Volloch V, Gabai V L, Rits S, Force T, Sherman M Y
Tufts University Biotechnology Center, Medford, MA 02155, USA.
Cell Stress Chaperones. 2000 Apr;5(2):139-47. doi: 10.1379/1466-1268(2000)005<0139:hcpcfh>2.0.co;2.
The major heat shock protein Hsp72 prevents heat-induced apoptosis. We have previously demonstrated that transiently expressed Hsp72 exerts its anti-apoptotic effect by suppressing the activity of stress-kinase JNK, an early component of the apoptotic pathway initiated by heat shock. On the other hand, constitutive expression of Hsp72 does not lead to suppression of heat-induced JNK activation, yet still efficiently prevents apoptosis. To address this apparent contradiction, we studied the effects of constitutively expressed Hsp72 on activation of JNK and apoptosis in Rat-1 fibroblasts. We found that the level of heat-induced apoptosis directly correlated with the duration rather than the magnitude of JNK activity following heat shock. Constitutively expressed Hsp72 strongly reduced the duration of JNK while it did not suppress initial JNK activation. These effects were due to Hsp72-mediated acceleration of JNK dephosphorylation. Addition of vanadate to inhibit JNK phosphatase activity completely prevented the anti-apoptotic action of Hsp72. Therefore, suppression of heat-induced apoptosis by Hsp72 could be fully accounted for by its effects on JNK activity.
主要热休克蛋白Hsp72可防止热诱导的细胞凋亡。我们之前已经证明，瞬时表达的Hsp72通过抑制应激激酶JNK的活性发挥其抗凋亡作用，JNK是热休克引发的凋亡途径的早期组成部分。另一方面，Hsp72的组成型表达不会导致热诱导的JNK激活受到抑制，但仍能有效防止细胞凋亡。为了解决这一明显的矛盾，我们研究了组成型表达的Hsp72对大鼠1型成纤维细胞中JNK激活和细胞凋亡的影响。我们发现，热诱导的细胞凋亡水平与热休克后JNK活性的持续时间直接相关，而不是与活性的大小相关。组成型表达的Hsp72强烈缩短了JNK的持续时间，而没有抑制JNK的初始激活。这些效应是由于Hsp72介导的JNK去磷酸化加速所致。添加钒酸盐以抑制JNK磷酸酶活性完全阻止了Hsp72的抗凋亡作用。因此，Hsp72对热诱导细胞凋亡的抑制作用可以完全由其对JNK活性的影响来解释。
