Saikumar P, Dong Z, Patel Y, Hall K, Hopfer U, Weinberg J M, Venkatachalam M A
Department of Pathology, University of Texas Health Science Centre at San Antonio, 78284-7750, USA.
Oncogene. 1998 Dec 31;17(26):3401-15. doi: 10.1038/sj.onc.1202590.
We investigated mechanisms of cell death during hypoxia/reoxygenation of cultured kidney cells. During glucose-free hypoxia, cell ATP levels declined steeply resulting in the translocation of Bax from cytosol to mitochondria. Concurrently, there was cytochrome c release and caspase activation. Cells that leaked cytochrome c underwent apoptosis after reoxygenation. ATP depletion induced by a mitochondrial uncoupler resulted in similar alterations even in the presence of oxygen. Moreover, inclusion of glucose during hypoxia prevented protein translocations and reoxygenation injury by maintaining intracellular ATP. Thus, ATP depletion, rather than hypoxia per se, was the cause of protein translocations. Overexpression of Bcl-2 prevented cytochrome c release and reoxygenation injury without ameliorating ATP depletion or Bax translocation. On the other hand, caspase inhibitors did not prevent protein translocations, but inhibited apoptosis during reoxygenation. Nevertheless, they could not confer long-term viability, since mitochondria had been damaged. Omission of glucose during reoxygenation resulted in continued failure of ATP production, and cell death with necrotic morphology. In contrast, cells expressing Bcl-2 had functional mitochondria and remained viable during reoxygenation even without glucose. Therefore, Bax translocation during hypoxia is a molecular trigger for cell death during reoxygenation. If ATP is available during reoxygenation, apoptosis develops; otherwise, death occurs by necrosis. By preserving mitochondrial integrity, BCL-2 prevents both forms of cell death and ensures cell viability.
我们研究了培养的肾细胞在缺氧/复氧过程中的细胞死亡机制。在无糖缺氧期间，细胞ATP水平急剧下降，导致Bax从细胞质转移到线粒体。同时，出现细胞色素c释放和半胱天冬酶激活。细胞色素c泄漏的细胞在复氧后发生凋亡。即使在有氧存在的情况下，线粒体解偶联剂诱导的ATP耗竭也会导致类似的改变。此外，在缺氧期间加入葡萄糖可通过维持细胞内ATP来防止蛋白质转移和复氧损伤。因此，ATP耗竭而非缺氧本身是蛋白质转移的原因。Bcl-2的过表达可防止细胞色素c释放和复氧损伤，但不能改善ATP耗竭或Bax转移。另一方面，半胱天冬酶抑制剂不能防止蛋白质转移，但可抑制复氧期间的凋亡。然而，它们不能赋予长期生存能力，因为线粒体已受损。复氧期间省略葡萄糖会导致ATP产生持续失败，细胞死亡并呈现坏死形态。相反，表达Bcl-2的细胞具有功能正常的线粒体，即使没有葡萄糖在复氧期间也能存活。因此，缺氧期间的Bax转移是复氧期间细胞死亡的分子触发因素。如果复氧期间有ATP可用，则发生凋亡；否则，通过坏死发生死亡。通过保持线粒体完整性，BCL-2可防止两种形式的细胞死亡并确保细胞存活。
