enzymes and transporters, GABA-A receptors and regulators, and voltage-dependent calcium channels. Infection challenge with the common coccidian parasites Toxoplasma gondii and Neospora caninum activated GABAergic signaling in phagocytes. Using gene silencing and pharmacological modulators in vitro and in vivo in mice, we identify the functional determinants of GABAergic signaling in parasitized phagocytes and demonstrate a link to calcium responses and migratory activation. The findings reveal a regulatory role for a GABAergic signaling machinery in the host-pathogen interplay between phagocytes and invasive coccidian parasites. The co-option of GABA underlies colonization of the host by a Trojan horse mechanism.

A Targeted Bioinformatics Assessment of Adrenocortical Carcinoma Reveals Prognostic Implications of GABA System Gene Expression

Adrenocortical carcinoma (ACC) is a rare but deadly cancer for which few treatments exist. Here, we have undertaken a targeted bioinformatics study of The Cancer Genome Atlas (TCGA) ACC dataset focusing on the 30 genes encoding the γ-aminobutyric acid (GABA) system—an under-studied, evolutionarily-conserved system that is an emerging potential player in cancer progression. Our analysis identified a subset of ACC patients whose tumors expressed a distinct GABA system transcriptome. Transcript levels of ABAT (encoding a key GABA shunt enzyme), were upregulated in over 40% of tumors, and this correlated with several favorable clinical outcomes including patient survival; while enrichment and ontology analysis implicated two cancer-related biological pathways involved in metastasis and immune response. The phenotype associated with ABAT upregulation revealed a potential metabolic heterogeneity among ACC tumors associated with enhanced mitochondrial metabolism. Furthermore, many GABA_A receptor subunit-encoding transcripts were expressed, including two (GABRB2 and GABRD) prognostic for patient survival. Transcripts encoding GABA_B receptor subunits and GABA transporters were also ubiquitously expressed. The GABA system transcriptome of ACC tumors is largely mirrored in the ACC NCI-H295R cell line, suggesting that this cell line may be appropriate for future functional studies investigating the role of the GABA system in ACC cell growth phenotypes and metabolism.

Tumor-induced neurogenesis and immune evasion as targets of innovative anti-cancer therapies

Normal cells are hijacked by cancer cells forming together heterogeneous tumor masses immersed in aberrant communication circuits that facilitate tumor growth and dissemination. Besides the well characterized angiogenic effect of some tumor-derived factors; others, such as BDNF, recruit peripheral nerves and leukocytes. The neurogenic switch, activated by tumor-derived neurotrophins and extracellular vesicles, attracts adjacent peripheral fibers (autonomic/sensorial) and neural progenitor cells. Strikingly, tumor-associated nerve fibers can guide cancer cell dissemination. Moreover, IL-1β, CCL2, PGE2, among other chemotactic factors, attract natural immunosuppressive cells, including T regulatory (Tregs), myeloid-derived suppressor cells (MDSCs), and M2 macrophages, to the tumor microenvironment. These leukocytes further exacerbate the aberrant communication circuit releasing factors with neurogenic effect. Furthermore, cancer cells directly evade immune surveillance and the antitumoral actions of natural killer cells by activating immunosuppressive mechanisms elicited by heterophilic complexes, joining cancer and immune cells, formed by PD-L1/PD1 and CD80/CTLA-4 plasma membrane proteins. Altogether, nervous and immune cells, together with fibroblasts, endothelial, and bone-marrow-derived cells, promote tumor growth and enhance the metastatic properties of cancer cells. Inspired by the demonstrated, but restricted, power of anti-angiogenic and immune cell-based therapies, preclinical studies are focusing on strategies aimed to inhibit tumor-induced neurogenesis. Here we discuss the potential of anti-neurogenesis and, considering the interplay between nervous and immune systems, we also focus on anti-immunosuppression-based therapies. Small molecules, antibodies and immune cells are being considered as therapeutic agents, aimed to prevent cancer cell communication with neurons and leukocytes, targeting chemotactic and neurotransmitter signaling pathways linked to perineural invasion and metastasis.

Competing Endogenous RNA and Coexpression Network Analysis for Identification of Potential Biomarkers and Therapeutics in association with Metastasis Risk and Progression of Prostate Cancer

Prostate cancer (PCa) is the most frequently diagnosed malignant neoplasm in men. Despite the high incidence, the underlying pathogenic mechanisms of PCa are still largely unknown, which limits the therapeutic options and leads to poor prognosis. Herein, based on the expression profiles from The Cancer Genome Atlas (TCGA) database, we investigated the interactions between long noncoding RNA (lncRNA) and mRNA by constructing a competing endogenous RNA network. Several competing endogenous RNAs could participate in the tumorigenesis of PCa. Six lncRNA signatures were identified as potential candidates associated with stage progression by the Kolmogorov-Smirnov test. In addition, 32 signatures from the coexpression network had potential diagnostic value for PCa lymphatic metastasis using machine learning algorithms. By targeting the coexpression network, the antifungal compound econazole was screened out for PCa treatment. Econazole could induce growth restraint, arrest the cell cycle, lead to apoptosis, inhibit migration, invasion, and adhesion in PC3 and DU145 cell lines, and inhibit the growth of prostate xenografts in nude mice. This systematic characterization of lncRNAs, microRNAs, and mRNAs in the risk of metastasis and progression of PCa will aid in the identification of candidate prognostic biomarkers and potential therapeutic drugs.

Transition from androgenic to neurosteroidal action of 5α-androstane-3α, 17β-diol through the type A γ-aminobutyric acid receptor in prostate cancer progression

Androgen ablation is the standard of care prescribed to patients with advanced or metastatic prostate cancer (PCa) to slow down disease progression. Unfortunately, a majority of PCa patients under androgen ablation progress to castration-resistant prostate cancer (CRPC). Several mechanisms including alternative intra-prostatic androgen production and androgen-independent androgen receptor (AR) activation have been proposed for CRPC progression. Aldo-keto reductase family 1 member C3 (AKR1C3), a multi-functional steroid metabolizing enzyme, is specifically expressed in the cytoplasm of PCa cells; and positive immunoreactivity of the type A γ-aminobutyric acid receptor (GABA_AR), an ionotropic receptor and ligand-gated ion channel, is detected on the membrane of PCa cells. We studied a total of 72 radical prostatectomy cases by immunohistochemistry, and identified that 21 cases exhibited positive immunoreactivities for both AKR1C3 and GABA_AR. In the dual positive cancer cases, AKR1C3 and GABA_AR subunit α₁ were either expressed in the same cells or in neighboring cells. Among several possible substrates, AKR1C3 reduces 5α-dihydrotesterone (DHT) to form 5α-androstane-3α, 17β-diol (3α-diol). 3α-diol is a neurosteroid that acts as a positive allosteric modulator of the GABA_AR in the central nervous system (CNS). We examined the hypothesis that 3α-diol-regulated pathological effects in the prostate are GABA_AR-dependent, but are independent of the AR. In GABA_AR-positive, AR-negative human PCa PC-3 cells, 3α-diol significantly stimulated cell growth in culture and the in ovo chorioallantoic membrane (CAM) xenograft model. 3α-diol also up-regulated expression of the epidermal growth factor (EGF) family of growth factors and activation of EGF receptor (EGFR) and Src as measured by quantitative polymerase chain reaction and immunoblotting, respectively. Inclusion of GABA_AR antagonists reversed 3α-diol-stimulated tumor cell growth, expression of EGF family members, and activation of EGFR and Src to the level observed in untreated cells. Results from the present study suggest that 3α-diol may act as an alternative intra-prostatic neurosteroid that activates AR-independent PCa progression. The involvement of AKR1C3-mediated steroid metabolisms in modulating GABA_AR activation and promoting PCa progression requires continued studies.

GABAB receptor regulates proliferation in the high-grade chondrosarcoma cell line OUMS-27 via apoptotic pathways

BACKGROUND

High-grade chondrosarcoma, which has a high incidence of local recurrence and pulmonary metastasis despite surgical resection, is associated with poor prognosis. Therefore, new and effective adjuvant therapies are urgently required for this disease. Gamma-aminobutyric acid (GABA), which acts as a neurotrophic factor during nervous system development, is related to the proliferation and migration of certain cancer cells. The GABAergic system, which is composed of GABA, the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD), and GABA receptors, has an important function in nerve growth and development of neural crest. Therefore, the GABAergic system may play important functional roles in the proliferation of chondrosarcoma cells, which are derived from neural crest cells. We examined the anti-tumor effects of the GABAergic system on a chondrosarcoma cell line.

METHODS

We evaluated the underlying mechanisms of the anti-tumor effects of the GABAergic system, such as the involvement of different signaling pathways, apoptosis, and cell cycle arrest, in the high-grade chondrosarcoma cell line OUMS-27. In addition, we performed whole-cell patch-clamp recordings for Ca²⁺ currents and evaluated the changes in intracellular Ca²⁺ concentration via Ca²⁺ channels, which are related to the GABA_B receptor in high-grade chondrosarcoma cells.

RESULTS

The GABA_B receptor antagonist CGP had anti-tumor effects on high-grade chondrosarcoma cells in a dose-dependent manner. The activities of caspase 3 and caspase 9 were significantly elevated in CGP-treated cells compared to in untreated cells. The activity of caspase 8 did not differ significantly between untreated cells and CGP-treated cells. However, caspase 8 tended to be up-regulated in CGP-treated cells. The GABA_B receptor antagonist exhibited anti-tumor effects at the G1/S cell cycle checkpoint and induced apoptosis via dual inhibition of the PI3/Akt/mTOR and MAPK signaling pathways. Furthermore, the changes in intracellular Ca²⁺ via GABA_B receptor-related Ca²⁺ channels inhibited the proliferation of high-grade chondrosarcoma cells by inducing and modulating apoptotic pathways.

CONCLUSIONS

The GABA_B receptor antagonist may improve the prognosis of high-grade chondrosarcoma by exerting anti-tumor effects via different signaling pathways, apoptosis, cell cycle arrest, and Ca²⁺ channels in high-grade chondrosarcoma cells.

GABABR-Induced EGFR Transactivation Promotes Migration of Human Prostate Cancer Cells

G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs) act in concert to regulate cell growth, proliferation, survival, and migration. Metabotropic GABAB receptor (GABABR) is the GPCR for the main inhibitory neurotransmitter GABA in the central nervous system. Increased expression of GABABR has been detected in human cancer tissues and cancer cell lines, but the role of GABABR in these cells is controversial and the underlying mechanism remains poorly understood. Here, we investigated whether GABABR hijacks RTK signaling to modulate the fates of human prostate cancer cells. RTK array analysis revealed that the GABABR-specific agonist baclofen selectively induced the transactivation of EGFR in PC-3 cells. EGFR transactivation resulted in the activation of ERK1/2 by a mechanism that is dependent on Gi/o protein and that requires matrix metalloproteinase-mediated proligand shedding. Positive allosteric modulators (PAMs) of GABABR, such as CGP7930, rac-BHFF, and GS39783, can function as PAM agonists to induce EGFR transactivation and subsequent ERK1/2 activation. Moreover, both baclofen and CGP7930 promoted cell migration and invasion through EGFR signaling. In summary, our observations demonstrated that GABABR transactivated EGFR in a ligand-dependent mechanism to promote prostate cancer cell migration and invasion, thus providing new insights into developing a novel strategy for prostate cancer treatment by targeting neurotransmitter signaling.

Aberrant Hypomethylation of Solute Carrier Family 6 Member 12 Promoter Induces Metastasis of Ovarian Cancer

PURPOSE

Ovarian cancer (OC) is the most fatal of gynecological malignancies with a high rate of recurrence. We aimed to evaluate the expression of solute carrier family 6, member 12 (SLC6A12) and methylation of its promoter CpG sites in a xenograft mouse model of metastatic OC, and to investigate the regulatory mechanisms that promote aggressive properties during OC progression.

MATERIALS AND METHODS

Expression of SLC6A12 mRNA was determined by reverse-transcription quantitative polymerase chain reaction (RT-qPCR), and DNA methylation status of its promoter CpGs was detected by quantitative methylation-specific PCR. The metastatic potential of SLC6A12 was evaluated by in vitro migration/invasion transwell assays. Gene expression and DNA methylation of SLC6A12 and clinical outcomes were further investigated from publicly available databases from curatedOvarianData and The Cancer Genome Atlas.

RESULTS

SLC6A12 expression was 8.1-14.0-fold upregulated and its DNA methylation of promoter CpG sites was 41-62% decreased in tumor metastases. After treatment with DNA methyltransferase inhibitor and/or histone deacetylase inhibitor, the expression of SLC6A12 was profoundly enhanced (~8.0-fold), strongly supporting DNA methylation-dependent epigenetic regulation of SLC6A12. Overexpression of SLC6A12 led to increased migration and invasion of ovarian carcinoma cells in vitro, approximately 2.0-fold and 3.3-fold, respectively. The meta-analysis showed that high expression of SLC6A12 was significantly associated with poor overall survival [hazard ratio (HR)=1.07, p value=0.016] and that low DNA methylation levels of SLC6A12 at specific promoter CpG site negatively affected patient survival.

CONCLUSION

Our findings provide novel evidence for the biological and clinical significance of SLC6A12 as a metastasis-promoting gene.

Different transcriptional levels of GABAA receptor subunits in mouse cumulus cells around oocytes at different mature stage

γ-Aminobutyric acid (GABA) is a principal inhibitory neurotransmitter in the central nervous system (CNS) of vertebrates. However, GABA and its receptor are found not only in peripheral neuronal tissue but also in many peripheral nonneuronal tissues, and thought to have multiple physiological functions. The bidirectional communication between oocytes and cumulus cells (CCs) plays a significant role in oocyte maturation and metabolism. In our previously study, the expression level of α5 subunit in CCs isolated from oocytes of patients with polycystic ovary syndrome had been found to be associated with oocyte nuclear maturity. In this study, we investigated the transcriptional levels of GABA_A receptor subunits in germinal vesicle (GV) and metaphase II (MII) mouse CCs, and explored the role of GABA-A receptor subunits during ovarian follicular development and oocyte maturation. We found that GABA_A receptor subunits exhibited differential transcriptional levels in CCs at different oocyte nuclear maturity stages. It suggested an involvement of GABA-A receptor subunits related to oocyte maturation and certain functions.

Autophagy-Dependent Secretion: Contribution to Tumor Progression

Autophagy is best known as a lysosomal degradation and recycling pathway to maintain cellular homeostasis. During autophagy, cytoplasmic content is recognized and packed in autophagic vacuoles, or autophagosomes, and targeted for degradation. However, during the last years, it has become evident that the role of autophagy is not restricted to degradation alone but also mediates unconventional forms of secretion. Furthermore, cells with defects in autophagy apparently are able to reroute their cargo, like mitochondria, to the extracellular environment; effects that contribute to an array of pathologies. In this review, we discuss the current knowledge of the physiological roles of autophagy-dependent secretion, i.e., the effect on inflammation and insulin/hormone secretion. Finally, we focus on the effects of autophagy-dependent secretion on the tumor microenvironment (TME) and tumor progression. The autophagy-mediated secreted factors may stimulate cellular proliferation via auto- and paracrine signaling. The autophagy-mediated release of immune modulating proteins changes the immunosuppresive TME and may promote an invasive phenotype. These effects may be either direct or indirect through facilitating formation of the mobilized vesicle, aid in anterograde trafficking, or alterations in homeostasis and/or autonomous cell signaling.

The mRNA-edited form of GABRA3 suppresses GABRA3-mediated Akt activation and breast cancer metastasis

Metastasis is a critical event affecting breast cancer patient survival. To identify molecules contributing to the metastatic process, we analysed The Cancer Genome Atlas (TCGA) breast cancer data and identified 41 genes whose expression is inversely correlated with survival. Here we show that GABA_A receptor alpha3 (Gabra3), normally exclusively expressed in adult brain, is also expressed in breast cancer, with high expression of Gabra3 being inversely correlated with breast cancer survival. We demonstrate that Gabra3 activates the AKT pathway to promote breast cancer cell migration, invasion and metastasis. Importantly, we find an A-to-I RNA-edited form of Gabra3 only in non-invasive breast cancers and show that edited Gabra3 suppresses breast cancer cell invasion and metastasis. A-to-I-edited Gabra3 has reduced cell surface expression and suppresses the activation of AKT required for cell migration and invasion. Our study demonstrates a significant role for mRNA-edited Gabra3 in breast cancer metastasis.

GABRA3, a subunit of the GABA receptor, is often highly expressed in brain metastasis and breast cancers. Here, the authors demonstrated that GABRA3 activates AKT to promote breast cancer cell invasion and that the A-to-I edited form of GABRA3, specifically expressed in noninvasive breast cancers, can suppress the function of wild type GABRA3.