Analysis of Nucleocytoplasmic Trafficking of the HuR Ligand APRIL and Its Influence on CD83 Expression

• Published in: The Journal of biological chemistry Vol. 282; no. 7; pp. 4504 - 4515
• Main Authors: Fries, Barbara, Heukeshoven, Jochen, Hauber, Ilona, Grüttner, Cordula, Stocking, Carol, Kehlenbach, Ralph H., Hauber, Joachim, Chemnitz, Jan
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16.02.2007; American Society for Biochemistry and Molecular Biology
• Subjects: Active Transport, Cell Nucleus - physiology; Animals; Antigen Presentation - immunology; Antigens, CD - biosynthesis; Antigens, CD - genetics; Antigens, CD - immunology; Antigens, Surface - genetics; Antigens, Surface - immunology; Antigens, Surface - metabolism; CD83 Antigen; Cell Nucleus - genetics; Cell Nucleus - immunology; Cell Nucleus - metabolism; Chlorocebus aethiops; COS Cells; Cytoplasm - genetics; Cytoplasm - immunology; Cytoplasm - metabolism; Dendritic Cells - cytology; Dendritic Cells - immunology; Dendritic Cells - metabolism; ELAV Proteins; ELAV-Like Protein 1; Gene Expression Regulation - physiology; HeLa Cells; Humans; Immunoglobulins - biosynthesis; Immunoglobulins - genetics; Immunoglobulins - immunology; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - immunology; Intracellular Signaling Peptides and Proteins - metabolism; Jurkat Cells; Ligands; Membrane Glycoproteins - biosynthesis; Membrane Glycoproteins - genetics; Membrane Glycoproteins - immunology; Mice; NIH 3T3 Cells; Nuclear Proteins - genetics; Nuclear Proteins - immunology; Nuclear Proteins - metabolism; Phosphorylation; Protein Processing, Post-Translational - physiology; Protein Sorting Signals - physiology; RNA, Messenger - biosynthesis; RNA, Messenger - genetics; RNA, Messenger - immunology; RNA-Binding Proteins - genetics; RNA-Binding Proteins - immunology; RNA-Binding Proteins - metabolism; T-Lymphocytes - cytology; T-Lymphocytes - immunology; T-Lymphocytes - metabolism; Tumor Necrosis Factor Ligand Superfamily Member 13 - genetics; Tumor Necrosis Factor Ligand Superfamily Member 13 - immunology; Tumor Necrosis Factor Ligand Superfamily Member 13 - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M608849200

Dendritic cells (DC) are the most potent antigen-presenting cells of the immune system and are able to sensitize even naïve 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.