Distinct effects of topoisomerase I and RNA polymerase I inhibitors suggest a dual mechanism of nucleolar/nucleoplasmic partitioning of topoisomerase I
Distinct effects of topoisomerase I and RNA polymerase I inhibitors suggest a dual mechanism of nucleolar/nucleoplasmic partitioning of topoisomerase I
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DOI：
10.1074/jbc.m400498200
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发表时间：
2004-05-21
影响因子：
4.8
通讯作者：
Mielke, C
中科院分区：
文献类型：
--
作者：
Christensen, MO;Krokowski, RM;Mielke, C
拓扑异构酶I主要是核仁的，因为它在核糖体DNA（rDNA）转录中起着卓越的作用。在暴露于稳定酶的共价DNA中间体的药物后，它从核仁中清除（例如，G.喜树碱）或抑制RNA聚合酶（例如，G.放线菌素D），该作用概括地归因于rDNA转录的阻断。在这里，我们表明有两种不同的机制在起作用：（i）两种药物都会诱导rRNA转录机制的失活和分离。放线菌素D导致RNA聚合酶I和拓扑异构酶I共同迁移到核仁周边.该过程具有缓慢的开始（> 20分钟），不依赖于拓扑异构酶I活性，但需要酶的N-末端结构域与RNA聚合酶I共定位。（ii）此外，喜树碱诱导活性拓扑异构酶I在基因组DNA上的固定化，导致快速核仁清除和酶扩散到整个核质。这种效应不依赖于rRNA转录的状态，涉及拓扑异构酶I从RNA聚合酶I的分离，具有快速的起始（< 1分钟），并且需要催化活性，但既不需要拓扑异构酶I的N-末端结构域也不需要其主要的类小泛素化位点。因此，拓扑异构酶I的核仁/核质分配受RNA聚合酶I和DNA相互作用的调节，但不受SUMO化的影响。
Topoisomerase I is mostly nucleolar, because it plays a preeminent role in ribosomal DNA ( rDNA) transcription. It is cleared from nucleoli following exposure to drugs stabilizing covalent DNA intermediates of the enzyme ( e. g. camptothecin) or inhibiting RNA polymerases ( e. g. actinomycin D), an effect summarily attributed to blockade of rDNA transcription. Here we show that two distinct mechanisms are at work: ( i) Both drugs induce inactivation and segregation of the rRNA transcription machinery. With actinomycin D this leads to a co- migration of RNA- polymerase I and topoisomerase I to the nucleolar perimeter. The process has a slow onset (> 20 min), is independent of topoisomerase I activity, but requires the N- terminal domain of the enzyme to colocalize with RNA polymerase I. ( ii) Camptothecin induces, in addition, immobilization of active topoisomerase I on genomic DNA resulting in rapid nucleolar clearance and spreading of the enzyme to the entire nucleoplasm. This effect is independent of the state of rRNA transcription, involves segregation of topoisomerase I from RNA polymerase I, has a rapid onset (< 1 min), and requires catalytic activity but neither the N- terminal domain of topoisomerase I nor its major sumoylation site. Thus, nucleolar/ nucleoplasmic partitioning of topoisomerase I is regulated by interactions with RNA polymerase I and DNA but not by sumoylation.