Analysis of nucleocytoplasmic trafficking of the HuR ligand APRIL and its influence on CD83 expression
Analysis of nucleocytoplasmic trafficking of the HuR ligand APRIL and its influence on CD83 expression
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DOI：
10.1074/jbc.m608849200
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发表时间：
2007-02-16
影响因子：
4.8
通讯作者：
Chemnitz, Jan
中科院分区：
文献类型：
--
作者：
Fries, Barbara;Heukeshoven, Jochen;Chemnitz, Jan
树突状细胞（DC）是免疫系统中最有效的抗原呈递细胞，并且能够使甚至幼稚T细胞致敏。成熟DC的特征在于表达CD83，CD83是一种被认为参与有效T细胞活化的表面分子。最近已经表明，CD83 mRNA以HuR和CRM 1依赖性方式从细胞核转运到细胞质。因此，我们在此研究了HuR的两种已知蛋白配体pp32和APRIL对CD83表达的影响。pp32（ANP32A）和APRIL（ANP32B）都是穿梭蛋白，并且先前已经报道这些HuR配体可以作为连接HuR和CRM1特异性核输出途径的衔接子。通过采用RNA干扰（RNAi）技术，我们证明pp32是CD83表达的抑制剂，而APRIL有助于核输出和随后的CD83 mRNA翻译。此外，我们还测定了人APRIL的核输入信号（NLS）和核输出信号（内斯）。此外，我们分析了内源性APRIL的磷酸化状态，并确定苏氨酸244是一个尚未识别的磷酸受体。最后，我们能够表明，磷酸化的这一特定的氨基酸残基调节APRIL的核输出。总之，我们在这里报告的信号序列在APRIL介导其胞内运输，并提供证据表明，这种蛋白质配体的HuR是一个重要的球员在转录后调节的CD83表达，通过影响核质易位的CD83 mRNA。
Dendritic cells (DC) are the most potent antigen-presenting cells of the immune system and are able to sensitize even naive T cells. Mature DC are characterized by expression of CD83, a surface molecule that is proposed to be involved in efficient T cell activation. It has been recently shown that CD83 mRNA is transported from the nucleus to the cytoplasm in a HuR- and CRM1-dependent manner. Therefore we here investigated the impact of two known protein ligands of HuR, pp32 and APRIL, on CD83 expression. Both pp32 (ANP32A) and APRIL (ANP32B) are shuttle proteins, and it has been reported earlier that these HuR ligands can act as adaptors that link HuR and the CRM1-specific nuclear export pathway. By employing RNA interference (RNAi) technology we demonstrate that pp32 is dispensable for CD83 expression, whereas APRIL contributes to the nuclear export and subsequent translation of CD83 mRNA. Furthermore, we have determined the nuclear import signal (NLS) as well as the nuclear export signal (NES) of human APRIL. Moreover, we analyzed the status of phosphorylation of endogenous APRIL and identified threonine 244 to be an as yet unrecognized phosphate acceptor. Finally, we were able to show that phosphorylation of this specific amino acid residue regulates the nuclear export of APRIL. In sum, we report here the signal sequences in APRIL that mediate its intracellular trafficking and provide evidence that this protein ligand of HuR is an important player in the post-transcriptional regulation of CD83 expression by affecting the nucleocytoplasmic translocation of CD83 mRNA.