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DNA Ligase and DNase Activities in Mouse Erythroleukemia Cells during Dimethyl Sulfoxide-induced Differentiation¹

Cancer Chemotherapy Foundation Laboratory, Division of Medical Oncology, Department of Medicine [W. S., A. R., S. W.] and Department of Microbiology [B. M. S.], Mount Sinai School of Medicine, New York, New York 10029

DNA ligase and DNase levels were measured in cell-free extracts from untreated mouse erythroleukemia (MEL) cells and from cells treated with dimethyl sulfoxide (Me₂SO) to induce erythroid differentiation. The DNase activity present in the extracts was sensitive to inhibition by G-actin and was, therefore, presumed to be DNase I. When the MEL cells were induced to differentiate by culturing in the presence of 1.8% Me₂SO for 3 or 4 days, the apparent activity of the DNA ligase decreased to approximately 12% of the value in untreated MEL cells. In contrast, the apparent DNase I activity of the extracts from Me₂SO-treated cells increased over that in extracts from untreated cells by a factor of 2. The activity of acid phosphatase, a lysosomal enzyme, remained unchanged. When strain DR-10, a mutant of the MEL cells which does not undergo Me₂SO-induced differentiation, was treated with Me₂SO, the DNA ligase and DNase activities of extracts from these cells remained unchanged as compared to extracts from untreated DR-10 cells. Therefore, the marked decrease in the level of DNA ligase activity appeared to be related to the process of differentiation in the Me₂SO-treated MEL cells.

¹ This work was supported by USPHS Grants AM 16690-06 from the National Institute of Arthritis, Metabolism, and Digestive Diseases; CA 24402-03 from the National Cancer Institute; CH-144 from the American Cancer Society; the Chemotherapy Foundation, Inc.; and the Charles E. Merrill Trust. Part of this work was presented at the 1980 meeting of the American Association for Cancer Research, San Diego, Calif. (30).

² To whom requests for reprints should be addressed, at Division of Medical Oncology, Mount Sinai School of Medicine, 1 Gustave L. Levy Place, New York, N. Y. 10029.

Received 3/26/81. Accepted 1/ 7/82.

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