Mishra Ritu, Kumar Meenakshi Sundaram, Karande Anjali A
Department of Biochemistry, Indian Institute of Science, Bangalore, 560012, Karnataka, India.
Mol Cell Biochem. 2015 May;403(1-2):255-65. doi: 10.1007/s11010-015-2355-9. Epub 2015 Mar 10.
Abrin obtained from the plant Abrus precatorius inhibits protein synthesis and also triggers apoptosis in cells. Previous studies from our laboratory suggested a link between these two events. Using an active site mutant of abrin A-chain which exhibits 225-fold lower protein synthesis inhibitory activity than the wild-type abrin A-chain, we demonstrate in this study that inhibition of protein synthesis induced by abrin is the major factor triggering unfolded protein response leading to apoptosis. Since abrin A-chain requires the B-chain for internalization into cells, the wild-type and mutant recombinant abrin A-chains were conjugated to native ricin B-chain to generate hybrid toxins, and the toxic effects of the two conjugates were compared. The rate of inhibition of protein synthesis mediated by the mutant ricin B-rABRA (R167L) conjugate was slower than that of the wild-type ricin B-rABRA conjugate as expected. The mutant conjugate activated p38MAPK and caspase-3 similar to its wild-type counterpart although at later time points. Overall, these results confirm that inhibition of protein synthesis is the major event contributing to abrin-mediated apoptosis.
从相思子植物中提取的相思子毒素可抑制蛋白质合成，并引发细胞凋亡。我们实验室之前的研究表明这两个事件之间存在联系。在本研究中，我们使用相思子毒素A链的活性位点突变体，其蛋白质合成抑制活性比野生型相思子毒素A链低225倍，证明相思子毒素诱导的蛋白质合成抑制是引发未折叠蛋白反应导致细胞凋亡的主要因素。由于相思子毒素A链需要B链才能内化进入细胞，因此将野生型和突变型重组相思子毒素A链与天然蓖麻毒素B链偶联以生成杂合毒素，并比较了两种偶联物的毒性作用。正如预期的那样，突变型蓖麻毒素B-rABRA（R167L）偶联物介导的蛋白质合成抑制速率比野生型蓖麻毒素B-rABRA偶联物慢。突变型偶联物与野生型类似，虽然在较晚时间点激活了p38丝裂原活化蛋白激酶和半胱天冬酶-3。总体而言，这些结果证实蛋白质合成抑制是相思子毒素介导的细胞凋亡的主要促成事件。
