Amplification and Hyperexpression of the Catalase Gene in Selenoperoxidase-Deficient Leukemia Cells

• Published in: Archives of biochemistry and biophysics 1995-02, Vol.317 (1), p.7-18
• Main Authors: Lin, F.B., Jackson, V.E., Girotti, A.W.
• Format: Article
• Language: English
• Subjects: Animals; Catalase - biosynthesis; Catalase - genetics; DNA, Neoplasm - analysis; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Humans; Hydrogen Peroxide - pharmacology; Leukemia - enzymology; Leukemia - genetics; Mice; Peroxidases - genetics; Peroxidases - metabolism; Proteins - genetics; Proteins - metabolism; Restriction Mapping; RNA, Messenger - analysis; Selenium - deficiency; Selenoproteins; Tumor Cells, Cultured
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1006/abbi.1995.1129

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 ∼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 H 2O 2-induced killing than Se(+) cells, evidently because SePX activity was important for peroxide detoxification. However, long-term Se(−) cells were markedly more resistant to H 2O 2 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.