alpha-Sarcin catalytic activity is not required for cytotoxicity
alpha-Sarcin catalytic activity is not required for cytotoxicity
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DOI：
10.1186/1471-2091-10-9
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发表时间：
2009-04-03
期刊：
影响因子：
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通讯作者：
Howard, Perry L.
中科院分区：
文献类型：
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作者：
Alford, Spencer C.;Pearson, Joel D.;Howard, Perry L.
背景：α-肌氨酸是由黑曲霉产生的一种蛋白毒素。属于细胞毒性核糖核酸酶家族，可包裹核糖体并抑制蛋白质合成。α-肌氨酸裂解核糖体大亚基的RNA骨架内的单个磷酸二酯键，这使得核糖体不能被延伸因子识别，并进而阻断蛋白质合成。尽管普遍认为毒素引起的蛋白质合成抑制导致细胞死亡，但尚未直接显示α-八叠球菌素的催化失活突变体在细胞质内直接表达时是无毒的。这是很重要的，因为最近的研究已经对蛋白质合成抑制是否足以启动apoptosis.Results：在这份报告中，我们测定α-sarcin细胞毒性和抑制蛋白质合成的能力，直接细胞质表达。我们表明，突变的α-八叠球菌，这损害α-八叠球菌的能力，抑制蛋白质合成，不影响其细胞毒性。突变体不能激活JNK，证实了sarcin-ricin环保持完整，并且α-sarcin突变体是催化失活的。此外，α-八叠球菌素的突变体和野生型变体均定位于细胞核和细胞质，并与核糖体标记RPS 6共定位。结论：蛋白质合成抑制可能导致细胞死亡，但不是必需的。因此，我们的研究结果表明，α-八叠球菌素可以促进细胞死亡，通过一个以前不受重视的机制，是独立的rRNA切割和JNK激活。
Background: alpha-Sarcin is a protein toxin produced by Aspergillus giganteus. It belongs to a family of cytotoxic ribonucleases that inactivate the ribosome and inhibit protein synthesis. alpha-Sarcin cleaves a single phosphodiester bond within the RNA backbone of the large ribosomal subunit, which makes the ribosome unrecognizable to elongation factors and, in turn, blocks protein synthesis. Although it is widely held that the protein synthesis inhibition caused by the toxin leads to cell death, it has not been directly shown that catalytically inactive mutants of alpha-sarcin are non-toxic when expressed directly within the cytoplasm of cells. This is important since recent studies have cast doubt on whether protein synthesis inhibition is sufficient to initiate apoptosis.Results: In this report, we assay alpha-sarcin cytotoxicity and ability to inhibit protein synthesis by direct cytoplasmic expression. We show that mutations in a-sarcin, which impair alpha-sarcin's ability to inhibit protein synthesis, do not affect its cytotoxicity. The mutants are unable to activate JNK, confirming that the sarcin-ricin loop remains intact and that the a-sarcin mutants are catalytically inactive. In addition, both mutant and wildtype variants of alpha-sarcin localize to the nucleus and cytoplasm, where they co-localize with ribosomal marker RPS6.Conclusion: We conclude that although protein synthesis inhibition likely contributes to cell death, it is not required. Thus, our results suggest that a-sarcin can promote cell death through a previously unappreciated mechanism that is independent of rRNA cleavage and JNK activation.