Distinct roles of mitochondria- and ER-localized Bcl-xL in apoptosis resistance and Ca2+ homeostasis.
Distinct roles of mitochondria- and ER-localized Bcl-xL in apoptosis resistance and Ca2+ homeostasis.
复制标题
DOI：
10.1091/mbc.e12-02-0090
复制
发表时间：
2012-07
影响因子：
3.3
通讯作者：
Li C
中科院分区：
文献类型：
--
作者：
Eno CO;Eckenrode EF;Olberding KE;Zhao G;White C;Li C
定位于线粒体的Bcl-xL对于凋亡保护是必要且足够的，但不能恢复Bcl-x-KO细胞中的Ca 2+稳态。ER定位的Bcl-xL是ER Ca 2+稳态所需的，但不影响凋亡，除非Bcl-xL存在于其他细胞隔室中。Bcl-2蛋白是细胞对内源性和外源性凋亡刺激反应的主要调节因子。其中，抗凋亡蛋白Bcl-xL的过表达调节细胞内Ca 2+稳态和细胞器特异性凋亡信号通路。然而，Bcl-xL在线粒体和内质网（ER）的具体活动尚未完全确定。为了进一步探索这一点，我们产生了Bcl-xL表达缺陷的小鼠胚胎成纤维细胞（MEF）细胞系（Bcl-x-KO）。Bcl-xL表达的缺陷并不诱导其他Bcl-2蛋白表达的代偿性变化，Bcl-x-KO MEF细胞与野生型MEF细胞相比，对各种凋亡刺激的敏感性增加。将Bcl-xL靶向于线粒体而非ER使Bcl-x-KO MEF细胞中的凋亡保护恢复至在野生型MEF细胞中观察到的程度。然而，需要ER靶向的Bcl-xL而不是血管靶向的Bcl-xL的表达来恢复Bcl-x-KO MEF细胞中的Ca 2+稳态。重要的是，ER靶向的Bcl-xL能够在内源性Bcl-xL存在下保护细胞免受死亡刺激。这些数据表明，线粒体Bcl-xL可以调节细胞凋亡独立的ER Bcl-xL，当专门定位在ER，Bcl-xL冲击钙离子稳态，但不影响细胞凋亡，除非Bcl-xL是存在于额外的细胞隔室。
Bcl-xL localized to mitochondria is necessary and sufficient for apoptotic protection but is unable to restore Ca2+ homeostasis in Bcl-x-KO cells. ER-localized Bcl-xL is required for ER Ca2+ homeostasis but does not affect apoptosis unless Bcl-xL is present in additional cellular compartments. Bcl-2 proteins are major regulators of cellular responses to intrinsic and extrinsic apoptotic stimuli. Among them, overexpression of the antiapoptotic protein Bcl-xL modulates intracellular Ca2+ homeostasis and organelle-specific apoptotic signaling pathways. However, the specific activities of Bcl-xL at mitochondria and the endoplasmic reticulum (ER) have not been fully defined. To further explore this, we generated mouse embryonic fibroblast (MEF) cell lines deficient in Bcl-xL expression (Bcl-x-KO). Deficiency in Bcl-xL expression did not induce compensatory changes in the expression of other Bcl-2 proteins, and Bcl-x-KO MEF cells showed increased sensitivity to various apoptotic stimuli compared with wild-type MEF cells. Targeting Bcl-xL at mitochondria but not at the ER restored apoptosis protection in Bcl-x-KO MEF cells to the degree observed in wild-type MEF cells. However, expression of ER-targeted Bcl-xL but not mitochondrially targeted Bcl-xL was required to restore Ca2+ homeostasis in Bcl-x-KO MEF cells. Of importance, ER-targeted Bcl-xL was able to protect cells against death stimuli in the presence of endogenous Bcl-xL. These data indicate that mitochondrial Bcl-xL can regulate apoptosis independently of ER Bcl-xL and that when localized exclusively at the ER, Bcl-xL impinges on Ca2+ homeostasis but does not affect apoptosis unless Bcl-xL is present in additional cellular compartments.