Miller D M, Polansky D A, Thomas S D, Ray R, Campbell V W, Sanchez J, Koller C A
Comprehensive Cancer Center, University of Alabama, Birmingham 35294.
Am J Med Sci. 1987 Nov;294(5):388-94. doi: 10.1097/00000441-198711000-00015.
Mithramycin induces a reversible inhibition of cellular RNA synthesis without affecting DNA synthesis. The authors have shown this drug induces myeloid differentiation of HL-60 promyelocytic leukemia cells and is an effective agent in certain patients with chronic granulocytic leukemia. In order to investigate the mechanism by which this drug inhibits RNA synthesis we have compared the effect of mithramycin on RNA synthesis by whole cells, isolated nuclei, and RNA synthesis by isolated E. coli RNA polymerase and eukaryotic RNA polymerase II. Exposure of HL-60 cells to mithramycin at concentrations of 4.6 X 10(-7) m or higher for 48 hours causes an almost immediate inhibition of RNA synthesis (up to 85% at 4 hours) with only modest cytotoxicity at these concentrations. Endogenous RNA synthesis by isolated nuclei can be inhibited by mithramycin only at high concentrations (greater than 10(-5) m), suggesting that mithramycin primarily may inhibit initiation, rather than elongation. Mithramycin inhibits in vitro transcription of salmon sperm DNA by E. coli RNA polymerase at DNA:drug ratios similar to those required for RNA synthesis inhibition in whole cells. Similar DNA binding studies with synthetic oligonucleotides demonstrate that mithramycin is a potent inhibitor of transcription of Poly dG.dC by E. coli RNA polymerase but has no effect on transcription of Poly dA.dT. The rapid inhibition of whole cell and isolated RNA polymerase transcription, and the relative insensitivity of isolated nuclei, suggest mithramycin may interact with specific DNA sequences in order to inhibit the initiation of RNA synthesis in intact cells.
光辉霉素可诱导细胞RNA合成的可逆性抑制，而不影响DNA合成。作者已表明，这种药物可诱导HL-60早幼粒细胞白血病细胞的髓系分化，并且对某些慢性粒细胞白血病患者是一种有效药物。为了研究这种药物抑制RNA合成的机制，我们比较了光辉霉素对全细胞RNA合成、分离细胞核RNA合成以及对分离的大肠杆菌RNA聚合酶和真核RNA聚合酶II的RNA合成的影响。将HL-60细胞暴露于浓度为4.6×10⁻⁷m或更高的光辉霉素中48小时，几乎可立即抑制RNA合成（4小时时高达85%），而在这些浓度下细胞毒性较小。只有在高浓度（大于10⁻⁵m）时，光辉霉素才能抑制分离细胞核的内源性RNA合成，这表明光辉霉素主要可能抑制起始，而非延伸。光辉霉素以与全细胞中RNA合成抑制所需的DNA:药物比例相似的比例抑制大肠杆菌RNA聚合酶对鲑鱼精子DNA的体外转录。用合成寡核苷酸进行的类似DNA结合研究表明，光辉霉素是大肠杆菌RNA聚合酶对Poly dG.dC转录的有效抑制剂，但对Poly dA.dT的转录没有影响。全细胞和分离的RNA聚合酶转录的快速抑制以及分离细胞核的相对不敏感性表明，光辉霉素可能与特定DNA序列相互作用，以抑制完整细胞中RNA合成的起始。
