AMPLIFICATION AND HYPEREXPRESSION OF THE CATALASE GENE IN SELENOPEROXIDASE-DEFICIENT LEUKEMIA-CELLS

Murine L1210 and human HL-60 leukemia cells grown for 5-7 days in medi um containing 1% serum without selenium supplementation [Se(-) cells] were severely depressed in selenoperoxidase (SePX) activity relative t o selenium-supplemented controls [Se(+) cells]. Catalase (CAT) activit y in Se(-) cells was unaffected up to this point, but thereafter began to increase. Two manifestations of this increase have been differenti ated for both cell lines: (a) short-term induction of CAT (up to appro x. twofold) after 2-3 weeks, followed by (b) long-term selection for c ells that irreversibly express much higher levels of CAT, e.g., >100 t imes (L1210) and >10 times (HL-60) the levels observed in Se(+) contro ls after similar to 20 weeks. Although superoxide dismutase, glutathio ne S-transferase, and glucose-6-P dehydrogenase activities were unchan ged in Se(-) cells, GSH levels were elevated by 50-100%; like short-te rm CAT elevation, this could be reversed by supplying Se. Short-term S e(-) cells were more sensitive to H2O2-induced killing than Se(+) cell s, evidently because SePX activity was important for peroxide detoxifi cation. However, long-term Se(-) cells were markedly more resistant to H2O2 than Se(+) counterparts, consistent with the much higher levels of CAT in the former. Southern blot analysis revealed that the copy nu mber of CAT DNA in a clone of long-term Se(-) L1210 cells was four- to fivefold greater than that in an Se(+) clone. Northern blot analysis of RNA from the same Se(-) clone showed a CAT mRNA level that was at l east 40 times higher than that of the Se(+) control. Similar trends we re observed for HL-60 cells. These results suggest that elevated CAT d uring long-term Se deprivation is a reflection of amplification and gr eater transcription of the CAT gene. (C) 1995 Academic Press, Inc.