The nutrient factor queuine protects HeLa cells from hypoxic stress and improves metabolic adaptation to oxygen availability.
Queuine (q), a cyclopentendiol derivative of 7-aminomethyl-7-deazaguanine, is a nutrient factor for lower and higher eukaryotes, except yeast; it is synthesized in eubacteria partly at the level of tRNA. In eukaryotes q is preferentially inserted into the wobble position of specific tRNAs in differentiated and adult tissues, but occurs mainly free in embryonic and fast proliferating cells. HeLa cells grow to a higher cell density under aerobic than under hypoxic conditions only when supplemented with q. Here we show that in hypoxically grown HeLa cells, sufficiently supplied with q, free q accumulated when serum factors become limiting while the respective tRNAs remained completely q deficient. In these cells the levels of lactate dehydrogenase A (LDH A) mRNA and of LDH A protein were at least twofold higher than in aerobically grown cells, independent of the absence or presence of q. In response to q the LDH A4 isoenzyme was further activated by a post-translational mechanism. In q-deficient HeLa cells the activity of the major anoxic stress protein, LDHk, increased as a result of hypoxia; this increase was suppressed by q. In aerobically grown, q-deficient cells significant activities of LDH A4 and LDHk were present; both activities were markedly lowered by q, while the mitochondrial electron flow was improved. The results show that free q is essential for relieving hypoxic stress in HeLa cells that results from oxygen limitation.
Reisser
T
T
Institut für Biochemie, Universität Erlangen-Nürnberg, Germany.
Langgut
W
W
Kersten
H
H
D000222:Adaptation, Physiological; D015152:Blotting, Northern; D002452:Cell Count / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology*; D004579:Electron Transport; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D010101:Oxygen Consumption; D012343:RNA, Transfer / Q000378:metabolism*
D007527:Isoenzymes; D006147:Guanine; C019549:queuine; D012343:RNA, Transfer; D007770:L-Lactate Dehydrogenase