The proteasome cap RPT5/Rpt5p subunit prevents aggregation of unfolded ricin A chain.
The proteasome cap RPT5/Rpt5p subunit prevents aggregation of unfolded ricin A chain.
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DOI：
10.1042/bj20130133
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发表时间：
2013-08-01
期刊：
影响因子：
--
通讯作者：
Spooner RA
中科院分区：
文献类型：
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作者：
Pietroni P;Vasisht N;Cook JP;Roberts DM;Lord JM;Hartmann-Petersen R;Roberts LM;Spooner RA
植物细胞毒素蓖麻毒素通过受体介导的内吞作用进入哺乳动物细胞，经逆行转运到内质网，在内质网中其催化A链(RTA)与全毒素还原分离，进入胞浆并使核糖体失活。目前公认的模型是内质网错位的RTA大部分被蛋白酶体降解。我们在本研究中表明，蛋白酶体在蓖麻毒素中毒中的作用比以前认识的更复杂，以前报道的哺乳动物细胞在蛋白酶体抑制剂存在下对蓖麻毒素敏感性的增加只是反映了抑制剂本身的毒性，RTA是蛋白酶体降解的非常差的底物。变性的RTA和酪蛋白竞争26S蛋白酶体调节颗粒上的结合位点，但它们的命运不同。酪蛋白被降解，但哺乳动物26S蛋白酶体AAA(与各种细胞活动相关的ATPase)-ATPase亚基RPT5在体外起伴侣作用，阻止变性的RTA聚集并刺激催化RTA活性的恢复。此外，在体内，Rpt5p的ATPase活性是从酿酒酵母ER上错位的RTA达到最大毒性所必需的。本研究的结果表明，RPT5/Rpt5p参与了底物的分类，在底物的分类中，可能启动了激活(折叠)或失活(降解)途径。
The plant cytotoxin ricin enters mammalian cells by receptor-mediated endocytosis, undergoing retrograde transport to the ER (endoplasmic reticulum) where its catalytic A chain (RTA) is reductively separated from the holotoxin to enter the cytosol and inactivate ribosomes. The currently accepted model is that the bulk of ER-dislocated RTA is degraded by proteasomes. We show in the present study that the proteasome has a more complex role in ricin intoxication than previously recognized, that the previously reported increase in sensitivity of mammalian cells to ricin in the presence of proteasome inhibitors simply reflects toxicity of the inhibitors themselves, and that RTA is a very poor substrate for proteasomal degradation. Denatured RTA and casein compete for a binding site on the regulatory particle of the 26S proteasome, but their fates differ. Casein is degraded, but the mammalian 26S proteasome AAA (ATPase associated with various cellular activities)-ATPase subunit RPT5 acts as a chaperone that prevents aggregation of denatured RTA and stimulates recovery of catalytic RTA activity in vitro. Furthermore, in vivo, the ATPase activity of Rpt5p is required for maximal toxicity of RTA dislocated from the Saccharomyces cerevisiae ER. The results of the present study implicate RPT5/Rpt5p in the triage of substrates in which either activation (folding) or inactivation (degradation) pathways may be initiated.