Inhibition of messenger RNA accumulation but not translation in ultraviolet irradiated hepatoma cells
Biochemical and Biophysical Research Communications (Impact Factor: 2.3). 05/1974; 57(3):949-956. DOI: 10.1016/0006-291X(74)90636-6
Irradiation by ultraviolet light at doses between 30 and 90 ergs/mm2 increasingly inhibited the hydrocortisone but not the insulin induction of tyrosine aminotransferase activity in Reuber (H35) hepatoma cells in culture. Incorporation of lecuine into cellular protein was only slightly inhibited in this dose range. Incorporation of uridine into RNA in the presence of low doses of actinomycin D (0.1 μg/ml) was increasingly inhibited by ultraviolet irradiation. Since cellular uptake of uridine into the acid soluble pool was not inhibited by ultraviolet irradiation, the inhibition of RNA labeling suggests inhibition of synthesis of heterogenous nuclear RNA by low doses of ultraviolet irradiation. “Unscheduled” DNA synthesis was initially stimulated 2 fold by 30 ergs/mm2 irradiation and returned to control levels in 8 hours. Thus, ultraviolet irradiation in the low dose range causes DNA repair synthesis, inhibits transcription and apparently tyrosine aminotransferase messenger RNA accumulation while pre-existing cytoplasmic messenger appears not to be inactivated nor its translation inhibited.
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ABSTRACT: Low doses of ultraviolet irradiation at 254 nm inhibited the dexamethasone induction of tyrosine aminotransferase (E.C. 184.108.40.206) in H-35 Reuber (H-4-II-E) hepatoma cells exposed to bromodeoxyuridine for approximately two generations of growth. The cells were transferred to a serum-free medium for the hormone induction studies so that growth inhibition would not be a factor in the experiments. Doses of 90 ergs/mm2 inhibited the glucocorticoid induction and resulted in a decline in tyrosine aminotransferase in both basal- and steroid-induced levels of the enzyme. Comparison of the inhibition of the glucocorticoid induction by low doses of ultraviolet irradiation at 254 nm in thymidine-treated versus bromodeoxyuridine-treated cells suggested that bromodeoxy-uridine-treated cells were more sensitive to low doses of irradiation. The basal activities of two other enzymes, alkaline phosphatase and leucine aminopeptidase, were only slightly inhibited 6 hours following irradiation of bromodeoxy-uridine-treated cells. These results suggest that studies using ultraviolet irradiation of monolayer cell cultures to study different mechanisms of hormonal regulation of cellular processes may provide an alternative approach for studies on modulation of gene expression.Biochemical and Biophysical Research Communications 02/1977; 74(1-74):92-99. DOI:10.1016/0006-291X(77)91379-1 · 2.30 Impact Factor
- Cancer Research 09/1978; 38(8):2533-8. · 9.33 Impact Factor
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ABSTRACT: —Germicidal ultraviolet light (UVC. 8–10 J/m2) induces ornithine decarboxylase (ODC) in mouse epidermal cells in vitro in a biphasic manner with maxima of 2–3 fold induction at 4–6 h and of 10–20 fold induction at 15–18 h after irradiation. At this dose of UVC overall protein synthesis is inhibited by 10–30% and RNA synthesis by 40–50%. Induction of both ODC peaks is prevented by actinomycin D or cycloheximide. Similar culture factors appear to influence the extent of ODC induction by UVC and by the tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA), since the ratio of peak activities is approximately constant at 2, whereas absolute values vary considerably between experiments. If cells are irradiated with UVC and then exposed to TPA, the effects are additive at 10 J/m2, less than additive at higher and enhanced at lower doses of UVC.Photochemistry and Photobiology 09/1980; 32(2):177-81. DOI:10.1111/j.1751-1097.1980.tb04006.x · 2.27 Impact Factor
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