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：

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


树突状细胞核蛋白-1 (DCNP1) 是一种与重度抑郁症相关的蛋白质。在抑郁症患者的大脑中，DCNP1 表达上调。然而，DCNP1如何参与重度抑郁症的发病机制仍不清楚。在本研究中，我们首先用EGFP-DCNP1转染HEK293细胞，并证明全长DCNP1蛋白定位于细胞核，RRK（残基117-119）组成其核定位信号（NLS）。 DCNP1 的 RRK 缺失形式 (DCNP1 ^ΔRRK ) 和截短形式 (DCNP1 ^1-116 ) 均缺乏 RRK 残基，在细胞中没有显示出像全长 DCNP1 那样的特定核定位。大鼠神经胶质瘤细胞系 C6 可以合成褪黑激素，这是一种在睡眠和抑郁中发挥重要作用的激素。然后我们发现，用全长 DCNP1 而不是 DCNP1 ^ΔRRK或 DCNP1 ^1-116转染 C6 细胞可显着降低褪黑激素水平。此外，C6 细胞中全长 DCNP1 的过表达（而非 DCNP1 ^ΔRRK或 DCNP1 ^1-116 ）显着降低了 N-乙酰转移酶（NAT）（褪黑激素合成中的关键酶）的 mRNA 和蛋白质水平。检测到全长 DCNP1（而非 DCNP1 ^ΔRRK或 DCNP1 ^1-116）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（而非突变体）与 BMAL1 相互作用并抑制其转录活性，BMAL1 是一种通过 E-box 基序反式激活 Nat 的转录因子。总之，我们证明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 表达和褪黑激素生物合成。我们的研究揭示了重度抑郁症候选蛋白 DCNP1、昼夜节律系统和褪黑激素生物合成之间的联系，这可能有助于抑郁症的发病机制。