PRR7 is a novel NMDA-dependent inhibitor of c-Jun ubiquitination in neurons

Elevated c-Jun levels result in apoptosis and are evident in neurodegenerative disorders such as Alzheimer's disease and dementia and after global cerebral insults such as stroke and epilepsy. NMDA receptor (NMDAR) antagonists block c-Jun upregulation and prevent neuronal cell death following excitotoxic insults. However, little is known about the molecular mechanisms that regulate c-Jun abundance in neurons. Here we show that PRR7, a component of synaptic junctions, can upregulate c-Jun levels by inhibiting its ubiquitination in neurons. PRR7 interacts with the GLUN1 subunit of NMDARs and is upregulated in the nucleus following NMDAR activation. We show that PRR7 interacts with the E3 ligase SCFFBW7 (FBW7) and blocks the FBW7-mediated ubiquitination of c-Jun. PRR7 overexpression increases c-Jun-dependent transcriptional activity and promotes neuronal death. Microarray assays indicate that both Prr7 knockdown or overexpression alter the abundance of c-Jun-regulated transcripts associated with cellular viability as well as synaptic function. Moreover, Prr7 knockdown attenuates NMDA-mediated excitotoxicity in primary neuronal cultures. Our results show that PRR7 links NMDAR activity to c-Jun function and provide insight into the processes that underlie NMDA-dependent excitotoxicity.c-Jun蛋白水平升高可引发细胞凋亡，且可见于阿尔茨海默病、痴呆等神经退行性疾病，以及中风、癫痫等全脑损伤事件后。N-甲基-D-天冬氨酸受体（N-methyl-D-aspartate receptor，NMDAR）拮抗剂可阻断c-Jun的上调，并在兴奋性毒性损伤后阻止神经元细胞死亡。然而，目前对于神经元中调控c-Jun蛋白丰度的分子机制仍知之甚少。本研究发现，作为突触连接组分的PRR7可通过抑制神经元内c-Jun的泛素化，上调其蛋白水平。PRR7可与NMDAR的GLUN1亚基相互作用，并在NMDAR激活后于细胞核内发生上调。本研究还发现，PRR7可与泛素连接酶E3 SCFFBW7（FBW7）相互作用，并阻断FBW7介导的c-Jun泛素化。PRR7过表达会增强c-Jun依赖的转录活性，并促进神经元死亡。基因芯片分析结果显示，Prr7基因敲低或过表达均会改变与细胞存活及突触功能相关的、受c-Jun调控的转录本的丰度。此外，在原代神经元培养体系中，Prr7基因敲低可减轻NMDAR介导的兴奋性毒性。本研究结果表明，PRR7可将NMDAR活性与c-Jun功能联系起来，并为理解NMDAR依赖的兴奋性毒性的潜在机制提供了新的见解。