Trans-acting factors governing acetylcholinesterase mRNA metabolism in neurons

Changes in the Acetylcholinesterase Enzymatic Activity in Tumor Development and Progression

Acetylcholinesterase is a well-known protein because of the relevance of its enzymatic activity in the hydrolysis of acetylcholine in nerve transmission. In addition to the catalytic action, it exerts non-catalytic functions; one is associated with apoptosis, in which acetylcholinesterase could significantly impact the survival and aggressiveness observed in cancer. The participation of AChE as part of the apoptosome could explain the role in tumors, since a lower AChE content would increase cell survival due to poor apoptosome assembly. Likewise, the high Ach content caused by the reduction in enzymatic activity could induce cell survival mediated by the overactivation of acetylcholine receptors (AChR) that activate anti-apoptotic pathways. On the other hand, in tumors in which high enzymatic activity has been observed, AChE could be playing a different role in the aggressiveness of cancer; in this review, we propose that AChE could have a pro-inflammatory role, since the high enzyme content would cause a decrease in ACh, which has also been shown to have anti-inflammatory properties, as discussed in this review. In this review, we analyze the changes that the enzyme could display in different tumors and consider the different levels of regulation that the acetylcholinesterase undergoes in the control of epigenetic changes in the mRNA expression and changes in the enzymatic activity and its molecular forms. We focused on explaining the relationship between acetylcholinesterase expression and its activity in the biology of various tumors. We present up-to-date knowledge regarding this fascinating enzyme that is positioned as a remarkable target for cancer treatment.

Study on the toxic effects of sodium pentachlorophenol (PCP-Na) on razor clam (Sinonovacula constricta)

Currently, research on toxic effects of PCP Na is greatly insufficient. The aim of this study is to explore the toxic effects of PCP-Na for better conducting future work on PCP-Na toxicology. For this purpose, S. constricta adults were exposed to PCP-Na for toxicity testing. The results showed that PCP-Na could easily bioaccumulate in S. constricta and significantly affected both phrase I and II metabolism enzymes. Meanwhile, PCP-Na strongly activated antioxidant system and caused PC, LPO and DNA damage. In addition, neurotoxicity and immunotoxicity of PCP-Na was demonstrated in this study. Interestingly, we observed that PCP-Na significantly affected the expression of genes of electron transport chain and induced key enzymes of glycolysis, indicating that PCP-Na may act as an uncoupler of oxidative phosphorylation, interfering with energy supply and causing energy compensation. This study is the first to fully analyze and provide a new perspective on the toxicity of PCP-Na.

Hu Antigen R (HuR) Protein Structure, Function and Regulation in Hepatobiliary Tumors

Simple Summary

Hepatobiliary tumors are a group of primary malignancies encompassing the liver, the intra- and extra-hepatic biliary tracts, and the gall bladder. Within the liver, hepatocellular carcinoma (HCC) is the most common type of primary cancer, which is, also, representing the third-most recurrent cause of cancer-associated death and the sixth-most prevalent type of tumor worldwide, nowadays. Although less frequent, cholangiocarcinoma (CCA) is, currently, a fatal cancer with limited therapeutic options. Here, we review the regulatory role of Hu antigen R (HuR), a ubiquitous member of the ELAV/Hu family of RNA-binding proteins (RBPs), in the pathogenesis, progression, and treatment of HCC and CCA. Overall, HuR is proposed as a valuable diagnostic and prognostic marker, as well as a therapeutic target in hepatobiliary cancers. Therefore, novel therapeutic approaches that can selectively modulate HuR function appear to be highly attractive for the clinical management of these types of tumors.

Abstract

Hu antigen R (HuR) is a 36-kDa ubiquitous member of the ELAV/Hu family of RNA-binding proteins (RBPs), which plays an important role as a post-transcriptional regulator of specific RNAs under physiological and pathological conditions, including cancer. Herein, we review HuR protein structure, function, and its regulation, as well as its implications in the pathogenesis, progression, and treatment of hepatobiliary cancers. In particular, we focus on hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), tumors where the increased cytoplasmic localization of HuR and activity are proposed, as valuable diagnostic and prognostic markers. An overview of the main regulatory axes involving HuR, which are associated with cell proliferation, invasion, metastasis, apoptosis, and autophagy in HCC, is provided. These include the transcriptional, post-transcriptional, and post-translational modulators of HuR function, in addition to HuR target transcripts. Finally, whereas studies addressing the relevance of targeting HuR in CCA are limited, in the past few years, HuR has emerged as a potential therapeutic target in HCC. In fact, the therapeutic efficacy of some pharmacological inhibitors of HuR has been evaluated, in early experimental models of HCC. We, further, discuss the major findings and future perspectives of therapeutic approaches that specifically block HuR interactions, either with post-translational modifiers or cognate transcripts in hepatobiliary cancers.

Overexpression of Rad51C splice variants in colorectal tumors

Functional alterations in Rad51C are the cause of the Fanconi anemia complementation group O (FANCO) gene disorder. We have identified novel splice variants of Rad51C mRNA in colorectal tumors and cells. The alternatively spliced transcript variants are formed either without exon-7 (variant 1), without exon 6 and 7 (variant 2) or without exon 7 and 8 (variant 3).

Real time PCR analysis of nine pair-matched colorectal tumors and non-tumors showed that variant 1 was overexpressed in tumors compared to matched non-tumors. Among 38 colorectal tumor RNA samples analyzed, 18 contained variant 1, 12 contained variant 2, 14 contained variant 3, and eight expressed full length Rad51C exclusively. Bisulfite DNA sequencing showed promoter methylation of Rad51C in tumor cells. 5-azacytidine treatment of LS-174T cells caused a 14 fold increase in variant 1, a 4.8 fold increase for variant 3 and 3.4 fold for variant 2 compared to 2.5 fold increase in WT.

Expression of Rad51C variants is associated with FANCD2 foci positive colorectal tumors and is associated with microsatellite stability in those tumors. Further investigation is needed to elucidate differential function of the Rad51C variants to evaluate potential effects in drug resistance and DNA repair.

Dioxin and dioxin-like compounds suppress acetylcholinesterase activity via transcriptional downregulations in vitro

Recently, acetylcholinesterase (AChE, EC 3.1.1.7) has received increased attention in the field of environmental sciences. Evaluation of the effects of environmental contaminants on AChE enzymatic activity not only can reflect, to some extent, the interference with the nervous system, but also can be used for monitoring pollution. Our previous study showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) suppressed neuronal AChE enzymatic activity via transcriptional downregulations mediated by aryl hydrocarbon receptor. In the present study, the effects of several other dioxin-like compounds (DLCs) on neuronal AChE activity were determined, including 1,2,3,7,8-pentachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzofuran, 2,3,4,7,8-pentachlorodibenzofuran, and 2,3,7,8-tetrabromodibenzo-p-dioxin. The results showed that the enzymatic activity of AChE was significantly decreased by approximately 15-30 % after exposure to a certain concentrations of the DLCs, whereas incubating neuronal cell lysates directly with these DLCs did not inhibit AChE enzyme. Subsequent molecular mechanism study showed that these chemicals could decrease ACHE promoter activity, as well as AChE T mRNA expression, thereby suggesting the involvements of transcriptional regulation in these effects. These findings on DLCs are similar with those on 2,3,7,8-TCDD, pointing to the possibility that exposure to dioxin and DLCs, which frequently coexist in the contaminated environments, may concurrently interfere with the cholinergic functions via AChE.

Emerging complexity of the HuD/ELAVl4 gene; implications for neuronal development, function, and dysfunction

Precise control of messenger RNA (mRNA) processing and abundance are increasingly being recognized as critical for proper spatiotemporal gene expression, particularly in neurons. These regulatory events are governed by a large number of trans-acting factors found in neurons, most notably RNA-binding proteins (RBPs) and micro-RNAs (miRs), which bind to specific cis-acting elements or structures within mRNAs. Through this binding mechanism, trans-acting factors, particularly RBPs, control all aspects of mRNA metabolism, ranging from altering the transcription rate to mediating mRNA degradation. In this context the best-characterized neuronal RBP, the Hu/ELAVl family member HuD, is emerging as a key component in multiple regulatory processes--including pre-mRNA processing, mRNA stability, and translation--governing the fate of a substantial amount of neuronal mRNAs. Through its ability to regulate mRNA metabolism of diverse groups of functionally similar genes, HuD plays important roles in neuronal development and function. Furthermore, compelling evidence indicates supplementary roles for HuD in neuronal plasticity, in particular, recovery from axonal injury, learning and memory, and multiple neurological diseases. The purpose of this review is to provide a detailed overview of the current knowledge surrounding the expression and roles of HuD in the nervous system. Additionally, we outline the present understanding of the molecular mechanisms presiding over the localization, abundance, and function of HuD in neurons.

Characterization of multiple exon 1 variants in mammalian HuD mRNA and neuron-specific transcriptional control via neurogenin 2

The RBP (RNA-binding protein) and Hu/ELAV family member HuD regulates mRNA metabolism of genes directly or indirectly involved in neuronal differentiation, learning and memory, and several neurological diseases. Given the important functions of HuD in a variety of processes, we set out to determine the mechanisms that promote HuD mRNA expression in neurons using a mouse model. Through several complementary approaches, we determined that the abundance of HuD mRNA is predominantly under transcriptional control in developing neurons. Bioinformatic and 5'RACE (rapid amplification of cDNA ends) analyses of the 5' genomic flanking region identified eight conserved HuD leader exons (E1s), two of which are novel. Expression of all E1 variants was determined in mouse embryonic (E14.5) and adult brains. Sequential deletion of the 5' regulatory region upstream of the predominantly expressed E1c variant revealed a well conserved 400 bp DNA region that contains five E-boxes and is capable of directing HuD expression specifically in neurons. Using EMSA (electrophoretic mobility shift assay), ChIP (chromatin immunoprecipitation), and 5' regulatory region deletion and mutation analysis, we found that two of these E-boxes are targets of Neurogenin 2 (Ngn2) and that this mechanism is important for HuD mRNA induction. Together, our findings reveal that transcriptional regulation of HuD involves the use of alternate leader exons and Ngn2 mediates neuron-specific mRNA expression. To our knowledge, this is the first study to identify molecular events that positively regulate HuD mRNA expression.