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 medium containing 1% serum without selenium supplementation [Se(-) cells] were severely depressed in selenoperoxidase (SePX) activity relative to selenium-supplemented controls [Se(+) cells]. Catalase (CAT) activity in Se(-) cells was unaffected up to this point, but thereafter began to increase. Two manifestations of this increase have been differentiated for both cell lines: (a) short-term induction of CAT (up to approx. twofold) after 2-3 weeks, followed by (b) long-term selection for cells that irreversibly express much higher levels of CAT, e.g., > 100 times (L1210) and > 10 times (HL-60) the levels observed in Se(+) controls after approximately 20 weeks. Although superoxide dismutase, glutathione S-transferase, and glucose-6-P dehydrogenase activities were unchanged in Se(-) cells, GSH levels were elevated by 50-100%; like short-term CAT elevation, this could be reversed by supplying Se. Short-term Se(-) cells were more sensitive to H2O2-induced killing than Se(+) cells, evidently because SePX activity was important for peroxide detoxification. 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 number 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 least 40 times higher than that of the Se(+) control. Similar trends were observed for HL-60 cells. These results suggest that elevated CAT during long-term Se deprivation is a reflection of amplification and greater transcription of the CAT gene.
Lin
F
F
Department of Biochemistry, Medical College of Wisconsin, Milwaukee 56226.
Jackson
V E
VE
Girotti
A W
AW
D000818:Animals; D002374:Catalase / Q000096:biosynthesis* / Q000235:genetics; D004273:DNA, Neoplasm / Q000032:analysis; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007938:Leukemia / Q000201:enzymology* / Q000235:genetics; D051379:Mice; D010544:Peroxidases / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D015183:Restriction Mapping; D012643:Selenium / Q000172:deficiency; D051140:Selenoproteins; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D011506:Proteins; D012333:RNA, Messenger; D051140:Selenoproteins; D006861:Hydrogen Peroxide; D010544:Peroxidases; D002374:Catalase; D012643:Selenium