Dendritic cell nuclear protein-1 (DCNP1) is a protein associated with major depression. In the brains of depression patients, DCNP1 is up-regulated. However, how DCNP1 participates in the pathogenesis of major depression remains unknown. In this study, we first transfected HEK293 cells with EGFP-DCNP1 and demonstrated that the full-length DCNP1 protein was localized in the nucleus, and RRK (the residues 117-119) composed its nuclear localization signal (NLS). An RRK-deletion form of DCNP1 (DCNP1^ΔRRK) and truncated form (DCNP1^1-116), each lacking the RRK residues, did not show the specific nuclear localization like full-length DCNP1 in the cells. A rat glioma cell line C6 can synthesize melatonin, a hormone that plays important roles in both sleep and depression. We then revealed that transfection of C6 cells with full-length DCNP1 but not DCNP1^ΔRRK or DCNP1^1-116 significantly decreased the levels of melatonin. Furthermore, overexpression of full-length DCNP1, but not DCNP1^ΔRRK or DCNP1^1-116, in C6 cells significantly decreased both the mRNA and protein levels of N-acetyltransferase (NAT), a key enzyme in melatonin synthesis. Full-length DCNP1 but not DCNP1^ΔRRK or DCNP1^1-116 was detected to interact with the Nat promoter and inhibited its activity through its E-box motif. Furthermore, full-length DCNP1 but not the mutants interacted with and repressed the transcriptional activity of BMAL1, a transcription factor that transactivates Nat through the E-box motif. In conclusion, we have shown that RRK (the residues 117-119) are the NLS responsible for DCNP1 nuclear localization. Nuclear DCNP1 represses NAT expression and melatonin biosynthesis by interacting with BMAL1 and repressing its transcriptional activity. Our study reveals a connection between the major depression candidate protein DCNP1, circadian system and melatonin biosynthesis, which may contribute to the pathogenesis of depression.

中文翻译：

---

树突状细胞核蛋白-1通过与BMAL1结合并抑制C6细胞中N-乙酰基转移酶的转录来调节褪黑素的生物合成。

树突状细胞核蛋白1（DCNP1）是一种与严重抑郁有关的蛋白。在抑郁症患者的大脑中，DCNP1上调。然而，DCNP1如何参与重度抑郁症的发病机制仍然未知。在这项研究中，我们首先用EGFP-DCNP1转染了HEK293细胞，并证明全长DCNP1蛋白位于细胞核中，而RRK（残基117-119）构成其核定位信号（NLS）。DCNP1的RRK删除形式（^DCNP1ΔRRK）和截短形式（DCNP1 ^1-116），每个都缺少RRK残基，没有像细胞中的全长DCNP1一样显示出特定的核定位。大鼠神经胶质瘤细胞系C6可以合成褪黑激素，褪黑激素是一种在睡眠和抑郁中都起着重要作用的激素。然后我们发现，用全长DCNP1转染C6细胞，但不转染^DCNP1ΔRRK或DCNP1 ^1-116，可显着降低褪黑激素的水平。此外，全长DCNP1，但不是DCNP1的过表达^ΔRRK或DCNP1 ^1-116在C6细胞中，mRNA和N-乙酰转移酶的蛋白水平（NAT），褪黑激素合成的关键酶显著降低。全长DCNP1，但不是^DCNP1ΔRRK或DCNP1 ^1-116被检测到与Nat启动子相互作用并通过其E-box基序抑制其活性。此外，全长DCNP1而不是突变体与BMAL1相互作用并抑制了BMAL1的转录活性，BMAL1是一种通过E-box基序激活Nat的转录因子。总之，我们已经表明RRK（残基117-119）是负责DCNP1核定位的NLS。核DCNP1通过与BMAL1相互作用并抑制其转录活性来抑制NAT表达和褪黑素生物合成。我们的研究揭示了主要的抑郁候选蛋白DCNP1，昼夜节律系统和褪黑素的生物合成之间的联系，这可能与抑郁的发病机理有关。