title: Mutations at serine 37 in mouse guanylate kinase confer resistance to 6-thioguanine.
abstract: Guanylate kinase (GMK) is an essential nucleoside monophosphate kinase that catalyzes the phosphorylation of guanine-monophosphate (GMP) and dGMP to yield GDP and dGDP, respectively, important precursors for nucleotide synthesis. GMK is also responsible for the activation of 6-thioguanine (6-TG), a drug widely used as chemotherapeutic agent to treat leukemia. Several mechanisms of resistance to 6-TG have been reported but a subset of drug resistant cells cannot be explained by these mechanisms. We propose that mutations in GMK could result in drug resistance. Because cells require the presence of a functional GMK for viability, mutations that arise that lead to 6-TG resistance must retain activity toward GMP. We report three amino acid substitutions at serine 37 (S37) in mouse GMK that display activity toward GMP by conferring genetic complementation to a conditional GMK-deficient Escherichia coli and in enzyme assays. When 6-TG is included in complementation studies, cells expressing wild-type GMK are sensitive whereas all S37 mutants examined are able to effectively discriminate against 6-TG and display a drug resistance phenotype. Activity of the three S37 mutant enzymes toward clinically relevant concentrations of 6-TGMP is undetectable. Mutations in GMK, therefore, represent a previously undescribed mechanism for 6-TG resistance.
authors.affiliation: School of Molecular Biosciences, Washington State University, PO Box 646534, Pullman,WA 99164-6534, USA.
authors.forename: Andressa
authors.initials: A
authors.lastname: Ardiani
authors.forename: Amanda
authors.initials: A
authors.lastname: Goyke
authors.forename: Margaret E
authors.initials: ME
authors.lastname: Black
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D005816:Genetic Complementation Test; D051528:Guanylate Kinases / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D013866:Thioguanine / Q000494:pharmacology*
chemical_list: D000964:Antimetabolites, Antineoplastic; D051528:Guanylate Kinases; D013866:Thioguanine