Absence of tRNA-guanine transglycosylase in a human colon adenocarcinoma cell line.
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.
Gündüz
U
U
Department of Microbiology and Immunology, University of Tennessee, Memphis 38163.
Elliott
M S
MS
Seubert
P H
PH
Houghton
J A
JA
Houghton
P J
PJ
Trewyn
R W
RW
Katze
J R
JR
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
D006147:Guanine; C019549:queuine; D012343:RNA, Transfer; D010430:Pentosyltransferases; C020837:queuine tRNA-ribosyltransferase; D001374:Azacitidine