Bcl‐X L disrupts death‐inducing signal complex formation in plasma membrane induced by hypoxia/reoxygenation

Hypoxia/reoxygenation (H/R) causes cellular injury and death. The cell death pathways induced by H/R remain incompletely understood. H/R can induce Bid and Bax mitochondrial translocation and cytochrome c release. Using mouse lung endothelial cells (MLEC), we examined the role of Bcl‐X L , an anti‐apoptotic Bcl‐2‐related protein, in H/R‐induced cell death. The expression of Bcl‐X L protected MLEC against H/R‐induced cell death by blocking Bax and Bid translocation and inhibiting mitochondrial cytochrome c release. Bcl‐X L expression inhibited caspase‐8 cleavage and death‐inducing signal complex (DISC) formation in plasma membrane. By isolating mitochondrial, nuclear, and Golgi fractions, we found that H/R induced DISC formation in these organelles. Bcl‐X L expression inhibited DISC formation in the nuclear and Golgi fractions relative to Lac Z ‐infected controls. In contrast, DISC formation was elevated in the mitochondrial fraction of Bcl‐X L ‐infected cells. GRASP65, a Golgi‐associated protein, physically associated with Fas and caspase‐8; Bcl‐X L expression decreased these associations. Bcl‐X L expression also up‐regulated FLIP, a caspase‐8 inhibitor. In conclusion, Bcl‐X L may inactivate caspase‐8 by decreasing DISC formation in the plasma membrane, nucleus, and Golgi complex while diverting DISC formation to the mitochondria. The inhibitory effects of Bcl‐X L on DISC formation may play significant roles in protecting endothelial cells from H/R‐induced cell death.—Wang, X., Zhang, J., Kim, H. P., Wang, Y., Choi, A. M. K., Ryter, S. W. Bcl‐X L disrupts death‐inducing signal complex formation in plasma membrane induced by hypoxia/reoxygenation. FASEBJ. 18, 1826‐1833 (2004)