Nur77 (NGFI-B) is a nuclear receptor that belongs to the Nr4a family of orphan nuclear receptors (Nr4a1). This transcription factor has been implicated in the regulation of multiple functions, such as cell cycle regulation, apoptosis, inflammation, glucose and lipid metabolism, and brain function. However, the mechanisms involved in its different regulatory properties remain unclear. In search for regulatory mechanisms of Nur77 function, we identified that Protein Inhibitor of Activated STAT gamma (PIASγ), an E3 SUMO-protein ligase, potently repressed Nur77 transcriptional activity in HEK-293T cells. This PIASγ activity was sensitive to Sentrin SUMO-specific protease 1 (SENP1). Substitution of two putative phylogenetically well-conserved small ubiquitin-like modifier (SUMO) acceptor sites, lysine 102 (K102) and 577 (K577) by arginine residues (R) modulated Nur77 transcriptional activity. In particular, Nur77-K102R and Nur77-K102R/K577R mutants strongly decreased the transcriptional activity of Nur77, whereas single K577R substitution increased transcriptional activity of Nur77. Repression of Nur77 transcriptional activity by SUMO2 and PIASγ was reduced by the K577R mutation, whereas the K102R mutant remained insensitive to SUMO2. Interestingly, the roles of these SUMO acceptor sites in Nur77 are distinct from previously observed activities on its close homolog Nurr1. Thus, the present study identified SUMO2 and PIASγ as important transcriptional co-regulators of Nur77.

Nur77（NGFI-B）是一种核受体，属于孤儿核受体（Nr4a1）的Nr4a家族。该转录因子与多种功能的调节有关，例如细胞周期调节，细胞凋亡，炎症，葡萄糖和脂质代谢以及脑功能。但是，其不同的监管属性所涉及的机制仍不清楚。在寻找Nur77功能的调节机制中，我们确定了激活的STATγ（PIASγ）（一种E3 SUMO蛋白连接酶）的蛋白抑制剂有效抑制了HEK-293T细胞中的Nur77转录活性。该PIASγ活性对Sentrin SUMO特异性蛋白酶1（SENP1）敏感。取代两个假定的系统发育上保守性好的小泛素样修饰子（SUMO）受体位点，赖氨酸102（K102）和577（K577）的精氨酸残基（R）调节Nur77转录活性。特别是，Nur77-K102R和Nur77-K102R / K577R突变体强烈降低了Nur77的转录活性，而单个K577R取代增加了Nur77的转录活性。SUMO2和PIASγ对Nur77转录活性的抑制因K577R突变而降低，而K102R突变体仍然对SUMO2不敏感。有趣的是，Nur77中这些SUMO受体位点的作用与其先前在其紧密同源物Nurr1上观察到的活性不同。因此，本研究确定SUMO2和PIASγ是Nur77的重要转录共调节因子。而单个K577R取代增加了Nur77的转录活性。SUMO2和PIASγ对Nur77转录活性的抑制因K577R突变而降低，而K102R突变体仍然对SUMO2不敏感。有趣的是，Nur77中这些SUMO受体位点的作用与其先前在其紧密同源物Nurr1上观察到的活性不同。因此，本研究确定SUMO2和PIASγ是Nur77的重要转录共调节因子。而单个K577R取代增加了Nur77的转录活性。SUMO2和PIASγ对Nur77转录活性的抑制因K577R突变而降低，而K102R突变体仍然对SUMO2不敏感。有趣的是，Nur77中这些SUMO受体位点的作用与其先前在其紧密同源物Nurr1上观察到的活性不同。因此，本研究确定SUMO2和PIASγ是Nur77的重要转录共调节因子。