Human acetylcholinesterase and butyrylcholinesterase are encoded by two distinct genes

Review on the recent progress in the development of fluorescent probes targeting enzymes

Enzymes are very important for biological processes in a living being, performing similar or multiple tasks in and out of cells, tissues and other organisms at a particular location. The abnormal activity of particular enzyme usually caused serious diseases such as Alzheimer's disease, Parkinson's disease, cancers, diabetes, cardiovascular diseases, arthritis etc. Hence, nondestructive and real-time visualization for certain enzyme is very important for understanding the biological issues, as well as the drug administration and drug metabolism. Fluorescent cellular probe-based enzyme detectionin vitroandin vivohas become broad interest for human disease diagnostics and therapeutics. This review highlights the recent findings and designs of highly sensitive and selective fluorescent cellular probes targeting enzymes for quantitative analysis and bioimaging.

Correlations between cholinesterase activity and cognitive scores in post-ischemic rats and patients with vascular dementia

The biochemical changes such as the activities of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) were investigated in rats with global cerebral ischemia and in vascular dementia (VaD) subjects in this study. The AChE activity showed a significant decrease in plasma and a significant increase in the hippocampus but not in the cerebral cortices in the post-ischemic rats as compared to the controls. The learning abilities and spatial memory were impaired in the post-ischemic rats as compared to controls. Furthermore, the AChE activity in plasma was significantly reduced in VaD subjects as compared to normal control subjects. The BuChE activity did not show any change in both post-ischemic rats and VaD patients. Interestingly, the decreased AChE activity in plasma from the post-ischemic rats and the VaD subjects showed a significant correlation with the declined learning and memory ability, and the Mini-Mental State Examination score, respectively. These data suggest that the AChE activity is involved in the cognitive recovery after ischemia, and the plasma level of AChE might be a reliable supplementary peripheral biomarker to evaluate the cognitive recovery degree of VaD patients.

Elongation by RNA polymerase II: structure-function relationship

RNA polymerase II is the eukaryotic enzyme that transcribes all the mRNA in the cell. Complex mechanisms of transcription and its regulation underlie basic functions including differentiation and morphogenesis. Recent evidence indicates the process of RNA chain elongation as a key step in transcription control. Elongation was therefore expected and found to be linked to human diseases. For these reasons, major efforts in determining the structures of RNA polymerases from yeast and bacteria, at rest and as active enzymes, were undertaken. These studies have revealed much information regarding the processes involved in transcription. Eukaryotic RNA polymerases and their homologous bacterial counterparts are flexible enzymes with domains that separate DNA and RNA, prevent the escape of nucleic acids during transcription, allow for extended pausing or "arrest" during elongation, allow for translocation of the DNA and more. Structural studies of RNA polymerases are described below within the context of the process of transcription elongation, its regulation and function.

Runx1/AML1 in leukemia: disrupted association with diverse protein partners

Runx1/AML1, a chromosome 21q22 hematopoietic regulator, is frequently translocated in leukemia. Its protein product, a relatively weak transcriptional activator, becomes an effective transcriptional enhancer or repressor, when co-operating with transcriptional co-activators or co-repressors. Runx1/AML1 association with its partners is disrupted in leukemia. For example, Runx1/AML1 mutations and translocations (e.g. t(8;21), t(12;21) and t(3;21)) impair binding of Runx1/AML1-CBFbeta complexes to Runt motifs in myelopoietically active promoters, preventing normal hematopoiesis. However, Runx1/AML1-associated translocations are not leukemogenic in animal models, suggesting the involvement of yet unidentified regulatory proteins. New candidates are cholinesterases, inhibition of which increases leukemic risk in a manner potentially associated with Runx1/AML1.

Acetylcholinesterase and butyrylcholinesterase histochemical activities and tumor cell growth in several brain tumors

BACKGROUND

The hydrolysis enzymes of the acetylcholine, acetylcholinesterase, and butyrylcholinesterase are involved in non-cholinergic functions such as proliferation processes and cellular adhesion. These enzymes have been found in several tumors other from brain tumors.

METHODS

Thirty fresh brain tumor specimens were obtained from biopsies taken during neurosurgical procedures. The specimens were cut in two parts, one designated for routine histopathological control and the other for histochemical and growth studies. The formalin fixed specimens were serially cut at 10 microm in a freezing cryostat, mounted in gelatin-coated slides, and processed for sensitive histochemical detection of acetylcholinesterase and butyrylcholinesterase. The other specimens were processed for a HMEM cell growth culture.

RESULTS

The results show the coexistence of acetylcholinesterase and butyrylcholinesterase in all tumors studied. Type II and III gliomas and oligodendrogliomas show moderate activity of both cholinesterases, whereas in type IV glioma and meningiomas the labeling of both cholinesterases was high. In the craniopharyngiomas a high acetylcholinesterase activity was observed and low level of butyrylcholinesterase labeling. The cell growth was high only in the cases in which butyrylcholinesterase activity was high, such as type IV glioma. In type II and III gliomas, oligodendroglioma, and craniopharyngioma the growth rate was slow.

CONCLUSIONS

These results could indicate a possible relationship between the presence of butyrylcholinesterase and acetylcholinesterase in brain tumor tissue and cellular proliferation in tumorigenesis.

Cholinesterases modulate cell adhesion in human neuroblastoma cells in vitro

Cholinesterases are expressed non-synaptically during embryonic development, neoplasia and neurodegeneration. We have investigated the effects of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and, conversely, anti-AChE and -BChE antibodies and inhibitors on cell adhesion and neurite outgrowth in human neuroblastoma cells. Analysis of cholinesterase levels and isoforms in undifferentiated and differentiated cells indicated a significant rise in AChE levels on differentiation. This increase was related to both cell-associated and secreted enzyme, and was predominantly the G4 isoform. BChE levels and isoforms, on the other hand, showed no significant variation. Coating the tissue culture plate with AChE stimulated neurite outgrowth, while BChE had an anti-adhesive effect. Cell adhesion was affected by the BChE inhibitor, ethopropazine, and the AChE peripheral site inhibitor, BW284c51, but not by eserine which binds to the active site. This indicates that the adhesion function is non-cholinergic, a finding supported by the lack of effect of AE-2, a monoclonal antibody that inhibits AChE, on cell adhesion. Four out of a panel of nine anti-AChE antibodies inhibited adhesion to varying degrees. Of these antibodies, two are catalytic, with epitopes associated with the peripheral anionic site of AChE, and the remaining two have epitopes overlapping this site. Neither of the two anti-BChE antibodies used had any effect on adhesion. These results indicate the importance of AChE in neuroblastoma cell adhesion and neurite outgrowth, and suggest that the peripheral anionic site may be involved in these processes.

The key role of butyrylcholinesterase during neurogenesis and neural disorders: an antisense-5'butyrylcholinesterase-DNA study

The wide tissue distribution of butyrylcholinesterase (BChE) in organisms makes specific roles possible, although no clear physiologic function has yet been assigned to this enzyme. In vertebrates, it appears e.g. in serum, hemopoietic cells, liver, lung, heart, at cholinergic synapses, in the central nervous system. in tumors and not at least (besides acetylcholinesterase, AChE) in developing embryonic tissues. Here, a functional role of BChE can be found in regulation of cell proliferation and the onset of differentiation during early neuronal development--independent of its enzymatic activity. For studies concerning this point, we have established a strategy for a specific and efficient inhibition of BChE to investigate how the expected decrease of enzyme and, therefore, the manipulation of cellular cholinesterase-equilibrium influences embryonic neurogenesis--among others to gain information about the significance of noncholinergic, activity-independent and cell growth functions of BChE. The antisense-5'BChE-DNA strategy is based on inhibition of BChE mRNA transcription and protein synthesis. For this, the BChE gene is cloned into a suitable vector system; this is done in antisense-orientation, so that a transfected cell will produce their own antisense mRNA to inhibit gene expression. For such investigations in neurogenesis, the developing retina is a good model and we are able to create organotypic, three-dimensional retinal aggregates in vitro (retinospheroids) using isolated retinal cells of 6-day-old chicken embryos. Using this in vitro retina and "knock out" of BChE gene expression, we could show a key role of BChE during neurogenesis. The results are of great interest because in tumorigenesis and some neuronal disorders, the BChE gene is amplified or abnormally expressed. It has to be discussed how the antisense-5'BChE strategy can play a role in the development of new and efficient therapy forms.

Blood cholinesterases as human biomarkers of organophosphorus pesticide exposure

The organophosphorus pesticides of this review were discovered in 1936 during the search for a replacement for nicotine for cockroach control. The basic biochemical characteristics of RBC AChE and BChE were determined in the 1940s. The mechanism of inhibition of both enzymes and other serine esterases was known in the 1940s and, in general, defined in the 1950s. In 1949, the death of a parathion mixer-loader dictated blood enzyme monitoring to prevent acute illness from organophosphorus pesticide intoxication. However, many of the chemical and biochemical steps for serine enzyme inhibition by OP compounds remain unknown today. The possible mechanisms of this inhibition are presented kinetically beginning with simple (by comparison) Michaelis-Menten substrate enzyme interaction kinetics. As complicated as the inhibition kinetics appear here, PBPK model kinetics will be more complex. The determination of inter- and intraindividual variation in RBC ChE and BChE was recognized early as critical knowledge for a blood esterase monitoring program. Because of the relatively constant production of RBCs, variation in RBC AChE was determined by about 1970. The source of plasma (or serum) BChE was shown to be the liver in the 1960s with the change in BChE phenotype to the donor in liver transplant patients. BChE activity was more variable than RBC AChE, and only in the 1990s have BChE individual variation questions been answered. We have reviewed the chemistry, metabolism, and toxicity of organophosphorus insecticides along with their inhibitory action toward tissue acetyl- and butyrylcholinesterases. On the basis of the review, a monitoring program for individuals mixing-loading and applying OP pesticides for commercial applicators was recommended. Approximately 41 OPs are currently registered for use by USEPA in the United States. Under agricultural working conditions, OPs primarily are absorbed through the skin. Liver P-450 isozymes catalyze the desulfurization of phosphorothioates and phosphorodithioates (e.g., parathion and azinphosmethyl, respectively) to the more toxic oxons (P = O(S to O)). In some cases, P-450 isozymes catalyze the oxidative cleavage of P-O-aryl bonds (e.g., parathion, methyl parathion, fenitrothion, and diazinon) to form inactive water-soluble alkyl phosphates and aryl leaving groups that are readily conjugated with glucuronic or sulfuric acids and excreted. In addition to the P-450 isozymes, mammalian tissues contain ('A' and 'B') esterases capable of reacting with OPs to produce hydrolysis products or phosphorylated enzymes. 'A'-esterases hydrolyze OPs (i.e., oxons), while 'B'-esterases with serine at the active center are inhibited by OPs. OPs possessing carboxylesters, such as malathion and isofenphos, are hydrolyzed by the direct action of 'B'-esterases (i.e., carboxylesterase, CaE). Metabolic pathways shown for isofenphos, parathion, and malathion define the order in which these reactions occur, while Michaelis-Menten kinetics define reaction parameters (Vmax, K(m)) for the enzymes and substrates involved, and rates of inhibition of 'B'-esterases (kis, bimolecular rate constants) by OPs and their oxons. OPs exert their insecticidal action by their ability to inhibit AChE at the cholinergic synapse, resulting in the accumulation of acetylcholine. The extent to which AChE or other 'B'-esterases are inhibited in workers is dependent upon the rate the OP pesticide is activated (i.e., oxon formation), metabolized to nontoxic products by tissue enzymes, its affinity for AChE and other 'B'-esterases, and esterase concentrations in tissues. Rapid recovery of OP BChE inhibition may be related to reactivation of inhibited forms. AChE, BChE, and CaE appear to function in vivo as scavengers, protecting workers against the inhibition of AChE at synapses. Species sensitivity to OPs varies widely and results in part from binding affinities (Ka) and rates of phosphorylation (kp) rather than rates of activation and detoxif

Organophosphate inhibition of human heart muscle cholinesterase isoenzymes

The rate of acetylcholine hydrolysis of mammalian heart muscle influences cardiac responses to vagal innervation. We characterized cholinesterases of human left ventricular heart muscle with respect to both substrate specificity and irreversible inhibition kinetics with the organophosphorus inhibitor N,N'-di-isopropylphosphorodiamidic fluoride (mipafox). Specimens were obtained postmortem from three men and four women (61 +/- 5 years) with no history of cardiovascular disease. Myocardial choline ester hydrolyzing activity was determined with acetylthiocholine (ASCh; 1.25 mM), acetyl-beta-methylthiocholine (AbetaMSCh; 2.0 mM), and butyrylthiocholine (BSCh; 30 mM). After irreversible and covalent inhibition (60 min; 25 degrees C) with a wide range of mipafox concentrations (50 nM-5 mM), residual choline ester hydrolyzing activities were fitted to a sum of up to five exponentials using weighted least-squares non-linear curve fitting. In each ease, quality of curve fitting reached its optimum on the basis of a four component model. Final classification of heart muscle cholinesterases was achieved according to substrate hydrolysis patterns (nmol/min per g wet weight) and to second-order organophosphate inhibition rate constants k2 (1/mol per min); one choline ester hydrolyzing enzyme was identified as acetylcholinesterase (AChE; k2/mipafox = 6.1 (+/- 0.8) x 10(2)), and one as butyrylcholinesterase (BChE; k2/mipafox = 5.3 (+/- 1.1) x 10(3)). An enzyme exhibiting both ChE-like substrate specificity and relative resistance to mipafox inhibition (k2/mipafox = 5.2 (+/- 1.0) x 10(-1)) was classified as atypical cholinesterase.

Regulation of cholinesterase gene expression affects neuronal differentiation as revealed by transfection studies on reaggregating embryonic chicken retinal cells

In the embryonic chicken neuroepithelium, butyrylcholinesterase (BChE) as a proliferation marker and then acetylcholinesterase (AChE) as a differentiation marker are expressed in a mutually exclusive manner. These and other data indicate a coregulation of cholinesterase expression, and also possible roles of cholinesterases during neurogenesis. Here, both aspects are investigated by two independent transfection protocols of dissociated retina cells of the 6-day-old chick embryo in reaggregation culture, both protocols leading to efficient overexpression of AChE protein. The effect of the overexpressed AChE protein on the re-establishment of retina-like three-dimensional networks (so-called retinospheroids) was studied. In a first approach, we transfected retinospheroids with a pSVK3 expression vector into which a cDNA construct encoding the entire rabbit AChE gene had been inserted in sense orientation. As detected at the mRNA level, rabbit AChE was heterologously overexpressed in chicken retinospheroids. Remarkably, this was accompanied by a strong increase in endogenous chicken AChE protein, while the total AChE activity was only slightly increased. This increase was due to chicken enzyme, as shown by species-specific inhibition studies using fasciculin. Clearly, total AChE activity is regulated post-translationally. As an alternative method of AChE overexpression, transfection of spheroids was performed with an antisense-5'-BChE vector, which not only resulted in the down-regulation of BChE expression, but also strongly increased chicken AChE transcripts, protein and enzyme activity. Histologically, a higher concentration of AChE protein (as a consequence of either AChE overexpression or BChE suppression) was associated with an advanced degree of tissue differentiation, as detected by immunostaining for the cytoskeletal protein vimentin.

Deletion of the acetylcholinesterase locus at 7q22 associated with myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML)

The genes for acetylcholinesterase (ACHE) and butyrylcholinesterase (BCHE) are located within regions subject to non-random chromosomal abnormalities in the myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML). Acetylcholinesterase is mapped to 7q22, within the critical deleted region presumed to contain a myeloid specific tumour suppressor gene. Butyrylcholinesterase is mapped to 3q26: abnormalities at this region are associated with sub-types of MDS and AML with thrombocytopenia, or with increased platelet counts. Both ACHE and BCHE have been implicated as playing a role in megakaryopoiesis and thrombopoiesis, and these genes have been observed to be co-amplified in acute myeloid leukaemia. Recent findings suggest a more significant role for the ACHE gene in haemopoiesis by regulating multipotent stem cell proliferation, and apoptosis in cells undergoing erythroid and myeloid differentiation. This led us to investigate gene copy-number alterations at these genes in MDS and AML. Samples were screened by slot-blot hybridization, and if changes were observed, by Southern blotting. A total of 42 samples from 31 de novo AML patients, 10 samples from eight cases of post-MDS AML and 85 samples from 67 MDS patients were analysed with probes for ACHE, BCHE, c-MYC, MDR-1 and globin control. Changes in ACHE and/or BCHE were observed in 9/31 de novo AML patients, and in 7/67 MDS patients: 1/37 cases of refractory anaemia (RA), 1/10 cases of refractory anaemia with excess blasts (RAEB) and 5/20 chronic myelomonocytic leukaemia (CMML) patients. The amplification events observed generated copy numbers no greater than 10, showed normal restriction patterns and had no clear correlation with megakaryopoiesis or thrombopoiesis. Loss of signal at the ACHE locus was observed: haploid signal intensity was seen in seven samples: one RA with thrombocytopenia, three CMML, one AML-M5a (no karyotypic abnormalities of chromosome 7), one AML-M4 (monosomy 7), and one case of AML-M7 (karyotype unknown). Homozygous deletion was observed at relapse of an additional patient with AML-M4. These data reinforce the possibility that ACHE may play a role as a myeloid tumour suppressor gene.

Engineering of human cholinesterases explains and predicts diverse consequences of administration of various drugs and poisons

The acetylcholine hydrolyzing enzyme, acetylcholinesterase, primarily functions in nerve conduction, yet it appears in several guises, due to tissue-specific expression, alternative mRNA splicing and variable aggregation modes. The closely related enzyme, butyrylcholinesterase, most likely serves as a scavenger of toxins to protect acetylcholine binding proteins. One or both of the cholinesterases probably also plays a non-catalytic role(s) as a surface element on cells to direct intercellular interactions. The two enzymes are subject to inhibition by a wide variety of synthetic (e.g., organophosphorus and carbamate insecticides) and natural (e.g., glycoalkaloids) anticholinesterases that can compromise these functions. Butyrylcholinesterase may function, as well, to degrade several drugs of interest, notably aspirin, cocaine and cocaine-like local anesthetics. The widespread occurrence of butyrylcholinesterase mutants with modified activity further complicates this picture, in ways that are only now being dissected through the use of site-directed mutagenesis and heterologous expression of recombinant cholinesterases.

Mapping the human acetylcholinesterase gene to chromosome 7q22 by fluorescent in situ hybridization coupled with selective PCR amplification from a somatic hybrid cell panel and chromosome-sorted DNA libraries

To establish the chromosomal location of the human ACHE gene encoding the acetylcholine hydrolyzing enzyme acetylcholinesterase (ACHE, acetylcholine acetylhydrolase, E.C. 3.1.1.7), a human-specific polymerase chain reaction (PCR) procedure that supports the selective amplification of ACHE DNA fragments from human genomic DNA was employed with 19 human-hamster somatic cell hybrids carrying one or more human chromosomes. Informative ACHE-specific PCR fragments were produced from two cell lines, both of which include human chromosome 7, but not with DNA from 17 cell hybrids carrying various combinations of all human chromosomes other than 7. Fluorescent in situ hybridization of biotinylated ACHE DNA with metaphase chromosomes from human peripheral blood lymphocytes revealed prominent labeling on the 7q22 position. Therefore, further tests were performed to confirm the chromosome 7 location. DNA samples from the two cell lines including chromosome 7 and the ACHE gene were positive with PCR primers informative for the human cystic fibrosis CFTR gene, known to reside at the 7q31.1 position, but negative for the ACHE-related butyrylcholinesterase (BCHE, acylcholine acylhydrolase, E.C. 3.1.1.8) gene, mapped at the 3q26-ter position, confirming that these lines contain chromosome 7 but not chromosome 3. In contrast, three other cell lines including chromosome 3, but not 7, were BCHE-positive and ACHE-negative. In addition, genomic DNA from a sorted chromosome 7 library supported the production of ACHE- but not BCHE-specific PCR products, whereas with DNA from a sorted chromosome 3 library, the BCHE but not the ACHE fragment was amplified.(ABSTRACT TRUNCATED AT 250 WORDS)

Butyrylcholinesterase from chicken brain is smaller than that from serum: its purification, glycosylation, and membrane association

Applying a new four-step isolation procedure, we have purified butyrylcholinesterase (BChE) from chicken serum to homogeneity with more than 250 U/mg specific activity. The serum enzyme was used for producing monoclonal antibodies. These BChE-specific also recognize BChE from brain, and thus enabled us to isolate the enzymes from embryonic and adult brain that occur only in minute amounts. More than 50% of the brain BChE is membrane-bound. The catalytic and inhibition properties of brain BChE are similar to those of serum BChE. However on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the serum enzyme is represented by a double-band of 79/82 kDa, whereas the brain enzyme has a size of 74 kDa. Limited digestion of the serum and brain preparations by V8-protease leads to similar peptide patterns. Enzymatic deglycosylation shows that their core proteins consist of 59-kDa subunits and that the different molecular weights are due to different glycosylation patterns. The differently sized glycosylation parts of brain and serum BChE may indicate that they subserve different functions. Furthermore, the membrane-bound brain BChE can be solubilized by Pronase or protease K, but not by phosphatidylinositol-specific phospholipase C.