Uo Takuma, Kinoshita Yoshito, Morrison Richard S
Department of Neurological Surgery, University of Washington School of Medicine, Seattle, Washington 98195-6470, USA.
J Neurosci. 2007 Nov 7;27(45):12198-210. doi: 10.1523/JNEUROSCI.3222-05.2007.
Recent studies in non-neuronal cells have shown that the tumor suppressor p53 can promote cell death through a transcription-independent mechanism involving its direct action with a subset of Bcl-2 family member proteins in the cytosol and at the mitochondria. In cultured cortical neurons, however, we could not find evidence supporting a significant contribution of the cytosolic/mitochondrial p53 pathway, and available evidence instead corroborated the requirement for the transcriptional activity of p53. When directly targeted to the cytosol/mitochondria, wild-type p53 lost its apoptosis-inducing activity in neurons but not in non-neuronal cells. The N-terminal p53 fragment (transactivation and proline-rich domains), which induces apoptosis in non-neuronal cells via the cytosolic/mitochondrial pathway, displayed no apoptogenic activity in neurons. In neuronal apoptosis induced by camptothecin or an MDM2 (murine double minute 2) inhibitor, nutlin-3, endogenous p53 protein did not accumulate in the cytosol/mitochondria, and transcriptional inhibition after p53 induction effectively blocked cell death. In addition, overexpression of a dominant-negative form of p53 (R273H) completely suppressed induction of proapoptotic p53 target genes and cell death. PUMA (p53-upregulated modulator of apoptosis) was one such gene induced by camptothecin, and its overexpression was sufficient to induce Bax (Bcl-2-associated X protein)-dependent neuronal death, whereas Noxa was not apoptogenic. These results collectively demonstrate that, in contrast to non-neuronal cells, the apoptotic activity of p53 in postnatal cortical neurons does not rely on its direct action at the cytosol/mitochondria but is exclusively mediated through its transcription-dependent functions. The uniqueness of p53-mediated apoptotic signaling in postnatal cortical neurons was further illustrated by the dispensable function of the proline-rich domain of p53.
最近在非神经元细胞中的研究表明，肿瘤抑制因子p53可通过一种不依赖转录的机制促进细胞死亡，该机制涉及其在细胞质和线粒体中与一部分Bcl-2家族成员蛋白的直接作用。然而，在培养的皮质神经元中，我们未找到支持细胞质/线粒体p53途径有显著作用的证据，现有证据反而证实了p53转录活性的必要性。当野生型p53直接靶向细胞质/线粒体时，它在神经元中失去了凋亡诱导活性，但在非神经元细胞中则不然。N端p53片段（反式激活域和富含脯氨酸结构域）通过细胞质/线粒体途径在非神经元细胞中诱导凋亡，但在神经元中不显示凋亡活性。在喜树碱或MDM2（小鼠双微体2）抑制剂nutlin-3诱导的神经元凋亡中，内源性p53蛋白未在细胞质/线粒体中积累，p53诱导后的转录抑制有效阻断了细胞死亡。此外，p53显性负性形式（R273H）的过表达完全抑制了促凋亡p53靶基因的诱导和细胞死亡。PUMA（p53上调的凋亡调节因子）是喜树碱诱导的此类基因之一，其过表达足以诱导依赖Bax（Bcl-2相关X蛋白）的神经元死亡，而Noxa不具有凋亡活性。这些结果共同表明，与非神经元细胞不同，出生后皮质神经元中p53的凋亡活性不依赖于其在细胞质/线粒体中的直接作用，而是完全通过其转录依赖性功能介导。p53富含脯氨酸结构域的可有可无的功能进一步说明了出生后皮质神经元中p53介导的凋亡信号的独特性。
