Deckwerth T L, Easton R M, Knudson C M, Korsmeyer S J, Johnson E M
Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Exp Neurol. 1998 Jul;152(1):150-62. doi: 10.1006/exnr.1998.6846.
The BCL2 family member BAX is required for the induction of apoptosis in neonatal sympathetic neurons after NGF withdrawal. Bax-deficient sympathetic neurons are NGF-independent for survival. To characterize the physiological state of neurons protected by BAX deficiency and to place BAX within the death pathway, we determine which of the molecular changes induced by NGF deprivation depend on BAX and compare the results with those for neurons protected by caspase inhibition. We find that neurons deficient in both Bax and Bcl2 resist NGF-deprivation similar to Bax-deficient neurons discounting a role for BCL2 in the mechanism by which Bax deficiency causes trophic factor independence. We identify two new molecular changes, phosphorylation of c-Jun on Ser63 and alpha-spectrin proteolysis, which precede and accompany apoptosis, respectively. Early reversible changes induced by NGF withdrawal, such as decreased protein synthesis and glucose uptake, increased c-Jun phosphorylation, increased steady state c-jun mRNA levels, and cellular atrophy, occur both in wild type and Bax-deficient neurons and thus are BAX-independent. In contrast to neurons protected by caspase inhibition, no c-fos induction occurs in Bax-deficient neurons. Terminal irreversible events of apoptosis such as caspase-mediated alpha-spectrin proteolysis are prevented by both Bax-deficiency and caspase inhibition. This places BAX downstream or in a different pathway of the early changes and upstream of the terminal events such as those leading to c-fos induction and caspase activation. This order indicates that the physiological state of NGF-deprived neurons protected by Bax deficiency may be less perturbed than that of caspase inhibitor-saved neurons.
BCL2家族成员BAX是NGF撤除后新生交感神经元凋亡诱导所必需的。缺乏Bax的交感神经元在存活方面不依赖NGF。为了表征受BAX缺乏保护的神经元的生理状态,并将BAX置于死亡途径中,我们确定了NGF剥夺诱导的哪些分子变化依赖于BAX,并将结果与受半胱天冬酶抑制保护的神经元的结果进行比较。我们发现,同时缺乏Bax和Bcl2的神经元抵抗NGF剥夺的方式与缺乏Bax的神经元相似,这排除了BCL2在Bax缺乏导致营养因子独立性的机制中的作用。我们确定了两个新的分子变化,分别是c-Jun在Ser63位点的磷酸化和α-血影蛋白的蛋白水解,它们分别在凋亡之前和伴随凋亡发生。NGF撤除诱导的早期可逆变化,如蛋白质合成减少和葡萄糖摄取增加、c-Jun磷酸化增加、稳态c-jun mRNA水平增加以及细胞萎缩,在野生型和缺乏Bax的神经元中均会发生,因此是不依赖BAX的。与受半胱天冬酶抑制保护的神经元不同,缺乏Bax的神经元中不会发生c-fos诱导。凋亡的终末不可逆事件,如半胱天冬酶介导的α-血影蛋白蛋白水解,可被Bax缺乏和半胱天冬酶抑制所阻止。这表明BAX在早期变化的下游或不同途径中,并且在终末事件(如导致c-fos诱导和半胱天冬酶激活的事件)的上游。这种顺序表明,受Bax缺乏保护的NGF剥夺神经元的生理状态可能比受半胱天冬酶抑制剂挽救的神经元受到的干扰更小。