The Nicotinic Acetylcholine Receptors of the Parasitic Nematode Ascaris suum: Formation of Two Distinct Drug Targets by Varying the Relative Expression Levels of Two Subunits

PLoS Pathogens

Adrian J. Wolstenholme¹  Sally M. Williamson¹  Richard J. Martin²  Alan P. Robertson²  Laurence Brown³  David B. Sattelle³  Tracey Williams⁴  Debra J. Woods⁴ 

[1] Department of Biology & Biochemistry, University of Bath, Bath, United Kingdom;Department of Biomedical Sciences, Iowa State University, Ames, Iowa, United States of America;MRC Functional Genomics Unit, Oxford, United Kingdom;Veterinary Medicine Research & Development, Pfizer Animal Health, Kalamazoo, Michigan, United States of America

关键词: Nicotinic acetylcholine receptors;    Caenorhabditis elegans;    Xenopus oocytes;    Muscle cells;    Oocytes;    Acetylcholine;    Nicotine;    Sequence motif analysis;   

DOI  :  10.1371/journal.ppat.1000517

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

Parasitic nematodes are of medical and veterinary importance, adversely affecting human health and animal welfare. Ascaris suum is a gastrointestinal parasite of pigs; in addition to its veterinary significance it is a good model of the human parasite Ascaris lumbricoides, estimated to infect ∼1.4 billion people globally. Anthelmintic drugs are essential to control nematode parasites, and nicotinic acetylcholine receptors (nAChRs) on nerve and muscle are the targets of cholinergic anthelmintics such as levamisole and pyrantel. Previous genetic analyses of nematode nAChRs have been confined to Caenorhabditis elegans, which is phylogenetically distinct from Ascaris spp. and many other important parasites. Here we report the cloning and expression of two nAChR subunit cDNAs from A. suum. The subunits are very similar in sequence to C. elegans UNC-29 and UNC-38, are expressed on muscle cells and can be expressed robustly in Xenopus oocytes to form acetylcholine-, nicotine-, levamisole- and pyrantel-sensitive channels. We also demonstrate that changing the stoichiometry of the receptor by injecting different ratios of the subunit cRNAs can reproduce two of the three pharmacological subtypes of nAChR present in A. suum muscle cells. When the ratio was 5∶1 (Asu-unc-38∶Asu-unc-29), nicotine was a full agonist and levamisole was a partial agonist, and oocytes responded to oxantel, but not pyrantel. At the reverse ratio (1∶5 Asu-unc-38∶Asu-unc-29), levamisole was a full agonist and nicotine was a partial agonist, and the oocytes responded to pyrantel, but not oxantel. These results represent the first in vitro expression of any parasitic nicotinic receptor and show that their properties are substantially different from those of C. elegans. The results also show that changing the expression level of a single receptor subunit dramatically altered the efficacy of some anthelmintic drugs. In vitro expression of these subunits may permit the development of parasite-specific screens for future anthelmintics.

【 授权许可】

CC BY