title: Absence of tRNA-guanine transglycosylase in a human colon adenocarcinoma cell line.
abstract: Queuosine (Q), found exclusively in the first position of the anticodons of tRNA(Asp), tRNA(Asn), tRNA(His) and tRNA(Tyr), is synthesized in eucaryotes by a base-for-base exchange of queuine, the base of Q, for guanine at tRNA position 34. This reaction is catalyzed by the enzyme tRNA-guanine transglycosylase (EC 2.4.2.29). We measured the specific release of queuine from Q-5'-phosphate (queuine salvage) and the extent of tRNA Q modification in 6 human tumors carried as xenografts in immune-deprived mice. Q-deficient tRNA was found in 3 of the tumors but it did not correlate with diminished queuine salvage. The low tRNA Q content of one tumor, the HxGC3 colon adenocarcinoma, prompted us to examine a HxGC3-derived cell line, GC3/M. GC3/M completely lacks Q in its tRNA and measurable tRNA-guanine transglycosylase activity; the first example of a higher eucaryotic cell which lacks this enzyme. Exposure of GC3/M cells to 5-azacytidine induces the transient appearance of Q-positive tRNA. This result suggests that at least one allele of the transglycosylase gene in GC3/M cells may have been inactivated by DNA methylation. In clinical samples, we found Q-deficient tRNA in 10 of 46 solid tumors, including 2 of 13 colonic carcinomas.
authors.affiliation: Department of Microbiology and Immunology, University of Tennessee, Memphis 38163.
authors.forename: U
authors.initials: U
authors.lastname: Gündüz
authors.forename: M S
authors.initials: MS
authors.lastname: Elliott
authors.forename: P H
authors.initials: PH
authors.lastname: Seubert
authors.forename: J A
authors.initials: JA
authors.lastname: Houghton
authors.forename: P J
authors.initials: PJ
authors.lastname: Houghton
authors.forename: R W
authors.initials: RW
authors.lastname: Trewyn
authors.forename: J R
authors.initials: JR
authors.lastname: Katze
mesh_terms: D000230:Adenocarcinoma / Q000201:enzymology*; D000818:Animals; D001374:Azacitidine / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D003110:Colonic Neoplasms / Q000201:enzymology*; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D051379:Mice; D009154:Mutation; D009368:Neoplasm Transplantation; D010430:Pentosyltransferases / Q000172:deficiency* / Q000235:genetics; D012323:RNA Processing, Post-Transcriptional; D012343:RNA, Transfer / Q000737:chemistry; D012208:Rhabdomyosarcoma / Q000201:enzymology; D014407:Tumor Cells, Cultured
chemical_list: D006147:Guanine; C019549:queuine; D012343:RNA, Transfer; D010430:Pentosyltransferases; C020837:queuine tRNA-ribosyltransferase; D001374:Azacitidine