PRESENCE OF A HETEROZYGOUS SUBSTITUTION AND ITS RELATIONSHIP TO DT-DIAPHORASE ACTIVITY

A point mutation in the mRNA of NADP(H): quinone oxidoreductase 1 (NQO (1), DT-diaphorase) is believed to be responsible for reduced enzyme a ctivity in the adenocarcinoma BE cell line. The present study examined nine cultured human non-cancerous fibroblast cell strains, five of wh ich were from members of a single cancer-prone family, which demonstra ted widely varying activity levels of DT-diaphorase (41-3462 nmol min( -1) mg(-1) protein), to determine if genetic alteration of the NQO(1) or NOQ(2) gene was involved in determining enzyme activity. All cell s trains expressed NQO(1) and NQO(2) mRNA as measured by a quantitative polymerase chain reaction amplification technique. No relationship was found between the level of mRNA expressed and the enzyme activity in the cells. Sequencing of the entire complementary DNA from the cell st rains revealed only a single base substitution at nucleotide 609 in on e allele encoding NQO(1) in every cell strain from members of the canc er-prone family, except for one cell strain which expressed only the T at nucleotide 609 in both alleles. Subsequent examination of genomic DNA from 44 individuals revealed that this base substitution is presen t in approximately 50% of the population. The presence of the T at nuc leotide 609 in the NQO(1) locus does not appear to be directly causal for altered DT-diaphorase activity.