Disease relevance of PNPLA6

• The Swiss Cheese protein which, when mutated, leads to widespread cell death in Drosophila brain [Kretzschmar, Hasan, Sharma, Heisenberg and Benzer (1997) J. Neurosci. 17, 7425-7432], was strikingly homologous to NTE, suggesting that genetically altered NTE may be involved in human neurodegenerative disease [1].
• In this study, we have investigated a possible role for NTE in the all-trans retinoic acid-induced differentiation of neuroblastoma cells [2].
• Measurement of neuropathy target esterase activity (NTE) in blood lymphocytes has been suggested as a possible biomonitor for organophosphate-induced delayed polyneuropathy [3].
• Here we show that NEST, a recombinant polypeptide expressed in Escherichia coli, reacts with an ester substrate and covalent inhibitors in a manner very similar to NTE [4].
• However, a number of other serine acylhydrolases (patatin, Group VI PLA(2)s, Pseudomonas aeruginosa ExoU and NTE) contain the Ser/Asp catalytic dyad characteristic of Group IV PLA(2)s, and recent structural analysis of patatin has confirmed its structural similarity to cPLA(2)alpha [5].

High impact information on PNPLA6

• CONCLUSION: Some Gulf War veterans may have delayed, chronic neurotoxic syndromes from wartime exposure to combinations of chemicals that inhibit butyrylcholinesterase and neuropathy target esterase [6].
• MAIN OUTCOME MEASURES: Associations of factor analysis-derived syndromes with risk factors for chemical interactions that inhibit butyrylcholinesterase and neuropathy target esterase [6].
• For a 500-1,000-A biological tissue section fixed with OsO4 and stained with uranyl acetate, we obtained resolution (half distance, HD) values of approximately 800 +/- 120 A using Ilford L4 emulsion and 500 +/- 70 A using a Kodak NTE-type emulsion [7].
• Diisopropyl fluorophosphate, which inhibits NTE esterase activity, reduces GPC accumulation, as does an siRNA that specifically reduces NTE protein abundance [8].
• Neuropathy target esterase (NTE) was recently shown to be a phospholipase B that catalyzes production of GPC from phosphatidylcholine [8].

Chemical compound and disease context of PNPLA6

• In this study we have investigated a possible role for NTE in the all-trans retinoic acid (ATRA)-induced differentiation of neuroblastoma cells by antisense RNA [9].
• A neuroblastoma cell line of human origin was used as an in vitro model system to examine early effects on inhibition of neuropathy target esterase (NTE, also known as neurotoxic esterase) in the presence of agents belonging to classes of chemicals previously demonstrated to modify organophosphorus-induced delayed neuropathy in hens [10].
• In addition, high repeated doses of phenyl N-methyl N-benzylcarbamate caused nearly 100% NTE inhibition and polyneuropathy in the hen model [11].
• Different levels of NTE inhibition as caused by different compounds were promoted by the same dose of phenylmethanesulfonyl fluoride to similar degrees of ataxia [12].
• These results indicate that NTE inhibition can be detected in neuroblastoma cells, that these cells respond in a manner similar to chicken brain, and that mipafox-induced inhibition of NTE can be decreased in the presence of aldicarb or verapamil [10].

Biological context of PNPLA6

• Neuropathic OPs react covalently with NTE in a rapid two-step process which not only inhibits catalytic activity but also leaves a negatively-charged OP group attached to the active site serine [13].
• NTE comprises an N-terminal regulatory domain (with some sequence similarity to cyclic nucleotide-binding proteins) and a C-terminal catalytic domain: the latter has three predicted transmembrane segments and requires membrane-association for activity [13].
• In vitro, NTE potently catalyses hydrolysis of phenyl valerate: however, its physiological substrate is likely to be a metabolite of a much longer chain carboxylic acid, possibly associated with cell membranes [13].
• We conclude that NTE and its homologues play a central role in membrane lipid homeostasis [14].
• In [(14)C]choline labeling experiments with cultured mammalian cell lines, production of [(14)C]GroPCho was enhanced by overexpression of catalytically active NTE and was diminished by reduction of endogenous NTE activity mediated either by RNA interference or organophosphate treatment [14].

Anatomical context of PNPLA6

• NTE was discovered originally as the primary target for those organophosphorus esters (OPs) which cause a delayed neuropathy with degeneration of long axons in peripheral nerves and spinal cord [13].
• Recent evidence suggests that NTE plays an important role in neural development, possibly via involvement in a signalling pathway between neurons and glial cells [13].
• Experiments involving proteinase treatment revealed that most of the NTE molecule is exposed on the cytoplasmic face of membranes [15].
• In cells expressing a moderate level of NTE and all cells expressing DeltaC-NTE, fluorescence was distributed in an endoplasmic reticulum (ER)-like pattern [15].
• YML059c, a Saccharomyces cerevisiae protein with sequence homology to NTE, had similar catalytic properties to the mammalian enzyme in assays of microsome preparations and, like NTE, was localized to the endoplasmic reticulum [14].

Associations of PNPLA6 with chemical compounds

• The overall in vivo findings with 16 compounds indicate the expected association of AChE inhibition with acute or cholinergic syndrome and >70% brain NTE inhibition with delayed neurotoxic action [16].
• The net damage to peripheral nerve axons is a balance between ongoing degenerative and repair processes: the latter involve serine hydrolases which can be inhibited by the same OPs used to modify NTE [13].
• NTE has homologues in Drosophila and yeast and is detected in vitro by assays with a non-physiological ester substrate, phenyl valerate [17].
• NTE was solubilized from a mixture of mitochondrial and microsomal membranes with Triton X-100 [18].
• A substantial amount of the NTE activity of a human lymphocyte preparation made using Ficoll/Pacque was due to contamination by platelets; further purification was achieved by sucrose-gradient centrifugation [19].

Enzymatic interactions of PNPLA6

• Bioelectrochemical analysis of neuropathy target esterase (NTE) and its inhibitors is based on the combination of the NTE-catalyzed hydrolysis of phenyl valerate and phenol detection by a tyrosinase carbon-paste electrode [20].

Other interactions of PNPLA6

• More generally, the studies revealed 12 selective in vitro inhibitors for FAAH (mostly octylsulfonyl and octylphosphonyl derivatives) and 9 for NTE (mostly benzodioxaphosphorin oxides and organophosphorus fluoridates) [16].
• However, recent evidence has shown that acetylcholinesterase (AChE) and the catalytic domain of human neuropathy target esterase (NEST) undergo aging by alternative mechanisms following their inhibition with N,N'-diisopropylphosphorodiamidofluoridate (mipafox, MIP) [21].
• The results of mutating the 11 histidines in NEST suggest that NTE does not use a conventional catalytic triad [4].
• NTE has serine esterase activity and efficiently catalyses the hydrolysis of phenyl valerate (PV) in vitro, but its physiological substrate is unknown [22].
• The use of the tyrosinase electrode improves 10-fold the sensitivity of NTE detection in comparison with a spectrophotometric method [20].

Analytical, diagnostic and therapeutic context of PNPLA6

• Esterase assays and Western blots of particulate and soluble fractions indicated that neither the TM nor R-domain is essential for NTE catalytic activity but that this activity requires membrane association to which the TM, R-, and C-domains all contribute [15].
• NEST comprises residues 727-1216 of human NTE, and site-directed mutagenesis revealed that serine 966 and two aspartate residues, Asp(1086) and Asp(960), are critical for catalysis [4].
• NTE preparations were obtained, which did not contain paraxon-sensitive or mipafox-resistant hydrolases, by selective reconstitution of detergent-solubilized NTE from chick embryo brain into asolectin vesicles during gel filtration [23].
• The biosensor enables NTE to be assayed in whole blood, whereas this cannot be done with the usual colorimetric method [24].
• Inhibition/aging of brain NTE within hours of exposure predicts the potential for development of OPIDN in susceptible animal models [24].

References