Gillissen Bernhard, Essmann Frank, Graupner Vilma, Stärck Lilian, Radetzki Silke, Dörken Bernd, Schulze-Osthoff Klaus, Daniel Peter T
Department of Hematology, Charité-Campus Berlin-Buch, Humboldt University, D-13125 Berlin-Buch, Germany.
EMBO J. 2003 Jul 15;22(14):3580-90. doi: 10.1093/emboj/cdg343.
Nbk/Bik (natural born killer/Bcl-2-interacting killer) is a tissue-specific BH3-only protein whose molecular function is still largely unknown. To investigate the mechanism of Nbk action, we established a single- vector adenoviral system based on the Tet-off conditional expression of Nbk. Upon Nbk expression, only Bax-positive, but not Bax-deficient cells were found to undergo apoptosis. Interestingly, Nbk failed to induce apoptosis in the absence of Bax, even despite expression of the related molecule Bak. Re-expression of Bax restored the sensitivity to Nbk. Similarly, Bax wild-type HCT116 cells were highly susceptible, whereas HCT116 Bax knock-out cells remained resistant to Nbk-induced apoptosis. In Bax-positive cells, Nbk induced a conformational switch in the Bax N-terminus coinciding with cytochrome c release, mitochondrial permeability transition and caspase-9 processing. Immunoprecipitation studies revealed that Nbk interacts with Bcl-x(L) and Bcl-2 but not with Bax. Since, in addition, Nbk did not localize to the mitochondria, our data suggest a model in which Nbk acts as an indirect killer to trigger Bax-dependent apoptosis, whereas Bak is not sufficient to confer sensitivity to Nbk.
Nbk/Bik（自然杀伤蛋白/Bcl-2相互作用杀伤蛋白）是一种组织特异性仅含BH3结构域的蛋白，其分子功能仍 largely未知。为了研究Nbk的作用机制，我们基于Nbk的Tet-off条件表达建立了单载体腺病毒系统。在Nbk表达后，发现只有Bax阳性细胞而非Bax缺陷细胞发生凋亡。有趣的是，即使存在相关分子Bak的表达，在没有Bax的情况下Nbk也无法诱导凋亡。Bax的重新表达恢复了对Nbk的敏感性。同样，Bax野生型HCT116细胞高度敏感，而HCT116 Bax基因敲除细胞对Nbk诱导的凋亡仍具有抗性。在Bax阳性细胞中，Nbk诱导Bax N端的构象转换，这与细胞色素c释放、线粒体通透性转换和半胱天冬酶-9加工过程同时发生。免疫沉淀研究表明，Nbk与Bcl-x(L)和Bcl-2相互作用，但不与Bax相互作用。此外，由于Nbk并不定位于线粒体，我们的数据提示了一种模型，即Nbk作为间接杀手触发Bax依赖的凋亡，而Bak不足以赋予对Nbk的敏感性。
