Department and Graduate Institute of Microbiology, College of Medicine, Taipei, Taiwan.
Cell Mol Life Sci. 2011 Aug;68(16):2769-84. doi: 10.1007/s00018-010-0591-4. Epub 2010 Nov 18.
Important to the function of calpains is temporal and spatial regulation of their proteolytic activity. Here, we demonstrate that cytoplasm-resident calpain 2 cleaves human nuclear topoisomerase I (hTOP1) via Ca(2+)-activated proteolysis and nucleoplasmic shuttling of proteases. This proteolysis of hTOP1 was induced by either ionomycin-caused Ca(2+) influx or addition of Ca(2+) in cellular extracts. Ca(2+) failed to induce hTOP1 proteolysis in calpain 2-knockdown cells. Moreover, calpain 2 cleaved hTOP1 in vitro. Furthermore, calpain 2 entered the nucleus upon Ca(2+) influx, and calpastatin interfered with this process. Calpain 2 cleavage sites were mapped at K(158) and K(183) of hTOP1. Calpain 2-truncated hTOP1 exhibited greater relaxation activity but remained able to interact with nucleolin and to form cleavable complexes. Interestingly, calpain 2 appears to be involved in ionomycin-induced protection from camptothecin-induced cytotoxicity. Thus, our data suggest that nucleocytoplasmic shuttling may serve as a novel type of regulation for calpain 2-mediated nuclear proteolysis.
钙蛋白酶的功能对于时间和空间调节其蛋白水解活性非常重要。在这里，我们证明细胞质驻留的钙蛋白酶 2 通过 Ca(2+)-激活的蛋白水解和核质蛋白酶的穿梭来切割人核拓扑异构酶 I（hTOP1）。这种 hTOP1 的蛋白水解是由离子霉素引起的 Ca(2+)内流或细胞提取物中添加 Ca(2+)诱导的。钙蛋白酶 2 敲低细胞中 Ca(2+)不能诱导 hTOP1 蛋白水解。此外，钙蛋白酶 2 在体外切割 hTOP1。此外，钙蛋白酶 2 在 Ca(2+)内流时进入细胞核，钙蛋白酶抑制剂干扰了这一过程。钙蛋白酶 2 的切割位点位于 hTOP1 的 K(158)和 K(183)。钙蛋白酶 2 截断的 hTOP1 表现出更大的松弛活性，但仍能够与核仁素相互作用并形成可切割的复合物。有趣的是，钙蛋白酶 2 似乎参与了离子霉素诱导的对喜树碱诱导的细胞毒性的保护。因此，我们的数据表明核质穿梭可能是钙蛋白酶 2 介导的核蛋白水解的一种新型调节方式。
