Tsuchiya Yuichi, Murai Shin, Yamashita Shigeru
Department of Biochemistry, Toho University School of Medicine, Tokyo, Japan.
FEBS J. 2005 May;272(9):2237-50. doi: 10.1111/j.1742-4658.2005.04648.x.
In many animal species including Xenopus, ovulated eggs possess an intrinsic apoptotic execution system. This program is inhibited for a limited time by some maternal apoptosis inhibitors, although their molecular properties remain uncharacterized. Baculovirus IAP repeat (BIR) family proteins contain evolutionarily conserved BIR domains and play important roles in apoptosis suppression, and are therefore good candidates as maternal apoptosis inhibitors. We identified four maternal BIR family proteins in Xenopus eggs and, using the biochemical advantages of egg extracts, examined their physiological functions. These molecules included two survivin-related proteins, xEIAP/XLX, and a possible ortholog of XIAP named xXIAP. The addition of recombinant xXIAP greatly delayed apoptotic execution, whereas the immunodepletion of endogenous xXIAP significantly accelerated the onset of apoptosis. In contrast, xEIAP/XLX was a poor apoptosis inhibitor, and neither of the survivin orthologs showed anti-apoptotic activity in our assay. Both xEIAP/XLX and xXIAP were degraded by activated caspases, and also by a novel proteolytic system that required the presence of C-terminal RING finger domain but was insensitive to proteasome inhibition. Our data suggest that the regulation of endogenous xXIAP concentration is important for the survival of Xenopus eggs.
在包括非洲爪蟾在内的许多动物物种中，排卵后的卵具有内在的凋亡执行系统。尽管一些母体凋亡抑制剂的分子特性尚不清楚，但该程序在有限的时间内会受到它们的抑制。杆状病毒IAP重复序列（BIR）家族蛋白含有进化上保守的BIR结构域，在抑制细胞凋亡中起重要作用，因此是母体凋亡抑制剂的良好候选者。我们在非洲爪蟾卵中鉴定出四种母体BIR家族蛋白，并利用卵提取物的生化优势研究了它们的生理功能。这些分子包括两种与生存素相关的蛋白，xEIAP/XLX，以及一种可能是XIAP直系同源物的xXIAP。添加重组xXIAP大大延迟了凋亡的执行，而内源性xXIAP的免疫耗竭则显著加速了凋亡的发生。相比之下，xEIAP/XLX是一种较差的凋亡抑制剂，在我们的实验中，两种生存素直系同源物均未显示出抗凋亡活性。xEIAP/XLX和xXIAP都被活化的半胱天冬酶降解，也被一种新型的蛋白水解系统降解，该系统需要C末端的RING指结构域的存在，但对蛋白酶体抑制不敏感。我们的数据表明，内源性xXIAP浓度的调节对非洲爪蟾卵的存活很重要。
