美国加州南旧金山基因技术公司Vishva M. Dixit和Kim Newton等研究人员近日合作取得一项成果。他们发现caspase-8介导的RIPK1剪切对抑制细胞凋亡和坏死起着至关重要的作用。相关论文2019年9月11日在线发表在《自然》上。

研究人员发现表达催化失活的caspase-8（C362A）的敲入小鼠由于MLKL依赖的程序性凋亡而死亡，类似于caspase-8缺陷型小鼠。因此，caspase-8必须切割自身、其他蛋白质或两者以抑制坏死性凋亡。表达不能自我切割的caspase-8（D212A / D218A / D225A / D387A）的小鼠是能存活的，表达c-FLIP或CYLD蛋白（已被突变以防止caspase-8的切割）的小鼠也是如此。相比之下，表达RIPK1（D325A）的小鼠，其中caspase-8切割位点Asp325已经突变，在妊娠中期死亡。通过RIPK1的失活、TNFR1的丧失或MLKL和caspase-8衔接蛋白FADD的丧失来防止胚胎致死，但单独缺失MLKL不行。因此，RIPK1（D325A）似乎引发TNF介导的细胞死亡，即RIPK1和FADD-caspase-8的激酶活性。因此，在Ripk1D325A / D325A胚胎的卵黄囊中，含有切割的caspase-3的垂死内皮细胞异常丰富。杂合的Ripk1D325A / +细胞和小鼠是能存活的，但与野生型细胞或小鼠相比，对TNF诱导的细胞死亡也更敏感。这些数据显示，RIPK1的Asp325位点对于限制对TNF响应的异常细胞死亡是必需的，这与通过caspase-8切割RIPK1是拆除死亡诱导复合物的机制一致。

据介绍，天冬氨酸特异性半胱氨酸蛋白酶caspase-8抑制由RIPK3和MLKL介导的坏死性细胞死亡。实际上，缺乏caspase-8的小鼠在胚胎发生过程中以RIPK3和MLKL依赖性方式死亡。在人类中，caspase-8缺乏与免疫缺陷或极早期炎症性肠病相关。被caspase-8切割以防止体内坏死凋亡的底物尚未确定。

附：英文原文

Title:Cleavage of RIPK1 by caspase-8 is crucial for limiting apoptosis and necroptosis

Author:Kim Newton, Katherine E. Wickliffe, Debra L. Dugger, Allie Maltzman, Merone Roose-Girma, Monika Dohse, László K?m?ves, Joshua D. Webster, Vishva M. Dixit

Issue&Volume: 2019-09-11

Abstract:The aspartate-specific cysteine protease caspase-8 suppresses necroptotic cell death mediated by RIPK3 and MLKL. Indeed, mice that lack caspase-8 die in a RIPK3- and MLKL-dependent manner during embryogenesis1,2,3. In humans, caspase-8 deficiency is associated with immunodeficiency4 or very early onset inflammatory bowel disease5. The substrates that are cleaved by caspase-8 to prevent necroptosis in vivo have not been defined. Here we show that knock-in mice that express catalytically inactive caspase-8(C362A) die as embryos owing to MLKL-dependent necroptosis, similar to caspase-8-deficient mice. Thus, caspase-8 must cleave itself, other proteins or both to inhibit necroptosis. Mice that express caspase-8(D212A/D218A/D225A/D387A), which cannot cleave itself, were viable, as were mice that express c-FLIP or CYLD proteins that had been mutated to prevent cleavage by caspase-8. By contrast, mice that express RIPK1(D325A), in which the caspase-8 cleavage site Asp325 had been mutated, died mid-gestation. Embryonic lethality was prevented by inactivation of RIPK1, loss of TNFR1, or loss of both MLKL and the caspase-8 adaptor FADD, but not by loss of MLKL alone. Thus, RIPK1(D325A) appears to trigger cell death mediated by TNF, the kinase activity of RIPK1 and FADD–caspase-8. Accordingly, dying endothelial cells that contain cleaved caspase-3 were abnormally abundant in yolk sacs of Ripk1D325A/D325A embryos. Heterozygous Ripk1D325A/+ cells and mice were viable, but were also more susceptible to TNF-induced cell death than were wild-type cells or mice. Our data show that Asp325 of RIPK1 is essential for limiting aberrant cell death in response to TNF, consistent with the idea that cleavage of RIPK1 by caspase-8 is a mechanism for dismantling death-inducing complexes.

DOI: 10.1038/s41586-019-1548-x

Source: https://www.nature.com/articles/s41586-019-1548-x