Hawkins Timothy E, Das Debipriya, Young Barry, Moss Stephen E
Department of Physiology and Laboratory for Molecular Cell Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
Proc Natl Acad Sci U S A. 2002 Jun 11;99(12):8054-9. doi: 10.1073/pnas.132598099.
Annexins are widely expressed Ca(2+)-dependent phospholipid-binding proteins with poorly understood physiological roles. Proposed functions include Ca(2+) channel activity and vesicle trafficking, but neither have been proven in vivo. Here we used targeted gene disruption to generate B-lymphocytes lacking annexin 5 (Anx5) expression and show that this results in reduced susceptibility to a range of apoptotic stimuli. By comparison B-lymphocytes lacking annexin 2 (Anx2) showed no such resistance, providing evidence that this effect is specific to loss of Anx5. The defect in the ANX5(-/-) cells occurs early in the apoptotic program before nuclear condensation, caspase 3 activation, and cell shrinkage, but downstream of an initial Ca(2+) influx. Only UVA/B irradiation induced similar levels of apoptosis in wild-type and ANX5(-/-) cells. Unexpectedly, ANX5(-/-) cells permeabilized in vitro also failed to release mitochondrial cytochrome C, suggesting a possible mechanism for their resistance to apoptosis. These findings demonstrate a role for Anx5 in determining the susceptibility of B-lymphocytes to apoptosis.
膜联蛋白是广泛表达的依赖钙离子的磷脂结合蛋白，其生理作用尚不清楚。推测的功能包括钙离子通道活性和囊泡运输，但均未在体内得到证实。在此，我们利用靶向基因敲除技术生成了缺乏膜联蛋白5（Anx5）表达的B淋巴细胞，并表明这导致对一系列凋亡刺激的敏感性降低。相比之下，缺乏膜联蛋白2（Anx2）的B淋巴细胞没有表现出这种抗性，这证明这种效应是Anx5缺失所特有的。ANX5（-/-）细胞中的缺陷发生在凋亡程序的早期，在核浓缩、半胱天冬酶3激活和细胞收缩之前，但在初始钙离子内流之后。只有紫外线A/B照射在野生型和ANX5（-/-）细胞中诱导了相似水平的凋亡。出乎意料的是，体外通透化的ANX5（-/-）细胞也未能释放线粒体细胞色素C，这提示了它们抗凋亡的一种可能机制。这些发现证明了Anx5在决定B淋巴细胞对凋亡的敏感性方面的作用。
