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-deazaguan ine, is a nutrient factor for lower and higher eukaryotes, except yeas t; it is synthesized in eubacteria partly at the level of tRNA. In euk aryotes q is preferentially inserted into the wobble position of speci fic tRNAs in differentiated and adult tissues, but occurs mainly free in embryonic and fast proliferating cells. HeLa cells grow to a higher cell densitiy under aerobic than under hypoxic conditions only when s upplemented with q. Here we show that in hypoxically grown HeLa cells, sufficiently supplied with q, free q accumulated when serum factors b ecome limiting while the respective tRNAs re mained completely q defic ient. In these cells the levels of lactate dehydrogenase A (LDH A) mRN A and of LDH A protein were at least twofold higher than in aerobicall y grown cells, independent of the absence or presence of q. In respons e to q the LDH A(4) isoenzyme was further activated by a post-translat ional mechanism. In q-deficient HeLa cells the activity of the major a noxic stress protein, LDH(k), increased as a result of hypoxia; this i ncrease was suppressed by q. In aerobically grown, q-deficient cells s ignificant activities of LDH A(4) and LDH(k) were present; both activi ties were markedly lowered by q, while the mitochondrial electron flow was improved. These results show that q is essential for relieving hy poxic stress in HeLa cells that results from oxygen limitation.