NOVA1 acts as an oncogenic RNA-binding protein to regulate cholesterol homeostasis in human glioblastoma cells

NOVA1 is a neuronal RNA-binding protein identified as the target antigen of a rare autoimmune disorder associated with cancer and neurological symptoms, termed paraneoplastic opsoclonus-myoclonus ataxia. Despite the strong association between NOVA1 and cancer, it has been unclear how NOVA1 function might contribute to cancer biology. In this study, we find that NOVA1 acts as an oncogenic factor in a GBM (glioblastoma multiforme) cell line established from a patient. Interestingly, NOVA1 and Argonaute (AGO) CLIP identified common 3' untranslated region (UTR) targets, which were down-regulated in NOVA1 knockdown GBM cells, indicating a transcriptome-wide intersection of NOVA1 and AGO-microRNA (miRNA) targets regulation. NOVA1 binding to 3'UTR targets stabilized transcripts including those encoding cholesterol homeostasis related proteins. Selective inhibition of NOVA1-RNA interactions with antisense oligonucleotides disrupted GBM cancer cell fitness. The precision of our GBM CLIP studies point to both mechanism and precise RNA sequence sites to selectively inhibit oncogenic NOVA1-RNA interactions. Taken together, we find that NOVA1 is commonly overexpressed in GBM, where it can antagonize AGO2-miRNA actions and consequently up-regulates cholesterol synthesis, promoting cell viability.

Nova proteins direct synaptic integration of somatostatin interneurons through activity-dependent alternative splicing

Somatostatin interneurons are the earliest born population of cortical inhibitory cells. They are crucial to support normal brain development and function; however, the mechanisms underlying their integration into nascent cortical circuitry are not well understood. In this study, we begin by demonstrating that the maturation of somatostatin interneurons in mouse somatosensory cortex is activity dependent. We then investigated the relationship between activity, alternative splicing, and synapse formation within this population. Specifically, we discovered that the Nova family of RNA-binding proteins are activity-dependent and are essential for the maturation of somatostatin interneurons, as well as their afferent and efferent connectivity. Within this population, Nova2 preferentially mediates the alternative splicing of genes required for axonal formation and synaptic function independently from its effect on gene expression. Hence, our work demonstrates that the Nova family of proteins through alternative splicing are centrally involved in coupling developmental neuronal activity to cortical circuit formation.

Nova1 or Bim Deficiency in Pancreatic β-Cells Does Not Alter Multiple Low-Dose Streptozotocin-Induced Diabetes and Diet-Induced Obesity in Mice

The loss of functional pancreatic β-cell mass is an important hallmark of both type 1 and type 2 diabetes. The RNA-binding protein NOVA1 is expressed in human and rodent pancreatic β-cells. Previous in vitro studies indicated that NOVA1 is necessary for glucose-stimulated insulin secretion and its deficiency-enhanced cytokine-induced apoptosis. Moreover, Bim, a proapoptotic protein, is differentially spliced and potentiates apoptosis in NOVA1-deficient β-cells in culture. We generated two novel mouse models by Cre-Lox technology lacking Nova1 (βNova1^-/-) or Bim (βBim^-/-) in β-cells. To test the impact of Nova1 or Bim deletion on β-cell function, mice were subjected to multiple low-dose streptozotocin (MLD-STZ)-induced diabetes or high-fat diet-induced insulin resistance. β-cell-specific Nova1 or Bim deficiency failed to affect diabetes development in response to MLD-STZ-induced β-cell dysfunction and death evidenced by unaltered blood glucose levels and pancreatic insulin content. In addition, body composition, glucose and insulin tolerance test, and pancreatic insulin content were indistinguishable between control and βNova1^-/- or βBim^-/- mice on a high fat diet. Thus, Nova1 or Bim deletion in β-cells does not impact on glucose homeostasis or diabetes development in mice. Together, these data argue against an in vivo role for the Nova1-Bim axis in β-cells.

Electroacupuncture at PC6 (Neiguan) Attenuates Angina Pectoris in Rats with Myocardial Ischemia-Reperfusion Injury Through Regulating the Alternative Splicing of the Major Inhibitory Neurotransmitter Receptor GABRG2

Angina pectoris is the most common manifestation of coronary heart disease, causing suffering in patients. Electroacupuncture at PC6 can effectively alleviate angina by regulating the expression of genes, whether the alternative splicing (AS) of genes is affected by acupuncture is still unknown. We established a rat model of myocardial ischemia-reperfusion by coronary artery ligation and confirmed electroacupuncture alleviated the abnormal discharge caused by angina pectoris measured in EMG electromyograms. Analysis of the GSE61840 dataset established that AS events were altered after I/R and regulated by electroacupuncture. I/R decreased the expression of splicing factor Nova1 while electroacupuncture rescued it. Further experiments in dorsal root ganglion cells showed Nova1 regulated the AS of the GABRG2, specifically on its exon 9 where an important phosphorylation site is present. In vivo, results also showed that electroacupuncture can restore AS of GABRG2. Our results proved that electroacupuncture alleviates angina results by regulating alternative splicing.

LncRNA MALAT1 mediates doxorubicin resistance of hepatocellular carcinoma by regulating miR-3129-5p/Nova1 axis

Drug resistance is one of the major challenges for cancer therapies. In recent years, research on disease-related molecular signaling pathways has become the key ways to understand and overcome obstacles. Dysregulation of MALAT1 could regulate doxorubicin resistance of hepatocellular carcinoma (HCC), but how MALAT1 involving in managing doxorubicin resistance remains unclear yet. We aimed to elucidate the specific molecular mechanism of MALAT1 with doxorubicin resistance in HCC cells. Quantitative real-time polymerase chain reaction (qRT-PCR) was engaged to detect the expression levels of MALAT1, miR-3129-5p and Nova1 mRNA; MTT, western blot, flow cytometry and luciferase reporter assays were executed to identify the influence of MALAT1 on doxorubicin resistance of HCC cells. Xenograft tumor model was created to confirm the biological function of MALAT1 in doxorubicin resistance of HCC cells in vivo. MALAT1 and Nova1 were upregulated, while miR-3129-5p expression was decreased in doxorubicin-resistant HCC tissues and cells. Knockdown of MALAT1 regulated doxorubicin resistance of HCC cells through inhibiting cell proliferation, migration, invasion and promoting apoptosis, but antisense miR-3129-5p released the functional effect of MALAT1 knockdown. Nova1, as a target gene of miR-3129-5p, reversed the results of miR-3129-5p expression and enhanced doxorubicin resistance of HCC cells. Xenograft tumor model suggested that dysregulation of MALAT1 regulated tumor growth and Nova1 to mediate doxorubicin resistance of HCC cells by as a sponge for miR-3129-5p in vivo. Elevation of LncRNA MALAT1 mediated doxorubicin resistance and the progression of HCC via a MALAT1/miR-3129-5p/Nova1 axis. This study would be expected to enrich the understanding of doxorubicin resistance of HCC and provide new ideas for HCC treatment strategies.

17β-estradiol regulates the RNA-binding protein Nova1, which then regulates the alternative splicing of estrogen receptor β in the aging female rat brain

Alternative RNA splicing results in the translation of diverse protein products arising from a common nucleotide sequence. These alternative protein products are often functional and can have widely divergent actions from the canonical protein. Studies in humans and other vertebrate animals have demonstrated that alternative splicing events increase with advanced age, sometimes resulting in pathological consequences. Menopause represents a critical transition for women, where the beneficial effects of estrogens are no longer evident; therefore, factors underlying increased pathological conditions in women are confounded by the dual factors of aging and declining estrogens. Estrogen receptors (ERs) are subject to alternative splicing, the spliced variants increase following menopause, and they fail to efficiently activate estrogen-dependent signaling pathways. However, the factors that regulate the alternative splicing of ERs remain unknown. We demonstrate novel evidence supporting a potential biological feedback loop where 17β-estradiol regulates the RNA-binding protein Nova1, which, in turn, regulates the alternative splicing of ERβ. These data increase our understanding of ER alternative splicing and could have potential implications for women taking hormone replacement therapy after menopause.

RNA binding protein Nova1 promotes tumor growth in vivo and its potential mechanism as an oncogene may due to its interaction with GABAA Receptor-γ2

Background

The mechanism of Nova1’s role in hepatocellular carcinoma has not been delineated. Also its interaction with GABA_A receptor γ2 in HCC is unveiled. This study is aimed to make it clear the distribution, prognostic value of GABA_ARγ2 in human hepatocellular carcinoma. And its role in HCC tumorigenesis under the regulation of its alternative splicing factor Nova1.

Methods

Immunohistochemistry staining was used to investigate the distribution and clinical significance of GABA_ARγ2 protein expression in hepatocellular carcinoma. In vivo tumorigenticity test was conducted in nude mice by regulation the expression of Nova1. Later, western blot and co-immunoprecipitation were carried out to verify the interaction between Nova1 and GABA_ARγ2 in HCC tissue.

Results

Immunohistochemical staining showed GABA_ARγ2 expression in HCC. Survival analysis showed intratumoral GABA_ARγ2 was an independent prognostic factor for overall survival (OS) and disease free survival (DFS). Up-regulation of Nova1 expression promotes subcutaneous HCC growth in nude mice and western blot showed the ectopic expression of Nova-1 restro-regulates the expression of GABA_ARγ2 and GABA. Protein level interaction of GABA_ARγ2 and Nova-1 was evidenced by co-immunoprecipitation.

Conclusions

Nova1 interacts with GABA_ARγ2 not only in CNS but also in HCC. Nova1’s potential mechanism as an oncogene may due to its interaction with GABA_A Rγ2. A better understanding of the mechanism of Nova1 for HCC progression provides a novel target for an optimal immunotherapy against this fatal malignancy.

RBM4-Nova1-SRSF6 splicing cascade modulates the development of brown adipocytes

Alternative splicing (AS) is a pivotal mechanism for the expansion of gene diversity, which determines the cellular fate or specification. However, the effect of AS networks on brown adipogenesis has not been comprehensively investigated. In this study, we identified the discriminative splicing profiles of RNA-binding motif protein 4a-knockout (RBM4a^-/-) brown adipocytes (BAs) and compared them with those of their wild-type counterparts through deep RNA-sequencing. Among these candidates, RBM4a ablation enhanced the relative level of exon 4-excluded neuro-oncological ventral antigen 1 (Nova1^-4) transcripts, which were predominantly generated in embryonic BAs. By contrast, most of the Nova1 transcripts were exon 4-included (Nova1⁺⁴) in mature BAs. The Nova1 isoforms exhibited differential effects on repressing the development of BAs. Moreover, overexpression of Nova1 proteins reduced the serine/arginine splicing factor 6 (SRSF6) level by enhancing the generation of intron 2-included (SRSF6^{+intron 2}) transcripts, which are a putative candidate of the AS-coupled nonsense-mediated decay mechanism. Furthermore, we observed the positive effect of SRSF6 on BA development. These results highlight the hierarchical role of RBM4a in an AS cascade that manipulates brown adipogenesis.

A large-scale functional screen identifies Nova1 and Ncoa3 as regulators of neuronal miRNA function

MicroRNAs (miRNAs) are important regulators of neuronal development, network connectivity, and synaptic plasticity. While many neuronal miRNAs were previously shown to modulate neuronal morphogenesis, little is known regarding the regulation of miRNA function. In a large-scale functional screen, we identified two novel regulators of neuronal miRNA function, Nova1 and Ncoa3. Both proteins are expressed in the nucleus and the cytoplasm of developing hippocampal neurons. We found that Nova1 and Ncoa3 stimulate miRNA function by different mechanisms that converge on Argonaute (Ago) proteins, core components of the miRNA-induced silencing complex (miRISC). While Nova1 physically interacts with Ago proteins, Ncoa3 selectively promotes the expression of Ago2 at the transcriptional level. We further show that Ncoa3 regulates dendritic complexity and dendritic spine maturation of hippocampal neurons in a miRNA-dependent fashion. Importantly, both the loss of miRNA activity and increased dendrite complexity upon Ncoa3 knockdown were rescued by Ago2 overexpression. Together, we uncovered two novel factors that control neuronal miRISC function at the level of Ago proteins, with possible implications for the regulation of synapse development and plasticity.