Imre Gergely, Berthelet Jean, Heering Jan, Kehrloesser Sebastian, Melzer Inga Maria, Lee Byung Il, Thiede Bernd, Dötsch Volker, Rajalingam Krishnaraj
MSU-FZI, Institute of Immunology, University Medical Center Mainz, JGU, Mainz, Germany.
Institute of Biophysical Chemistry and Center for Biomolecular Magnetic Resonance, Goethe University, Frankfurt, Germany.
EMBO Rep. 2017 May;18(5):733-744. doi: 10.15252/embr.201643744. Epub 2017 Mar 23.
Caspases are key enzymes responsible for mediating apoptotic cell death. Across species, caspase-2 is the most conserved caspase and stands out due to unique features. Apart from cell death, caspase-2 also regulates autophagy, genomic stability and ageing. Caspase-2 requires dimerization for its activation which is primarily accomplished by recruitment to high molecular weight protein complexes in cells. Here, we demonstrate that apoptosis inhibitor 5 (API5/AAC11) is an endogenous and direct inhibitor of caspase-2. API5 protein directly binds to the caspase recruitment domain (CARD) of caspase-2 and impedes dimerization and activation of caspase-2. Interestingly, recombinant API5 directly inhibits full length but not processed caspase-2. Depletion of endogenous API5 leads to an increase in caspase-2 dimerization and activation. Consistently, loss of API5 sensitizes cells to caspase-2-dependent apoptotic cell death. These results establish API5/AAC-11 as a direct inhibitor of caspase-2 and shed further light onto mechanisms driving the activation of this poorly understood caspase.
半胱天冬酶是介导凋亡性细胞死亡的关键酶。在整个物种中，半胱天冬酶-2是最保守的半胱天冬酶，因其独特的特性而格外突出。除了细胞死亡外，半胱天冬酶-2还调节自噬、基因组稳定性和衰老。半胱天冬酶-2需要二聚化才能激活，这主要通过募集到细胞中的高分子量蛋白质复合物来实现。在此，我们证明凋亡抑制因子5（API5/AAC11）是半胱天冬酶-2的内源性直接抑制剂。API5蛋白直接结合半胱天冬酶-2的半胱天冬酶募集结构域（CARD），并阻碍半胱天冬酶-2的二聚化和激活。有趣的是，重组API5直接抑制全长而非已加工的半胱天冬酶-2。内源性API5的缺失导致半胱天冬酶-2二聚化和激活增加。一致地，API5的缺失使细胞对半胱天冬酶-2依赖性凋亡性细胞死亡敏感。这些结果确立了API5/AAC-11作为半胱天冬酶-2的直接抑制剂，并进一步揭示了驱动这种了解甚少的半胱天冬酶激活的机制。
